Is it worth inoculating common bean (Phaseolus vulgaris L.)?

Legume inoculation is an established agricultural practice which has contributed to increased N-2 fixation and yield. Despite this evidence there is still an ongoing debate as to whether inoculation is necessary in grain legume production. Over the period 2003-05 a series of field experiments were conducted at Lincoln University, Canterbury, New Zealand to evaluate the effect of inoculation on common bean (Phaseolus vulgaris L.) production. Two white seeded bean cultivars, Scylla and T-49, were inoculated with six strains of Rhizobium phaseoli Dangeard, CC 511, RCR 3644, UK 2, H 20, PRF 81 and PhP 17 to determine their nodulation capabilities. Nodulation was variable and appeared to be affected by cultivar and Rhizobium strain. The two planting areas used, which had similar cropping histories, gave contrasting results. In the first season (Paddock 1), when a peat based inoculum was used, no nodulation was observed. In the second season (Paddock 2) liquid inoculum was used and nodulation ranged form 0 to 7.3 nodules plant(-1) at 21 days after sowing (DAS) to 0 to 75 nodules plant(-1) at 70 DAS. Cultivar also significantly affected the number of nodules plant(-1); ranging between 2-5 nodules plant(-1) at 21 DAS to 18-19 nodules plant(-1) at 70 DAS. Shoot dry matter (DM) over the two growing seasons ranged from 370-894 g m(-2), while green pod yield (taken at an average green seed length of I I mm) ranged from 138 to 471 g m(-2). Total DM at final harvest ranged from 530 to 1, 180 g m(-2) and seed yield ranged from 266 to 635 g m(-2). Strains H 20 and PRF 81 consistently out performed the other strains in most measured parameters. The results confirm the difficulty of predicting nodulation, and question the benefits of inoculating Phaseolus beans in Canterbury.