Emissões de óxido nitroso e fornecimento de nitrogênio ao milho e trigo com doses de dejetos líquidos de suínos injetados no solo com e sem dicianodiamida

Abstract

Pig slurry (PS) has a high proportion of nitrogen (N) in ammoniacal form, whose losses by ammonia (NH3) volatilization can be high when PS is broadcast, as it is done in no-till crops. The shallow injection of PS significantly reduces such losses, but increases the emissions of nitrous oxide (N2O) into the atmosphere, which can be mitigated by adding nitrification inhibitors (IN) to PS at the time of its injection into the soil. There is little research information involving the addition of IN to PS doses injected into the soil and its effect on N2O emissions and N supply to crops. In the present study, the effect of adding the IN dicyandiamide (DCD) to PS doses equivalent to 33, 66, 100 and 133% of the amount of N recommended for wheat and corn was evaluated on these two variables, in addition to a control treatment and a treatment with mineral fertilizer (NPK) recommended to crops, both without IN addition. The IN proportion was constant in each dose and equivalent to 10% of the ammoniacal N applied to the soil with the PS. All PS doses were evaluated with and without the addition of IN. The study was carried out for two years, with treatments always being applied in the same plots, at the time of sowing the crops, following a randomized block design with four replications. N2O emission was evaluated using static chambers. The shallow injection of PS into the soil increased N2O emission and this increase was not directly proportional to the increase in PS dose, but it was exponential. The addition of DCD to the PS was efficient in mitigating N2O emissions, especially when the PS dose was equal to or greater than the N recommendation for the crops. The average N2O emission factor (EF) of the DLS doses with the addition of DCD was 1.33% and 2.56% without DCD. Despite the efficiency of DCD in reducing N2O emissions, this IN was not efficient in increasing crop grain yield, contrary to what we hypothesized that this could occur with the addition of the IN to at suboptimal PS doses. Through models adjusted to crop productivity and N2O emissions data, it was possible to estimate that, with the reduction of the PS dose to 87% of the recommended amount of N for corn and wheat and with the addition of DCD, it would be possible to maintain the productivity of these two crops, with a 50.2% reduction in N2O emissions, compared to injecting the recommended dose of PS into the soil without DCD.