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

This study aimed at evaluating soil nitrous oxide (NO) and methane (CH) emissions from integrated farming systems. Soil NO and CH 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 NO 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 NO 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 NO emissions. In the rainiest season of summer-2, the soil had the highest WFPS (on average 71.4%) and thus the highest NO emission (on average 9.79 kg NO-N ha season) and the lowest CH consumption (on average - 0.40 kg CH-C ha season); while the opposite trend occurred in the driest season of winter-2 (on average 57.3% WFPS; 0.64 kg NO-N ha season and -0.90 kg CH-C ha season). Integrated farming systems including crop-livestock, livestock-forestry and crop-livestock-forestry reduced soil NO emissions relative to sole livestock by 27-40%, but did not affect CH emissions. Seasonal variations of precipitation, and therefore WFPS were driving factors of the NO and CH emissions. Overall, integrated farming systems show the potential to mitigate soil NO emission compared to livestock system.