Three quarters of Zimbabwe's population live in rural areas and most depend on farming as their main source of food and income. About 90% of the country's rural community are small holders, living in zones with low and erratic rainfall, poor soil quality and low crop production, due to inadequate nitrogen and phosphorus in the soil. Chemical fertilizers are simply unaffordable for most small farmers.
Since 1996 communal farmers in three provinces (Mashonaland East, West and Central), who traditionally cultivated maize, have started soybean production and tested the effects of Rhizobium "biofertilizer". Field trials have shown that inoculation of seeds with biofertilizer on average more than doubled soybean grain yields, and performed better than fields treated with 145 kg per hectare of commercial ammonium nitrate fertilizer. This means a saving of over US$ 50 per hectare at the present world market price of the fertilizer. The marginal rate of return from shifting from "uninoculated" to "inoculated" treatment has been found to be about US$ 100 for every dollar invested. Yields on communal farms are now comparable to those obtained by large commercial farmers. Smallholder farmers in Zimbabwe find it not only profitable to grow soybean as a cash crop but have also started to process it into products like soy milk, flour and "coffee" beans. This provides an important alternative source of protein for the farmers, as they cannot readily afford animal protein.
The increased agricultural productivity comes thanks to a technique developed by the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, using nitrogen-15 (15 N) isotope tracer techniques in identifying efficient Rhizobium bacteria strains for making biofertilizers. Atmospheric nitrogen can enter plants only after it has been captured or "fixed" in the root nodules of legumes by a bacterium called Rhizobium that lives in the soil. Under natural conditions, legumes often do not find the best bacteria in the soil to fix high quantities of nitrogen needed to produce high yields. Says Dr. M. Peter Salema, Deputy Director of the Joint FAO/IAEA Division, who is overseeing the IAEA Project's progress, "Rhizobium bacteria, inoculated in liquid form to the seed of a suitable pulse legume, such as soybeans, stimulate the production of root nodules in plants. They act as a biological nitrogen fertilizer factory by converting atmospheric nitrogen to plant-usable form. The natural nitrogen, produced by the nodules, not only promotes growth in the host pulse, but is also available to other crops grown subsequently in the same field".
Zimbabwe's Soil Productivity Research Laboratory (SPRL) has been pioneering the BNF technology in the country. "Our laboratory's job is to solve the soil productivity and fertility problems in communal areas" explains Linus Mukurumbira, Officer-in-Charge at SPRL. The IAEA project has been helping SPRL to use the nitrogen-15 (15 N) tracer technique in selecting Rhizobium strains and in matching them with pulse cultivars. "Nitrogen-15 analysis allows us to monitor nitrogen through the entire plant growth cycle," explains Mike Nyika, a senior microbiologist at SPRL. "We are then able to calculate the amount of nitrogen taken up by into the plant, and the relative efficiency of the particular inoculant". SPRL has now sufficient capacity to mass produce 120,000 packets of Rhizobium inoculant per year, which are distributed to small farmers through the Government's extension system. Each packet is potent enough to treat about 50 kg of seed. This capacity will soon be increased to about 300,000 packets per year for wide distribution.
In co-operation with the Government of Zimbabwe, the IAEA Project will further promote the BNF technology and its use by small farmers in all provinces of the country. As the market for soybean is expanding, its production provides a great potential for export, eg to South Africa, and better income and living standards for rural farmers. Kenya, Senegal, Tanzania and Zambia have already indicated interest in applying the BNF technology, and the potential for biofertilizer use in these countries is enormous.
In Bangladesh another IAEA Model Project has established a demonstration plant for large scale production of Rhizobium biofertilizers. Early field trials have already shown that the technology increases yields between 30 and 70% for lentils, soybeans, chick-peas and peanuts. Large scale adoption can thus save the country an estimated US$ 23 million per year in imported grains and some US$ 6 million annually in imported chemical fertilizers.
For further information please contact:
Dr. Manase Peter Salema
Deputy Director, Joint FAO/IAEA Division, Vienna, Austria
phone: +43 1 2060 Ext. 21613
fax: + 43 1 20607
e-mail: m.p.salema@iaea.org