Both the contribution of soil nitrogen and of biological N2 fixation to sugarcane can increase with the inoculation of diazotrophic bacteria

This study was performed to determine if the contribution of biological N2 fixation (BNF) associated with Brazilian sugarcane cultivars could be increased by the inoculation with N2-fixing bacteria. The field experiment was planted with two sugarcane cultivars, inoculated or not, with five N2-fixing bacteria. All plant tissues, including belowground, were harvested for determination of dry matter, N accumulation and 15N abundance at five occasions until 450 days after planting. Inoculation significantly increased total N accumulation in the aerial tissue of cultivar RB867515 from 147 to 199 kg N ha−1 and cultivar RB92579 from 126 to 192 N kg ha−1. At final harvest 15N abundances of entire sugarcane plants compared to that of plant-available N indicated that BNF inputs were over 64%. Total N derived from BNF and the soil was increased by inoculation, by 50 and 17 kg N ha−1 and 36 and 67 kg N ha−1, for the two cultivars respectively. Without inoculation, the two sugarcane cultivars obtained over 65% of N from BNF. Inoculation with the five component inoculant increased N accumulation from soil and BNF but with little impact on the proportion of N derived from BNF.