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CIMMYT Sustainable Maize and Wheat Systems for the Poor Research on soil fertility in Southern Africa: Ten awkward questions Larry Harrington and Peter Grace Keynote paper for the Soil Fertility Network
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CIMMYT Sustainable Maize and Wheat Systems for the Poor Research on soil fertility in Southern Africa: Ten awkward questions Larry Harrington and Peter Grace Keynote paper for the Soil Fertility Network Workshop, Africa University, Mutare, Zimbabwe, July 7-11, 1997 Natural Resources Group Reprint Series 98-01 CIMMYT is an internationally funded, nonprofit scientific research and training organization. Headquartered in Mexico, the Center works with agricultural research institutions worldwide to improve the productivity and sustainability of maize and wheat systems for poor farmers in developing countries. It is one of 16 similar centers supported by the Consultative Group on International Agricultural Research (CGIAR). The CGIAR comprises over 50 partner countries, international and regional organizations, and private foundations. It is co-sponsored by the Food and Agriculture Organization (FAO) of the United Nations, the International Bank for Reconstruction and Development (World Bank), the United Nations Development Programme (UNDP), and the United Nations Environment Programme (UNEP). Financial support for CIMMYT s research agenda currently comes from many sources, including the governments of Australia, Austria, Belgium, Canada, China, Denmark, France, Germany, India, Iran, Italy, Japan, the Republic of Korea, Mexico, the Netherlands, Norway, the Philippines, Spain, Switzerland, the United Kingdom, and the USA, and from the European Union, the Ford Foundation, the Inter-American Development Bank, the Kellogg Foundation, the OPEC Fund for International Development, the Rockefeller Foundation, the Sasakawa Africa Association, UNDP, and the World Bank. The Soil Fertility Research Network for Maize-Based Cropping Systems in Malawi and Zimbabwe is a network of national program scientists and extension staff working on soil fertility issues. It contributes to the improved management of scarce soil nutrient resources through targeted research and enhanced interaction between researchers, extension specialists, and farmers. SoilFertNet is funded by the Rockefeller Foundation. An agronomist in CIMMYT s regional office at Harare, Zimbabwe, serves as coordinator and technical advisor. Correct citation: Harrington, L., and P. Grace Research on Soil Fertility in Southern Africa: Ten Awkward Questions, NRG Reprint Mexico, D.F.: CIMMYT. Abstract: By raising important, sometimes ignored questions about research on soil fertility management in the subsistence, risk-prone maize-based cropping systems of sub-saharan Africa, this paper seeks to improve the quality of problem definition, spatial and temporal extrapolation, and farmer participation, as well as promoting careful consideration of the factors governing adoption, links with policies, and longer-term and off-site consequences of changes in management practices. The article is targeted to Southern Africa, but the issues and their treatment are relevant to smallholder maize cropping and related research throughout the developing world. AGROVOC Descriptors: Africa; Africa South of Sahara; Southern Africa; Soil fertility; Soil conservation; Soil management; Maize; Zea mays; Crop management; Cropping systems; Farming systems; Small farms; Technological changes; Innovation adoption; Development policies; Research projects AGRIS Category Codes: E14 Development Economics and Policies; P35 Soil Fertility Dewey Decimal Classification: ISBN: Printed in Mexico Tables Page 5 Table 1. The minimum dataset for simulation of cropping systems. Figures 6 Figure 1. Seasonal rainfall (bars) and simulated maize grain yield (points) for a local cultivar grown at Chitedze, Malawi (nil fertilizer), using the CERES-Maize model. 6 Figure 2. Daily rainfall (lines) and simulated accumulation of aboveground maize biomass (shaded) for a local cultivar grown at Chitedze, Malawi (nil fertilizer), in and Figure 3. Distribution of simulated maize yields for a local cultivar grown at Chitedze, Malawi, for seven single seasons ( to ) under identical initial conditions. 