Differences in contribution of biological nitrogen fixation to yield performance of common bean cultivars as assessed by the 15N natural abundance technique

Aims Identification of variability in biological N(2)fixation (BNF) contribution among common bean (Phaseolus vulgarisL.) cultivars under field conditions requires a reliable methodology. This study aimed to assess different common bean cultivars for plant growth and grain yield and to quantify the BNF contribution to the crop using the N-15 natural abundance technique. Methods Two field experiments were conducted in an Oxisol in Brazil over two consecutive years, with eight common bean cultivars inoculated with rhizobium or fertilized with mineral N. Plants were analysed at mid-pod filling stage (two weeks after full-flowering) and at grain maturity. BNF was estimated by the N-15 natural abundance technique. Results Average grain yields were 1614 or 2942 kg ha(-1) in Experiment I, and 3284 or 3919 kg ha(-1) in Experiment II, with rhizobium inoculation or mineral N, respectively. The average contributions of N derived from atmosphere were 14 and 26%, and amounts of N-2-fixed were 7 and 22 kg N ha(-1), in bean plants at mid-pod filling, respectively, in Experiment I and Experiment II. Conclusions The contributions of BNF increase when common bean crop reached its optimum yield potential even though soil N was the most important source for the plants. There is good relationship between delta N-15 values of grains and shoots, provided cultivars are of similar growth habit. The(15)N natural abundance technique allowed identifying cultivars with relatively high BNF capability for commercial crop and breeding purposes.