Demand for food and feed is rising, and it is expected to continue to rise, placing more pressure on already strained natural resources. In response, ICARDA scientists and their partners in Africa are conducting research into soil, water, and nutrient management. Their approach combines modern science with traditional practices.

y year 2030, the world's population is expected to increase by more than 2 billion to 8.27 billion people. This is an alarming prospect given that more food and feed will have to be produced from land resources already suffering degradation due to human and livestock pressure. Agenda 21 of the United Nations Conference on Environment and Development, held in Rio de Janeiro in 1992, and the 2020 Vision Initiative of the Consultative Group on International Agricultural Research (CGIAR) question the capacity of available production systems to meet the demands of this growing population for food and other agricultural commodities without simultaneously accelerating the degradation of the natural resource base.
    The situation in Africa is critical. Land available for expansion of agricultural area is limited to a few parts of the continent where the production potential has been proven but current output is low due to poor soils and mismanagement. Production increases from fertile lands have been reported to be declining. Marginal and fertile lands are currently undergoing varying degrees of degradation, including nutrient depletion, soil acidification, soil erosion, and reduction in soil water retention. As a result, water is becoming scarce in some areas and its quality is deteriorating.

    Studies estimate that nearly a quarter of the world's agricultural land, pasture, and forests have been degraded in the last 50 years. Soil quality, fertility, and water supplies need to be managed effectively, conserved through better husbandry of natural resources and through investments in land improvement. Effective soil, water, and nutrient management (SWNM) requires action, not only at the farm level, but also at the community, regional, and national levels.
   As global food production has expanded to meet growing demand, the soils of both marginal and fertile lands have suffered. The effects of degradation, which also bring problems of water quantity and quality, cannot always be compensated for, even partially, by application of fertilizers. Instead, natural soil fertility must be maintained and conserved. This demands that greater emphasis be placed on research into soil, water, and nutrient management.

    The SWNM Program at ICARDA addresses this challenge by bringing together four complementary research consortia that develop strategies to implement improved management practices for sustainable agricultural production on both fertile and marginal soils.
    SWNM activities focus on four themes involving several partners:
   • Combating nutrient depletion (CNDC) in East and West African sub-humid savannas and hillsides: International Fertilizer Development Center (IFDC), Tropical Soil Biology and Fertility Programme (TSBF), Kenya Agricultural Research Institute (KARI)
   • Managing infertile soils (MIS) in Latin America and Africa: Centro Internacional de Agricultura Tropical (CIAT), Colombia, Universidad Nacional Agraria, Nicaragua (UNA), Nicaragua),
   • Managing soil erosion in South and Southeast Asia: International Board for Soil Research and Management (IBSRAM) now incorporated into International Water Management Institute (IWMI), Sri Lanka and Center for Soil and Agroclimate Research, Indonesia (CSAR)
   • Optimizing soil water use (OSWU) in West Asia and North Africa and sub-Saharan Africa: International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), India, Agricultural Research Council-Institute for Soil, Climate and Water (ARC-ISCW), South Africa.

Program goals

The goals of the SWNM program are to increase long-term agricultural productivity, reduce human poverty, and conserve and enhance land and water resources. The program has the following objectives:
   • Effective, efficient, and environmentally sound technologies and systems for land management and conservation developed and made available to farmers and other users
   • Community-based new institutional mechanisms developed, tested, and promoted, which encourage the use of sustainable SWNM technologies
   • Partnerships and capacity of all stakeholders of the ecoregional program (national agricultural research systems and non-governmental organizations) enhanced in order to plan and implement research and dissemination programs for sustainable land management systems
   • Workable policy options and advice, including issues concerning equity (gender, resource access, tenure), developed and promoted.
The corresponding anticipated outputs linked to program objectives include:

• Economically viable, socially acceptable, and environmentally sound technologies for SWNM
• Improved methodologies and diagnostic tools for participatory SWNM research
• Improved indicators for sustainable and unsustainable land use systems that monitor environmental and economic impacts
• Easily accessible decision support systems (models, expert systems, geographical information systems, global data bases, etc.) for generating, testing, and extrapolating SWNM options
• Better trained people capable of implementing SWNM programs and policies
• Effective framework for full cooperation and partnership between stakeholder groups
• Appropriate policy dialog that promotes sustainable SWNM practices
• Effective mechanisms for information exchange.
The long-term goal of the OSWU project, is to achieve sustainable and profitable agricultural production in dry areas based upon the optimal use of the limited available water at different watershed scales.
The overall objective of the project is to develop and promote the adoption of integrated land management strategies and techniques that capture and retain rainwater, using crop husbandry techniques that maximize productive transpiration and minimize evaporative and drainage losses.

