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

In cowpea, efficient N2-fixing genotypes are being selected to promote sustainable cropping systems in southern Came roon (SC). However, N2 fixation and growth of these geno types are largely hampered by low levels of soil plant-avail able P. To evaluate the genotypic variation in N2 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 N2 fixation of the cowpea genotypes ranged from 29 to 51 kg N ha–1 on both TK and RK soils and was sig nificantly increased with P application. Significant genotypic variations in N2 fixation were observed with superior ability of the genotypes IT89KD-391 and IT90K-59 to fix N2. 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 effi cient 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 phy siological characteristics in IT89KD-391 were the most impor tant factors for inc
This article is Published by Wiley, 2006 and is also available at DOI: 10.1002/jpln.200520563
J. Plant Nutr. Soil Sci. 2006, 169, 816–825