Carbon sequestration and global warming potential of rainfed agriculture

Abstract

Worldwide, more than 80 percent of the cropped area depends on rainfall alone. Rainfed agriculture is practiced in almost all hydroclimatic zones, and can be highly productive. However, in many dry subhumid regions, tropical semiarid and arid regions, as well as in some temperate regions yields tend to be relatively low. With highly variable rainfall, long dry seasons, recurrent droughts and dry spells as well as floods, water tends to be a key constraint for agricultural production systems in these regions. Especially in Sub-Saharan Africa, where 96 percent of the cropland is rainfed, erratic and sparse rainfall often combines with arid conditions, high temperatures, and shallow soils with poor nutrient status to provide extremely uncertain conditions for agriculture. Farmers, and especially the poor, are intrinsically risk-averse, and in these conditions they tend to adopt low-input strategies with limited yield potential even in good rainfall years. The need to improve water management in water-constrained rainfed areas is often emphasized. In particular by increasing timely water availability and the water uptake of crops, yields can be significantly enhanced and agricultural productivity improved. Research has shown that better water management, coupled with improved soil and crop management, can more than double agricultural productivity in rainfed areas with currently low yields. With climate change and increasing food prices, even more emphasis needs to be placed on addressing water management in rainfed agriculture as a key determinant for agricultural production and productivity. However, governments and donors have tended to pay relatively little attention to this area, and investments remain low. During the last decade, for example, commitments to improving water management in rainfed agriculture in World Bank-supported projects amounted to less than 15 percent of the commitments to the irrigation and drainage subsector. Improvements in agricultural water management can be categorized into four broad approaches (one physical and three non-physical), with each comprising a variety of measures. The most usual approach comprises soil and water management techniques, including structural measures (such as stone barriers, bunds or terraces) and in-field or agronomic practices (such as mulching, fertilizing, intercropping, crop rotation, agroforestry and reduced tillage).