6 Figure 4. Distributions of simulated maize yields for a local cultivar grown at Chitedze, Malawi, for seven single seasons ( to ) under identical initial conditions and fertilizer N addition of 0, 60, 120 and 180 kg N/ha in the form of urea. i Research on soil fertility in Southern Africa: Ten awkward questions Larry Harrington and Peter Grace 1 Introduction Success in agricultural research calls for a unique blend of unconstrained creativity and painstaking discipline creativity in designing technical options intended to be attractive to farm families, tempered by discipline in assessing their performance and attractiveness. Research on soil fertility management is especially difficult, in part because of: The many combinations of technical options available (inorganic fertilizers, crop residues, numerous species of green manures, animal manures, intercrops, rotations, agroforestry systems, improved germplasm, etc.). The variability in performance of these technical options under different soil and weather conditions. The complex ways in which technical options can impinge on existing farming practices. The possible importance of their long-term and off-site consequences. The complexity of identifying potential areas for extrapolation of research results. The importance of policies and institutional arrangements in shaping the farm-level costbenefit equation that drives adoption. Research on soil fertility management in maize systems may be difficult, but it is also supremely important for sustainable food security, particularly in sub-saharan Africa. Adoption of improved maize germplasm has accounted for a little over half of the 1% annual growth in maize yields in sub-saharan Africa since 1970; improved productivity and sustainability in maize systems must come increasingly from improved soil management practices that fit the infrastructural and institutional circumstances of many African farming systems: low population densities, seasonal labor bottlenecks, poor infrastructure (which increases the cost of external inputs), and price instability (Byerlee et al. 1994). 1 Director and Soil Scientist, respectively, CIMMYT Natural Resources Group, Mexico. Given the complexity of research on soil fertility management, many researchers concentrate their efforts on a small subset of the important questions, but neglect the more awkward ones. Specific examples include issues relating to problem definition, spatial and temporal extrapolation, farmer participation, factors governing adoption, links with policies, and longer-term and off-site consequences of change. This paper raises several of these awkward questions without trying to provide any definitive answers. By raising them, however, we hope to stimulate discussion among reseachers about themes which may have been ignored and new ones that contribute to understanding and solving important soil fertility problems in Southern African maize systems. Question 1 - Are soil fertility problems in maize systems well defined? New soil fertility management practices should aim to solve important problems. But how well defined are the problems? Soil fertility problems are normally multi-dimensional (Harrington 1996), involving: The biophysical processes that underpin soil fertility in maize systems. The direct causes of the problems (which result from the above processes). Problem incidence. The consequences of problems. The pace of change with which these consequences are felt. Given the exemplary work of the International Fertilizer Development Center (IFDC), the Tropical Soil Biology and Fertility Program (TSBF), the International Center for Research in Agroforestry (ICRAF), national agricultural research systems, and 11 other research organizations (Woomer and Swift 1994), one might assume that the biophysical processes associated with soil degradation and low soil fertility in Southern African maize systems were well understood, especially relative to soil fertility depletion (Smaling and Braun 1996) and the requirements for recapitalizing soil fertility, particularly for phosphate (Sanchez 1996). In addition, there has been considerable work aimed at understanding water and nutrient cycling and improving synchrony the capacity of soils to provide nutrients to plants at the time when they are most needed. Despite the work to date, however, we cannot presume to have a total or even satisfactory grasp of the many biophysical processes that underlie soil fertility problems in maize based agriculture in Southern Africa. Even in Asia, where considerably more research resources have gone into elucidating the processes that drive soil degradation and yield stagnation in intensive rice systems (Cassman et al. 1994), those processes have only recently been satisfactorily described, and the underlying causes of declining yields in rice-wheat systems in the Indo- Gangetic Plains remain poorly understood, despite intense study (Hobbs and Morris 1996). As we ask about important unknowns regarding soil biophysical processes in maize systems in Southern Africa, it may be useful to subdivide process issues into two types: Degradation; for example, the on-going loss of organic matter and nutrients in lands with relatively high proportions of clay. Management of low fertility soils; for instance, farming on shallow, granitic sands where there may simply be no degradation processes at work. Problem incidence refers to the simple questions: Which biophysical problems are found on which soils, and where are these soils located? Simple though they may be, these queries have important implications for technology targeting, the selection of representative sites, site characterization, the georeferencing of experimental locations, the pooling of data across sites, and priority-setting