Sistema de comércio de terras secas

Sistema de comércio de terra seca
De acordo com a FAO (2001a), um sistema agrícola é definido como & # 147; uma população de sistemas agrícolas individuais que possuem bases de recursos amplamente semelhantes, padrões de empresas, meios de subsistência familiar e restrições, e para as quais estratégias e intervenções de desenvolvimento semelhantes seriam apropriadas. Dependendo da escala da análise, um sistema agrícola pode abranger algumas dezenas ou milhões de famílias. A compreensão dos principais sistemas agrícolas em terras áridas fornece a estrutura necessária para o desenvolvimento de estratégias e intervenções agrícolas. Com base na classificação de sistemas agrícolas de regiões em desenvolvimento especificada pela FAO (2001a), a maioria dos sistemas agrícolas em terras secas se enquadra na categoria de sistemas de cultivo de sequeiro em áreas de baixo potencial seco. Estes sistemas são caracterizados pela mistura de sistemas agropecuários e pastoris, que se fundem em sistemas esparsos e muitas vezes dispersos, com baixa produtividade atual ou potencial devido à extrema aridez ou frio.
Entender o mundo dos pequenos proprietários em ambientes de sequeiro é a chave para projetar atividades de CS adequadas e bem-sucedidas. É importante entender que o CS para o alívio da pobreza deve ser muito mais amplo em termos de alcance de práticas e benefícios (ou seja, não apenas em termos monetários) do que esquemas similares na agricultura comercial e florestal.
Existem vários parceiros em potencial, ou grupos-alvo, para programas de CS em terras secas. De uma perspectiva puramente escalável, a agricultura intensiva em capital de larga escala pode ser a mais atraente. No entanto, do ponto de vista biofísico, como discutido no Capítulo 4, sistemas que usam quantidades significativas de fertilizantes ou que dependem pesadamente de combustível fóssil para fornecer água de irrigação não devem ser geralmente considerados porque são geralmente emissores líquidos de carbono. Somente se a mudança da alta dependência de fertilizantes e combustíveis fósseis para insumos mais amigáveis ​​ao carbono, tecnologias ou uso da terra for previsível a curto prazo, caso a agricultura em larga escala seja considerada. Existem alguns sistemas de uso intensivo de capital, tais como os esquemas agrícolas mecanizados no leste do Sudão (onde grandes áreas de terra foram severamente degradadas) que oferecem grande potencial para a CS do solo se reabilitadas através do uso da terra de baixa intensidade.
Além dessas razões técnicas, os sistemas agrícolas de grande escala e intensivos em capital provavelmente não são parceiros potenciais para a CS do solo porque a pequena renda adicional que o sequestro pode trazer seria pouco atraente em comparação com os lucros de outras fontes, muitas das quais dependem de carbono. materiais emissivos.
Assim, os principais grupos-alvo da CS do solo em agroecossistemas degradados são, principalmente, agricultores de pequena escala e pobres em recursos, em ambientes incertos e propensos a riscos, para os quais os benefícios antecipados poderiam constituir um aumento de sua subsistência. A referência a esses grupos de agricultores é feita como pequenos agricultores. Eles dependem da baixa agricultura baseada na subsistência e são geralmente caracterizados pela diversidade, variabilidade e flexibilidade (Mortimore e Adams, 1999).
Características da agricultura familiar.
As características primárias da agricultura familiar em países em desenvolvimento semi-áridos são a sua diversidade no espaço, a sua variabilidade através do tempo e a sua multidimensionalidade em termos das formas como opera e sobrevive (Mortimore e Adams, 1999). Isso ocorre principalmente porque os pequenos produtores de terra seca devem ser altamente responsivos a um ambiente variado, mutável e perigoso. Assim, suas operações são muito diferentes daquelas das fazendas de grande porte, impulsionadas por objetivos comerciais, equipadas com créditos e tecnologias orientadas para a eficiência e cobertas pelos sistemas de seguro contra riscos e perdas. Essa diversidade, variabilidade e multidimensionalidade significa que cada sistema em particular deve ser abordado com atenção cuidadosa a sua mistura indevida de características.
Outra característica importante dos pequenos produtores, que também os diferencia dos produtores comerciais, é que poucos são motivados apenas pelo objetivo do lucro agrícola. Em vez disso, os pequenos proprietários perseguem metas básicas de subsistência e sobrevivência, equilibrando riscos diários e oportunidades diretamente através de suas opções de subsistência e práticas de manejo em vez de através de instituições externas (Collinson, 2000). Muitos pequenos proprietários têm uma profunda ligação com suas terras, que continuam a cultivar, mesmo quando a lucratividade é baixa, por razões como a manutenção da posse e a manutenção de laços familiares. Ao mesmo tempo, muitos têm rendimentos adicionais, e muitas vezes mais elevados, provenientes de fontes não agrícolas. Estes incluem: pequeno comércio; a coleta de produtos silvestres, incluindo lenha; trabalho de parto; e remessas de membros da família. O resultado é & # 147; unidades de produção multi-empresa & # 148; (Hunt, 1991).
Os pequenos agricultores são ainda mais diferenciados dos agricultores comerciais de alto custo por sua necessidade de gerenciar múltiplos riscos. Quase todas as entradas e saídas estão sujeitas a grandes variações e incertezas, como a mão-de-obra, que geralmente é a variável mais crítica. Outro risco crítico decorre da alta variabilidade da precipitação, que em si tem duas consequências importantes no que diz respeito ao seqüestro. Uma é a variação no tempo da bioprodutividade, o que significa que o plantio e a colheita (e a maioria das outras atividades agrícolas e não-agrícolas) podem ter que ser reajustados rapidamente, às vezes dentro de uma estação, e freqüentemente entre as estações. Por exemplo, pousios que pareciam seguros por anos podem ter que ser limpos após uma temporada particularmente fraca. A outra conseqüência é a variabilidade entre campos, alguns dos quais podem receber chuvas suficientes, e alguns podem não receber. Existem outros riscos que têm consequências semelhantes. Estes incluem: ataques de pragas (contra os quais os pesticidas são muito caros); doença, resultando na indisponibilidade de trabalho em algum ponto crítico na estação; e variabilidade em relação a preços de insumos como sementes, trabalho, alimentos e produtos, principalmente culturas.
De acordo com Mortimore e Adams (1999), as respostas dos pequenos proprietários a essas várias restrições seguem três caminhos principais: (i) diversificação de recursos de recursos naturais, econômicos, técnicos e sociais com o racional subjacente para disseminar riscos da forma mais eficiente possível; (ii) flexibilidade na gestão diária desses recursos na forma de decisões ativas para enfrentar e adaptar-se à variabilidade de curto prazo; e (iii) adaptabilidade a longo prazo, percebida como tomada de decisão cumulativa e intencional que resultará em sistemas novos ou alterados ou caminhos de subsistência. Ao espalhar os riscos, é importante que os agricultores tenham um mix de produtos em que tanto o tipo de produtos quanto o preço desses produtos sejam independentes uns dos outros, um critério que potencialmente se aplica muito bem ao CS.
Uma outra característica da agricultura familiar é o acesso variável a recursos de todos os tipos. Dentro de uma aldeia, alguns têm acesso imediato, e outros têm menos acesso, para: garantir propriedades rurais; produtos silvestres, como lenha; crédito; contratou mão de obra; pecuária; e mercados. O acesso também varia entre aldeias e entre países. As implicações de tal acesso desigual a recursos para esquemas de seqüestro são discutidas abaixo.
Finalmente, esses sistemas agrícolas estão e há muito estão passando por mudanças contínuas em resposta a mudanças ambientais e sociais. Ambientes secos agora são amplamente reconhecidos como tendo um histórico complexo de mudanças, baseados em dinâmicas de não-equilíbrio em vez de mudanças previsíveis, graduais e lineares (Leach e Mearns, 1999; Scoones, 1999; Scoones, 2001), algumas vezes chamados de sistemas baseados em eventos (Reenberg, 2001; Sorbo, 2003). Assim, os sistemas agrícolas tiveram que se adaptar continuamente às condições ambientais e à mudança dos processos políticos e econômicos. Na vida de um esquema de CS do solo, pode-se esperar muitas mudanças na configuração da paisagem agrícola, além das mudanças que o projeto em si pode trazer. Planejar em tal ambiente será um desafio. Em vez de abordagens simplificadas e padronizadas e de soluções técnicas predefinidas, os esquemas de CS nesses sistemas precisarão oferecer uma gama de opções tecnológicas e de gerenciamento a partir das quais os agricultores possam escolher de acordo com suas necessidades.
Exemplos de sistemas de pequenos agricultores.
Dentro dessa ampla descrição das características da agricultura familiar de pequeno porte, existem vários sistemas agrícolas. Estes são sistemas como plantios anuais, plantações, florestas, savanas, pastagens naturais, pousios e hortas. Dentro de cada um, há uma interação específica entre culturas, gado e árvores, e entre terras cultivadas e não cultivadas (FAO, 2000a).
Os sistemas agrícolas em terras secas variam desde a agricultura itinerante embutida em pastagens extensas e arborizadas até a agricultura intensiva de pequenos produtores, onde toda a terra está sendo cultivada e a integração entre cultivo e criação de animais é maximizada. No entanto, esses dois extremos não devem ser entendidos como pontos fixos ao longo de um eixo de desenvolvimento agrícola, mas sim como exemplos de caminhos '' '' ''. de mudança agrícola e ambiental (Scoones, 2001) que são possíveis tanto entre como dentro de sites. Tais caminhos de mudança refletem os agricultores & # 146; meios de subsistência, restrições e oportunidades dentro de um contexto histórico. A Figura 7 fornece uma ilustração esquemática dos sistemas de pequenos produtores de terras áridas.
Intensificação Agrícola.
A intensificação, como definida por Tiffen e Mortimore (1993), implica o aumento de insumos médios de mão-de-obra ou de capital em uma pequena propriedade, seja em terras cultivadas, seja em terras cultivadas e de pastagem, com o objetivo de aumentar o valor da produção. por hectare & # 148 ;. A intensificação assume muitas formas, que podem ser classificadas de várias maneiras. No caso dos sistemas de pequenos produtores de terras áridas, a intensificação tende a estar relacionada ao aumento de mão de obra local por hectare e tecnologias de baixo custo em vez de inovações intensivas em capital. Mortimore e Adams (1999) descrevem essa intensificação como um processo indígena e adaptativo & # 148; cujo caminho pode ser reconstruído através de análises históricas.
Existem muitos exemplos de tais & # 147; indígenas & # 148; intensificação. Nos sistemas de agricultura de sequeiro, a intensificação ocorre frequentemente como consequência da crescente pressão populacional. Em muitos lugares, os períodos de pousio tornaram-se cada vez mais curtos e, eventualmente, até abandonados. Todos os campos podem então estar sob cultivo e a fertilidade do solo é mantida por uma maior intensidade de trabalho. As técnicas podem incluir: consociação com leguminosas fixadoras de nitrogênio; capina e colheita intensivas em tempo; a utilização de esterco e cobertura morta; e a proteção de certas espécies de árvores. A rotação de culturas é praticada, sempre que possível, para garantir o uso e a absorção diferenciados de nutrientes entre culturas, tais como milheto e sorgo, e a Nfixagem de culturas, como o amendoim e o feijão-frade. As árvores, especialmente aquelas conhecidas por suas capacidades de fixação de N e de restauração do solo, são protegidas. A aplicação de estrume, tanto de gado como de pequenos ruminantes, é um elemento chave. Para manter a oferta em face da crescente escassez de terras, os rebanhos devem ser administrados de forma mais intensiva, por ex. alimentando-os com resíduos agrícolas e ervas daninhas.
Em áreas de terra firme, onde há disponibilidade de água superficial suficiente, a irrigação tem sido um método fundamental de intensificação dos sistemas de uso da terra desde os tempos antigos. Requer suprimentos de água e energia para levar a água aos campos e jardins. A água pode vir de riachos, rios, nascentes e poços. Riachos e rios podem variar de pequenos cursos d'água efêmeros, como em muitas partes da Ásia central, até grandes rios como o Nilo, Níger, Amu-Darya, Hwang He e Indus.
Onde há um bom & # 147; cabeça & # 148; De água, como em terreno montanhoso (por exemplo, em partes do altiplano Iêmen e Omã), ou nos grandes sistemas em planícies de inundação, como dos rios Nilo e Indo, a água pode ser tomada por gravidade em pequenos canais para os campos ou jardins. Onde o rio corre em uma planície de inundação levemente inclinada, os métodos que o elevam aos campos de pequenos esquemas são os mesmos dos poços: dispositivos movidos a animais ou humanos, como saqqias, parafusos de Arquimedes e shadufs. Os sistemas de qanat, que são particularmente bem desenvolvidos no Irã e nas áreas vizinhas, mas também são encontrados em outras partes da Ásia e no norte da África, são mais elaborados, envolvendo poços dos quais a água é canalizada no subsolo e alimentada pelos campos por gravidade. Outro sistema antigo, que viu grande expansão e desenvolvimento nos últimos anos, é a coleta de água (ou a agricultura de escoamento superficial). Neste sistema, o escoamento altamente intermitente é concentrado e, em seguida, mantido em calhas rasas, onde é normalmente utilizado para culturas arvenses.
FIGURA 7 Sistemas de pequenos agricultores no Sahel e estratégias de gestão no contexto do carbono.
Fonte: Tschakert, trabalho de campo, 2001.
Uso extensivo da terra.
Em áreas onde as densidades populacionais e as chuvas são baixas, os padrões de uso extensivo da terra predominam como um estado de sistema de longo prazo ou um caminho de mudança mais recente (Mortimore e Adams, 1999). O último é verdade para algumas áreas no centro do Senegal, onde compostos inteiros migraram recentemente para a cidade de Touba, deixando parentes e vizinhos com mais terras disponíveis do que nas décadas anteriores (Tschakert e Tappan, 2004). Como a escassez de terra não representa um constrangimento neste caso, os pousios constituem um elemento importante do sistema agrícola, permitindo a regeneração do solo a curto e médio prazo. Em geral, os tamanhos dos campos são significativamente maiores do que nas áreas sob intensificação. Dada a quantidade de terra disponível para os agregados familiares individuais, o estrume é geralmente usado apenas para os campos que estão sob cultivo contínuo, principalmente os adjacentes aos assentamentos e outros nas proximidades. Campos remotos e aqueles deixados em pousio são acessíveis a animais em pastejo durante todo o ano. Ao contrário dos animais em sistemas intensificados, os rebanhos não são forçados a partir para a transumância e, assim, contribuem para um fluxo contínuo de entrada de matéria orgânica. As atividades de capina e colheita podem ocorrer com menos intensidade, enquanto mais resíduos agrícolas são deixados nos campos.
