Roles for Herbaceous and Grain Legumes, Kraal Manure, and Inorganic Fertilizers for Soil Fertility Management in Eastern Uganda

Abstract

Grain sorghum [Sorghum bicolor (L.) Moenich] is an important food crop in semi-arid areas of sub-Saharan Africa. Crop yields are generally low and declining partly due to low soil fertility. Therefore on-farm research was conducted on 108 farms at three locations over 3 years to evaluate alternative low-input strategies for soil fertility improvement in sorghum-based cropping systems. The strategies were use of herbaceous legumes in improved fallow, a grain legume in rotation with sorghum, use of cattle manure, and application of low levels of N and P fertilizers. Mucuna (Mucuna pruriens) on average produced 7 t ha–1 of aboveground dry matter containing 160 kg N ha–1. Application of 2.5 t ha–1 of kraal manure and a combination of 30 kg N and 10 kg P ha–1 both increased grain yield by a mean of 1.15 t ha–1. A combination of 2.5 t ha–1 manure with 30 kg N ha–1 increased grain yield by 1.4 t ha–1 above the farmer practice (1.1 t ha–1 grain). The increase in sorghum grain yield in response to 30 kg N ha–1, to a Mucuna fallow, and to a rotation with cowpea (Vigna unguiculata) was 1.0, 1.4, and 0.7 t ha–1, respectively. These alternative strategies were found to be cost-effective in increasing sorghum yield in the predominantly smallholder agriculture where inorganic fertilizer is not used. Results of the study indicated that on-farm profitability and food security could be improved through integration of inorganic fertilizers, herbicides, manure, Mucuna fallow, and cowpea rotation into grain sorghum cropping systems.