Okogun J.A., Sanginga N., Abaidoo R., Dashiell K.E., Diels J.
International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria; Tropical Soil Biology and Fertility Institute of CIAT (TSBF-CIAT), United Nations Avenue, Nairobi, Kenya; Division of Agricultural Sciences and Natural Resources, Oklahoma
Okogun, J.A., International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria, IITA, c/o L.W. Lambourn and Co., 26 Dingwall Rd., Croydon CR9 3EE, United Kingdom; Sanginga, N., International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria, Tropical Soil Biology and Fertility Institute of CIAT (TSBF-CIAT), United Nations Avenue, Nairobi, Kenya; Abaidoo, R., International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria; Dashiell, K.E., International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria, Division of Agricultural Sciences and Natural Resources, Oklahoma State University, United States; Diels, J., International Institute of Tropical Agriculture (IITA), Oyo Road, Ibadan, Nigeria
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. © Springer 2005.