Managing grazing intensity to reduce the global warming potential in integrated crop-livestock systems under no-till agriculture

Agricultural intensification has been associated with increased greenhouse gas (GHG) emissions. Using integrated crop-livestock systems (ICLs) under no-till agriculture can increase soil organic carbon (SOC) accumulation, thereby helping mitigate such emissions. The aim of this study was to assess the net global warming potential (net GWP) of no-till ICLs at variable grazing intensities of winter black oat pasture in a subtropical ecosystem. A 3.5-year field experiment involving three different grazing intensities (i.e., intensive, moderate and light as defined by a pasture height of 10, 20 and 30 cm, respectively) and grazing exclusion in winter and no-till soybean cropping in summer was conducted on a Ferralsol in southern Brazil. Net GWP, in Mg CO(2)eq ha(-1) year(-1), was assessed in terms of SOC sequestration relative to intensive grazing as a reference, including methane (CH4) and nitrous oxide (N2O) emissions, and energy costs of farming operations and inputs. Moderate grazing reduced net GWP relative to intensive grazing (from 0.09 to 4.92 Mg CO(2)eq ha(-1) year(-1)), the latter leading to the highest GWP levels. The decrease in net GWP was mainly the result of SOC accumulation, which offset 34-98% of all GHG emissions. Light grazing and grazing exclusion proved to be less efficient than moderate grazing in decreasing net GWP (1.84 Mg CO(2)eq ha(-1) year(-1) on average), mainly as a result of decreased SOC accumulation. Based on our findings, moderate grazing (20 cm high pasture) of winter black oat pasture is an effective strategy to reduce the C-footprint of ICLs in subtropical no-till agriculture. Highlights On-farm assessment of net GWP in subtropical no-till ICLs Conversion from intensive to moderate grazing reduced net GWP SOC accumulation is the main driver of net GWP reduction under no-till ICLs.