A agrossilvicultura pode desempenhar um papel importante nesses sistemas extensivos. Um exemplo é o sistema sudanês de produção de goma-arábica, onde uma árvore que cresce nas terras em pousio é uma importante fonte de renda para os pequenos agricultores (Elmqvist e Olsson, 2003). Em outros pousios longos, árvores que produzem outros produtos úteis, como frutas, nozes, fibras e medicamentos, são plantadas. As árvores também fornecem uma importante fonte de alimento de emergência.
Os exemplos acima de sistemas agrícolas intensivos e extensivos ilustram que uma abordagem específica do contexto, baseada em múltiplos caminhos de mudança, oferece diretrizes úteis para esquemas potenciais de CS. O desenho e a implementação do projeto devem começar com um entendimento local da mudança ambiental e seus processos subjacentes. O próximo passo é identificar caminhos positivos de mudança no nível local e, finalmente, avaliar as oportunidades para encorajar esses caminhos em uma escala maior.
Manejo da fertilidade do solo.
O conceito de CS em agroecossistemas degradados é tipicamente baseado em duas suposições. A primeira é que qualquer melhoria no manejo da fertilidade do solo e no uso da terra resultará automaticamente em maiores quantidades de C sequestradas da atmosfera e armazenadas nos solos. A segunda é que os pequenos proprietários locais e pastores, que devem ser os principais beneficiários das intervenções planejadas, precisam ser conscientizados e treinados em tais práticas de manejo aprimoradas.
Dado o mundo complexo, diversificado e dinâmico da agricultura familiar em ambientes de sequeiro, essas duas suposições parecem simplificadas demais. Em geral, as práticas de manejo propostas e as opções de uso da terra refletem apenas as opções técnicas mais eficientes, concentrando-se em alcançar uma situação agronômica ideal. No entanto, como ilustrado acima, os pequenos agricultores estão mais preocupados com o gerenciamento de risco cotidiano e estratégias adaptativas de longo prazo do que com a obtenção de um novo equilíbrio assumido. A agricultura oportunista tem tudo a ver com a disseminação de riscos, um processo adaptativo durante o qual ocorrem perdas e ganhos, muitas vezes intencionalmente. A eficiência pura não deixaria espaço para manobras flexíveis & # 148; (Mortimore e Adams, 1999).
O que de fato constitui o & # 147; melhorado & # 148; o manejo da fertilidade do solo ou as opções de uso da terra podem ser compreensíveis apenas a partir de uma abordagem de pesquisa holística do sistema agrícola. Os agricultores que desenvolveram práticas de gestão de fertilidade do solo altamente dinâmicas e flexíveis para lidar com a variabilidade e a incerteza estão, muitas vezes, na melhor posição para levar esse holismo a um projeto de desenvolvimento. Embora os agricultores muitas vezes tenham muita experiência em deliberar sobre tecnologias dentro de um quadro muito mais amplo de vida real, eles são mais frequentemente considerados receptores passivos de assistência externa do que recursos-chave no próprio processo.
Assim, um primeiro passo para vincular solos e C a pessoas é investigar práticas que os pequenos proprietários em ambientes de sequeiro conhecem e usam atualmente, para entender suas razões subjacentes e fatores de mudança, e para identificar exemplos de caminhos positivos de mudança que poderiam ser replicado em uma escala maior (Tschakert e Tappan, 2004).
As práticas de manejo da fertilidade do solo podem ser agrupadas de acordo com o movimento de nutrientes dentro, dentro e fora de um sistema. Aqui, as práticas são classificadas em quatro grupos (Hilhorst e Muchena, 2000): (i) adicionando nutrientes ao solo; (ii) reduzir as perdas de nutrientes do solo; (iii) reciclagem de nutrientes; e (iv) maximizar a eficiência da absorção de nutrientes. Os exemplos abaixo são baseados principalmente nos estudos de caso do Senegal e do Sudão.
Adicionando nutrientes ao solo.
Pousio é uma prática bem conhecida para reabastecer nutrientes nos solos. Idealmente, os períodos de pousio são alternados com períodos de cultivo, permitindo que a terra se recupere de anos de cultivo. No entanto, em muitas partes das terras secas do mundo, tanto a área de pousio quanto a duração diminuíram ao longo do tempo. Na maioria das vezes, esse declínio é causado pelo aumento da pressão populacional, a introdução de máquinas agrícolas modernas, como o arado e períodos de seca, ou uma combinação dos três. Alguns acreditam que este processo está atingindo proporções de crise. Hoje, em muitas terras secas, a duração do pousio é reduzida para apenas um ano. Em áreas com grave escassez de terras, desapareceu completamente. Como conseqüência, os agricultores mudaram para outras práticas de manejo da fertilidade do solo, como adubação e compostagem (veja abaixo) ou continuam a cultivar com rendimentos excepcionalmente baixos e decrescentes. Ao mesmo tempo, menos terra em pousio também significa reduzir as possibilidades de pastagem ou menos forragem para os animais, reduzindo assim a quantidade de esterco que pode ser produzido (Breman, Groot e van Keulen, 2000). No entanto, em áreas com menor pressão populacional, o pousio ainda constitui uma opção importante para o manejo da fertilidade do solo. Isto é particularmente verdadeiro para os países onde os pacotes de ajuste estrutural foram implementados e os subsídios para fertilizantes removidos.
Muitos sistemas agrícolas incluem o pastoreio de animais nos campos imediatamente após as colheitas das colheitas. Os animais pastam restolho e caules deixados no campo, enquanto os solos se beneficiam da deposição de fezes ao longo da duração da prática. Dependendo do tamanho e da situação da forragem de um campo, bem como do número total de animais, o gado é normalmente mantido por 1 a 7 meses no mesmo campo, onde é girado entre diferentes partes durante intervalos de tempo mais curtos.
No geral, o ganho em matéria orgânica da pastagem de restolho pode ser substancial. No Sahel, a deposição de excrementos varia de 1 tonelada / ha a 50 toneladas / ha, dependendo do tempo que os animais são mantidos no mesmo campo (Sagna-Cabral, 1989; Garin e Faye, 1990; Hoffmann e Gerling, 2001). No entanto, a exposição direta aos elementos pode reduzir consideravelmente o valor nutricional do esterco e excrementos. Embora o pastoreio tenha uma longa tradição em terras áridas, o aumento da escassez de terras, o limitado poder aquisitivo de muitos pequenos proprietários e o aumento do risco de roubo de animais em muitas áreas contribuíram para um declínio geral no tamanho dos rebanhos e, em alguns casos, levaram ao abandono das terras. restolho pastando completamente.
O uso de fertilizantes inorgânicos tem sido um dos meios mais amplamente promovidos para aumentar a produção desde o início do século XX. Em muitas das terras secas do mundo em desenvolvimento, esse tipo de fertilizante era subsidiado e disponibilizado aos agricultores com a ajuda do governo e com o apoio de organizações não-governamentais (ONGs). No âmbito dos programas de ajustamento estrutural, os subsídios foram frequentemente removidos e, portanto, os fertilizantes tornaram-se cada vez mais onerosos para os agricultores. Como é mostrado no exemplo do Senegal (e ilustrado na Figura 8), o uso de fertilizantes diminuiu nos anos 90. Do ponto de vista da SC, o uso de fertilizantes sintéticos não resulta em nenhum ganho líquido de fixação de carbono (Schlesinger, 1999). A emissão de CO 2 durante a fabricação, transporte e aplicação dos fertilizantes compensa qualquer ganho na produção biológica.
FIGURA 8 Mudanças no uso do solo e manejo da fertilidade do solo, expressas em pontos de importância / extensão ponderados (1-10), como percebido pelos agricultores em um sistema intensificado de cultivo no Senegal.
Fonte: Tscharkert, trabalho de campo, 2001.
Rotação e associação de culturas.
A prática de rotação e associação de culturas, especialmente quando envolve cereais e leguminosas, é bem conhecida entre os agricultores como uma prática de manejo da fertilidade do solo. Em muitos lugares, as culturas fixadoras de N incluem feijões e amendoim. No entanto, nos sistemas agrícolas onde a escassez de terra se tornou um fator limitante, a prioridade é dada aos cereais. Além disso, a disponibilidade de sementes para legumes pode depender de subsídios ou créditos do Estado, como foi o caso dos amendoins no Sahel.
Reduzindo perdas de nutrientes do solo.
As árvores podem ser um componente importante em muitos agroecossistemas. Com seus sistemas radiculares profundos e extensos, eles podem capturar nutrientes não acessíveis às culturas e disponibilizá-los novamente para a produção agrícola por meio da queda de lixo. Do ponto de vista do CS, as árvores não apenas armazenam C em sua biomassa acima do solo, mas também contribuem para a biomassa subterrânea através de seus sistemas radiculares e sua entrada de lixo no solo (galhos e folhas). De uso particular são leguminosas (N-fixação) árvores, entre os quais Faidherbia albida e Acacia senegal são dois dos mais apreciados. As árvores também podem desempenhar um papel na redução das perdas de nutrientes causadas pela erosão eólica. Especial consideração deve ser dada ao uso de biocombustível em vez de combustível fóssil.
Vedações e cercas vivas podem capturar sedimentos e partículas de argila suspensas no ar e podem, assim, aumentar localmente o conteúdo de argila do solo, um fator benéfico para CS (El Tahir e Madibo, no prelo). A serapilheira produzida pelas plantas lenhosas é benéfica devido ao seu maior teor de polifenóis (ligninas e taninos), o que diminui a taxa de decomposição (Abril e Bucher, 2001), quando comparada com gramíneas e ervas anuais.
A erosão e o transporte e depósito subsequentes têm uma relação complexa com o armazenamento de carbono no solo. Onde a erosão hídrica predomina, uma alta proporção de solo C pode ser lavada em depósitos aluviais próximos ao local da erosão, e armazenados lá em formas que decaem mais lentamente do que nos solos-mãe. Portanto, esse tipo de erosão pode ter um efeito positivo no CS do solo. A erosão nem sempre diminui a produtividade, mas, se fosse possível, seria perverso favorecer a diminuição da produtividade para um ganho de médio prazo e, talvez, um ganho único em C. Os mesmos argumentos provavelmente não se aplicam onde a erosão eólica é a O principal processo de erosão, para a matéria orgânica é geralmente soprado grandes distâncias e dispersos para locais onde pode decair rapidamente e liberar seu C. Opções de manejo que aumentam a quantidade de biomassa viva e morta deixada em áreas agrícolas diminuem a erosão em geral enquanto aumentam simultaneamente o C entrada no solo (Tiessen e Cuevas, 1994).
Limpeza de campo e capina.
Limpar os campos de ervas daninhas antes do plantio, bem como capinar durante a época agrícola, é uma prática importante para reduzir a competição entre a cultura e as ervas daninhas. No entanto, do ponto de vista da fertilidade do solo e CS, é importante reciclar o máximo possível de ervas daninhas no solo. Limpeza seletiva e capina implica que apenas as ervas daninhas que competem diretamente com a cultura são removidas enquanto outras permanecem no campo.
Reciclagem de nutrientes
A dispersão de estrume do gado que é mantido dentro ou próximo dos compostos é uma das práticas mais generalizadas de gestão da fertilidade do solo. Os agricultores estão bem conscientes dos efeitos fertilizantes do estrume, mas também apreciam o facto de estabilizar o solo arenoso e reduzir a erosão pelo vento. O estrume de capoeira (FYM) e o estrume produzido nos cercados são geralmente de maior qualidade do que o estrume e os excrementos deixados nos campos pelos animais que pastam. Pode ser combinada com resíduos agrícolas, lixo doméstico e cinzas acumulados dentro de um agregado familiar. O fator mais limitante do uso do esterco, além da falta de animais, é a falta de material de transporte, muitas vezes resultando em campos bem-manejados mais próximos da propriedade e não em campos mais remotos.
Gerenciamento de resíduos de culturas.
Resíduos da cultura, como caules e feno, podem ser deixados ou devolvidos ao campo na forma de cobertura morta ou arados no final da safra. No entanto, na maioria dos sistemas de cultivo em terras secas, os resíduos das colheitas são contestados e são removidos após a colheita como forragem, material de construção, combustível ou lixo para compostagem. O que permanece no campo é freqüentemente queimado antes da próxima safra. Em alguns casos, os resíduos da lavoura também são vendidos no mercado local, gerando renda adicional.
Gestão de outras matérias orgânicas.
Resíduos domésticos, escamas de peixe, cinzas, serapilheira, podas e resíduos de culturas excedentes também são usados ​​para aumentar a fertilidade do solo. Muitas vezes, esses insumos adicionais são acumulados dentro da propriedade, às vezes adicionados às pilhas de esterco e, em seguida, transportados para os campos onde são distribuídos de acordo com as necessidades de nutrientes. Em vários lugares, a compostagem resultou em melhores taxas de decomposição. Embora o uso de tal matéria orgânica alternativa, principalmente o lixo doméstico, tenha aumentado, as quantidades totais raramente são suficientes para fertilizar campos inteiros de maneira sustentável.
Maximizar a eficiência da absorção de nutrientes.
Embora alguns agricultores apreciem o cultivo para o controle de ervas daninhas e a aeração do solo, parece haver um crescente reconhecimento de que a lavoura também destrói a cobertura vegetal protetora e, como resultado, expõe os nutrientes do solo aos elementos. Em áreas onde arados e animais de tração estão disponíveis para pequenos produtores, a lavoura ainda é amplamente praticada. Em outras áreas, como a Bacia do Amendoim do Senegal, os agricultores substituíram a lavoura profunda por preparo superficial, principalmente devido à falta de maquinário (Tschakert e Tappan, 2004). Para fins de CS, é preferível a redução ou o plantio direto, simplesmente porque eles aumentam o armazenamento de C no solo.
Muitos fazendeiros freqüentemente combinam culturas e práticas de manejo com o status de fertilidade de campos específicos e, em menor escala, com pontos específicos dentro de um campo. Dada a relativa escassez de insumos orgânicos e inorgânicos, as quantidades disponíveis são distribuídas seguindo um esquema patch-by-patch.
