Contribution of biological nitrogen fixation to Elephant grass (Pennisetum purpureum Schum.)

Aims Because of its high dry matter (DM) productivity, elephant grass (Pennisetum purpureum) is an ideal candidate for biomass production for biofuel production if low N fertilizer rates are used to avoid high fossil fuel inputs. The objective of this study was to investigate the potential of different elephant grass genotypes to obtain contributions of plant-associated biological N2 fixation (BNF). Methods Three field experiments with 4 or 5 different genotypes were conducted on low-fertility Acrisols, two in Rio de Janeiro State and one in Espirito Santo for the evaluation of DM and N accumulation and 15N abundance. Results DM and N accumulation rates of four genotypes in the two experiments in Rio State stabilized at high levels after 2 years of growth. In all experiments the spontaneously-occurring weeds in the plots were significantly higher in 15N abundance than the elephant grass genotypes. The lower 15N abundance of the elephant grass was shown not to be due to lower δ15N abundance at depth in the soil. Conclusions Four of the grass genotypes obtained between 18 and 70% of their N from BNF amounting to inputs of between 36 and 132 kg N ha−1 yr−1.