Nutrient Management for Grain Legume Crop Production in Africa

IPNI-2012-GBL-49

05 Mar 2013

2012 Annual Interpretive Summary


Grain legumes are an important source of dietary protein and income for farmers in most parts of sub-Saharan Africa. In the past, grain legumes have been grown mainly as subsistence food crops, but there has been a rapid increase in their commercial importance over the past five years, mainly driven by increased demand from the agro-processing industry. The ability to fix atmospheric N makes grain legumes an excellent component within the farming systems dominated by maize because they provide supplementary N. Despite the major opportunities that grain legume crops provide to improve human nutrition, household income and soil N budgets in Africa, their contribution has been curtailed by several factors including low priority given to proper nutrient management.

Multi-location nutrient omission trials were initiated in Western Kenya and Central Uganda to assess the impact of P, K, S, and micronutrients on the productivity of soybean. Additional manure and lime treatments were added to the full fertilizer treatments to evaluate the effects of integrated nutrient management on soybean productivity. In Uganda, the mean soybean grain yield was 0.85 t/ha in control plots, which increased significantly to 1.8 t/ha with the application of inoculum and NPK basal fertilizers. Yields were further significantly increased to 2.2 t/ha with additional application of S and micronutrients. Maximum yield of 3.8 t/ha was obtained when manure was added to the full fertilizer treatment. In Western Kenya, yields in control plots ranged substantially from 0.1 t/ha in degraded soils to 2.4 t/ha in fertile soils that had received large additions of manure in the past. In degraded soils, inoculation had no effects on soybean yields, and yields were only increased to a maximum of 0.5 t/ha in the full fertilizer treatment. However, soybean yield increased substantially to 1.3 t/ha when lime and manure were applied to the full fertilizer treatments. On fertile soils, maximum yields of 2.5 to 3.6 t/ha were achieved with full fertilizer treatments. These results highlight good potential for soybean production intensification with balanced nutrient management, and strong responses to nutrient application across all sites in Africa. In degraded soils, application of manure, lime and other organic resources in addition to fertilizers is necessary to significantly increase soybean yields. IPNI-49