Estratégias para mitigar as emissões de óxido nitroso e aumentar a eficiência de uso do nitrogênio de dejetos líquidos de suínos injetados no solo

Abstract

The injection of pig slurry (PS) into the subsurface is an efficient alternative to reduce N losses via ammonia volatilization. However, this way of using PS enhances the formation of N2O, the potent greenhouse gas. This study aimed to evaluate strategies for using PS to increase the efficiency of N use and mitigate N2O emissions in a no-tillage system with a biannual cultivation system (maize-wheat). The experiment was carried out in Typic Hapludalf, under a subtropical climate for 3 years. The experimental design was randomized blocks with four replications. The treatments were: without fertilizer (Control), urea (U) and PS applied to the soil surface (PSs), PS injected into the subsurface at pre-sowing (PSi) (reference treatment), and three strategies for using PS: 50 % N via PS injected at pre-sowing + 50% applied on the surface in topdressing (PSi+PSs), 50% N via PS injected at pre-sowing + 50% N via urea applied to the surface in the topdress (PSi+U) and 50% N via PS + dicyandiamide (DCD) injected pre-sowing + 50% N via urea applied to the surface in the cover (PSi+DCD+U). N2O emissions were evaluated using the static chamber method for two years and the determination of grain yield and dry matter were determined for three years. The PS use strategies (PSi+PSs, PSi+U, and PSi+DCD+U) reduced the availability of nitrate in the soil, which reduced N2O emission by 10, 36, and 64% and 53, 59 and 72% in the year 1 and 2, respectively, compared to PSi. The most efficient strategy in reducing N2O emission was PSi+DCD+U, which reduced the N2O emission factor (EF) from 2.56 and 2.13% in the PSi treatment to 0.87 and 0.51% in years 1 and 2, respectively, resulting in EFs below the value defined by the Intergovernmental Panel on Climate Change (IPCC) (1%). PSi+PSs and PSi+U did not differ in grain yield and agronomic efficiency of nitrogen use (EAN) when compared to PSi in maize and wheat. The PSi+DCD+U increased the productivity of maize (+1.7 Mg ha-1) and wheat (+0.9 Mg ha-1) grains, the EAN of maize (+7.7 kg grain kg-1 N) and wheat (+4.2 kg grain kg-1 N), and the apparent N recovery (RAN) of wheat (+21.9%) compared to PSi. In both years and both crops, the scaled yield was lower in the PSi+PSs, PSi+U, and PSi+DCD+U strategies than in the PSi, except for wheat in year 1. Our results indicate that the strategy that had the lowest N2O emission and the best increase in grain yield was PSi+DCD+U, which had an average yieldscaled 72% lower than PSi, which is the best strategy for using PS among those evaluated.