Nitrous oxide, methane, and ammonia emissions from cattle excreta on Brachiaria decumbens growing in monoculture or silvopasture with Acacia mangium and Eucalyptus grandis

Abstract

We quantified nitrous oxide (N2O), methane (CH4), and ammonia (NH3) emissions from cattle urine and dung patches on Brachiaria decumbens growing in a long-term silvopasture (SPS) or in monoculture (MONO) during the annual rainy and dry periods in southwest Brazil. We hypothesized that microenvironmental changes triggered by dense shade and litter, provided by trees, and pasture quality in SPS would affect greenhouse gas emissions from cattle excreta. Two field trials (rainy and dry season) were carried out using manual closed static chambers in a 3 × 2 factorial scheme, corresponding to three excreta types (urine, dung, and control without excreta) and two pasture systems (SPS and MONO), in a block design with three blocks and two replicates per block (n = 6 per treatment). Generally, N2O and CH4 fluxes were higher in SPS than in MONO. Notably, N losses in the form of N2O did not exceed 0.10 %, except for N2O emissions from urine deposited during the rainy season in SPS (0.39 % of applied N). Cattle dung was also a source of CH4. The highest fluxes were observed under SPS during the rainy season, but emissions were generally low, with emission rates < 0.1 kg CH4 head−1 yr−1. The highest N losses by NH3 volatilization were observed for urine under MONO, amounting to 8.3 % of total N applied during the rainy season and 17.1 % during the dry season. Our results demonstrate that N2O, CH4, and NH3 emissions from cattle are influenced by pasture system, excreta type, and season. N2O and CH4 emissions increase in long-term SPS, while NH3 losses reduce.