Biological nitrogen fixation potential by soybeans in two low-P soils of southern Cameroon

Biological nitrogen fixation (BNF) potential of 12 soybean genotypes was evaluated in conditions of low and sufficient phosphorus (P) supply in two acid soils of southern Cameroon. The P sources were phosphate rock (PR) and triple superphosphate (TSP). The experiment was carried out during two consecutive years (2001 and 2002) at two locations with different soil types. Shoot dry matter, nodule dry matter, and nitrogen (N) and P uptake were assessed at flowering and the grain yield at maturity. Shoot dry matter, nodule dry matter, N and P uptake, and grain yield varied significantly with site and genotypes (P < 0.05). On Typic Kandiudult soil, nodule dry matter ranged from 0.3 to 99.3 mg plant^?1 and increased significantly with P application (P < 0.05). Total N uptake of soybean ranged from 38.3 to 60.1 kg N ha^?1 on Typic Kandiudult and from 18 to 33 kg N ha^?1 on Rhodic Kandiudult soil. Under P-limiting conditions, BNF ranged from ?5.8 to 16 kg N ha^?1 with significantly higher values for genotype TGm 1511 irrespective of soil type. Genotype TGm 1511 can be considered as an important companion crop for the development of smallholder agriculture in southern Cameroon.