The efficacy of soybean inoculation on acid soil in tropical Africa

Abstract

The efficacy of inoculating soybean cvs. TGm294-4 and TGm80 in an acid soil (pH 4.6, water) was studied in a field trial in Nigeria.Rhizobium japonicum strains CB1809str r and 46spc r which had been selected for symbiotic competence in the acid soil were used as inocula. Other treatments included no inoculation, combined nitrogen (150 kg N ha−1) and lime (1 t ha−1). Plants grown in acid soil without inoculation and lime had very few nodules, were nitrogen deficient and grain yields were poor (0.3–0.4 t ha−1). Yield responses to combined nitrogen were generally small due to fertilizer loss through leaching. Inoculation greatly increased nodulation, shoot dry matter and shoot N%; grain yields were between 1.6 and 2.0 t ha−1. Lime improved all harvest measurements in the uninoculated and nitrogen treatments but not in the inoculated treatments. In a duplicate trial without lime on near-neutral soil, similar inoculation responses were obtained at 6 weeks. However, at final harvest there were no significant differences in grain yield between treatments due to late, effective nodulation by unidentified strains in the uninoculated treatments. Assays for strain identity confirmed the successful establishment of the inocula in both soils, with 100% of nodules from inoculated plants containing an introduced strain.