O fogo é uma ferramenta muito comum para os administradores de terras em terras áridas. O fogo é freqüentemente usado para limpar os campos de ervas daninhas antes do plantio. Outra razão importante para o pré-plantio é matar uma variedade de pragas agrícolas. O papel do fogo no balanço de carbono do solo foi investigado por modelagem e encontrado para ter um efeito significativo no SOC. Quando o período de retorno ao fogo aumentou de 3 para 15 anos, o nível de SOC aumentou em 30% (Poussart e Ard & ouml ;, 2002).
Essas descrições de métodos individuais de manejo da fertilidade do solo não captam toda a complexidade das maneiras pelas quais elas são combinadas. Parte dessa complexidade é descrita em mais detalhes abaixo.
Práticas de gestão da fertilidade do solo no Sahel.
Nas terras secas, os agricultores conhecem e usam toda uma gama de práticas de manejo da fertilidade do solo. No entanto, essas práticas podem variar de sistema de cultivo para sistema de cultivo, de agricultor para agricultor e de campo para campo, e até mesmo dentro dos campos, dependendo do acesso diferencial e da utilização dos recursos. Para ilustrar a complexidade das práticas de fertilidade do solo, a Tabela 9 apresenta um exemplo detalhado do Senegal.
Além da variabilidade espacial, as práticas de manejo da fertilidade do solo tendem a variar com o tempo. À medida que os agricultores se adaptam aos riscos, choques e incertezas a longo prazo e sistemas novos ou alterados ou vias de subsistência emergem, os agricultores & # 146; carteiras de práticas de gestão também mudam. A Figura 8 ilustra as mudanças nas práticas de manejo em uma aldeia que seguiu um caminho de & # 147; indígenas e adaptativos & # 148; intensificação (Tschakert e Tappan, 2004). Com o aumento da pressão populacional e a escassez da terra, ocorreu uma mudança geral de práticas extensivas de manejo (pousio e restolho) para estratégias mais intensivas (aplicação de esterco, lixo doméstico, composto, plantio de árvores e cercas). Essa transição está sobreposta a uma mudança nas políticas governamentais, refletida no desligamento do estado após 1980, principalmente após o ajuste estrutural, implicando na redução ou ausência de subsídios ou créditos para fertilizantes minerais, sementes de amendoim e equipamentos agrícolas.
Exemplo de práticas de manejo da fertilidade do solo usadas na antiga Bacia do Amendoim, Senegal, 1999/2000.

Lidando com a seca: o desafio de usar as tecnologias do sistema de água para quebrar as armadilhas da pobreza da terra seca.
Nós exploramos estratégias entre agricultores na Tanzânia semi-árida para lidar com a seca, e investigamos se o acesso a um sistema de irrigação suplementar local (o sistema Ndiva) pode melhorar a capacidade de enfrentamento. Os resultados mostram uma alta dependência dos serviços ecossistêmicos locais quando as colheitas fracassam e indicam que os agricultores geralmente esgotam as reservas de ativos durante as secas. O acesso de Ndiva não teve nenhum efeito direto na capacidade de enfrentamento, mas pareceu ter alguns efeitos indiretos. Com base em nossas descobertas, discutimos a complexidade de escapar da persistente pobreza da terra seca e delineamos as circunstâncias sob as quais as tecnologias de sistemas de água de pequena escala, como a irrigação com Ndiva, podem ajudar.
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Sistema de comércio de terra seca
FIGURA 44 Principais benefícios do melhor manejo do carbono do solo em várias escalas espaciais.
Fonte: Izac (1997).
Os resultados obtidos nos estudos de caso do Senegal e do Sudão apresentados no Capítulo 5 foram analisados ​​para ilustrar alguns aspectos econômicos da SC. O aumento do solo C pode gerar benefícios locais, nacionais e globais. A figura 44 representa esses três níveis. It also shows that these benefits can occur on an individual farm as increased crop, timber and livestock yields resulting from increased soil fertility, or in the form of off-farm social benefits on all three levels. On the local level, this second type of benefit constitutes an enhanced land and soil-resource base for future generations. Benefits on the national scale refer primarily to improved food security and agricultural sustainability. On the global level, anticipated benefits from improved soil carbon management are: enhanced biodiversity, increased carbon offsets, and climate change mitigation. Thus, CS in dryland soils could be a win - win situation.
However, as stressed by Izac (1997), caution is required as the costs will be primarily local while the benefits will be local, national and global. From a cost/benefit perspective, it would be rational for farmers to manage their carbon resources with respect to on-farm benefits while ignoring the broad social off-farm benefits. In other words, in the absence of policy interventions and external financial support, local smallholders would use improved management practices at individually optimal levels but at socially suboptimal levels. The following sections provide an overview of the anticipated benefits and costs both from carbon trading (policy intervention) and from direct investment at local level.
Benefits from carbon trading.
One of the anticipated benefits for smallholders benefiting in CS schemes is the financial gain that could be achieved from carbon trading. Currently, carbon credit values as set by carbon exchange and trading systems range between US$1 and US$38 per tonne of C (FAO, 2001b).
In order to put the estimated gain from CS into the farmer’s perspective, prices of agricultural products and assumed prices of C as a tradable good were compared for the Senegal and Sudan case studies. In both cases, farmers were assumed to use an improved management practice or an alternative type of land use on all their current croplands (Tables 44 and 45). Total amounts of croplands vary depending on the wealth status of the farming populations studied. Annual increases in C, as estimated by CENTURY, were assumed to generate US$15/ha, resulting in financial gains per group of households. These financial gains were then compared with the average value of food and cash crops that farmers would grow on these lands if no other alternative existed.
Anticipated economic benefits from carbon trading (1 tonne C = US$15).
C sequestration (tonnes/ha)
Annual gains poor HH (US$15)
Annual gains average HH (US$15)
Annual gains rich HH (US$15)
% of annual crop value.
Compost (2 tonnes).
Conversion of croplands to grasslands + tree protection.
Cattle manure (4 tonnes) + chem. fertilizer.
Sheep manure (10 tonnes)
Rotation 10-year fallow - Leucaena (2 tonnes) and 6 years crops.
Source: Tschakert (fieldwork).
In the Senegal case, average farm sizes in the study villages vary between 3.2 and 15.5 ha, of which 2.8 - 8.9 ha are cultivated (Tschakert, 2004a). If C were sequestered on these lands following the management practices in Table 43, the potential financial gains from carbon trading would range from US$1.4 to US$31 per year. Such gains are expected to be significantly lower for poor households compared with average and rich households. This is because the poor households have less land that could be used for alternative management practices and/or land uses. As Table 44 shows, the maximum annual gains would amount to about US$16 for poor households, US$41 for average households, and US$49 for rich households. A comparison of the expected benefits from carbon trading with the actual value of millet and groundnuts (the main crops in the study area) indicates that the anticipated benefits would range from less than 1 percent to 4 percent of the annual crop values. These values are extremely low and, hence, highly unlikely to represent a sufficient financial incentive for smallholders to participate in a CS programme.
In the Sudan example, similar calculations on the potential economic importance of CS are rather different. Because of the larger farm size and lower economic inputs, CS could play a larger role.
Based on a census of two villages concerning landholdings and agricultural practices (Warren and Khatir, 2003), two categories of households were assumed for the calculation of the economics of CS: a rich household having 5 ha of millet and 2 ha of sesame; and a poor household having 5 ha of millet. If C were sequestered on these lands according to the CENTURY estimations above, the potential economic gain would be as shown in Table 45. At a price of US$15/tonne, the economic gain from converting cultivation to grazing land would be about 17 percent and 4 percent of the crop yield normally obtained by the poor and rich households, respectively. However, when costs and labour required to produce the crop are taken into account, the economic gain from CS is much more significant. A study carried out in a neighbouring region (International Fund for Agricultural Development, 1988) showed that the economic gains from several crops were negative. On average, the study showed that only the income from watermelons and karkade gave a surplus while millet, sorghum, sesame and groundnuts all cost more to produce than the income from selling the produce. This economic comparison indicates that the level at which CS becomes economically important is very low for farmers in the Sudan case study.
Annual economic gain from adopting land management changes for millet for different price levels of carbon.
Management options (crop to fallow ratio)
C sequestration (kg/ha)
Annual gains poor HH (US$15)
Annual gains rich HH (US$15)
% of annual crop value (poor)
% of annual crop value (rich)
Source: Olsson and Ardö (2002).
The results from the two case studies suggest that the benefits from carbon trading per participating farmer are relatively low. An alternative to small individual cash income that should be considered during project negotiations with local smallholders and designated institutions might be new or improved communal infrastructure, such as schools, wells and health services.
Direct local costs and benefits.
Direct benefits for local smallholders are expected to occur at the field level primarily through increased soil fertility and crop yields that, in turn, will contribute to improved livelihood and food security at the national scale (Figure 45). Practices that involve animals for the production of manure can be combined with income generating activities, such as animal fattening and sale, also creating additional incomes. Switching from cropping to alternative types of land uses, such as grasslands and grazing lands, would free up agricultural labour, primarily during the main cropping season. Such gains in time and energy could be used for alternative, income-generating activities in rural and urban areas. Well-managed agroforestry systems are expected to generate incomes from controlled wood harvesting, seeds and the sale of fruit. However, such gains are unlikely to occur in the short term. In the case of N-fixing species, such as Faidherbia albida , positive impacts can also be expected on yields if they can be introduced into the fields.
On the cost side, the use of improved management practices or the shift from one management practice to another might include significant transaction costs. Today, the vast majority of smallholders in drylands are unlikely to have the necessary inputs to implement improved management practices as assumed with CENTURY. Costs at the local level would include the purchase of animals, fodder, agricultural equipment, and labour, depending on the actual resource endowment of smallholders interested in such a CS scheme. Farmers are also likely to demand compensation for foregone production on croplands converted to alternative land uses (grassland and grazing lands) and long-term fallow periods. As, in most cases, at least half of all croplands are used for subsistence crops, such compensation could occur in kind. A detailed cost - benefit analysis carried out for the Old Peanut Basin revealed significant differences in anticipated net benefits for 15 management options in crop-fallow systems, ranging from - US$1 400 to US$9 600/tonne C (Tschakert, 2004a). These differences are primarily the result of: differential resource endowments of farmers; highly unequal first-year investment costs; and maintenance costs over an assumed period of 25 years.
In addition to local transaction costs, CS schemes would also involve costs related to project design, implementation, monitoring and verification. Costs for monitoring and verification might be substantial because direct soil sampling at the field level would be required in order to obtain reliable and effective results. As shown by Poussart and Ardö (2002), relatively high numbers of soil samples would be needed to detect differences in soil C with satisfactory confidence. In the case of semi-arid Sudan, at least 100 samples would be needed in order to detect a difference of 50 g C/m2 90 percent of the time, testing at a significance level of 0.05. The value 50g C/m2 corresponds to the average amount that could be sequestered in this area in 100 years. If monitoring and verification were to occur every ten years, the number of samples required would be at least ten times higher. Technues to use remotely sensed imagery to assess carbon changes from the air exist, but they lack the precision to detect small-scale variation within farms and farming systems.
Given the results from the case studies, it can be concluded that substantial funds from development organizations or carbon investors will be necessary in order to make soil CS projects in dryland small-scale farming systems a reality. The expected benefits are probably insufficient to compensate farmers for costs occurring at the local level. In addition to these purely economic calculations, there is an ethical concern. Expecting local smallholders to adopt management practices at socially and globally optimal levels implies that they would subsidize the rest of society in their respective countries and as well as the global society, especially the large polluters in the North (Izac, 1997).
Thus, institutional arrangements and policy interventions are perceived as crucial to rectifying this situation.
Institutional and policy factors.
There seems to be increasing recognition among stakeholders, researchers and policymakers that policies in blueprint format, including broad plans of action and universal solutions to a highly dynamic and diverse rural environment, are insufficient and might be counterproductive. As noted by Scoones and Chibudu (1996), efforts to collect more data and build more impressive models in order to construct a more precise picture of reality will not necessarily yield better policies. Only if the uncertainties and complexities of living in risk-prone dryland environments are taken seriously and are consciously integrated into policy formulation, will superior policies be possible.
If one of the main goals of CS in drylands is to contribute simultaneously to sustainable agriculture, environmental restoration, and poverty alleviation on a large scale and over a longer period of time, a more flexible and adaptive management and policy approach is needed (Tschakert, 2004a). Such a policy approach needs to be based on a more detailed understanding of farming systems. It should generate possibilities to strengthen farmers’ own strategies for dealing with uncertainty while providing the necessary incentives to encourage successful pathways. Mortimore and Adams (1999) offer nine principles for inclusion into a new policy framework, all of which are of relevance for the success of anticipated CS programmes. Esses princípios são:
countering variability; promoting diversity in adaptive technologies; facilitating the flexible use of labour; enabling agricultural intensification (through closer integration of crops and livestock); multisectoral scope; promoting open-market conditions; alleviating poverty among vulnerable groups: poor households; alleviating poverty among vulnerable groups: women; reducing the impact of sickness.
As a starting point, it is necessary to understand current and historical links between policies and decision-making processes among smallholders. Of most relevance are policies with respect to agriculture, environment, and land-tenure arrangements. Especially in Sahelian countries, the deterioration of basic rural services that has occurred as a result of structural adjustment policies and State disengagement since the 1980s has had major impacts on farming systems. Figure 45 shows the range of policies that are likely to affect crop production, revenues, and soil management decisions at local level.
In addition to agriculture and environment policies, farmers’ decision-making about possible pathways in farming-system strategies is, to a large extent, determined by access to and control over land, usually regulated by both formal and informal land tenure arrangements. It is critical to understand the extent to which official land tenure laws are enforced and, where not, how strong the influence of informal/customary arrangements might be.
One of the main concerns of potential investors in CS in drylands is insecure title to land. There is considerable debate as to what land tenure security means to local smallholders and whether or not supposedly insecure titles prevent them from making long-term commitments to and investments in improved land and soil management (Zeeuw, 1997; Kirk, 1999). Results from the Senegal study show that farmers perceive usufruct rights as sufficient to invest in “their” lands, although these lands are officially State-owned (Tschakert and Tappan, 2004). What is considered more important than an official title to the land is the possibility to engage freely and flexibly in long-term land transactions, including free loans, rental agreements and mortgages. Currently, the Senegalese law on land tenure (Loi sur le Domaine National) prohibits any type of transaction as well as non-productive uses of land (fallowing) exceeding the duration of one year. Thus, farmers are less inclined to use management practices with longerterm effects on land they will cultivate for no longer than one year. Where they have the means, they will probably buy fertilizers to extract as much as possible from this land in the short period of time allowed.
