To meet future food demands we need to change from annual grain legumes to multipurpose semi-perennial legumes

Summary

The last meal of an Iron Age man buried in a Danish bog included at least 60 plant species, including barley, linseed and species we now consider weeds. A modern man relies in contrast on a remarkable small number of crop plants, mostly cereal stables like wheat, rice and maize (Evans, 1998). Both land and people in Sub-Saharan Africa are suffering. Natural resource management is in distress and most rural Africans remain poor and food insecure despite widespread macroeconomic, political and sectorial reforms. Most predictions are that these Africans will remain food insecure in the foreseeable future (Pinstrup-Andersen & Pandya-Lorch, 2001). Innovations are, however, changing this landscape much faster than we could expect.
A market-oriented agriculture has been promoted by many agents of change. And change is happening. The last 10 years a renewed optimism has taking root in the fact that a number of African countries are demonstrating high economic growth rates (Radelet, 2010). We do not know the winners and the losers yet – just that they are there. Not all farmers will have the capacity to join the market orientations by high-value commodities. They are simply not able to innovate.
Nitrogen is a major limiting nutrient for food production but the growing demand for food is met in two ways. One through fossil fuel driven fixation of nitrogen, Haber-Bosch nitrogen (Erisman et al., 2008), is one way and symbiotic fixation of nitrogen, leguminous nitrogen (Giller, 2001) is the other. Feeding approximately half of humanity is made possible by Haber-Bosch nitrogen, the other half by leguminous nitrogen. With the current focus on reducing emissions of greenhouse gasses while simultaneously increasing the biomass production for food, fibre, feed and fuel, the use efficiency of the leguminous nitrogen must be improved.
Annual grain legumes basically satisfy their own need for nitrogen via their capability for fixing atmospheric nitrogen (see e.g. Unkovich et al., 2010). However, they seldom contribute much to soil fertility or to subsequent crops. Further, due to their annual structure they must be reseeded every season with consequences for investing resources and potential sensibility for unfavourable growth conditions during the renewed crop establishment phase.
Legume seeds hold a carbon-nitrogen ratio of approximately 10 compared to values up to 30 for cereals. Thus from a diet point of view, grain legumes are very valuable protein sources. This importance has been recognized since ancient history (Cohen, 1977). In addition to the nitrogen located in the grain, some nitrogen pools are located in the residues, which can be utilized for fodder or returned to the soil. Another important leguminous nitrogen pool is in the roots and rhizodeposits (Wichern et al., 2008).