Legacy effects of land use on soil nitrous oxide emissions in annual crop and perennial grassland ecosystems

Land use conversions into and out of agriculture may influence soil-atmosphere greenhouse gas fluxes for many years. We tested the legacy effects of land use on cumulative soil nitrous oxide (N2O) fluxes for five years following conversion of 22 year-old Conservation Reserve Program (CRP) grasslands and conventionally tilled agricultural fields (AGR) to continuous no-till corn, switchgrass, and restored prairie. An unconverted CRP field served as a reference. We assessed the labile soil C pool of the upper 10 cm in 2009 (the conversion year) and in 2014 using short-term soil incubations. We also measured in situ soil N2O fluxes biweekly from 2009 through 2014 using static chambers except when soils were frozen. The labile C pool was ~2-fold higher in soils previously in CRP than in those formerly in tilled cropland. Five-year cumulative soil N2O emissions were ~3-fold higher in the corn system on former CRP than on former cropland despite similar fertilization rates (~184 kg N ha-1 yr-1...