Thus, current farming systems have also to be seen as a result of land tenure arrangements. The notion of setting aside land for alternative land-use types (conversion of croplands into grassland or grazing lands, tree plantations, or improved and long-term fallow lands) needs to be understood in this context. The extent to which changes in land-use patterns for large-scale CS activities are feasible will depend on: the degree to which formal tenure arrangements are enforced; the perseverance of customary tenure arrangements; and the flexibility of social networks to circumvent one or the other.
The “principle of subsidiarity” (Scoones and Chibudu, 1996) also needs to be included in a more flexible and adaptive management and policy approach. According to this principle, tasks related to CS programmes will have to be divided between various levels of decision-making. These levels range from institutions at the local level (farmers and farmers’ organizations) to community and district-level institutions and service providers (rural and regional councils, extension services, and research organizations) and up to the national government, State institutions, and international agencies.
A long-term and large-scale CS programme that might include several thousand individual smallholders is unlikely to succeed if all programme decisions are taken following an interventionist, top-down approach. This kind of “macro control” is likely to disillusion local farmers and increase the risk that will opt out of agreements.
A first important step towards institutional integration is to identify already existing local and/or regional institutions that might be best suited to function as a vehicle for an anticipated CS programme. In addition to being trusted by the majority of smallholders, such an institution should be able and willing to: participate in the design of a local/regional programme; ensure the necessary participation of an aggregate of smallholders; guarantee a fair distribution of costs; coordinate monitoring and verification; and channel expected benefits in a most desirable and equitable way (Tschakert, 2004b).
Farmers in the Senegal case study defined the following requirements as key for an institution chosen to organize, mobilize and monitor local farmers participating in a carbon programme:
capable of making a detailed assessment of all villages within their scope of influence, including all households, their food needs, farming systems, environmental conditions, land availability, and major constraints for agricultural development;
capable of identifying the most promising as well as feasible land-management options and land-use changes for their land units with and without modifications in agricultural and environmental policies (subsidies and credits) and land-tenure arrangements;
have sufficient influence to request changes in regional and national policies if considered essential;
capable of identifying villages and households with a history of innovativeness and commitment (especially in terms of credit reimbursements);
capable of ensuring a fair distribution of costs and benefits;
capable of deciding for which purpose benefits and additional funds might be used best (rural infrastructure, environmental monitoring, etc);
capable of ensuring the fulfilment of commitments by participating smallholders.
Carbon accounting and verification.
Accounting and verification of the sequestered C is an integral component of a CS project. Accounting implies that all removals by sinks and emissions by sources of CO 2 must be recorded and accounted for. Verification implies that any net removals of CO 2 by sequestration in the soil or in the biomass must be verified through actual measurements.
Verification will usually be carried out by an independent organization. However, continuous monitoring of carbon losses and gains in the farming system must be an integral part of a project for which a designated local institution could be responsible. The overall procedure for verification is that a baseline survey is carried out before any project activities start and after a certain period of time, governed by a project contract. Another survey is carried out to verify any changes in the carbon stock.
Both baseline and follow-up surveys will make use of modelling and stratification as tools for improving the reliability and reducing the costs of surveys, but direct soil sampling will also be required. The number of samples necessary to verify changes in soil carbon stock over time is related to:
uma. the spatial variability of the soil carbon stocks in the project area;
b. the minimum change of carbon stock that must be detected;
c. the statistical level of significance that must be obtained.
Table 46 and Figure 46 illustrate an example of the soil sampling required for verification (Poussart and Ardö, 2002). The study included three different but adjacent agricultural fields in the Sudan case study. The fields all had similar natural conditions in terms of soil, relief and climate, but different land-uses. The land use of the three fields were: cultivation of millet since 1996; fallow with trees for more than 20 years; and grazing only for 18 years. Table 46 shows the descriptive statistics for the three fields. Figure 46 illustrates the number of samples required to verify a change in carbon stocks for different levels of detectable difference and different levels of statistical significance.
Measured soil data for the experimental sites in the Sudan case study.

Dryland trading system

The goal of FP2 is to strengthen agri-food system mechanisms to respond and adapt to context-specific and evolving needs of women, men and young farmers, and value chain and governance actors. It will deliver on multiple System Level Outcomes (SLOs) by catalyzing agri-food system changes that stimulate and support the expansion of production, value addition and trading of dryland cereals and legumes. To achieve these goals, FP2 will actively support agri-food system stakeholders in achieving the following objectives:
The development, adaptation and application of a range of decision support, business development, systems analysis and stakeholder engagement tools needed to unlock dryland cereal and legume utilization opportunities. Improved capacity of agri-food system stakeholders to use the aforementioned tools. The development, in collaboration with key agri-food systems actors and stakeholders, of business models, organizational and institutional innovations, and partnerships and governance arrangements that link farmers to input and output markets and that support the development of equitable, transparent and sustainable value chains. The establishment of functional links between emerging consumer and other agri-food system demands and crop improvement and related production and post-production research. An assessment of the social, economic and environmental impacts of FP2’s agri-food system interventions and implications for future investment and the policy-enabling environment. Development of scalable lessons on the suite of tools, interventions, capacities and processes that are effective in realizing dryland legume and cereal utilization opportunities in ways that are catalytic in agri-food systems transformation in different contexts. Promote agribusiness opportunities and scale-out models using the Innovation Fund that can address the gaps and enhanced market participation of smallholder farming communities in the value chain.
FP2 intends to achieve impact through provision of underpinning research expertise to scale-out partners that seek systemic change and the development of integrated design solutions to address market gaps and enhance market opportunities.
The Flagship envisions positive impact on beneficiaries across different segments of value chains in the target countries. The various segments of the beneficiaries are conservatively estimated to be in the range of: (i) 1,000,000 women and children benefitting from exploring Agri-Food Systems opportunities in terms of improved nutrition; (ii) 400,000 farm women labor benefitting from improved postharvest technologies; (iii) 800,000 households and 5,000 traders using improved post-harvest handling and storage technologies, (iv) benefits from entrepreneurship development and diverse enterprise opportunities will benefit Small and Medium Entrepreneurs (SME) – 1,000; (v) 10,000 young people – in particular young women – trained on business development skills; and (vii) 1,000 value chain stakeholders benefitting due to new linkage of processors to markets. These shall feed into the SLOs towards achieving the overall targets as part of achieving the Intermediate Development Outcomes (IDOs) aligned to the CGIAR SRF.
The Cluster of Activities include:
Incubating and unlocking opportunities at scale Tools, models and processes to support at-scale innovation Systems analysis and learning for at-scale innovation.

Dryland trading system

Location: 11095 61st St. NE, Albertville MN.
The facility is located in the strip mall adjacent to STMA Arena and next door to Westside luor.
The door has “STMA Dryland Facility” signage on the glass.
Click here to visit the Dryland facility website.
Players should wear comfortable workout clothing this would include shorts, sweats, t-shirts & socks.
DRY CLEAN Tennis Shoes (Please don’t wear them in the snow and rain)
Players will need their stick, gloves, and a water bottle for the training.
Players will be divided into small groups (2-3 players) and will rotate between shooting, conditioning/plyometric, and Power skater stations.
Only socks and clean tennis shoes are allowed in the training area. Wet shoes, boots, and jackets should remain in the entrance lobby. This is to keep the synthetic ice free of debris and to prevent damage and injury.
Teams are scheduled back to back. Please be sure to arrive 15 minutes early to allow time for restroom use, change into dry shoes, determining station rotation, and limiting delays/loss of training time for you and the adjacent team.
There will be benches and hooks in the lobby to place your wet shoes/boot, jackets, and bags.
There are no changing facilities so players should come dressed and ready to go in gym clothing.
There is limited floor space. We ask you wait in the main lobby. This allows the walkways to remain un-cluttered and free for player access and rotation.
Coaches need clean dry shoes and be present to instruct (shooting/skating) as this is a supplement to limited ice availability.
Prior to dryland your team manager will divide your team into groups of 2 or 3 player per groups.
Each group will spend equal time at all stations.
When players arrive at the facility they should place wet shoes/boot and jacke ts in the entry .
Power Skater: Group will stand by individual Power Skater (Resistance will be set by coach/trainer)
Workout/Conditioning Station: Groups will go to station assigned by trainer.
Shooting group will lineup on the wall or bench outside the shooting entrance.
Groups will rotate in a clockwise rotation (Trainer will direct groups to next station)
When your training sessions are complete, please use the entrance as a place to congregate rather than the facility training areas. With one team coming and another leaving it will get crowded and we need the training areas free for player movement.
We look forward to developing the players.
STMA TEAMS TRADING DRYLAND HOURS.
IF YOUR TEAM NEEDS TO CHANGE Scheduled DRY LAND:
You may find another team to trade with. Once you have found a team to trade with, please contact Bill Weiser with any dry land scheduling changes, as early as possible, at very least three days ahead of time. (I need to hear from BOTH teams.)
IF YOU CAN'T FIND A TEAM TO TRADE, AND YOUR TEAM DOES NOT SHOW UP FOR DRY LAND:
Your team will be responsible financially for your scheduled time slot at the full rate, and the time will not be made up. Please notify Bill if you plan to not attend a session.
***Please do not trade sessions with another team without notifying Bill ahead of time. As you may know, your team is only covered by insurance if they are scheduled on our official hockey calendar. (Bill would also need to notify Dawn Kyono of any changes and for official calendar changes.)

Dryland trading system

FIGURE 44 Main benefits of improved soil carbon management at various spatial scales.
Source: Izac (1997).
The results obtained in the Senegal and Sudan case studies presented in Chapter 5 were analysed in order to illustrate some economic aspects of CS. Increasing soil C can yield local, national and global benefits. Figure 44 depicts these three levels. It also shows that these benefits can occur on an individual farm as increased crop, timber and livestock yields resulting from increased soil fertility, or in the form of off-farm social benefits on all three levels. On the local level, this second type of benefit constitutes an enhanced land and soil-resource base for future generations. Benefits on the national scale refer primarily to improved food security and agricultural sustainability. On the global level, anticipated benefits from improved soil carbon management are: enhanced biodiversity, increased carbon offsets, and climate change mitigation. Thus, CS in dryland soils could be a win - win situation.
However, as stressed by Izac (1997), caution is required as the costs will be primarily local while the benefits will be local, national and global. From a cost/benefit perspective, it would be rational for farmers to manage their carbon resources with respect to on-farm benefits while ignoring the broad social off-farm benefits. In other words, in the absence of policy interventions and external financial support, local smallholders would use improved management practices at individually optimal levels but at socially suboptimal levels. The following sections provide an overview of the anticipated benefits and costs both from carbon trading (policy intervention) and from direct investment at local level.
Benefits from carbon trading.
One of the anticipated benefits for smallholders benefiting in CS schemes is the financial gain that could be achieved from carbon trading. Currently, carbon credit values as set by carbon exchange and trading systems range between US$1 and US$38 per tonne of C (FAO, 2001b).
In order to put the estimated gain from CS into the farmer’s perspective, prices of agricultural products and assumed prices of C as a tradable good were compared for the Senegal and Sudan case studies. In both cases, farmers were assumed to use an improved management practice or an alternative type of land use on all their current croplands (Tables 44 and 45). Total amounts of croplands vary depending on the wealth status of the farming populations studied. Annual increases in C, as estimated by CENTURY, were assumed to generate US$15/ha, resulting in financial gains per group of households. These financial gains were then compared with the average value of food and cash crops that farmers would grow on these lands if no other alternative existed.
Anticipated economic benefits from carbon trading (1 tonne C = US$15).
C sequestration (tonnes/ha)
Annual gains poor HH (US$15)
Annual gains average HH (US$15)
Annual gains rich HH (US$15)
% of annual crop value.
Compost (2 tonnes).
Conversion of croplands to grasslands + tree protection.
Cattle manure (4 tonnes) + chem. fertilizer.
Sheep manure (10 tonnes)
Rotation 10-year fallow - Leucaena (2 tonnes) and 6 years crops.
Source: Tschakert (fieldwork).
In the Senegal case, average farm sizes in the study villages vary between 3.2 and 15.5 ha, of which 2.8 - 8.9 ha are cultivated (Tschakert, 2004a). If C were sequestered on these lands following the management practices in Table 43, the potential financial gains from carbon trading would range from US$1.4 to US$31 per year. Such gains are expected to be significantly lower for poor households compared with average and rich households. This is because the poor households have less land that could be used for alternative management practices and/or land uses. As Table 44 shows, the maximum annual gains would amount to about US$16 for poor households, US$41 for average households, and US$49 for rich households. A comparison of the expected benefits from carbon trading with the actual value of millet and groundnuts (the main crops in the study area) indicates that the anticipated benefits would range from less than 1 percent to 4 percent of the annual crop values. These values are extremely low and, hence, highly unlikely to represent a sufficient financial incentive for smallholders to participate in a CS programme.
In the Sudan example, similar calculations on the potential economic importance of CS are rather different. Because of the larger farm size and lower economic inputs, CS could play a larger role.
Based on a census of two villages concerning landholdings and agricultural practices (Warren and Khatir, 2003), two categories of households were assumed for the calculation of the economics of CS: a rich household having 5 ha of millet and 2 ha of sesame; and a poor household having 5 ha of millet. If C were sequestered on these lands according to the CENTURY estimations above, the potential economic gain would be as shown in Table 45. At a price of US$15/tonne, the economic gain from converting cultivation to grazing land would be about 17 percent and 4 percent of the crop yield normally obtained by the poor and rich households, respectively. However, when costs and labour required to produce the crop are taken into account, the economic gain from CS is much more significant. A study carried out in a neighbouring region (International Fund for Agricultural Development, 1988) showed that the economic gains from several crops were negative. On average, the study showed that only the income from watermelons and karkade gave a surplus while millet, sorghum, sesame and groundnuts all cost more to produce than the income from selling the produce. This economic comparison indicates that the level at which CS becomes economically important is very low for farmers in the Sudan case study.
Annual economic gain from adopting land management changes for millet for different price levels of carbon.
Management options (crop to fallow ratio)
C sequestration (kg/ha)
Annual gains poor HH (US$15)
Annual gains rich HH (US$15)
% of annual crop value (poor)
% of annual crop value (rich)
Source: Olsson and Ardö (2002).
The results from the two case studies suggest that the benefits from carbon trading per participating farmer are relatively low. An alternative to small individual cash income that should be considered during project negotiations with local smallholders and designated institutions might be new or improved communal infrastructure, such as schools, wells and health services.
Direct local costs and benefits.
