Chapter 4 - Soil Carbon Sequestration in Central U.S. Agroecosystems

Abstract

Cropland soils of the central U.S. represent a large potential sink for atmospheric carbon (C). This chapter reviews recent literature on C storage in cropland soils of the central U.S. to define agricultural management impacts on soil C sequestration. The most widely adopted management practice to enhance C sequestration in this region is conservation tillage. Recent research has demonstrated that no-tillage (NT) management has greater surface soil organic C (SOC) than plow tillage, but in some studies subsoil C content can be greater under plowing. There is evidence that changes in tillage management has altered C cycling processes resulting in greater retention of corn-derived C in NT compared to plowed systems. However, greater subsoil C content in plowed soils has led to similar total-profile SOC contents (0–100 cm) for NT and plowed soils in several studies, except in the western Corn Belt, where NT has been shown to retain greater soil C than plow tillage. For the few studies that included initial SOC contents measured at the beginning of the field experiment, SOC declined in both NT and plowed soils relative to baseline. These results suggest that NT may not necessarily facilitate C sequestration, but rather simply prevents additional SOC losses associated with conventional tillage (CT). Enhanced crop rotation complexity fosters soil C sequestration, especially when small grains and forage legumes are included in extended rotations and through planting of perennial grasses and trees on marginally productive cropland. Some studies have reported that N fertilizer application increased SOC, others reported decreased SOC, and still others reported no change in SOC. Although we have made some progress in the past decade towards defining the effects of agricultural management practices on surface and subsurface SOC, we still have a poor understanding of the mechanisms that determine observed SOC patterns in response to land management practices. Further research is needed to increase our understanding of the interactive effects of agricultural management practices, increased atmospheric CO 2 , and changing climate variables on C sequestration in central U.S. agroecosystems.