Closing Yield Gaps in the Sahel
The question of whether our crop production can sustain all of our needs for food, fiber and fuel has gained increasing urgency as biofuels have captured a significant share of world crop production in just the last few years. A substantial rise in world food prices in 2007-2008 combined with the growing presence of biofuels encouraged closer scrutiny of crop yields around the world. According to global scale analyses, a number of regions fall substantially behind their expected levels of production, among them, Sub-Saharan Africa’s Sahel, the belt of dry but still productive land south of the Sahara Desert. Some nations and corporations that have worked to acquire land in the region contend that the region’s under-productivity can be improved by outsiders bringing in new technologies.
Areas of Africa are long overdue for their own Green Revolution of the kind seen in Asia in the 1970’s, where campaigning researchers like Norman Borlaug were said to have prevented the deaths of millions by introducing new crop hybrids and their associated fertilization and pest-control techniques. Why do regions like the Sahel still lag behind in crop yields? Can outside investment alone overcome the barriers to higher yields? Analysis of the agricultural systems important to the region reveals that any changes in agricultural systems will have to overcome a unique set of barriers. Extraordinarily poor soils, lack of infrastructure like transportation and agricultural extension and inadequate crop research combine with a variety of socioeconomic constraints to make increasing yields a unique challenge. As climate change brings higher maximum temperatures and increasingly variable rainfall to the region, farmers will need more assistance from research and extension to make appropriate changes to their systems. More investment will therefore be part of the solution to improving yields in the Sahel, but the investment must be carefully targeted to the base causes of low yields.
What are yield gaps?
Limits to crop production are often defined in terms of yield gaps. A yield gap can be defined as the difference between the yield potential, or maximum possible yield, and the average on-farm yield. Yield potential in the Sahel is often described as the yields obtained on the area’s research stations. The yield gap, by that definition, is usually quite high. Yields on research stations may be three to six times higher than average yields, or even greater.Why are yield gaps in the Sahel so large?
The region has some of the poorest soils in the world. In geological terms, the soils are among the oldest on Earth. Millions of years of wind erosion and leaching of soil nutrients by heavy seasonal rains have left the soils deficient in most of the substances necessary to sustain plant life. They contain very little phosphorous, one the most important plant nutrients, and insufficient amounts of other essential minerals and of organic matter. Further diminishing the soils’ productivity is the presence of large amounts of aluminum, which inhibits plants’ ability to absorb other nutrients. Comparable soils occur only in northern Australia, which sustains a population only four percent as dense as the Sahel’s.Adding to the area’s difficulties is a long-term lack of crop research as compared to areas that have experienced Green Revolution production shifts. The predominant crops grown here-- millet, sorghum, cowpeas, cassava-- have never been the research priorities of global agricultural research. Since dryland India grows similar crops, research there has made major advances in producing new crop varieties that improve production. Few of the Indian innovations have made
their way to the Sahel, though, and even crops developed in Africa’s research stations have not been nearly as widely adopted by farmers as they have been in other world regions.
Soils and lack of research are only a part of the region’s agricultural challenges. Just as important are the socioeconomic constraints of farmers. Manufactured fertilizers are too expensive for most farmers to afford for their staple crops (Figure 1). Since most farmers cannot access credit, they cannot obtain capital to invest in fertilizers. Lack of crop price regulation causes crop prices to drop just when farmers are ready to sell their crops, further prohibiting them from investing in farm improvements. Those research innovations that have occurred often do not ever reach farmers’ ears due to an underfunded and inadequate agricultural extension system. Improved seed is difficult to access. Moreover, the most impoverished farmers often have the least secure access to land. Poor farmers, especially the region’s ubiquitous female farmers, often have to depend on others for access to land, and find that their access is denied if spouses or other powerful men want land to grow cash crops. Such insecure access means farmers have less ability and desire to invest in the future of the lands they farm.