Direct benefits for local smallholders are expected to occur at the field level primarily through increased soil fertility and crop yields that, in turn, will contribute to improved livelihood and food security at the national scale (Figure 45). Practices that involve animals for the production of manure can be combined with income generating activities, such as animal fattening and sale, also creating additional incomes. Switching from cropping to alternative types of land uses, such as grasslands and grazing lands, would free up agricultural labour, primarily during the main cropping season. Such gains in time and energy could be used for alternative, income-generating activities in rural and urban areas. Well-managed agroforestry systems are expected to generate incomes from controlled wood harvesting, seeds and the sale of fruit. However, such gains are unlikely to occur in the short term. In the case of N-fixing species, such as Faidherbia albida , positive impacts can also be expected on yields if they can be introduced into the fields.
On the cost side, the use of improved management practices or the shift from one management practice to another might include significant transaction costs. Today, the vast majority of smallholders in drylands are unlikely to have the necessary inputs to implement improved management practices as assumed with CENTURY. Costs at the local level would include the purchase of animals, fodder, agricultural equipment, and labour, depending on the actual resource endowment of smallholders interested in such a CS scheme. Farmers are also likely to demand compensation for foregone production on croplands converted to alternative land uses (grassland and grazing lands) and long-term fallow periods. As, in most cases, at least half of all croplands are used for subsistence crops, such compensation could occur in kind. A detailed cost - benefit analysis carried out for the Old Peanut Basin revealed significant differences in anticipated net benefits for 15 management options in crop-fallow systems, ranging from - US$1 400 to US$9 600/tonne C (Tschakert, 2004a). These differences are primarily the result of: differential resource endowments of farmers; highly unequal first-year investment costs; and maintenance costs over an assumed period of 25 years.
In addition to local transaction costs, CS schemes would also involve costs related to project design, implementation, monitoring and verification. Costs for monitoring and verification might be substantial because direct soil sampling at the field level would be required in order to obtain reliable and effective results. As shown by Poussart and Ardö (2002), relatively high numbers of soil samples would be needed to detect differences in soil C with satisfactory confidence. In the case of semi-arid Sudan, at least 100 samples would be needed in order to detect a difference of 50 g C/m2 90 percent of the time, testing at a significance level of 0.05. The value 50g C/m2 corresponds to the average amount that could be sequestered in this area in 100 years. If monitoring and verification were to occur every ten years, the number of samples required would be at least ten times higher. Technues to use remotely sensed imagery to assess carbon changes from the air exist, but they lack the precision to detect small-scale variation within farms and farming systems.
Given the results from the case studies, it can be concluded that substantial funds from development organizations or carbon investors will be necessary in order to make soil CS projects in dryland small-scale farming systems a reality. The expected benefits are probably insufficient to compensate farmers for costs occurring at the local level. In addition to these purely economic calculations, there is an ethical concern. Expecting local smallholders to adopt management practices at socially and globally optimal levels implies that they would subsidize the rest of society in their respective countries and as well as the global society, especially the large polluters in the North (Izac, 1997).
Thus, institutional arrangements and policy interventions are perceived as crucial to rectifying this situation.
Institutional and policy factors.
There seems to be increasing recognition among stakeholders, researchers and policymakers that policies in blueprint format, including broad plans of action and universal solutions to a highly dynamic and diverse rural environment, are insufficient and might be counterproductive. As noted by Scoones and Chibudu (1996), efforts to collect more data and build more impressive models in order to construct a more precise picture of reality will not necessarily yield better policies. Only if the uncertainties and complexities of living in risk-prone dryland environments are taken seriously and are consciously integrated into policy formulation, will superior policies be possible.
If one of the main goals of CS in drylands is to contribute simultaneously to sustainable agriculture, environmental restoration, and poverty alleviation on a large scale and over a longer period of time, a more flexible and adaptive management and policy approach is needed (Tschakert, 2004a). Such a policy approach needs to be based on a more detailed understanding of farming systems. It should generate possibilities to strengthen farmers’ own strategies for dealing with uncertainty while providing the necessary incentives to encourage successful pathways. Mortimore and Adams (1999) offer nine principles for inclusion into a new policy framework, all of which are of relevance for the success of anticipated CS programmes. Esses princípios são:
countering variability; promoting diversity in adaptive technologies; facilitating the flexible use of labour; enabling agricultural intensification (through closer integration of crops and livestock); multisectoral scope; promoting open-market conditions; alleviating poverty among vulnerable groups: poor households; alleviating poverty among vulnerable groups: women; reducing the impact of sickness.
As a starting point, it is necessary to understand current and historical links between policies and decision-making processes among smallholders. Of most relevance are policies with respect to agriculture, environment, and land-tenure arrangements. Especially in Sahelian countries, the deterioration of basic rural services that has occurred as a result of structural adjustment policies and State disengagement since the 1980s has had major impacts on farming systems. Figure 45 shows the range of policies that are likely to affect crop production, revenues, and soil management decisions at local level.
In addition to agriculture and environment policies, farmers’ decision-making about possible pathways in farming-system strategies is, to a large extent, determined by access to and control over land, usually regulated by both formal and informal land tenure arrangements. It is critical to understand the extent to which official land tenure laws are enforced and, where not, how strong the influence of informal/customary arrangements might be.
One of the main concerns of potential investors in CS in drylands is insecure title to land. There is considerable debate as to what land tenure security means to local smallholders and whether or not supposedly insecure titles prevent them from making long-term commitments to and investments in improved land and soil management (Zeeuw, 1997; Kirk, 1999). Results from the Senegal study show that farmers perceive usufruct rights as sufficient to invest in “their” lands, although these lands are officially State-owned (Tschakert and Tappan, 2004). What is considered more important than an official title to the land is the possibility to engage freely and flexibly in long-term land transactions, including free loans, rental agreements and mortgages. Currently, the Senegalese law on land tenure (Loi sur le Domaine National) prohibits any type of transaction as well as non-productive uses of land (fallowing) exceeding the duration of one year. Thus, farmers are less inclined to use management practices with longerterm effects on land they will cultivate for no longer than one year. Where they have the means, they will probably buy fertilizers to extract as much as possible from this land in the short period of time allowed.
Thus, current farming systems have also to be seen as a result of land tenure arrangements. The notion of setting aside land for alternative land-use types (conversion of croplands into grassland or grazing lands, tree plantations, or improved and long-term fallow lands) needs to be understood in this context. The extent to which changes in land-use patterns for large-scale CS activities are feasible will depend on: the degree to which formal tenure arrangements are enforced; the perseverance of customary tenure arrangements; and the flexibility of social networks to circumvent one or the other.
The “principle of subsidiarity” (Scoones and Chibudu, 1996) also needs to be included in a more flexible and adaptive management and policy approach. According to this principle, tasks related to CS programmes will have to be divided between various levels of decision-making. These levels range from institutions at the local level (farmers and farmers’ organizations) to community and district-level institutions and service providers (rural and regional councils, extension services, and research organizations) and up to the national government, State institutions, and international agencies.
A long-term and large-scale CS programme that might include several thousand individual smallholders is unlikely to succeed if all programme decisions are taken following an interventionist, top-down approach. This kind of “macro control” is likely to disillusion local farmers and increase the risk that will opt out of agreements.
A first important step towards institutional integration is to identify already existing local and/or regional institutions that might be best suited to function as a vehicle for an anticipated CS programme. In addition to being trusted by the majority of smallholders, such an institution should be able and willing to: participate in the design of a local/regional programme; ensure the necessary participation of an aggregate of smallholders; guarantee a fair distribution of costs; coordinate monitoring and verification; and channel expected benefits in a most desirable and equitable way (Tschakert, 2004b).
Farmers in the Senegal case study defined the following requirements as key for an institution chosen to organize, mobilize and monitor local farmers participating in a carbon programme:
capable of making a detailed assessment of all villages within their scope of influence, including all households, their food needs, farming systems, environmental conditions, land availability, and major constraints for agricultural development;
capable of identifying the most promising as well as feasible land-management options and land-use changes for their land units with and without modifications in agricultural and environmental policies (subsidies and credits) and land-tenure arrangements;
have sufficient influence to request changes in regional and national policies if considered essential;
capable of identifying villages and households with a history of innovativeness and commitment (especially in terms of credit reimbursements);
capable of ensuring a fair distribution of costs and benefits;
capable of deciding for which purpose benefits and additional funds might be used best (rural infrastructure, environmental monitoring, etc);
capable of ensuring the fulfilment of commitments by participating smallholders.
Carbon accounting and verification.
Accounting and verification of the sequestered C is an integral component of a CS project. Accounting implies that all removals by sinks and emissions by sources of CO 2 must be recorded and accounted for. Verification implies that any net removals of CO 2 by sequestration in the soil or in the biomass must be verified through actual measurements.
Verification will usually be carried out by an independent organization. However, continuous monitoring of carbon losses and gains in the farming system must be an integral part of a project for which a designated local institution could be responsible. The overall procedure for verification is that a baseline survey is carried out before any project activities start and after a certain period of time, governed by a project contract. Another survey is carried out to verify any changes in the carbon stock.
Both baseline and follow-up surveys will make use of modelling and stratification as tools for improving the reliability and reducing the costs of surveys, but direct soil sampling will also be required. The number of samples necessary to verify changes in soil carbon stock over time is related to:
uma. the spatial variability of the soil carbon stocks in the project area;
b. the minimum change of carbon stock that must be detected;
c. the statistical level of significance that must be obtained.
Table 46 and Figure 46 illustrate an example of the soil sampling required for verification (Poussart and Ardö, 2002). The study included three different but adjacent agricultural fields in the Sudan case study. The fields all had similar natural conditions in terms of soil, relief and climate, but different land-uses. The land use of the three fields were: cultivation of millet since 1996; fallow with trees for more than 20 years; and grazing only for 18 years. Table 46 shows the descriptive statistics for the three fields. Figure 46 illustrates the number of samples required to verify a change in carbon stocks for different levels of detectable difference and different levels of statistical significance.
Measured soil data for the experimental sites in the Sudan case study.

Carbon management in dryland agricultural systems. A review.
Daniel Plaza-Bonilla Email author José Luis Arrúe Carlos Cantero-Martínez Rosario Fanlo Ana Iglesias Jorge Álvaro-Fuentes.
Dryland areas cover about 41 % of the Earth’s surface and sustain over 2 billion inhabitants. Soil carbon (C) in dryland areas is of crucial importance to maintain soil quality and productivity and a range of ecosystem services. Soil mismanagement has led to a significant loss of carbon in these areas, which in many of them entailed several land degradation processes such as soil erosion, reduction in crop productivity, lower soil water holding capacity, a decline in soil biodiversity, and, ultimately, desertification, hunger and poverty in developing countries. As a consequence, in dryland areas proper management practices and land use policies need to be implemented to increase the amount of C sequestered in the soil. When properly managed, dryland soils have a great potential to sequester carbon if financial incentives for implementation are provided. Dryland soils contain the largest pool of inorganic C. However, contrasting results are found in the literature on the magnitude of inorganic C sequestration under different management regimes. The rise of atmospheric carbon dioxide (CO 2 ) levels will greatly affect dryland soils, since the positive effect of CO 2 on crop productivity will be offset by a decrease of precipitation, thus increasing the susceptibility to soil erosion and crop failure. In dryland agriculture, any removal of crop residues implies a loss of soil organic carbon (SOC). Therefore, the adoption of no-tillage practices in field crops and growing cover crops in tree crops have a great potential in dryland areas due to the associated benefits of maintaining the soil surface covered by crop residues. Up to 80 % reduction in soil erosion has been reported when using no-tillage compared with conventional tillage. However, no-tillage must be maintained over the long term to enhance soil macroporosity and offset the emission of nitrous oxide (N 2 O) associated to the greater amount of water stored in the soil when no-tillage is used. Furthermore, the use of long fallow periods appears to be an inefficient practice for water conservation, since only 10–35 % of the rainfall received is available for the next crop when fallow is included in the rotation. Nevertheless, conservation agriculture practices are unlikely to be adopted in some developing countries where the need of crop residues for soil protection competes with other uses. Crop rotations, cover crops, crop residue retention, and conservation agriculture have a direct positive impact on biodiversity and other ecosystem services such as weed seed predation, abundance and distribution of a broad range of soil organisms, and bird nesting density and success. The objective of sequestering a significant amount of C in dryland soils is attainable and will result in social and environmental benefits.
1 Introduction.
Dryland areas are characterized by a low ratio of mean annual precipitation to potential evapotranspiration (ranging from 0.05 to 0.65) and cover about 41 % of the surface of the Earth (Lal 2004 ; Middleton and Thomas ( 1997 ). The soils of these areas have an inherent low stock of organic carbon (C) due to climatic limitations. On the contrary, they contain a significant amount of inorganic C, of a persistent nature, mainly present in the form of soil carbonates (Denef et al. 2008 ). Given the almost nonexistent chance for expanding irrigation in most dryland agroecosystems, other ways of land use optimization need to be identified (Hall and Richards 2013 ).
Mismanagement such as intensive tillage, excessive grazing, or elimination of vegetative cover has resulted in the loss of some 13–24 Pg C in grasslands and drylands (Ojima et al. 1995 ), leading to important degradation processes such as soil erosion, loss of ecosystem services, and, ultimately, to desertification (Zika and Erb 2009 ). Desertification has been directly related to global sustainability threats such as malnourishment and poverty and huge economic losses, particularly in dry climate areas (Zika and Erb 2009 ). Currently, dryland areas are facing new challenges such as the impact of climate change on hydrological regimes and net primary productivity, as well as an increasing human population pressure (Mouat and Lancaster 2008 ).
A semiarid dryland agricultural system in the Ebro valley (NE Spain): a tillage and fertilization experiment was established in 2010 in a commercial 4-year no-tilled field devoted to winter cereal production. The impact of a single pass of disk plow (15-cm depth) before sowing ( plots of the right ) and of the maintenance of no-tillage ( plots of the left ) on crop performance is shown.
Livestock use of stubble and straw from winter cereals and forage grazed from fallows is a common feature of large dryland regions such as the Mediterranean basin. The activity contributes to maintain a mosaic of cultivated and natural areas enhancing ecosystem services. If properly managed, livestock integration in dryland areas contributes to the increase in soil organic carbon contents.
Approach to evaluate research needs for optimizing C management in dryland agroecosystems.
