Evans School Policy Analysis & Research Group (EPAR)

A farmer’s decision of how much land to dedicate to each crop reflects their farming options at the extensive and intensive margins. The extensive margin represents the total amount of agricultural land area that a farmer has available in a given year (referred to interchangeably as ‘farm size’ or ‘agricultural land’). A farmer increases land use on the extensive margin by planting on new agricultural land. The intensive margin represents area planted of crops as a proportion of total farm size. A farmer increases the intensive margin by increasing output within a fixed area. This analysis examines cropping patterns for households in Tanzania between 2008 and 2010 using data from the Tanzania National Panel Survey (TZNPS).  This brief describes changes in farm size, total area planted, and area planted of select annual crops to highlight the dynamic nature of farmer’s cropping choices for a sample population of 2,246 agricultural households that reported having any agricultural land in 2008 or 2010. Throughout the brief, we present summary statistics at the national level and compare them with household-level data to show how results vary depending on how the sub-population is defined and how average measures can mask household level changes. We analyze these questions in the context of smallholders (defined as households with total agricultural land area as less than two hectares) and farming systems.  

Aid donors are interested in the arguments for allocating aid via bilateral versus multilateral channels, and specifically in understanding which channel is more “effective” at supporting positive development and social outcomes. We contribute to the literature on this subject by summarizing recent OECD data on aid flows and reviewing the theoretical arguments from the aid literature on the different characteristics supporting effectiveness of bilateral versus multilateral aid. We then review the empirical literature, analyzing 40 papers that study the effectiveness of different aid channels on various outcomes. Many studies do not directly compare the effectiveness of aid channels, and the studies vary in how aid channels are defined, measured, and evaluated. Further, these studies do not directly test the hypothesized advantages of one channel of aid versus another; rather they test bilateral versus multilateral aid flows associations with development outcomes, assuming some causal mechanism is at work to explain differences in impact. We evaluate studies reporting the impacts of aid on GDP growth, governance, government investment spending, health, the HDI, poverty, and private investment, and find no consistent evidence that either bilateral or multilateral aid is more effective. The lack of conclusive evidence supporting either aid channel is likely related to differences in the methodologies of the studies included in this review, but may also be due to differences in how the theoretical arguments for the effectiveness of either channel apply in different circumstances.

This report reviews the literature on textural attributes of Root, Tuber, and Banana (RTB) crops with a focus on studies relevant for crop research and development in Sub-Saharan Africa. The texture of cooked root and tuber crops is often cited as a primary determinant of consumer acceptability of new varieties, including those produced through traditional breeding and through genetic engineering. Evidence from texture-related consumer preferences studies for the RTB crops tropical yam, sweetpotato, banana/plantain, cassava, and potato, as well as the results of physicochemical and genetic studies detailing the current scientific understanding of drivers of textural traits, is reviewed and synthesized.

After cereals, root and tuber crops - including sweetpotato and yam (in addition to cassava and aroids), are the second most cultivated crops in tropical countries. This literature review examines the environmental constraints to, and impacts of, sweetpotato and yam production systems in Sub-Saharan Africa (SSA) and South Asia (SA). The review highlights crop-environment interactions at three stages of the sweetpotato/yam value chain: pre-production (e.g., land clearing), production (e.g., soil, water, and input use), and post-production (e.g., waste disposal, crop storage and transport). We find that sweetpotato and yam face similar environmental stressors. In particular, because sweetpotato and yam are vegetatively propagated, the most significant (and avoidable) environmental constraints to crop yields include disease and pest infection transmitted through the use of contaminated planting materials. Published estimates suggest yield gains in the range of 30–60% can be obtained through using healthy planting material. Moreover, reducing pest damage in the field can greatly increase the storage life of root and tuber crops after harvest – currently losses from rot and desiccation can claim up to 100% of stored sweetpotato and yam on smallholder farms.