Effect of plant genotype and nitrogen fertilizer on symbiotic nitrogen fixation by soybean cultivars

Isotopic as well as non-isotopic methods were used to assess symbiotic nitrogen fixation within eight soybean (Glycine max (L.) Merr.) cultivars grown at 20 and 100 kg N/ha levels of nitrogen fertilizer under field conditions. The present study reveals the great variability between legume germplasms in the ability to fix N sub(2) at different inorganic N levels, and also the potential that exists in breeding for nitrogen fixation associative traits. The super(15)N methodology offers a unique tool to evaluate germplasms directly in the field for their N sub(2) fixation abilities at different N fertilizer levels.