Symbiotic efficiency of Sesbania rostrata and S. cannabina as affected by agronomic practices

A field experiment was conducted to study the N2 fixation efficiency of Sesbania rostrata and S. cannabina as affected by agronomic practices in semi-arid subtropical climate. Sowing seeds resulted in smaller numbers of nodules, lower dry weight, lower total biomass, less N uptake, and less N2 fixation for S. rostrata than S. cannabina, while cut-stem planting improved the symbiotic efficiency. Flooding the soil increased the relative humidity of the crop micro-environment by 4-11% and induced early appearance of stem nodules in S. rostrata. Only 67 kg N ha-1 was fixed by S. rostrata compared to 160 kg N ha-1 by S. cannabina when normal agronomic practices (sowing and non-flooding) were followed. In contrast, planting stem cuttings and flooding resulted in greater biological N2 fixation, 307 and 209 kg N ha-1 by S. rostrata and S. cannabina, respectively. Therefore, S. rostrata can be successfully exploited as a green manure when stem cuttings are planted under flooded conditions.