Nitrous oxide and methane emissions from soil under integrated farming systems in southern Brazil

This study aimed at evaluating soil nitrous oxide (N₂O) and methane (CH₄) emissions from integrated farming systems. Soil N₂O and CH₄ fluxes were assessed in a subtropical Cambisol in southern Brazil, using manual static chambers, over two years, in five farming systems (cropland, livestock, integrated crop-livestock, integrated livestock-forestry, and integrated crop-livestock-forestry). The study was conducted in four growing seasons: summer-1, winter-1, summer-2, winter-2. Integrated farming systems had lower soil N₂O emissions than livestock. The observed reduction was possibly due to lower water-filled pore space (WFPS) in soils under integrated systems (average 59.5-64.7%, vs 70.4% in livestock) as indicated by correlation (r = 0.74). Cropland, including cover-crops and maize, also had lower N₂O emission (by 40%) relative to livestock, of levels similar to those observed in integrated systems. Methane was consumed in soil, but it was not affected by farming systems, and offset only ~1.4% of the N₂O emissions. In the rainiest season of summer-2, the soil had the highest WFPS (on average 71.4%) and thus the highest N₂O emission (on average 9.79 kg N₂O-N ha^-1 season^-1) and the lowest CH₄ consumption (on average - 0.40 kg CH₄-C ha^-1 season^-1); while the opposite trend occurred in the driest season of winter-2 (on average 57.3% WFPS; 0.64 kg N₂O-N ha^-1 season^-1 and -0.90 kg CH₄-C ha^-1 season^-1). Integrated farming systems including crop-livestock, livestock-forestry and crop-livestock-forestry reduced soil N₂O emissions relative to sole livestock by 27-40%, but did not affect CH₄ emissions. Seasonal variations of precipitation, and therefore WFPS were driving factors of the N₂O and CH₄ emissions. Overall, integrated farming systems show the potential to mitigate soil N₂O emission compared to livestock system.