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• N 2 O and CH 4 emissions were greater in SPS than in MONO. • N 2 O and CH 4 emissions were greater in rainy season compared with dry season. • Urine was the most relevant N 2 O and NH 3 source. • NH 3 emissions were greater in dry season and in MONO than in SPS. • N 2 O, CH 4 and NH 3 emission factors were lower than the IPCC default estimates. We quantified nitrous oxide (N 2 O), methane (CH 4), and ammonia (NH 3) 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, N 2 O and CH 4 fluxes were higher in SPS than in MONO. Notably, N losses in the form of N 2 O did not exceed 0.10 %, except for N 2 O emissions from urine deposited during the rainy season in SPS (0.39 % of applied N). Cattle dung was also a source of CH 4. The highest fluxes were observed under SPS during the rainy season, but emissions were generally low, with emission rates < 0.1 kg CH 4 head−1 yr−1. The highest N losses by NH 3 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 N 2 O, CH 4 , and NH 3 emissions from cattle are influenced by pasture system, excreta type, and season. N 2 O and CH 4 emissions increase in long-term SPS, while NH 3 losses reduce. [ABSTRACT FROM AUTHOR]