Cover crop effects on the fate of N following soil application of swine manure

Biological nitrogen fixation (BNF) in sugarcane is considered one of the principal reasons for the success of the Brazilian Ethanol Program (PRO-ALCOOL) for motor car fuel. The BNF influences positively the energy balance of sugarcane crops for alcohol production. Gluconacetobacter diazotrophicus is a nitrogen-fixing bacterium associated with sugarcane, and is particularly abundant and active in the early stages after germination. The objective of this work was to evaluate the effect of the addition of increasing amounts of two sources of mineral nitrogen (ammonium sulphate and calcium nitrate) on the population of G. diazotrophicus and also to evaluate its effect on nitrogenase (acetylene reduction) activity and accumulation of N by two sugarcane hybrids, SP 701143 and SP 792312. The results showed that both varieties differed in the form of nitrogen they prefer to uptake from the soil. The variety SP 701143 preferred ammonium sulphate, whilst the variety SP 792312 preferred N from calcium nitrate. In both varieties, the addition of increased doses of ammonium and nitrate inhibited the population of G. diazotrophicus but in the variety SP 701143 the inhibition was more pronounced in the presence of calcium nitrate. The acetylene reduction activity was inhibited in both varieties, especially in variety SP 792312 in the presence of either of the two nitrogen sources.