On-farm Evaluation of Biological Nitrogen Fixation Potential and Grain Yield of Lablab and Two Soybean Varieties in the Northern Guinea Savanna of Nigeria

Abstract

Several legumes with high biological nitrogen fixation (BNF) potentials have been studied in on-station trials. The processes involved in BNF and the benefits of these species to crop production need to be evaluated using farmers' management practices in farmers' fields. An on-farm trial with 20 farmers was conducted in the northern Guinea savanna (NGS) of Nigeria. The aims were to evaluate the BNF potentials of an improved soybean variety (TGx 1448-2E) and a local variety (Samsoy-2) when inoculated with Bradyrhizobium strains, and of Lablab in farmer-managed and researcher-managed soybean-maize and Lablab-maize crop rotation systems. The level of soil P was generally low with more than 50% of the fields having less than the critical P level. The plant available P content was statistically significantly (P = 0.05) correlated with P in grain (r = 0.60), P in the shoot (r = 0.68), grain yield (r = 0.40) and nodule weight (r = 0.35). Variations in plant parameters (nodulation, shoot dry matter, percentage nitrogen derived from the air [%Ndfa], grain yield, and nutrient uptake) among and within farmers’ fields were attributed to differences in soil fertility and crop management. About 60% of the fields were moderately fertile, sufficient to support legume establishment, while about 30% of the farmers' fields had a low fertility level. For farmers in the study area to benefit from the BNF potentials of the legumes, an external P fertilizer input was necessary as well as suitable crop management practices because all parameters measured in the researcher-managed plots were higher than in the farmer-managed plots.