Genotypic variation for phosphorus uptake dinitrogen fixation in cowpea on low‐phosphorus soils of southern Cameroon

In cowpea, efficient N 2 ‐fixing genotypes are being selected to promote sustainable cropping systems in southern Cameroon (SC). However, N 2 fixation and growth of these genotypes are largely hampered by low levels of soil plant‐available P. To evaluate the genotypic variation in N 2 fixation and P uptake among cowpea ( Vigna unguiculata L.) genotypes, field experiments were conducted over two years on two acid soils low in available P. The experiments were laid out in a split‐block design with four replications on typic (TK) and rhodic (RK) Kandiudult soils with seven cowpea genotypes. Phosphorus (P) fertilizers were applied on the main plots with 0 kg P, 30 kg P ha –1 as triple superphosphate (TSP) and 90 kg P ha –1 as Togo phosphate rock (PR). Nodule dry matter (DM), shoot DM, grain yield, and P uptake of cowpea significantly varied with site, P application, and genotype ( p < 0.05). The N 2 fixation of the cowpea genotypes ranged from 29 to 51 kg N ha –1 on both TK and RK soils and was significantly increased with P application. Significant genotypic variations in N 2 fixation were observed with superior ability of the genotypes IT89KD‐391 and IT90K‐59 to fix N 2 . The harvest index (HI) did not significantly differ between soils and P application levels ( p > 0.05). Four genotypes were selected to investigate root mechanisms responsible for efficient P acquisition in pot experiments. The results suggest that a better root infection by arbuscular mycorrhizal fungi (AMF) in genotype IT90K‐59 and root morphological and physiological characteristics in IT89KD‐391 were the most important factors for increasing P uptake.