Research on nutrient flows and balances in west Africa: state-of-the-art

West Africa is poorly endowed when it comes to soil fertility. Unlike for example the Rift Valley area, west African soils never enjoyed volcanic rejuvenation. At low agricultural intensity, this does not matter as nutrients cycle through the soil and the natural vegetation and losses are few. However, the past decades have shown high population increases, the breakdown of traditional shifting cultivation systems, and a rapid decline of land productivity and soil fertility in particular. The present review paper shows how much is known about the severity of this process and the technologies at hand that can stop it. The information provided shows that on the technical side much is known now, but research output still is poorly integrated into development efforts

Sustainable intensification of crop– livestock systems through manure management in eastern and western Africa: Lessons learned and emerging research opportunities

In the mixed farming systems that characterise the semi-arid zones of eastern and western Africa, low rural incomes, the high cost of fertilisers, inappropriate public policies and infrastructural constraints prevent the widespread use of inorganic fertilisers. As population pressure increases and fallow cycles are shortened, such organic sources of plant nutrients as manure, crop residues and compost remain the principal sources of nutrients for soil fertility maintenance and crop production. In this paper, the effect of manure on soil productivity and ecosystem functions and services is discussed. This is followed by highlights of the management practices required to increase manure use efficiency. We end with a discussion of emerging new research opportunities in soil fertility management to enhance crop–livestock integration. Although the application of manure alone produces a significant response, it is not a complete alternative to mineral fertilisers. In most cases the use of manure is part of an internal flow of nutrients within the farm and does not add nutrients from outside the farm. Furthermore, the quantities available are inadequate to meet nutrient demand on large areas. Research highlights have shown that efficiency is enhanced by different management practices including the timing and methods of manure application, its sources and integrated nutrient management. Research opportunities include analysing and understanding the ecosystem functions and services of manure use, the establishment of fertiliser equivalency for different manure sources, the assessment of the best ratios of organic and inorganic plant nutrient combinations, the crop–livestock trade-offs required to solve conflicting demands for feed and soil conservation and the use of legumes to enhance soil fertility and for animal feed. The establishment of decision support system guides and assessment of the economic viability of manure-based technologies in farmer-focused research are presented as powerful management tools intended to maximise output while preserving the environment in the mixed farming systems of the semi-arid zones