in technology design. Have the questions of problem incidence been answered to everyone s satisfaction? Is it generally known which problems are concentrated on which soils? Are trials georeferenced? Are data pooled across sites in a way that draws on suitable soil characteristics? Consequences of soil-related problems may be found not only on-site (near-term productivity or longerterm resource quality and system sustainability; e.g., the build-up of Striga), but off-site as well (downstream or off-site economic, environmental or ecological effects of land degradation). Off-site consequences of land degradation can be more important than on-site consequences (Anderson and Thampapillai 1990). For example, erosion on sloping hillsides in Indonesia often does not affect the productivity of hillside maize systems, but the resulting siltation can ruin downstream irrigation infrastructure. What are the major off-site economic, environmental, or ecological consequences of land degradation in maize systems in Southern Africa? Pace of change is also important problems may be more significant if they unfold swiftly. What is the pace of change for major problems of soil degradation in maize systems in Southern Africa? Finally, it is important to understand the underlying, non-biophysical causes of problems to develop viable solutions (Tripp and Woolley 1989). In sub-saharan Africa, soil fertility problems have been traced to increasing land scarcity, shortened fallow periods, periodic labor shortages, and low use of inorganic fertilizers. The latter factor in turn derives from unfavorable grain/fertilizer price ratios, driven by poor infrastructure, unsuitable input and product pricing policies, and uneven performance of private sector companies (Mwangi 1997). Have the important cause and effect relationships been fully worked out for soil fertility problems in Southern Africa? Do they change over sub-regions? Farmers are particularly skilled at helping unravel cause and effect relationships among complex system interactions (Lightfoot et al. 1989). Has their experience been tapped? Question 2 - Does the current menu of technical options include promising farmer-developed practices? There is a tendency in on-farm research for scientists to choose (often rather casually) a small number of technical practices which they subsequently assess in considerable detail. It can be awkward to ask whether the right practices were chosen to begin 22 with. Sometimes, important farmer-developed options are overlooked. There is a fair literature on multiple sources of innovation (e.g., Bebbington 1989) which teaches us that farmers frequently can contribute innovative new practices to the pool of technical options being assessed. The numerous examples include: Farmer-developed methods for inserting mucuna in maize systems in Southern Veracruz, Mexico (Buckles 1993). Farmer-developed surface-seeding practices for establishing wheat after rice in Bangladesh (Hobbs and Morris 1996) and Thailand (Connell 1992). Farmer-developed methods of transplanting maize to enable a conversion of a two-crop per year to a three-crop per year system in the Red River Delta of Northern Vietnam (Tinh et al. 1992). Farmer-developed land management systems for flood-prone areas of the lower Indo-Gangetic Plains (John et al. 1993). Farmer-developed methods of dealing with erosion in Central Kenya (Tiffen et al. 1994). In Southern Africa, it would be unusual indeed if farmers had no insights into soil management nor options for regenerating soils that have lost their fertility. What are farmers strategies for regenerating soils? What conditions govern the success of these strategies? Have these approaches been considered in a research program? For soils that may not necessarily be undergoing degradation but that are of low inherent fertility, what are farmers management practices? Is the Soil Fertility Network research agenda adequately rich in options for and developed by farmers? Question 3 - What have been farmers experiences in using new practices suggested? Not only can farmers help provide new technical prototypes and options; they are frequently good sources of insights on technical options already under study. Often farmers will have previous experience with a technology and thus possess a reasonable understanding of its performance under different circumstances. In the Soil Fertility Network agenda, the following technical interventions are among those emphasized in research: legume green manures to foster regeneration of exhausted soils; groundnut cropping patterns in long-term trials; crop sequences involving legumes, maize, and sunflower; soybean-maize rotations; cattle manure x inorganic N; overcoming limiting nutrients on the Kalahari sands; and many, many more. Local farmers must surely have some knowledge of these practices. Have systematic efforts been made to tap farmers past experiences with new practices being developed within the Network? How has such information been incorporated into Network findings? Question 4 - Which new