Surface-soil carbon stocks greater under well-managed grazed pasture than row crops

Abstract

Under the intensifying effects of climate change, agricultural practices that increase soil organic C (SOC) provide an opportunity to offset greenhouse gas emissions. Grazed pasture has the potential to increase SOC, but knowledge gaps remain about the effects of grazing frequency and intensity on SOC pools. We explored SOC quantity and quality in paired pastures and row crops and across grazing management gradients in southern and central Wisconsin. On average, pastures had 12.41 Mg ha−1 more SOC in surface soils (0–15 cm) than their row crop counterparts, but were not different in subsurface soils (15–30 cm). Soil organic C was inversely correlated with grazing frequency (i.e., rest period) but no correlation with grazing intensity (i.e., residual height) was observed. Less stable particulate organic matter-C (POM-C) was correlated with grazing frequency and intensity in the same way as SOC, whereas more stable mineral-associated organic matter-C was not correlated with either grazing management parameter. Sol organic C and POM-C increased linearly with pasture age (∼32 g C m−2 yr−1). Well-managed grazing on cool-season perennial pastures with undisturbed soils offers the best agricultural opportunity for helping to mitigate climate change via SOC sequestration.