2 The need for carbon management improvement in dryland agroecosystems.
2.1 Better understanding of agricultural management and soil carbon issues.
2.1.1 Soil erosion and carbon losses.
Dryland environments are usually prone to soil erosion due to the lack of a significant soil cover, which is usually aggravated by the high intensity of rainstorms (typical in some dryland areas such as the Mediterranean basin), a reduced soil structural stability, which is generally associated to a limited amount of SOC, and a high human pressure. Other factors such as the presence of steep slopes also exacerbate the susceptibility to soil erosion in drylands (García-Ruiz 2010 ). Moreover, as a consequence of climate change, some projections suggest that erosion rates could increase by 25–55 % during the twenty-first century (Delgado et al. 2013 ). In turn, the erosion of soil surface layers can also lead to the exposure of carbonates to climatic elements and acid deposition, aspects that could increase the loss of C from soils to the atmosphere (Lal 2004 ; Yang et al. 2012 ).
Three main mechanisms explain the flux of organic C between soil and the atmosphere as a result of an erosive process: (i) at eroding sites, SOC is decreased because plant inputs are decreasing with decreased productivity; (ii) SOC decomposition is enhanced due to physical and chemical breakdown during detachment and transport; and (iii) decomposition of the allochthonous and autochthonous C fraction buried is reduced (Van Oost et al. 2007 ).
In dryland areas, the critical role played by vegetative covers on soil erosion reduction and SOC maintenance has been long recognized. However, in these areas, conventional management technues hinder the presence of an adequate protection of the soil surface: (i) the use of intensive tillage in herbaceous and tree crops (Álvaro-Fuentes et al. 2008 ), (ii) feed needs for animal production (López et al. 2003 ), (iii) excessive grazing (Hoffmann et al. 2008 ), and (iv) the recent high feedstock demand for bioenergy (Miner et al. 2013 ). In developing countries of Asia and Africa, the extractive nature of using crop residues as fodder for cattle and animal dung as a cooking fuel poses a serious problem to soil quality and the sustainability of crop production (Lal 2006 ). In those countries, soil organic carbon decline needs to be counteracted by increasing the amount of crop residues produced. However, due to the highly weathered nature of soils in some developing regions such as West Africa, some fertilization is needed to avoid the depletion of soil nutrients (Bationo et al. 2000 ).
Obviously, there is a need for a reliable economic assessment of the long-term benefits of maintaining crop residues on the soil surface in terms of C sequestration, erosion reduction, nutrient cycling, and water retention. This information would be of a great value for farmers in order to reduce the amount of crop residues that is currently removed from agricultural fields given the concomitant short-term economic returns of this practice.
The use of conservation tillage and more recently no-tillage practices leave the soil covered by crop residues, which has long been recognized as an excellent means of decreasing soil erosion (Delgado et al. 2013 ). For instance, given their potential in reducing soil degradation, the Chinese government is promoting the use of conservation tillage practices throughout vast dryland regions of northern China (Wang et al. 2007 ). According to data from the Chinese national projects regarding conservation tillage, the last authors reported a 60 to 79 % decrease in soil erosion when using no-tillage. Similarly, in a modeling study, Fu et al. ( 2006 ) reported a decrease of soil erosion from 17.7 to 3.9 t ha −1 year −1 when adopting no-tillage, due to mitigation of rill generation. Different tillage experiments have been carried out by the International Center for Agricultural Research in the Dry Areas (ICARDA) in the Central Asia region. According to Thomas ( 2008 ), those experiments show that conservation tillage performed well in terms of energy and soil conservation and that crop yields were either not affected or slightly increased. Unfortunately, the benefits of no-tillage have not been tested in all the dryland agricultural areas of the world. For instance, in Central Asia, only Kazakhstan has a brief history in adopting no-tillage farming with locally manufactured machinery (Thomas, 2008 ). The study about the potential use of no-tillage in Africa carried out by the German Agency for Technical Cooperation ( 1998 ) concluded that in the semiarid and arid regions of West and Southeastern Africa, different constraining factors such as (i) short growing season, (ii) low levels of biomass production, and (iii) competition for crop residues would make more viable the use of reduced tillage methods. Similarly, for semiarid West Africa, Lahmar et al. ( 2012 ) concluded that it is unlikely that conservation agriculture practices, which are based on the presence of crop residues on the soil surface, will be adopted by farmers due to the competition with other residue uses.
Recent technological advances can improve the performance of no-tillage in dryland areas. For instance, in field crop production, the development and use of stripper-headers as attachments for combines has a great potential to reduce soil erosion risks when no-tillage is used. This technological improvement virtually leaves all crop residues on the soil surface, thus reducing harvest costs by lower fuel consumption (Spokas and Steponavicius 2011 ) and, as a result, diminishing CO 2 emissions to the atmosphere. This technology is also of great interest in areas that receive winter snow for its capacity to trap the snow (Henry et al. 2008 ). Moreover, the presence of taller vertical crop stalks reduces the wind speed, thus lowering the chance of losing soil C due to wind erosion and minimizing water evaporation (Henry et al. 2008 ).
Soil management in tree-cropping (e. g., vine, olives, almonds, etc.) traditionally involves frequent tillage because uncontrolled weed growth competes for water resources with crops. However, some studies have shown that soil erosion can be minimized while maintaining yields with the use of a properly managed vegetative cover (Gómez et al. 1999 ; Kairis et al. 2013 ). In this context, more research is needed to find the optimum technological choices for cover cropping in order to enhance SOC stocks while reducing the susceptibility to soil erosion under water-limiting environments. This would imply the identification of (i) the best species to act as vegetative cover, (ii) optimum termination strategies such as chemical weeding or physical clearing, and (iii) the best dates for termination according to local rainfall distribution and crop water needs.
Future research also must address the impacts of the demand for cellulosic-based fuels on soil conservation and SOC stocks maintenance (Wilhelm et al. 2007 ). In this line, Miner et al. ( 2013 ) modeled the impact of harvesting crop residues for biofuel production, in a wheat-corn-fallow cropping system in the semiarid central Great Plains. These authors observed unsustainable wind erosion rates after harvesting 10 to 30 % of corn residues, while up to 80 % of wheat residues could be removed without reaching the tolerable soil loss limit. However, they also found that any removal of wheat or corn residues implied a loss of SOC. This study clearly indicates that the use of crop residues for bioenergy needs to be considered with caution in dryland areas. Similarly, in grassland systems, the management of livestock grazing intensities needs to be optimized to reduce soil compaction and surface sealing, processes that can exacerbate the loss of SOC by wind and water erosion and reduce the production of biomass (Delgado et al. 2013 ). For instance, in these systems, it has been reported that erosion can lower soil productivity by at least 10–20 % due to a reduction of SOC and nutrients and to related negative impacts on other soil properties (Delgado et al. 2013 ). In developing countries, the lack of affordable nutrients and soil mining makes crops entirely reliant on soil organic matter (Samaké et al. 2005 ).
Current research on the effects of agricultural management practices on soil erosion and C stabilization has been performed at the plot scale. For that reason, the role of erosion-deposition processes on SOC balance at the landscape scale has not been accurately assessed (Govaerts et al. 2009 ; Izaurralde et al. 2007 ). This would also help us clarify the current controversial and site-specific effects of soil erosion on the global C cycle (Kuhn et al. 2009 ) without forgetting the pool of inorganic C. Currently, there is a lack of understanding regarding the impact of wind and water erosion on greenhouse gas emissions (Kuhn et al. 2012 ), mainly methane (CH 4 ) and nitrous oxide (N 2 O). For instance, erosion can increase indirectly N 2 O emissions in upper slope landscape positions due to the greater application of nitrogen (N) fertilizers carried out by the farmers to compensate for the reduction in soil fertility. In dryland ecosystems, the maintenance of a protective vegetative cover appears as the most practical and straightforward strategy to reduce soil C losses by erosion. Consequently, agricultural activity in those areas must be based on conservation agriculture practices, leaving crop residues on the soil surface.
2.1.2 Soil inorganic carbon sequestration and dynamics.
There is a growing recognition that the interaction of agricultural practices and soil inorganic carbon is of key importance to the global C cycle. However, the lack of information on soil inorganic carbon dynamics in cropland soils as affected by land use and management, as well as the uncertainties regarding pedogenic inorganic C in relation to soil inorganic carbon sequestration, were identified in the late 1990s as major knowledge gaps regarding the C sequestration potential of agricultural activities (Lal and Kimble 2000 ). These authors pointed out the need to quantify the dynamics of the soil inorganic carbon pool in dryland soils of arid and semiarid regions and proposed several land use and soil management strategies for soil inorganic carbon sequestration in dryland ecosystems, through the formation of secondary carbonates. Through the latter process, Lal ( 2004 ) reported an average soil inorganic carbon sequestration rate of 0.1–0.2 Mg ha −1 year −1 in dryland ecosystems.
Apart from its potential as atmospheric CO 2 sink, soil inorganic carbon may play an indirect positive role in soil aggregation through the interaction between carbonates and soil organic matter. According to Bronick and Lal ( 2005 ), the beneficial effect of carbonates on soil structure is regulated by soil organic matter. At low organic matter contents, the water stability of soil macroaggregates is strongly correlated with the carbonate content (Boix-Fayos et al., 2001 ). Carbonates can also contribute to soil organic matter protection and stabilization. In calcareous soils, with high exchangeable Ca, high carbonate contents enhance physical SOC protection within aggregates due to a cation bridging effect that leads to slower SOC decomposition rates compared with non-calcareous soils (Clough and Skjemstad 2000 ). However, depending on soil management, the relative role of carbonates and soil organic matter in soil aggregation may alter the aggregates hierarchy as observed by Virto et al. ( 2011 ) in carbonate-rich soils in semiarid Spain.
However, in the last decade, few studies have evaluated the impacts of land use and management practices on soil inorganic carbon dynamics in semiarid lands (Denef et al. 2011 ). In some of those studies, soil inorganic carbon storage has proven to be significantly higher in cultivated dryland soils compared with native grassland soils (Cihacek and Ulmer 2002 ; Denef et al. 2008 ), but the reduction of tillage may have differing effects in the long term. Hence, contrasting results have been obtained when comparing the amount of soil inorganic carbon under different types of tillage (Blanco-Canqui et al. 2011 ; Moreno et al. 2006 ; Sainju et al. 2007 ).
Carbon sequestration as inorganic forms has been proposed as a viable alternative in irrigated soils in semiarid and arid regions (Entry et al. 2004 ). However, the literature on this issue is scarce and also with contrasting arguments and results. Hence, while some authors consider that secondary carbonate precipitation is an important mechanism of soil C sequestration, others argue that dissolution of carbonates should be considered sequestration (Sanderman 2012 ). In this context, when calcium-enriched groundwaters are used for irrigation, CaCO 3 is formed, thus leading to the release of CO 2 (Schlesinger 2000 ).
Likewise, the studies on soil inorganic carbon dynamics under long-term irrigated farming have shown mixed results. While Entry et al. ( 2004 ) and Wu et al. ( 2009 ) reported a greater amount of soil inorganic carbon in irrigated treatments compared with native soils, Denef et al. ( 2008 ) did not find significant difference in soil inorganic carbon between irrigated and dryland treatments. In turn, Halvorson and Schlegel ( 2012 ) found that under limited irrigation, soil inorganic carbon tends to increase with time in all soil depths, supporting the results by Blanco-Canqui et al. ( 2010 ). In any case, an account of the entire C footprint would be needed when considering soil inorganic carbon sequestration with irrigation, taking into account the energetic cost of pumping water and the concomitant release of CO 2 in the case of pump-based irrigation systems (Schlesinger 2000 ).
Other studies have linked soil inorganic carbon sequestration with the quality of the irrigation water. For instance, Eshel et al. ( 2007 ) found that long-term irrigation of semiarid soils undergo significant losses of soil inorganic carbon in the root zone compared with non-irrigated soils and that these soil inorganic carbon losses are much larger in soils irrigated with potable fresh water compared with effluent-irrigated soils. They concluded that effluent water inhibited carbonate dissolution. Data provided by Artiola and Walworth ( 2009 ) suggest that the release and leaching of both SOC and soil inorganic carbon are directly linked to the dissolution of soil carbonates, and therefore related to irrigation water quality. However, the literature on the effects of agricultural land management on leaching of dissolved inorganic C is also limited (Walmsley et al. 2011 ).
Furthermore, most of the studies dealing with CO 2 emission from agricultural soils to the atmosphere assume that all the CO 2 emissions are due to respiration. Some authors, however, have questioned whether this assumption is valid in calcareous soils. For instance, Tamir et al. ( 2011 ) reported that the dissolution of soil carbonates can contribute up to 30 % of the CO 2 emitted from calcareous soils in Israel. In contrast, in an incubation experiment, Ramnarine et al. ( 2012 ) estimated that the proportion of CO 2 originating from carbonates was up to 74 % in both conventional tillage and no-tillage samples from a calcareous soil in Canada. The last findings suggest that the CO 2 emitted by respiration could be largely overestimated in calcareous soils.
The complex nature of the accumulation and depletion processes involved in soil inorganic carbon sequestration might partially explain not only the knowledge gaps mentioned above but also the contrasting results found in the literature on the magnitude of soil inorganic carbon sequestration under different management regimes (Rodeghiero et al. 2011 ). As pointed out by Sanderman ( 2012 ), in his recent review on the major soil inorganic carbon transformations in soils as affected by the agricultural management in Australia, more research is needed to determine the real importance that management-induced changes in soil inorganic carbon stocks have on net greenhouse gas emissions.
Despite its potential in semiarid and arid regions, the implementation of key practices for soil inorganic carbon sequestration through pedogenic carbonate formation is still impeded by our limited knowledge on this particular issue.
2.1.3 Soil biodiversity and ecosystem services.
Biodiversity is considered fundamental for the stability of ecosystem services in agricultural systems (Naeem et al. 2012 ). Plant biodiversity represented by polycultures, crop rotations, cover crops, and agroforestry with perennial vegetation can provide important ecosystem services (Perfecto and Vandermeer 2008 . In agricultural systems, the use of that diversity in combination with other agricultural practices such as vegetative mulches, fertilization, irrigation, and the reduction of tillage intensity affects soil C pools, increasing net productivity (Hoyle et al. 2013 ; Stockmann et al. 2013 ).
In dryland agroecosystems, the lack of water is the main limiting factor affecting crop diversity, net primary productivity, SOC dynamics, and soil microbial activity (Skopp et al. 1990 ). In dryland agriculture, there are four important aspects to improve productivity, provide ecosystem services, and increase SOC: (i) taking advantage of plant diversity (i. e., use of legumes, agroforestry), (ii) establishing proper crop residue management, (iii) improving our knowledge about the importance of soil biology on C cycling, and (iv) determining the optimum level of ecological crop intensification (i. e., rotations, fertilization, etc.).
