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 (CH 4) and nitrous oxide (N 2 O) 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.

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Grazing stimulates root and forage mass of perennial pastures, but few studies have addressed the effects of grazing on annual pastures which are often grown in short periods within integrated crop–livestock systems (ICLS). In these pastures, N fertilization is a common practice to increase forage mass, but its effects on root morphology are unclear. In a field experiment, we evaluated how grazing intensities (ungrazed, moderate, and heavy grazing) and N fertilization rates (0, 75, and 150 kg N ha−1) affected morphological attributes of oat (Avena strigosa Schreb.) roots and forage accumulation in ICLS in Brazilian subtropics. Forage mass was evaluated in each grazing cycle and roots were sampled to a 30‐cm depth at the end of the grazing season in 2 years. Heavy and moderate grazing reduced (p < 0.05) forage accumulation by 15%–37% compared to ungrazed (4867 kg DM ha−1) in the first year, characterized by extended periods of water deficit, but in the second year forage accumulation from grazed and ungrazed was similar (p > 0.05), averaging 4273 kg ha−1. N fertilization increased forage accumulation in both the years, without differences between 75 and 150 kg N ha−1 in grazed treatments. Grazing and N rates mainly reduced root diameter and increased root N concentration. Increasing N fertilization rates increased root length but it was more expressive in the first year. Nitrogen fertilization with 75 or 150 kg N ha−1 on moderately grazed oat is an alternative to increase forage accumulation as it stimulates fine root development and increase N uptake, mainly when adverse climatic conditions can affect pasture growth.

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