Nitrogen fixation of Poaceae and Leguminoseae in a green manure experiment in the Brazilian semiarid region

Mixtures of green manure species, including Leguminosae and Poaceae, planted prior to commercial crops may incorporate more biomass than Leguminosae alone and fix more nitrogen than Poaceae alone.Biomass and nitrogen incorporation of three plant treatmens were compared under irrigation condition.In two mixture treatments, the same seven green manure species were planted together but with different seeding proportions.Treatment (1) (low-legume) had 50% the recommended seeding rate of the legume species (jack beans, cowpea and sunn hemp) and 150% the recommended seeding rate of the non-legume species (maize, pearl millet, sorghum and sun flower).The other treatment (2) (high-legume) had opposite proportions.In the third treatment, no green manure plants were sown and weed plants were allowed to grow.The results showed that biomass (9.1 and 8.2 Mg ha -1 ) and nitrogen accumulation (160 and 161 kg ha -1 ) did not differ between the low-legume and high-legume treatments, respectively, which were 2.5 times higher than those of the weed treatment (3.3 Mg ha -1 and 58.1 kg ha -1 ).Despite the higher non-legume biomass proportion and lower nitrogen concentration, the low-legume treatment symbiotically fixed as much N (52 kg ha -1 ) as the high-legume treatment because sorghum derived more N from the atmosphere (79 %) and maize in the same range as the legume species (37 to 54%).Therefore, sorghum and maize can have high N endophytic fixation and green manure prior to commercial crops can be produced both with legume and Poaceae species mixed together, providing a high input of N and biomass in a short period.