Plant diversity promoted by crop rotations (West and Post 2002 ) usually increases aerial biomass and favors the diversification of root systems (i. e., belowground C allocation), with a diverse effect on SOC by root-derived products (Stockmann et al. 2013 ). Deep rooting can contribute to the enhancement of soil C stock in depth (Hoyle et al. 2013 ; Jobbagy and Jackson 2000 ). In rainfed agriculture, the development of practices for efficient use of the whole soil profile, such as the use of species and cultivars with deeper and improved root systems, must be considered, as it is highlighted in section 2.2 . The development of better-adapted root systems needs to be accompanied by an improvement in the current knowledge about the changes that occur in soil biodiversity with soil depth and their effects on C cycling (Witt et al. 2011 ).
Given the low reliability of seasonal precipitation forecasts in semiarid areas, the selection of crops with assured positive net returns is a difficult task (Saseendran et al 2013 ). The inclusion of legumes in crop rotations has been proposed as a practice for increasing SOC in dryland conditions (Sanderson et al. 2013 ). Legumes play a positive role in the reduction of subsequent crop fertilization needs. However, the higher mineralization rate of leguminous crop residues can increase the risk of N leaching during fallow periods, since most semiarid dryland systems give small opportunities to the use of cover crops. Furthermore, the addition of N-rich crop residues from legumes is not always followed by higher SOC stocks as a consequence of the greater rate of decomposition (Stockmann et al. 2013 ). Moreover, under a purely economic perspective, the inclusion of legumes in semiarid dryland crop rotations is not always beneficial (Álvaro-Fuentes et al. 2009a ) and could also lead to greater N losses as N 2 O (Sanderson et al. 2013 ).
Crop residue properties (i. e., quantity, quality, placement, and supply interval) affect SOC and soil fauna, bacteria, and fungi (Agren and Bosatta 1996 ; Dalal and Chan 2001 ). The amount and composition of crop residues are directly affected by crop species, and also by agricultural practices such as fertilization or irrigation. An increase of crop residues could improve N use efficiency and reduce N losses (Blanco-Canqui 2010 ). However, as it has been already mentioned in section 2.1.1 , under rainfed conditions, the low availability of crop residues reduces the potential for C storage (Blanco-Canqui et al. 2011 ; Stockmann et al. 2013 ). As a consequence, in drylands, it is important to develop an integrated strategy to maintain and manage crop residues according to plant and soil biodiversity and economics.
The soil microbial community is an indicator of soil quality and soil fertility, and its functional diversity and changes deserve further study (Dalal and Chan 2001 ). The microbial community has the capacity of suppressing the impacts of pathogens (Verhulst et al. 2010 ) and directly affects SOC dynamics. Moreover, other important indicators of soil biological activity such as earthworm abundance and community composition result in larger and interconnected pores increasing water infiltration (Verhulst et al. 2010 ), a fact that has a direct effect on C inputs to the soil, microbial activity, and SOC decomposition. Other organisms such as arbuscular mycorrhizal fungi play an important role in nutrient acquisition, drought resistance, and maintenance of soil stable aggregates (Oehl et al. 2005 ; Sanderson et al. 2013 ).
A reduction in cropping intensification decreases species diversity and plant biomass and could lead to the reduction of the loss of natural resources (Tongway and Hindley 2004 ). In dryland agricultural systems, crop rotations, cover crops, crop residue retention, and conservation agriculture increase water use efficiency, biomass production, and SOC and have a direct impact on biodiversity and different ecosystem services such as weed seed predation (Baraibar et al. 2011 ), abundance and distribution of a broad range of soil organisms (Buckerfield et al. 1997 ; Henneron et al. 2015 ; Sapkota et al. 2012 ), or bird nesting density and success (Van Beek et al. 2014 ). On the other hand, there are some complex interactions that determine crop productivity and C storage in soils, making difficult the observation of real patterns and the development of management recommendations (Corsi et al. 2012 ). Then, before establishing the degree of ecological intensification to be applied in dryland agroecosystems, it is needed to determine how the interactions between soil microbial diversity, plant communities, and cropping practices can improve productivity and affect SOC (Duffy 2009 ; Zavaleta et al. 2010 ). The use of various management practices (e. g., polycultures, crop rotations, agroforestry, reduction of tillage, etc.) enhances the positive feedback existing between soil carbon sequestration and biodiversity in rainfed farming systems.
2.2 Adoption of more efficient water management practices.
The productivity of dryland agricultural systems is hindered by the water deficit created by the difference between precipitation and potential evapotranspiration. Given the irregularity of rainfall in most dryland areas, there is a strong need to develop regional decision tools to establish the most appropriate agricultural management strategies (i. e., choice of crop, sowing time, management of soil cover, timings and rates of N application, etc.) according to the amount of water held in the soil. Implementing proper decisions would increase the amount of biomass produced and SOC sequestered. To achieve this objective, the information obtained in long-term field trials is essential for improving current knowledge. To increase the amount of biomass produced and, consequently, the above - and belowground inputs of C to the soil, the amount of plant available water needs to be enhanced. To accomplish this, three factors need to be maximized: (i) precipitation capture; (ii) water retention in the soil, and (iii) crop water use efficiency (Peterson and Westfall 2004 ). The amount of precipitation captured is strongly related to soil structural stability and to the abundance and continuity of macropores in the soil surface. Agricultural management practices play a major role on the buildup and breakdown of soil surface aggregates (Plaza-Bonilla et al. 2013b ), thus directly affecting soil structure. In dryland areas, soil aggregate stability needs to be maximized to guarantee (i) a continuous network of soil macropores and (ii) a durable physical protection of SOC against microbial decomposition. The accumulation of C in the soil surface (i. e., C stratification) as a consequence of the use of different agricultural practices (e. g., no-tillage, biochar addition) usually improves water infiltration and saturated hydraulic conductivity (Franzluebbers 2002 ; Jordán et al. 2010 ). Recent advances in X-ray computed tomography are increasing our knowledge about soil structure and the impacts of agricultural management on soil macroporosity (Perret et al. 1999 ). Other tools such as the measurement of soil sorptivity are used to assess the potential of soil to capture rainfall (Shaver et al. 2013 ). Nevertheless, with the current knowledge, it is still difficult to develop tools (i. e., models) that quantify with precision the impact of agricultural management on the dynamics of the soil porous network (Pachepsky and Rawls 2003 ). The development of these models would be of great interest to identify the best practices to capture rainfall in dryland areas as a function of soil characteristics. Another important strategy to enhance the amount of water retained in the soil is rainwater harvesting, which consists in collecting and storing runoff water in shallow troughs. This system is widely used in developing countries and in specific tree-cropping systems in some developed ones (FAO, 2004 ). A thorough review about the implementation of rainwater harvesting technues in the sub-Saharan Africa can be found in Vohland and Barry ( 2009 ).
Once water has infiltrated into the soil profile, the efforts must be placed on its retention. In dryland areas, maintaining the soil surface covered is critical to preserve water (Montenegro et al. 2013 ). Different cropping technologies have been proposed in order to increase soil water retention. Traditionally, fallow has been used in dryland areas to increase soil water content, N availability, and weed control. Many studies have pointed out the inefficiency of this practice in terms of water storage. Thus, the works by Lampurlanés et al. ( 2002 ) and Hansen et al. ( 2012 ) showed that only 10–35 % of the rainfall received was available for the next crop when fallow was included in the rotation. Water is lost during fallow periods due to evaporation given (i) the low amount of residues covering the soil surface and (ii) the frequent use of tillage to eliminate weeds in most of the dryland agroecosystems. Thus, research has also been oriented to reduce bare fallow periods by intensifying cropping systems and the use of green manures such as legumes. According to Álvaro-Fuentes et al. ( 2008 ), the suppression of long-fallowing leads to an improvement of soil structural stability, thus increasing water infiltration and retention. Moreover, when fallow is eliminated, C inputs are increased due to a higher production of biomass which enhances the amount of SOC sequestered (Álvaro-Fuentes et al. 2009b ; Virto et al. 2012 ). However, in areas with a high water deficit, the benefits of using cover crops as green manure are offset by water lost for subsequent cash crops (Hansen et al. 2012 ). The use of legumes as green manure could also have a detrimental impact on SOC as it has been discussed in the previous section.
The use of conservation tillage systems such as reduced tillage or no-tillage has been pointed out as one of the most promising strategies to enhance SOC stocks in dryland areas due to its beneficial effect on soil water storage (Fig. 1 ), which results in turn in greater biomass production and higher C protection within soil aggregates (Aguilera et al. 2013a ). Significant rates of C sequestration have been reported in different dryland cropping systems when using no-tillage. For instance, Vågen et al. ( 2005 ) reported a rate of 0.05 to 0.36 Mg C ha −1 year −1 in sub-Saharan Africa while Farina et al. ( 2011 ) reported a rate of 0.31 Mg C ha −1 year −1 in a no-till sunflower-wheat rotation in Italy.
However, the general hypothesis that no-till is always followed by SOC sequestration is still controversial since in most of the studies comparing the effects of different tillage systems on soil C, only the surface soil (0–30-cm depth) has been taken into account (Govaerts et al. 2009 ; Palm et al. 2013 ). Furthermore, attention has to be paid to a possible increase in the emission of N 2 O when using low-intensity soil management systems, as a result of the greater amount of water stored in the soil. That increase could offset the amount of C sequestered under reduced tillage and no-tillage, since N 2 O has a global warming potential 298 times greater than CO 2 (Six et al. 2004 ). However, recent works have found lower N 2 O emissions when no-tillage is practiced in the long term due to a reduction of anaerobic microsites in the soil (Plaza-Bonilla et al. 2014 ; van Kessel et al. 2013 ). These last aspects indicate that future research must take into account the whole C footprint associated to the long-term effects of agricultural practices on greenhouse gas emissions in dryland soils, taking advantage of long-term field experiments and properly validated models.
Once retained in the soil, water needs to be used efficiently by plants, a process that can be improved by using a proper crop management and election of plant material. Drought-prone environments need specific breeding programs in order to find traits related to an efficient water use through stomatal transpiration (Blum 2005 ). For instance, an improved stomatal control, higher photosynthetic rates, and increased stay green have been enumerated in new drought-tolerant corn cultivars (Roth et al. 2013 ). Similarly, the improvement of root systems to enhance water use in dryland environments remains a critical issue (Hall and Richards 2013 ). The selection for more adapted root systems would also impact positively on C sequestration, since belowground biomass constitutes an essential input of C to the soil, given its longer time of residence compared with the aerial biomass inputs (Rasse et al. 2005 ). There also is an urgent need to identify genotypes with traits better adapted to no-tillage conditions, such as a more vigorous emergence or a higher resistance to different diseases (Herrera et al. 2013 ).
Crop water use is significantly affected by other management practices such as crop fertilization, which affects leaf area and transpiration. In drylands, the use of fertilizers is not always followed by an increase of SOC stocks due to the low crop response to the application of nutrients such as N as a consequence of lack of water. As a result, in dryland agriculture, the effects of N fertilization on SOC usually appear in the long term (Álvaro-Fuentes et al. 2012 ) and still are a controversial issue (Khan et al. 2007 ), especially if the energy cost associated with the N fertilizer production is taken into account. In this context, the use of organic fertilizers (i. e., slurries or manures), which is a common practice in some drylands, has the potential to increase SOC stocks and C physical protection within soil aggregates (Plaza-Bonilla et al. 2013a ). However, this strategy is only applicable in certain developed areas with nutrient surpluses. Another recent work shows a decrease in N 2 O emissions when using organic fertilizers in comparison with the use of synthetic products in dryland areas (Aguilera et al. 2013b ).
Maximizing soil water availability for plants is of paramount importance in dryland areas for enhancing C sequestration in soils. To achieve this, long bare fallow periods need to be suppressed and soil tillage must be reduced or eliminated.
2.3 Livestock integration into dryland farming systems.
The impact of livestock activities on the environment is either direct like grazing (in extensive livestock systems) or indirect through production of forage crops for confined livestock feeding. Presently, livestock production accounts for 70 % of all world agricultural land and 30 % of the Earth’s land area (Steinfeld et al. 2006 ). In relation to ecological conditions and environmental changes, the increase in the demand of animal products will affect more intensely grasslands in arid, semiarid, and tropical regions (Follett and Schuman 2005 ) (Fig. 2 ). Despite the inherently low SOC sequestration rates that have been reported in grasslands when compared with other land uses, their global impact can be significant given the surface covered by this land use (Follett and Schuman 2005 ). The potential C storage in grasslands varies according to climatic conditions and management (Silver et al. 2010 ). For instance, the last authors reported soil C contents of 200 Mg C ha −1 in the first 100-cm soil depth in annual grass-dominated rangelands in California.
Soil C can be affected by more than one process when grasslands are used for grazing: soil compaction, a decrease of standing biomass, diminution of vegetation coverage, changes in root biomass, and potential increases in erosive processes (Jing et al. 2014 ). Conflicting results have been reported regarding the effect of grazing intensity on SOC. While some authors found an increase in SOC stock with intensively managed grasslands (Conant et al. 2003 ; Reeder et al. 2004 ), others concluded that high stocking rates reduce the aboveground grass biomass and, as a consequence, diminish soil C stocks, which affect the labile fractions such as the particulate organic matter (Silveira et al. 2013 ; Smith et al. 2014 ). Regarding to this subject, Han et al. ( 2008 ) observed a decrease of 33 and 24 % in SOC and total N (0–30-cm depth), respectively, under heavy grazing when compared to light grazing in a semiarid continental steppe in northeastern Inner Mongolia. These results were confirmed by Steffens et al. ( 2008 ), who found a deterioration of different soil properties including organic carbon in a heavily grazed steppe in the same semiarid region. Furthermore, the intensity of grazing can also influence soil inorganic carbon dynamics. Reeder et al. ( 2004 ) reported an increase of soil inorganic carbon of 10.3 Mg ha −1 in the 45- to 90-cm depth of a heavily grazed treatment compared to its exclosure in an experiment carried out in the Central Plains of the USA. However, in this study, the authors were not able to distinguish whether the increase in soil inorganic carbon represented newly fixed C or a redistribution of the existing material.
