ICARDA Caravan, Issue No. 23

Focus

Restoring Soil Fertility
in Dry Areas

Hanadi El Dessougi

Over one-third of the world's land area is classified as ‘dry’. These regions are characterized by severe water shortages and extreme hot and cold temperatures. The soils are shallow, alkaline and often stony, with inherently low fertility, poor nutrient and organic matter content, and low water-holding capacity. Dry areas are an important part of the global ecosystem, home to one-third of the world's population – and highly vulnerable to desertification. Clearly, it is imperative to improve the productivity and sustainability of agriculture in these areas – which in turn means improving soil fertility.

Soil fertility decline is a major problem in dry areas worldwide. But it can be tackled, provided researchers work together with farmers and other stakeholders.

Studied, published…
but used?

We know a great deal about how to use fertilizers and legumes to enhance soil fertility in dry areas. Published studies cover various aspects – timing and amount of fertilizers, application methods, crop responses, effects of crop rotations, dryland fallowing, and water-use efficiency. But many of these technologies remain on the shelf. Technologies that require capital investments, or were developed without farmer involvement, have limited potential for adoption. This is largely because farmers have to cope with specific micro-ecological or socio-economic conditions that were not factored into the research.

Scientific recommendations that work in one area may not work in another. To ensure adoption and practical applicability of new soil fertility technologies, farmers must be fully involved, and research must build on farmer experimentation.

This farmer-participatory approach has many advantages. First, technologies developed this way are more likely to spread, because adoption is farmer-led. Second, the approach allows researchers to incorporate indigenous knowledge when they make recommendations or design technologies to cope with adverse (and highly variable) environmental conditions. Third, it recognizes that for poor farmers, avoiding risk is as important as increasing output. For example, they may choose not to buy fertilizer, preferring less risky options (e.g. crop rotations) to maintain fertility.

Finally, farmer participation helps researchers characterize the biophysical, socio-economic and political environment. This is a basic prerequisite for analyzing land use systems, understanding their history and impact on soil fertility, and finding practical solutions that farmers will adopt.

Not just soil, but the system

The community is involved at all stages, from planning through dissemination of results.

The main concern for soil fertility researchers: how to increase output and quality of food production without damaging the environment or disrupting the supply of ecosystem services? Research that focuses narrowly on soil health without considering soil as one part of a large complex system, is unlikely to meet these objectives. Hence the concept of integrated soil management, which looks at the entire continuum of soil, pest and crop management. For example, good soil management will include manipulation of a range of physi-cochemical and biological soil processes, which in turn influence hydrological flows and water storage, gaseous exchange, carbon sequestration, regulation of nutrient cycles, biological pest control, and microbial biodiversity.

Organic resources
The health of an ecosystem often depends on how much organic matter the soil contains. Soil organic matter represents a large fraction of the soil's fertility. It also forms and maintains soil structure, thus facilitating aeration, nutrient storage and uptake, plant growth, and erosion control. Organic matter is lost through decomposition, but this can be compensated by adding organic inputs. However, some important research questions remain unanswered, for dryland conditions. How does the cropping system influence the quality and quantity of organic matter; what amounts and types of organic inputs are required in different soils; how does synthesis and decomposition occur?.

Nutrient cycling
Most dryland farmers keep livestock, as part of an integrated system: livestock feed on crop residues and native vegetation, and return nutrients to the soil in the form of manure. The research question is, how to improve this system; for example, what crop/animal husbandry practices will maximize nutrient recycling?

Nutrient recycling can also be improved by better resource management, to maximize nutrient recovery and uptake and use inputs more efficiently. Low-cost organic inputs (e.g. compost made from household waste) can improve soil properties and re-stock nutrients. Planting crops with differing root architecture, or the ability to solubilize specific nutrients, will increase the efficiency of nutrient capture. Incorporating crop residues into the soil, or planting fields with green manure crops instead of leaving them fallow, can also improve nutrient cycling.

These methods should go hand in hand with research to understand the chemical and biological processes governing nutrient flows, and develop practical management methods to enhance these processes. Such knowledge for drylands is very scarce.

Water management is equally important. In many dry areas, water scarcity, rather than soil fertility, is the most important factor limiting nutrient availability. Hence the need to use water more efficiently, for example by harvesting rainwater, recycling wastewater etc.

Resource maps, drawn by farmers, are the starting point for designing interventions.

Soil micro-organisms
The integrity and productivity of any ecosystem depends on micro-organisms, which are responsible for many key processes: decomposition; nutrient acquisition, storage and cycling; soil organic matter synthesis and mineralization; modification of soil structure; and regulation of atmospheric composition. Some soil micro-organisms also produce bioherbicides that control parasitic weeds and soilborne pests and diseases. Choosing appropriate crops and fallow systems, and managing residues, can help build up and maintain micro-organism populations, and thus increase crop yields and soil fertility.

Researchers must quantify the role of micro-organisms in dryland agriculture; and develop management strategies to optimize the quantity and quality of organic inputs so as to create conditions favorable for beneficial micro-organisms.

Managing rangelands
Rangelands are the single largest component of dryland areas, and the most important resource for livelihoods. But vast rangeland areas suffer from poor soil fertility, and varying levels of degradation. As a result of misuse and overgrazing, severe cutting of trees and removal of vegetation, valuable species are dying out and being replaced by less valuable species unpalatable to livestock.

Livestock are the key to efficient nutrient cycling; and their contribution can be further enhanced by improving manure treatment and storage methods.

Simultaneously, lack of property rights leaves individuals and communities with no motivation to conserve rangelands, and hinders the development of efficient management strategies to conserve and regenerate them. Numerous measures are available: reseeding, water harvesting, increasing water use efficiency, enhancing soil fertility, policy reform on land tenure. The challenge is to implement some or all of these measures in poor dryland communities.

Solutions that work
How to arrest the decline in soil fertility and prevent further degradation of dryland soil systems? This will require integrated management approaches that make efficient use of all available resources, and do not make excessive demands on household resources, e.g. large-scale application of expensive fertilizer.

Field experiments help link modern science with farmers' perceptions and practices on fertility management.

Instead, solutions must focus on nutrient cycling and efficient use of water and nutrients. They should seek to manipulate soil biological processes for farmers' benefit – by designing more efficient agro-ecosystems, improving the quality of organic resources and soil microflora, and encouraging crop diversification, crop-livestock integration and tree production. Research must provide an understanding of nutrient fluxes and cycling under water-scarcity conditions, and of interactions between soil fertility, pests and diseases. Ultimately, research must lead to policies that motivate farmers and pastoralists to conserve natural resources.

These solutions must be developed by all stakeholders working together. In particular, they should build on indigenous knowledge, and the innovations and experiences of farmers, who are the best managers of their soils.

	___________________________________________
	Dr Hanadi El Dessougi (h.dessougi@cgiar.org) is a Post-Doctoral Fellow at ICARDA, working on nutrient and water flows and soil fertility management.

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