Avaliação das emissões de gases do efeito estufa em pastagem de trigo submetida a diferentes somas térmicas como intervalo de pastoreio

Abstract

With the aim of optimizing pasture productivity and sustainability, this study evaluated the effects of different strategies, including the use of thermal sum (TS) and nitrogen fertilization, on the bromatological and structural composition of wheat pasture, greenhouse gas (GHG) emissions and soil nitrogen dynamics. The grazing interval was set at two STs, 330 and 550 degree days, and the pastures were subjected to nitrogen fertilization or not, in an experimental block design with subdivided plots. The bromatological and structural composition of the pasture was analyzed as a function of STs. The STs did not affect (P > 0.05) the dry matter (DM), organic matter (OM), in vitro digestibility of dry matter (DIVMS), percentage of leaves (PF) and percentage of other species (POE). However, there was an increase (P < 0.05) in the content of neutral detergent fiber (NDF) of 0.8% and 5.5% and in acid detergent fiber (FDA) of 2.5% and 6.5%, respectively for 330 and 550 degree days, from the first to the second year of evaluation. The variables percentage of dead material (PMM), height (cm), percentage of stalk + sheath (PC) and percentage of dry matter per cycle (PMSC) also differed (P < 0.05), increasing when the interval between grazing was reduced from 550 to 330 degree days. Dry matter (DM) decreased by 22% when at higher ST in both evaluation years. The crude protein (CP) and hemicellulose (HEM) contents increased with 330 degree days, and the lignin (LDA) and cellulose (CEL) contents showed an interaction between ST and year of evaluation. GHG emissions were analyzed according to whether or not N and STs were applied. There was a reduction (P < 0.001) in N2O emissions, with average flows of 6.40 and 17.5 g N ha-1 d -1 at 330 degree days and 5.81 and 12.6 g N ha-1 d -1 at 550 degree days, without and with N application, respectively. CO2 fluxes showed an interaction (P < 0.001) between STs and collection days, with an increase of 7.33 kg N ha-1 d -1 at higher STs. The volatilization of N-NH3 decreased (P < 0.001) according to the cycle and day of N application. The concentrations of N-NO3 - increased (P = 0.005) when evaluated at lower ST, and the concentrations of N-NH4 + showed no differences in relation to ST and fertilization, but varied (P < 0.001) over the evaluation time. The emission factor (EF) and the calculated PEGp were higher at 330 degree days of ST. These results contribute to understanding sustainable management practices, with an emphasis on reducing GHG emissions and increasing pasture productivity, highlighting the importance of properly adjusting grazing and nitrogen fertilization.