Soyabeans and sustainable agriculture - Promiscuous soyabeans in southern Africa

Promiscuously nodulating varieties of soyabean have been developed which nodulate abundantly and effectively in most soils in southern Africa. Bred from genotypes collected in East Asia these promiscuous varieties nodulate with fast and slow-growing rhizobia representing several different genera, The symbiotic interaction between different soyabean genotypes and different rhizobial isolates varies widely both in terms of ability to nodulate and effectiveness in N-2 fixation, but all plant genotypes tested, including varieties considered to be highly specific, nodulated with indigenous isolates in at least one soil. Promiscuity in nodulation allows soyabean to be introduced into a range of environments where lack of suitable inoculants would otherwise preclude growing the crop. Smallholder farmers need only access to seed to be able to grow soyabean, which brings multiple benefits in improved household nutrition from the high protein and oil content, cash income from sales of the crop and inputs of N which enhance soil fertility and contribute to the sustainability of their cropping system. Promiscuous soyabean varieties therefore represent a highly appropriate technology for cultivation of soyabeans for smallholder farmers, whereas use of varieties with greater yield potential together with rhizobial inoculants is an appropriate technology for commercial production of soyabeans by farmers who have ready access to agricultural inputs. (C) 2000 Elsevier Science B.V. All rights reserved.