Evans School Policy Analysis & Research Group (EPAR)

This brief reviews the evidence of realized yield gains by smallholder farmers attributable to the use of high-quality seed and/or improved seed varieties. Our analysis suggests that in most cases, use of improved varieties and/or quality seed is associated with modest yield increases.  In the sample of 395 trials reviewed, positive yield changes accompanied the use of improved variety or quality seed, on average, in 10 out of 12 crops, with rice and cassava as the two exceptions.

Cassava production is prone to many constraints throughout the production cycle, including biotic, abiotic, and management constraints. This brief reviews the literature on the production impacts of two key cassava stressors: cassava bacterial blight (CBB) and postharvest physiological deterioration (PPD). We summarize available estimates of the frequency and magnitude of these constraints relative to other drivers of cassava production losses that affect smallholder farmers in Sub-Saharan Africa (SSA), review the control strategies proposed in the literature, report on the views of several experts in the field, and identify research gaps where relatively little appears to be known about CBB or PPD yield impacts or best practices for CBB or PPD management. 

Cassava (Manihot esculenta Crantz) is a widely-grown staple food in the tropical and subtropical regions of Africa, Asia, and Latin America. In this brief we examine the environmental constraints to, and impacts of, smallholder cassava production systems in Sub-Saharan Africa (SSA) and South Asia (SA), noting where the analysis applies to only one of these regions. We highlight crop-environment interactions at three stages of the cassava value chain: pre-production (e.g., land clearing), production (e.g., soil, water, and input use), and post-production (e.g., crop storage). At each stage we emphasize environmental constraints on production (poor soil quality, water scarcity, crop pests, etc.) and also environmental impacts of crop production (e.g., soil erosion, water depletion and pesticide contamination). We then highlight good practices for overcoming environmental constraints and minimizing environmental impacts in smallholder cassava production systems. Evidence on environmental issues in smallholder cassava production is relatively thin, and unevenly distributed across regions. The literature on cassava in South Asian smallholder systems is limited, reflecting a crop of secondary importance (though it is widely found elsewhere in Asia such as South East Asia), in comparison to cassava in much of SSA. The majority of the research summarized in this brief is from SSA. The last row of Table 1 summarizes good practices currently identified in the literature. However, the appropriate strategy in a given situation will vary widely based on contextual factors, such as local environmental conditions, market access, cultural preferences, production practices and the policy environment.

Agriculture and Climate Change: Part I

With estimated global emissions of 5,969-6,615 metric tons (Mt) of carbon dioxide (CO2) per year, agriculture accounts for about 13.5% of total global anthropogenic emissions of greenhouse gases (GHG). Deforestation contributes about 11.8% of total GHG emissions, releasing about 5,800 Mt CO2 per year. Developing countries are largely responsible for emissions from agriculture and deforestation, with the developing countries of South Asia and East Asia accounting for 17% and 25% of global agricultural emissions respectively. Sub-Saharan Africa (SSA) accounts for about 13% of global emissions from agriculture and 15% of emissions from land use change and forestry. This report examines the biophysical and economic potential of mitigating agriculture and land use GHG emissions, and provides a summary on the current and projected impact of global carbon market mechanisms on emission reductions. 

Agriculture and Climate Change: Part II

This report covers two topics related to agriculture and climate change in developing countries. The first section discusses the role of agricultural offsets in mitigating greenhouse gas emissions. Recent negotiations around a post-Kyoto Protocol agreement have included debate about whether agricultural carbon sequestration projects should be eligible under the Clean Development Mechanism (CDM). We examine the reasons for supporting or opposing this type of CDM reform and how these reasons relate to impacts on development goals and smallholder farmers, scientific uncertainty about carbon sequestration, and philosophical disagreement about the use of emission offsets. The second section covers proposed agricultural adaptation activities in Africa and other developing countries. While the majority of developing countries have outlined immediate adaptation needs in National Adaptation Programs of Action (NAPAs), few have made progress in implementing adaptation activities. We find that issues related to financial resources, scientific and technical information, and capacity building continue to challenge developing countries in preparing for the impacts of climate change.