Soils of the marginal arid and semi­arid lands in Africa are generally deficient in nitrogen. In order to raise crop production, nitrogen enrichment is required. The most common way to achieve this is through the application of chemical nitrogen fertilizers. However, most of the small­scale farmers, about 60 per cent of Africa's population, can not afford them. Biological nitrogen fixation (BNF) might help to solve the problem.

Many African countries have a growing need for fertilizers. This is partly due to the expansion of agricultural activities into some of the marginal areas. Moreover, the soils of some of the potential areas have lost their fertility over the years, resulting in the need for more fertilizers to enhance crop yields. In the case of Kenya, the increased availability of foreign currency has contributed to an increased consumption.
Between 1965 and 1989, the annual consumption of nitrogen fertilizers in Kenya and Tanzania varied from 90,000 to 150,000 tonnes. By 1993, the Kenyan consumption was expected to rise to over 250,000 tonnes, while the Tanzanian consumption has a growth rate of 6.6 per cent per year since 1965.
More than 75 per cent of Africa's consumption of chemical fertilizers is imported. This has put considerable strain on the foreign exchange pool of African countries. For example, it has been estimated that Kenya spends about 40 per cent of its foreign exchange on the import of fertilizer. Most African countries could possibly reduce their expenditures on fertilizer imports through full exploitation of biological nitrogen fixation (BNF).

Prospects
Rhizobium is one of the most important bacteria that fix nitrogen from the atmosphere into ammonia, a form of nitrogen which can easily be assimilated by plants. It is estimated that Rhizobium alone could provide for more than 50 per cent of the fertilizer required for crop production in most of the marginal areas of Kenya, Zimbabwe and Tanzania. The application of conventional techniques and biotechnology to optimize conditions for symbiosis of plants and bacteria could contribute to an increasing exploitation of BNF. Currently, various African countries are engaged in research on nitrogen fixation. The research aims include enhancing soil fertility and increasing crop production; increasing residual nitrogen for some non­leguminous crops; and reducing the pollution of the ground and fresh water resources caused by the heavy application of fertilizers.

Kenya
For the last fifteen years, the Kenya Agricultural Research Institute (KARI) has undertaken research on BNF. Most of this research has drawn from previous efforts of the colonial agricultural research system to develop nitrogen inoculants for pasture legumes, in order to raise the livestock productivity from exotic breeds of cattle. In collaboration with the Crop Science Department of the University of Nairobi and the Egerton University, Kenya, KARI has extended the research to cover bean inoculation. The research has demonstrated that the common bean (Phaseolus vulgaris) has the potential of fixing nitrogen up to the equivalent of 50 kg of nitrogen per hectare per year.

Because of the importance of BNF in improving crop production, various research projects have been established under the Microbial Resources Centres Network (MIRCEN) programme of the United Nations Educational, Scientific and Cultural Organization (UNESCO). The Kenyan MIRCEN programme, located at the University of Nairobi, has resulted in the development of Rhizobium inoculants for crop legumes. Research under the Kenyan MIRCEN involves:

• assessment of the effects of high soil temperatures (38­42⁰ Celsius) on survival, growth and effectiveness of locally isolated Rhizobium phaseoli;
• evaluation of the nodulation, growth and nitrogen fixation of high­yielding bean lines;

screening of the Rhizobium phaseoli strains for acid tolerance to determine if acid­tolerant strains would improve BNF by the common bean.

Zimbabwe
The roots of non­leguminous crops are not colonized by nitrogen­fixing bacteria, and research on the improvement of nitrogen­fixation for these plants is extremely complicated. The Department of Crop Sciences of the University of Zimbabwe in Harare is experimenting with the use of bacterial inoculants to increase the nitrogen fixation abilities of cereals. With the help of gene­gun technology, genes that could confer nitrogen­fixing abilities to cereals were transferred. This kind of research, however, is still in its infancy, and it remains to be seen if the biological barriers can be overcome (see also Monitor no. 12).
The Department has also undertaken research on mycorrhizal inoculation in several regions of Zimbabwe. Mycorrhiza is a fungal strain on plant roots that assists the plant to extract phosphorus and other micro­organisms from the soil. The mycorrhiza used for the research was Glomus spp, which enhanced the mycorrhizal inoculation and increased the dry weight of cowpea by 100 per cent.

Tanzania
In Tanzania, the Food and Agriculture Organization of the United Nations (FAO) supports a project to identify better strains of Rhizobia. The project includes the establishment of a small fermenter for inoculant production at the University of Dar es Salaam. Furthermore, the University entered into an agreement on technical assistance with the University of Nijmegen, The Netherlands, to enhance its manpower capability in the domain of BNF. Tanzanian scientists are trained in applied microbiology at post­graduate levels, and conducting research on BNF. The arrangement also provides for the attachment of Dutch scientists to the Applied Microbiology Unit of the University of Dar es Salaam.
Recently, the Sokoine University of Agriculture developed on a commercial scale a biofertilizer called Nitrosua. Nitrosua has been developed through inoculation of soya beans with various strains of Rhizobium. Tests have shown an increasing percentage of infected roots and an increased nodule efficiency (the activity of the enzyme nitrogenase per weight of nodule of soya bean).
The University, in collaboration with the Ministry of Agriculture and some local non­governmental organizations, have established extension activities to disseminate the biofertilizer to local farmers. However, the dissemination is constrained by the fact that less than US$ 5,000 per year is allocated to the extension activities. Furthermore, the infrastructure in the rural areas, where most of the Tanzanian small­holders live, is poor.

Lack of policy
The potential of BNF to promote sustainable utilization of marginal lands and increasing crop yields at small­scale farms has been recognized by some researchers in African countries. At the governmental level, however, policies on BNF research are generally lacking. The current research efforts on BNF have evolved as a result of individual efforts with limited governmental support. The challenge to governments is to reconsider their policy formulation and action plans on agricultural biotechnological research in order to provide a strong institutional basis on BNF. This should go hand in hand with efforts to create and mobilize scientific expertise for research in nitrogen fixation.
John Mugabe

Sources
C. Juma and J. Mugabe (1994), Coming to life: Biotechnology in Africa's economic recovery. Nairobi: ACTS

J.M. Gopo (1991), Biotechnology in Zimbabwe. Nairobi: ACTS

A. Sasson (1988), Biotechnologies and Development. Paris: UNESCO

World Bank (1992), Development and the Environment. World Development Report 1992. Oxford: Oxford University Press