Manejo do nitrogênio e emissão de gases de efeito estufa na produção de capim-elefante para bioenergia

Abstract

Elephant grass is highly efficient in dry matter accumulation and has suitable quality parameters for energy production. The use of elephant-grass biomass depends on the energy balance and the greenhouse gas emissions associated with management practices used for biomass for energy production. Generally, the contribution of biological nitrogen fixation serves less than half the crop N demand, it is necessary to replace the N removed from the soil. N fertilization is usually recommended, however the impact on N2O emissions to atmosphere is unknown. The aim of this study was to carry out studies to measure N fertilizer losses in the form of ammonia volatilization and N2O emissions. Ammonia volatilization was evaluated since it is related to indirect N2O emissions. The effects of nitrogen doses, sources and application forms were studied, to identify the best pathway to provide nitrogen for the crop, with less impact on N2O emissions. The N2O emissions resulting from the soil tillage and four urea fertilizer doses (40, 80, 120 and 160 kg N ha-1) were evaluated. Different nitrogen fertilizer sources (urea and ammonium sulfate) and urea application forms (incorporated or surface) compared with ammonium sulfate, respectively, and green manure were evaluated, compared to application of urea and polymer-coated urea, to evaluate the nitrogen efficiency by the plants and soil N2O emissions. The results showed that nitrogen fertilization is essential to reach high biomass yield of elephant grass. N2O emissions were higher with urea application than with ammonium sulfate, with no effect on the quantity of urea incorporated. The use of green manure resulted in higher N2O emissions compared to urea. The NH3 volatilization losses ranged from 40 to 60% when urea was applied and 11% with the application of ammonium sulfate. The NH3 volatilization losses were 35% lower when urea was incorporated, resulting in higher elephant grass biomass yield. The polymercoated urea resulted in a decrease of 6% in the NH3 volatilization losses. Nitrogen fertilizer is essential to reach high elephant grass biomass yield, and the environmental impact caused by this practice may be reduced by changing the source and form of the fertilizer application.