Closing the Sahel’s Yield Gaps
With such extraordinary challenges, improving agriculture in the Sahel requires novel thinking and an understanding of the region’s complexity. For example, the fertilization solutions for Asia’s Green Revolution, if used in isolation, would not be appropriate because: 1) the lack of organic matter in soils here means that fertilizers are only useful if more organic materials (e.g crop residues) are added to soils with fertilizers; 2) farmers can’t afford to purchase fertilizers without assistance; 3) the solutions that led to improvements in Asia also led to some significant problems with water pollution, a problem we should be reluctant to replicate elsewhere and 4) we are now aware of the contribution of manufactured fertilizers to global warming, so massive investments in them have the potential to worsen the overarching problems of the region’s agriculture. Helping farmers improve their soils in the Sahel therefore means helping farmers find green manure crops to grow alongside their main crops. Appropriate green manure crops would include trees that do not substantially decrease yields, and whose branches and leaves can be cut and placed on the soil after harvest to increase organic matter enrichment. At the same time, international assistance aimed toward both decreasing prices of manufactured fertilizer and teaching farmers effective techniques of micro-fertilization would be necessary to round out soil improvement measures. Micro-fertilization, in which tiny amounts of fertilizer are placed in a planting hole along with the crop’s seeds, has had success in research contexts. It also allows for a much smaller amount of fertilizer to be purchased than in conventional techniques, and has a far lower likelihood of contributing to environmental problems like water contamination.Along with soil enhancements, improving the genetics of crops grown in the region is one of the central pieces of agricultural science that will be key for the Sahel. Improved understanding of the area’s variable rainfall and the ways in which farmers have adapted to it must combine with new crop varieties produced on research stations. Farmers typically plant genetically varied seed that is derived from their previous year’s harvest. The variety of plants that results ensures that farmers will have a harvest in almost any year, regardless of droughts or floods, because at least a portion of the plants in their fields will survive. Research station production, on the other hand, has often focused on producing single varieties that improve yields under ideal soil and water conditions. Farmers who grew only one or a few of such ideal varieties would risk complete crop failure, imperiling their food stores for an entire year. Yet, new varieties are needed to respond to the increases in maximum temperatures expected to occur in the region. Ideally, researchers and farmers can collaborate on improving existing varieties while creating mixes of crop varieties that minimize risks of failure due to rainfall variability. Such a joint effort would react to both of the expected climatic shifts predicted here.
An alliance between farmers and researchers-- as well as extension-- could help produce a wider adoption of improved varieties and farmer-friendly, risk-averse techniques like low-density plantings, seed combinations with both late and early-maturing varieties and more targeted applications of animal manure. The international community could assist with improved farmer and researcher communication by investing in training and expansion of agricultural extension. In addition to knowledge, farmers need more access to credit in order to purchase needed inputs, but the riskiness of credit can ruin farmers almost as thoroughly as can a poor harvest. Assistance should therefore also be targeted to research on appropriate ways to extend credit, potentially through joint farmer networks that build on existing (and growing) networks of social support.
Along with the challenges already mentioned, the need to incorporate transhumant (seasonally-migrating) pastoralists into the system will continue to be important. Livestock contributes substantially to the GDP of all of the area’s countries, and also supplies a large portion of the soil fertility for crops as animals drop their manure. Outsiders who have invested in land here have often invested in prime land, with high water availability from rivers or in the ground. Such areas are necessary to pastoral systems because they provide water that livestock need as they migrate. Therefore, investors’ land purchases are limiting pastoral mobility, and are therefore constraining one of the greatest contributors to soil fertility in the region. The cutting off of herder routes highlights the importance of understanding the full system as completely as possible in making policy and research choices.
As science and society become increasingly aware of the contributions of modern agriculture to climate change, appreciation of the need for low-input methods of improving agriculture is emerging. The Sahel, with its minimal current financial resources and susceptibility to continued climate change, will particularly benefit from low-input methods to decrease yield gaps. Yet developing and refining such low-input methods will require financial support from the international community. In addition, policy makers must build their knowledge of the system as they work to increase production in the region. The importance of the interactions of pastoralism with agriculture, for example, must be recognized. If the Sahel’s agriculture is to keep pace with its population growth and catch up with the rest of the world, researchers and policy makers have a steep learning curve ahead of them.
References
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Bationo, A. and A.U. Mokwunye. 1991. Alleviating soil fertility constraints to increased crop production in Africa: The experience in the Sahel. Nutrient Cycling in Agroecosystems 29:95-115.
Deb, M.C.S. and U.K. Bantilan. 2003. Impacts of Genetic Improvement in Sorghum. Chapter 9 in Crop Variety Improvement and Its Effect on Productivity: The Impact of International Agricultural Research. Cambridge, MA and Oxford, UK: CABI Publishing. Accessible at: http://www.fao.org/docs/eims/upload/282053/9780851995496.pdf
Mazzucato, V. and D. Neimeijer. 2001. Overestimating land degradation, underestimating farmers in the Sahel. IIED Drylands Program Issue Paper no. 101.
Nin-Pratt, A., M. Johnson, E. Magalhaes, L. You, X. Diao and J. Chamberlin. 2011. Yield Gaps and Potential Agricultural Growth in West and Central Africa. Washington, D.C.: International Food Policy Research Institute.
