Impact of degraded acidic soils on nitrogen fixation, and yields of soybean on smallholder farms

Soybean is an ideal crop for improving nutrition, food security and plays an important function in the natural ecosystem and agriculture. In Uganda, the crop is produced in the Northern and Eastern regions by smallholder farmers in degraded acidic soils. Degraded acidic soils remain a major constraint to soybean production with farmers’ yields below global production average. In spite of its economic importance, little investment has been made to research on soybean in degraded acidic soils in Uganda. Maksoy 1N, Maksoy 3N, Maksoy 4N, Maksoy 5N etc. are some of the improved soybean varieties that are currently being cultivated across farmers’ fields in Uganda. This paper reviews the current state of soybean production in Sub Saharan Africa; highlights the soil fertility trends and the effects on soybean yields in the region, addresses the importance of lime to degraded acidic soils, biological nitrogen fixation (BNF) as influenced by rhizobial inoculants, and climatic requirement. Past and current studies showed that soybean grown in degraded acidic soils under different lime regimes had varied growth and yield. However, there were no clear trends on maximum soybean yield under different lime regimes in degraded acidic soils. Key words: Degraded acidic soils, lime levels, nitrogen fixation, Rhizobial inoculants, Soybean yield, Uganda