OSWU achievements in Africa

   • The Agricultural Production Systems Simulator (APSIM) package: APSIM, a state of the art cropping systems simulator, has been further developed to make it more useful in the African semi-arid tropics. Pigeonpea and pearl millet growth and development modules have been developed jointly with the Agricultural Production Systems Research Unit (APSRU), which is a partnership between scientists from several organizations, including the Commonwealth Scientific and Industrial Research Organization, the Queensland Departments of Primary Industries and Natural Resources, and the University of Queensland in Australia. A manure module that simulates decomposition and nutrient mineralization of manure in relation to manure quantity and quality; a phosphorus module developed by APSRU with assistance from OSWU; and a weeds module for maize are also now in use at ICRISAT to assist research in African semi-arid tropical regions.
   • Key research and development issues in the context of optimizing soil water use in the semi-arid regions include soil surface management to increase infiltration and decrease run-off and evaporation, and the manipulation and adaptation of cropping systems to optimize crop water use. Ways to optimize soil water use in low-input production systems are often different from those in high-input situations. A decision support tool for choosing optimum technologies was developed for use by researchers, extension agents, and farmers.
   • OSWU has looked at the use of organic amendments to increase nutrient uptake by millet grown using the zai water harvesting technique in the Nigerien Sahel. This study addressed the issue of resource use efficiency of organic inputs (animal manure, compost, and millet stover) with different sized catchment areas (zero, 25 cm diameter, and 50 cm diameter). Zai is one of many traditional techniques used in sub-Saharan Africa to reduce the risks to production in drought-prone areas, where there is a great variation in rainfall across and within the seasons. Other techniques include half-moons, stone bunds, and other surface management practices, such as tied-ridging, plowing, and crop residue management. These technologies are mostly related to appropriate soil management, including no-till options for conservation, the use of adapted crop cultivars, inorganic fertilizer, crop residue management, cropping system management, pest control, integrated watershed management, and combinations of these factors. A steady release of nutrients from the organic amendment, in combination with the water collected in the zai, favors the development of a larger rooting system to make better use of water and nutrients.
   • The potential impact of OSWU research was evaluated using the 'Bayesian belief network approach,' which is a method for representing relationships between variables, even if those relationships involve uncertainty, unpredictability, or imprecision.  Preliminary analysis using a simple belief network showed that the impact on agricultural production could be significant in areas with a high demand for OSWU technologies and where there is significant scope for yield improvement.
   • In South African semi-arid areas, runoff and evaporation limit the efficient use of water for crop production. Runoff can be minimized by use of basins and in-field water harvesting, and evaporation can be reduced during fallow and cropping periods. OSWU researchers conducted summer and winter studies on sandy loam and clay soils to evaluate the effects of crop residue and stone mulches on evaporation from the soil surface, and on soil temperature. A 50% stone mulch was as effective as a 50% organic mulch in inhibiting evaporative water losses and reducing soil temperatures. This result has beneficial socioeconomic implications for smallscale farmers, because crop residues are important animalfeedstuffs. The effects were more pronounced on the clay than on the sandy loam soils.
   • On-farm experimentation in Zimbabwe is aimed at increasing the productivity and incomes of small-scale farmers in the semi-arid tropics. The work follows an on-farm participatory approach at three locations representing a transect from the better-endowed to the marginal semi-arid tropics. Included are researcher-designed, replicated trials implemented by farmers, and farmer-led and implemented unreplicated trials. Technologies tested included those aimed at making more efficient use of water (modified tied ridging, seed priming, weed management) and nutrients (manure inputs using different types and storage, small inputs of fertilizer with or without manure, legume rotations). The results of the experiments were evaluated both by researchers and farmers. In some cases the design of the experiments was aided by using the APSIM simulation model to provide an ex ante scenario analysis of promising technologies. Modified tied ridging is a less labor-intensive modification of tied ridging that conserves rainwater in the field, controls weeds, and reduces erosion. Both farmyard manure and fertilizer-N increased yield in an average season. On-farm research at these sites is brought together through modeling using the APSIM package.

Farmer-researcher dialog

Can the knowledge of agricultural researchers be made compatible with what small-scale farmers know about farming systems? Can the participatory researchers communicate with the computer-based modelers? OSWU scientists were well represented at an international workshop in Bulawayo, Zimbabwe, in September 2001, that put farmers and scientists on equal terms. The participants (50 researchers and 150 farmers) tested the hypothesis that computer models could help promote collaboration between farmers and researchers, and could provide new insights into farmers' production systems in a climatically risky environment. While many participants were initially skeptical about the value of models, most left the workshop convinced that models are an exciting new tool that can help farmers in the semi-arid tropics. In fact, the Zimbabwe researchers are back in the villages, because the farmers requested continued collaboration. And researchers in other countries are considering how they can use the modeling tool.

Conclusions

The actual water-use efficiency in farming systems in the drought-prone countries of sub-Saharan Africa is often very low, and a surprisingly small proportion of the available water is actually transpired by crops. At the field level, water is lost through surface runoff, percolation below the rooting zone, evaporation from the soil surface, seepage in deep cracks, and transpiration by weeds. These vary according to site- and situation-specific conditions, which are often poorly quantified. Viable farm-level techniques, such as those developed by ICARDA for Central and West Asia and North Africa (see Caravan No. 13), can be put to good use in many dry countries to reduce these losses and to increase the capture and retention of water, as well as to maximize the proportion of water that is productively transpired by crops. Development of water-efficient cultivars is one way to achieve this. Such new varieties, often developed by national programs from material supplied by ICARDA, ICRISAT, and other CGIAR Centers, usually can only achieve their potential with improved soil, crop, and cropping system management. Better soil and crop management can make a major contribution to improved productivity from scarce and erratic rainfall if tested through farmer participation, from planning to implementation and evaluation.