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Benin Farmers Inoculate Their Legumes to Improve Soil Fertility and Yield

(© Benin UAC/Pascal Houngnandan)

The farmers of Benin constantly struggle with poor soil fertility which requires them to use expensive fertilizers in order to have a good crop yield – fertilizers that they often cannot afford. But now, through work supported by the Joint FAO/IAEA Division, more than 5 000 farmers have been trained to improve their soil fertility by inoculating their legume crops – inoculating them with a dose of bacteria needed to facilitate the process of nitrogen fixation. The Government of Benin supports a laboratory that produces the inoculum locally and makes it available to farmers. Since this concept was brought to Benin, yields have increased dramatically for both grain legumes and cereal crops. The process decreases the amount of nitrogen fertilizer required for cereal crops, which means farmers spend less on production.

The process of nitrogen fixation has long been known as one way for nature to improve soil fertility in farmers’ fields. Legumes planted in a field absorb nitrogen (N) from the  air and convert it, through a natural biological process involving nodules that form on its roots. They then leave that nitrogen behind in the soil after they are harvested, meaning for the next season’s planting, farmers need much less nitrogen fertilizer for the subsequent crop. Except, there is often something missing from this scenario. For nitrogen fixation to work, the right bacteria must be present in the soil to make those nodules grow in the first place.

The Joint Division, in part through the IAEA’s technical cooperation programme, has promoted cropping systems that add nitrogen to the soil through nitrogen fixation since the 1960s. The process calls for introducing legumes into crop rotations and inter-cropping. Farmers who have adopted this system have seen enormous increases in their yields as they have alternated legumes with their cereal grain crops.

The Joint Division, through work in its laboratory in Seibersdorf, Austria, has also identified the specific bacteria needed for legume roots to produce the nodules that fix nitrogen – bacteria that will initiate the process of helping the roots form nodules. Researchers can quantify this process with an isotopic technique that calls for the addition of N-15 isotope fertilizer to the soil to measure how much nitrogen the legume absorbs from the fertilizer and the soil, and how much from the air, so the amount of fertilizer can be adjusted if needed. Scientists also use this method to determine which legumes perform best in improving soil fertility and increasing crop yield in any specific cropping system.