Silvopastoral system as a climate-smart alternative for beef production: Enteric methane emission neutralization and animal thermal comfort increase

CONTEXT: Climate-smart agricultural systems must mitigate climate change and adapt to it. OBJECTIVES: (i) test the ability of a silvopastoral system (SPS) in Brazil to neutralize the CH4 enteric emission by tree carbon (C) assimilation, considering solely the stem-C destined to Products with Higher Added Value (HVAP) and furniture as valid, due to their long-term stability; (ii) test the SPS ability to provide increased animal thermal comfort and; (iii) compare the SPS productivity, animal thermal comfort and CH4 emission with a full sun system (FS). METHODS: The systems had four areas managed under rotational stocking with beef cattle and were established with Piata palisadegrass [Urochloa brizantha Stapf cv. BRS Piata] in 2007. In the SPS, eucalyptus trees (Eucalyptus urograndis clone GG100) were planted in 2011, in single east-west oriented rows, with a 15 m x 2 m spacing, and thinned to 15 m x 4 m spacing in 2016. Microclimate data were collected in weather stations to determine the Black Globe and Humidity Index (BGHI). The CH4 enteric emission was estimated using the Tier-2 equation (IPCC Methodological Guide - 2019). Tree height and diameter at breast height were measured every six months from October/2017 to April/2019 to estimate the stem biomass using an allometric equation. The stem biomass was multiplied by its carbon content and by 40 % to consider the break-through yield in sawmill. RESULTS AND CONCLUSIONS: BGHI was lower in the SPS than in the FS. Even considering the stem-C appropriate for HVAP and furniture in a SPS with a stocking rate 256 % greater than the Brazilian average, 77 % of the CH4 enteric emission was offset. When considering all the stem-C, the net C balance was-14.28 Mg CO2 eq. ha- 1 year- 1. SIGNIFICANCE: SPS are interesting alternatives to mitigate climate change while providing satisfactory animal production and increased animal thermal comfort. (AU)