Nitrous oxide and methane emissions from beef cattle excreta deposited on feedlot pen surface in tropical conditions

Abstract As feedlot beef production systems are expanding into tropical climates, considerably less is known on their environmental impact specific to these regions. Our objective was to investigate the dynamics of nitrous oxide (N2O) and methane (CH4) fluxes in a feedlot system representative of Brazil, in order to aggregate new emission data for the characterization of intensive cattle raising in tropical regions. Excreta was obtained from Nellore steers in a feedlot (n = 25, BW = 393 ± 31 kg). Urine (1.3 L) and feces (1.3 kg) were applied separately in plots on an open-lot feedlot pen surface at the beginning of the trial and fluxes were monitored 92 d with static chambers. Although CH4 fluxes were variable, all treatments were a sink for CH4 as the average of the monitoring period (−8.9, −3.1, and −15.4 μg C m−2 h−1 for feces, urine, and control, respectively). The N2O fluxes were higher in the urine affected area, which was related to the higher soil moisture and mineral N availability in comparison to the area with feces. The occurrence of rainfall from 67 to 70 DAA was determinant of very high N2O fluxes either for urine or feces. Hence, GHG emissions from individual excreta were characterized by a period of small but significant fluxes, followed by a period of indistinguishable fluxes at the background level. A third period after rainfall portrayed the large impact of excreta on GHG emissions from the feedlot. The direct N2O emission factor (EF) for the N in urine was significantly higher than for the N in feces (2.83 vs. 0.32%, respectively, P