soil fertility management practices are best suited to which soil types? In our first question, the issue of problem incidence was raised: Which biophysical problems are found on which soils, and where are these soils located? A similar question can be asked regarding the targeting of solutions to these problems: Which soil management practices are best suited to which soils, and where are these soils located? Clearly, for example, research to identify the nutrients that limit maize productivity in Kalahari sands is most relevant to those soils. Are there differential responses by soil type for other aspects of fertility management in maize based production systems? As suggested earlier, how does this affect site selection, data analysis, and synthesis of results? Which data can sensibly be shared over which sites? What are the potential extrapolation areas for different technologies? Are test sites georeferenced? Are they and their soils characterized? Are the results of soil analyses used in answering some of the above questions? Should the Soil Fertility Network organize a database on soil fertility management practices by soil type? 33 Question 5 - How can new practices be adapted most efficiently to the conditions of different systems? Soil variability is only one factor that affects the cross-site synthesis of research results and the adaptation of prototype practices to farmers circumstances. Indeed, adapting prototype practices to defined farming systems is a classic area for farmer participation in research. Much of the literature on participatory experimentation farmer involvement in technology adaptation deals with crop improvement. Examples include farmer participation in selecting advanced lines of common bean in Colombia (Ashby et al. 1987) and Rwanda (Sperling and Scheidegger 1995), and farmer participation in selecting rice varieties in Nepal (Sthapit et al. 1996). However, farmers and researchers have also worked together to tailor crop and system prototype technologies. Here we can cite the use of vining legumes to rehabilitate Imperata infested lands in the Philippines (Lightfoot et al. 1988) or the use of grassy strips with farmer-selected trees for erosion control in hillside maize systems in Southern Philippines (Fujisaka 1989). In fact, a whole new literature has grown up around participatory adaptive experimentation (e.g., ILEIA 1989). Have researchers in the Soil Fertility Network worked with farmers to tailor prototype technologies studied by the Network to the needs and circumstances of different farming systems? This would require, of course, a characterization of the major farming systems in the target area. Is there a need to strengthen the capacity of Network members to engage in participatory experimentation for technology adaptation? Is there a need to re-examine the balance between researcher-managed strategic research vs. participatory adaptive research? Question 6 - How do the new practices perform under drought? The attractiveness of new soil management practices to farmers will, in part, depend on how these practices perform under drought conditions; Southern Africa is, after all, a region noted for rainfall variability and weather-related risk. Other things being equal, soil management practices that perform poorly under drought conditions are likely to be less attractive to farmers. First, however, what is meant by the term drought? To be useful, the concept itself must be described more precisely. For instance, does it refer to: Late onset of rains? Early end of rains? Erratic dry spells during the rainy season? Concentration of rains in fewer events? Reduced average seasonal rainfall? Most importantly, what climatic scenarios are of most concern to farmers? Maize itself is especially susceptible to droughtoccasioned yield losses during flowering and grain filling, crop development phases which occur from mid-season to late in the season (Westgate 1997). Unreliable rainfall during seedling establishment early in the season has also been cited as a major cause of yield reductions and even crop losses in maize (Bänziger et al. 1997). In the absence of a rich dataset (one that features multiple long-term experiments that extend over a large number of years and that suitably reflect variation in weather patterns), stability of performance of soil management practices best can be assessed through modeling. An example of modeling to assess the riskiness of a given technology option is offered in the following section. Note, however, that fruitful simulations from validated models also require input specifically, data from trials accompanied by a minimum dataset (Table 1) (though these need not come from long-term trials). Simulation models and risk management - an example To demonstrate the use of simulation models in assessing yield variability under different weather conditions, an example is maize response to fertilizer at Chitedze, Malawi. Crop production practices are those as described by Thornton et al.
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