Source: Boddey, R.M., J.C. Sa, B.J. Alves, and S. Urquiaga. 1997. The contribution of biological nitrogen fixation for sustainable agriculture systems in the tropics. Soil Biology Biochem. 29:787-799.

Crop yields must be increased in order to meet the nutrient demand of steadily escalating Third World populations. Most tropical agricultural systems today have widespread erosion and degraded soil because of poor management practices. Soil nutrient loss can also be attributed to poor management. In a sustainable agriculture system, it is essential to replace these nutrients and maintain their availability to the crops. Inorganic fertilizers and other agrochemicals are effective in increasing yield; however, the use of natural gas to produce these fertilizers makes this practice unsustainable. One management practice that can be used as an alternative to chemical fertilizer is the use of nitrogen from biological nitrogen fixation (BNF), particularly from legumes. Most types of soils in the tropics are lattice clays which have low capacity to retain minerals and water. Soils under undisturbed crops are usually high in organic matter and therefore highly fertile. Soil organic matter (SOM) must be maintained by preserving crop residues and using crop rotation and fallow for superior fertility. The authors examined several agricultural systems used in the tropics including pastures, ley cropping, zero-tillage and the use of green manure. Crop productivity can be enhanced by using BNF through the incorporation of forage legumes into these systems. With their addition, pasture, ley cropping, and zero-tillage systems would help maintain the SOM content and offer promising increase in yield and reduction of nutrient loss. The nitrogen fixed by the legumes could be transferred to the surrounding crops. Although more research will have to be done to prove its potential, BNF is both an economical and sustainable approach to increase tropical crop production.

Abstract author: Tammi Gayle Hessler, 11 November 1999.

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