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

Abstract

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.

Editorial for the special issue on “opportunities and challenges in no‐till farming”

“…In another long‐term experiment (9 years), Ramalho et al (2020) also found that grazing did not compromise SOC gains under NT on a Ferralsol (Food and Agriculture Organization (FAO) soil classification). Ribeiro, Ibarr, Besen, Bayer, & Piva (2020) carried out an on‐farm assessment of net global warming potential (GWP) in NT integrated crop–livestock systems on a Ferralsol, and reported that moderate grazing was optimal for reducing GWP due to the SOC accumulation in comparison to no, light or intensive grazing options.…”

Does the residual effect of n-fertilization applied on corn phase maintain forage production of the following pasture phase in an integrated crop-livestock system?

“…Thus, the nutrient cycling, in the pasture phase, starts when the first leaf senesces and returns to soil in form of nutrients and organic matter, thereby the nutrient cycling occurs constantly throughout the grazing period. According to Ribeiro et al (2019), the grazing period in an ICLS can increase the soil carbon stock and accelerate the nutrient cycling due to the continuous pasture growth and the higher forage yield stimulated by grazing.…”

Integrating beef cattle on cropland affects net global warming potential

“…Previous GWP evaluations of ICL systems have been conducted in Brazil, where pasture-based production of cattle (Bos taurus) is common (Cardoso et al 2016). In southern Brazil, Ribeiro et al (2019) found ICL systems under a black oat (Avena strigosa Schreb.) -soybean (Glycine max L.) rotation and notill management reduced net GWP under moderate grazing compared to intensive grazing (0.09 vs. 4.92 kg CO 2equiv.…”