The type of grazing can also influence SOC content. For instance, the multi-paddock system usually leads to greater C contents than the light continuous system (Teague et al. 2011 ). A synthesis of the effects of grazing on SOC stocks can be found in the work of Pineiro et al. ( 2010 ). Proper grazing management should maintain a favorable C balance in the ecosystem versus haymaking or combined practices (Oates and Jackson 2014 ; Ziter and MacDougall 2013 ). For example, the use of conservative practices to avoid overgrazing or to fence plots has represented a solution to erosion damages in Chinese grasslands (Fang et al. 2010 ; Han et al. 2008 ).
Domestic herbivores tend to uncouple C and N cycles by releasing digestible C as CO 2 and CH 4 , and by returning digestible N at high concentrations in urine patches. The latter aspect is directly linked to the stocking rate and the period of grazing, and can potentially increase the emissions of N 2 O (Soussana and Lemaire 2014 ). The use of short grazing periods or nitrification inhibitors has been reported to lower N 2 O emissions from urine patches (Li et al. 2013 ). However, the effectiveness of nitrification inhibitors is arguable given the spatial and temporal heterogeneity of the urine patches in grazed systems.
The rapid population growth after the Second World War and the increase in the demand of animal products has facilitated the transformation of natural vegetation to arable land to produce feed for animals. Traditionally, extensive livestock production was based in local available feed resources such as crop residues and rough vegetation that had no value as human food. The conversion of pastures to arable crops caused changes in soil C distribution due to soil aggregation disturbance and changes in crop residue inputs and decomposability, thus resulting in C losses (Matos et al. 2011 ; Su 2007 ). A study conducted in 27 European soils quantified C losses when grasslands were converted to croplands (i. e., a loss of 19 ± 7 Mg C ha −1 ), and an accumulation of 18 ± 7 Mg C ha −1 when cropland was converted to grassland (Poeplau and Don 2013 ). Similarly, in a study about the potential for soil C sequestration in Central Asia, Sommer and de Pauw ( 2011 ) pointed out that the conversion of native land into agricultural land and the degradation of rangelands led to a loss of 4.1 % of the total SOC pool. In turn, global warming and drought in grasslands will change the physiology of grassland species and, consequently, the SOC balance (Sanaullah et al. 2014 ). In Europe (the EU25 plus Norway and Switzerland), some predictions suggest that cropland SOC stocks from 1990 to 2080 would decrease by 39 to 54 %, and grassland SOC stock could increase up to 25 % under the baseline scenario, but could decrease by 20–44 % under other scenarios (Smith et al. 2005 ).
Current knowledge about the synergies and trade-offs in adaptation and mitigation strategies in grasslands is still limited and requires further research (Soussana et al. 2013 ). In this regard, three specific actions are suggested: (i) in all cases, grazing management should be adapted to increase the resilience of plant communities to climatic variability (Su 2007 ), (ii) special attention should be paid to the improvement of agro-silvo-pastoral systems (Gómez-Rey et al. 2012 ), and (iii) natural margins should be considered due to their role in SOC sequestration (D’Acunto et al. 2014 ; Francaviglia et al. 2014 ).
2.4 Climate change adaptation and mitigation.
In the agricultural and forestry sectors, climate change adaptation refers to the adoption of practices that minimize the adverse effects of climate change, while mitigation deals with the reduction of greenhouse gas emissions from agricultural and animal husbandry sources and the increase in soil C sequestration. Since the mid-eighteenth century, anthropogenic activities have contributed 169 Gt CO 2 , 43 % of which have accumulated in the atmosphere (IPCC 2013 ). Raising atmospheric CO 2 levels favors plant photosynthesis and also the reduction in stomatal conductance, which in turn promotes higher water use efficiency (Ko et al. 2012 ). The increase in water use efficiency may be hindered by the rise in canopy temperature expected under CO 2 enrichment, resulting in higher leaf transpiration (Kimball et al. 2002 ). Despite this latter process, results from different free-air concentration enrichment (FACE) experiments have demonstrated the positive general effect of rising atmospheric CO 2 levels on plant production, especially in C3 crops (Ainsworth and Long 2005 ; Long et al. 2006 ). Likewise, it has been demonstrated that the increase in plant production under CO 2 enrichment conditions has a direct impact on C dynamics, and particularly on long-term SOC storage if accompanied with increased inputs or reduced losses of N, although not all FACE experiments have reported a final increase in SOC (Prior et al. 2005 ; van Groenigen et al. 2006 ).
However, under climate change conditions, the C cycle in agricultural systems will not only be affected by the increase in atmospheric CO 2 concentration, but also by the predicted changes in other variables (i. e., amount and intensity of rainfall) and also by the management practices implemented. In particular, for dryland areas, general circulation models predict significant increases in mean surface temperatures and expected decreases in total annual precipitation with both changes in the seasonal distribution pattern and higher occurrence of extreme events (Gao et al. 2006 ; IPCC 2013 ). Consequently, in dryland agroecosystems, the predicted changes in climate will likely condition the positive response found in some FACE experiments between CO 2 enrichment and SOC levels (Dijkstra and Morgan 2012 ; Liebig et al. 2012 ).
Crop growth and productivity respond to changes in surface temperature. Although this response can be either positive or negative (Wilcox and Makowski 2014 ), in southern latitudes and semiarid areas, acceleration of maturation and/or heat stress due to warming can have negative impacts on crop production (Lavalle et al. 2009 ), thus offsetting the potential gain in SOC stocks expected under CO 2 enrichment. In some African countries, for example, crop yields could be reduced by 50 % by 2020 (Marks et al. 2009 ). Limited information exists in the literature about the interactive effects of warming and CO 2 increases in C dynamics in agricultural systems. The few available studies show that warming increases SOC losses due to the acceleration of soil organic matter decomposition (Dijkstra and Morgan 2012 ; Liebig et al. 2012 ). However, the increase in surface temperatures may also increase soil drying. This is critical in dryland agroecosystems in which soil water availability is the most limiting factor for C dynamics. Thus, the warming effect on soil water content, together with the general decrease in precipitation predicted by climate models for dryland areas, may result in situations of extremely limited soil water supply. The impact of low water availability in dryland areas on soil C is shown in the work of Li et al. ( 2015 ), who estimated a loss of 0.46 Pg C in Central Asia drylands during the 10-year drought period from 1998 to 2008, possibly related to extended La Niña episodes. Decreases in soil moisture limit microbial activity and, thus, soil organic matter decomposition (Skopp et al. 1990 ). Indeed, acceleration of microbial activity as a response of warming might be offset by exceptionally limited soil moisture (Almagro et al. 2009 ). However, the adoption of certain management practices could ameliorate this situation by increasing soil water available for crop growth and microbial activity. One main strategy would be tillage systems and in particular decreasing soil tillage intensity, since it has been identified as a promising management strategy to increase soil water content in dryland systems (Cantero-Martínez et al. 2007 ). Under a climate change scenario, the complete elimination of tillage through the adoption of no-tillage could help to maintain or even to increase crop growth and, thus, C inputs into the soil. But, it is important to consider that depending on the warming and drought extent, the adoption of this technue could stimulate soil C losses, due to an acceleration of soil microbial activity, which may not be compensated by the increase in C inputs. This last situation would imply C losses under no-tillage systems. Simulation studies in dryland systems under different climate change scenarios predicted future increases in SOC under no-tillage (Álvaro-Fuentes and Paustian 2011 ). Obviously, more experimental data is needed to determine the effect of no-tillage and other management practices on soil C changes under climate change conditions.
2.5 Social and economic barriers and opportunities.
Drylands sustain over 2 billion people and contribute to climate change mitigation (Neely et al. 2009 ). Environmental and social co-benefits resulting from increased soil C sequestration in drylands can increase agroecosystems’ resilience and decrease social vulnerability to disasters and climate variability (Lipper et al. 2010 ). Past investments in drylands focused on improved land productivity by expansion of irrigated areas. This approach is unsustainable in most agricultural areas. Furthermore, dryland policies need to consider poverty reduction and environmental benefits.
2.5.1 Improved management viewed as an externality.
Soils in dryland areas have potential social and economic benefits to improve sustainability of agricultural systems, environmental restoration, and poverty alleviation. Evidence for the benefits for increasing dryland C is clear at the local (i. e., increased crop productivity), regional (i. e., enhanced agricultural sustainability), and global levels (i. e., mitigation of climate change). As a consequence, the resulting benefits of the actions of farmers may produce positive externalities on other stakeholders and may take effect in the present or future.
The presence of externalities implies the need for policy interventions to ensure that improved C management is produced at the social optimum. Policy may provide incentives to farmers to produce this social optimum through various mechanisms, such as improved technical knowledge at the farmer level or improved carbon trading schemes. Understanding uncertainty and how to evaluate the future benefits is a major challenge and includes defining the value that we give future goods.
2.5.2 Measures at farmer level and policy support.
At the farmer level, the main barriers are the initial investments. These investments are difficult to quantify, ranging from additional machinery to improved knowledge. The expected benefits at the farmer level may be insufficient to compensate farmers for the direct initial costs. Therefore, policy interventions are necessary. In regions where agriculture is heavily supported by policy (i. e., Europe, USA, Australia), most studies conclude that subsidies are necessary. In regions where farmers do not receive direct support, substantial funds from development organizations or C investors will be necessary in order to make soil C sequestration projects in dryland small-scale farming systems a reality (Neely et al. 2009 ).
In the short term, changes in management are implemented first by the most interested, motivated, and innovative farmers, that are often the ones that have other social and economic advantages. Marginal farmers are usually reluctant to participate in innovative programs and need different types of policy support. In the long term, the potential benefit of management practices that enhance C sequestration can be reversed as soon as they are abandoned. This might occur either as a consequence of natural hazards (such as a large drought), decreased policy support, or perspective of larger profits with another management alternative.
The success of a long-term and large-scale C sequestration program in drylands relies on the implementation by a large number of farmers. Top-down policy programs may only be successful if they provide financial incentives for implementation. At the same time, a program may build on already existing local and/or regional initiatives by farmers associations, for example. This would ensure that the measures proposed are supported by a large number of individuals.
2.5.3 Mainstreaming global development policies with C sequestration in drylands.
The process of land degradation in drylands also means that C stored in these ecosystems will be added to the atmosphere as greenhouse gas emissions. It is also clear that extensive land degradation in drylands may contribute to poverty increase in many regions. A purely carbon-market approach is unlikely to be successful for drylands since the approach needs to consider other aspects such as sustainable development and poverty alleviation. Then, the adoption of carbon management strategies, which aims also at providing important co‐benefits (e. g., climate change adaptation, biodiversity, plant nutrition, etc.) will gain more attraction in the mid ‐ and long-term perspective. Sustainable carbon sequestration policies must act locally at the scale of the small shareholder or village, and focus on the ecosystem services rather than on C sequestration solely (Marks et al. 2009 ).
Therefore, dryland C improvement policies are included into global development policies. This process is often referred to as mainstreaming, which is funded under other policies and could also be used to fund C sequestration programs in drylands. For example, the Convention to Combat Desertification (CCD) and the UN Framework Convention on Climate Change (UNFCCC) share the goal of improved management of C in drylands and poverty alleviation. As a consequence, there is a range of global policy mechanisms to promote dryland C storage for alleviation of poverty in least developed countries, such as the UN Global Mechanism program and the Global Environment Facility (GEF) land degradation focal area or the GEF Adaptation Fund (FAO 2004 ).
A key element of soil rehabilitation in drylands is the restoration of organic matter which has been widely depleted due to tillage, overgrazing, and deforestation (see preceding sections). The Clean Development Mechanism of the Kyoto Protocol does not include the possibility of payments for C sequestration in soils. However, other markets in carbon are being developed, which could enable developing countries to benefit from carbon trading for soil organic matter (Lipper et al. 2010 ).
3 Conclusions.
Dryland areas comprise about 41 % of the Earth surface and sustain over 38 % of the world’s human population. A meaningful fraction of C in dryland soils has been lost as a consequence of inadequate management practices and land use decisions. Global warming will exacerbate the current scarcity of water that most dryland areas face, thus adding great challenges for agricultural production and social development. However, with proper decisions, soils in dryland areas have a large potential to sequester C and will result in positive regional and global externalities.
Over the next decade, research on C management in dryland areas should focus on proper agricultural and livestock management practices that maximize C storage in soils taking into account their entire C footprint. Raising CO 2 levels and concomitant warming could also lead to heat stress that could offset the potential gain in SOC stocks expected under CO 2 enrichment conditions. Precipitation capture, water retention in the soil, and crop water use efficiency need to be maximized to guarantee an adequate soil cover and reduce soil erosion susceptibility. A range of agronomic practices such as crop residue management, soil management and fertilization, adequate design of cropping systems, and the availability of adapted plant material can help to increase soil C sequestration in water-limited environments. Livestock integration in dryland systems must be optimized to couple the C and N cycles and to take profit of the greater residence time of the C sequestered at soil depth. Future research should focus on the feedbacks between soil biodiversity and C cycling in order to enhance ecosystem services. Moreover, the areas of study must be upscaled in order to better represent complex landscape processes affecting C sequestration and to improve the comprehension of the interactive effects of management and global warming on C cycling in soils. Policy support should generate possibilities to strengthen farmers’ own strategies to deal with uncertainty while providing the necessary incentives to encourage successful C management pathways including an improved knowledge at the farmer level and strengthen the linkage between environmental and social sciences. The objective of sequestering a significant amount of C in dryland soils is attainable and will result in social and environmental benefits.
Acknowledgments.
This work has been partially supported by the Spanish Ministry of Economy and Competitiveness (grants AGL 2013-49062-C4-1-R and AGL 2013-49062-C4-4-R). The valuable comments of two anonymous reviewers have greatly improved the quality of this manuscript.
Referências.
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Dryland Pasture Assessment.
Learn strategies to improve your pasture or range condition.
Colorado Forage Guide.
Info on forages and grazing.
Livestock Management in the Mountains.
Managing livestock in the mountains.
Drought Resources.
Updated info about the 2018 Drought.
Schedule a Site Visit Today!
Contact us to set up a one-on-one site visit.
Your source for trusted information and educational materials for sustainable land management.
2018 Drought Resources.
Up-to-date drought-related resources from CSU Ext. & our partnering agencies. View the updated Drought Monitor for Colorado. See fact sheets, tip sheets and other Extension related resources dedicated to drought. Keep updated by viewing the latest drought forecasts.
Small Acreage Services Database.
The source for Colorado landowners to search for contractors, equipment, and land management services.
Colorado Small Acreage Newsletters.
Subscribe to the Colorado Small Acreage Newsletter and view archived newsletters with a host of articles written by experts. Newsletters are produced quarterly.