Soil carbon and nitrogen recovery on semiarid Conservation Reserve Program lands S.M. Munson a, b, * , W.K. Lauenroth c , I.C. Burke c, d, e a Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA b Department of Forest, Rangeland, and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523, USA c Department of Botany, University of Wyoming, Laramie, WY 82071, USA d Haub School of Environment and Natural Resources, University of Wyoming, Laramie, WY 82071, USA e Ruckelshaus Institute of Environment and Natural Resources, University of Wyoming, Laramie, WY 82071, USA article info Article history: Received 13 June 2011 Received in revised form 17 November 2011 Accepted 29 November 2011 Available online 20 December 2011 Keywords: Carbon sequestration Nitrogen Net primary production CRP Shortgrass steppe abstract Cropping practices in the Great Plains of the U.S. have led to large losses in soil organic carbon (SOC) and nitrogen (N). Land converted to perennial vegetation through the Conservation Reserve Program (CRP) has the potential to recover these losses and sequester anthropogenic carbon. We studied 18 years of SOC and N recovery in CRP fields seeded with native and non-native perennial grasses in the driest portion of the Great Plains. SOC and N under native perennial grasses in the surface soil increased by as much as 200 g C m 2 and 14 g N m 2 in 9 years. However, low plant basal cover in CRP fields limited SOC and N recovery at the field scale to 2 g C m 2 y 1 and 0.02 g N m 2 y 1 . After 18 years of recovery, CRP fields seeded with native perennial grasses had 60% of the total SOC and 67% of the total soil N in undisturbed shortgrass steppe, and fields seeded with non-native perennial grasses recovered less. Belowground plant inputs to SOC reached 70e85% under native and 50% under non-native perennial grasses within 18 years. Our results suggest low potential for CRP fields to offset anthropogenic C emissions in semiarid regions under current management practices, but this potential could be enhanced by lengthening CRP contracts or promoting the establishment of perennial vegetation with high basal cover. Published by Elsevier Ltd. 1. Introduction Soils are the largest terrestrial carbon pool and can be a signifi- cant source or sink of CO 2 and other greenhouse gases depending on land use practices (Schimel, 1995; Post and Kwon, 2000). Conversion of natural to cultivated ecosystems is a well-studied land use change that has historically transferred between 54 and 70 Gt (Gt ¼ 10 12 kg) of C from the soil to the atmosphere (Cole et al., 1997; Amundson, 2001). This has resulted in reductions of soil organic carbon (SOC) at individual sites by up to 60% (Guo and Gifford, 2002) through reduced plant inputs into SOC and increased outputs (Anderson and Coleman, 1985). Cessation of cropping and the establishment of perennial vegetation can sequester anthropogenic sources of C from the atmosphere and promote the recovery of SOC pools (IPCC, 2007). Since carbon uptake and storage is tightly linked to the nitrogen (N) cycle, it is equally important to understand how N pools and fluxes may be affected by land use change. Agricultural incentive programs, such as the U.S. Conservation Reserve Program (CRP), have tremendous potential to recover SOC and N from formerly cropped fields through payments to farmers to take their marginal fields out of production and seed them with perennial vegetation (Skold, 1989). CRP is an extensive land use in the U.S. and currently includes nearly 1 million hectares of former shortgrass steppe in Colorado (USDA Farm Service Agency, 2010). CRP contracts are for 10 years, but many fields have been reenrolled in the program and have been out of production for two decades. This has created an opportunity to evaluate SOC recovery at a longer time scale than most CRP studies (Robles and Burke, 1998; Reeder et al., 1998), while accounting for seed mix and the potential plant community composition, which is often lacking in long-term studies (Burke et al., 1995a; Kucharik et al., 2006). The shortgrass steppe is a semiarid grassland of the western Great Plains. The high allocation of net primary production to roots of native perennial grasses and slow decomposition rates of the region create potential for SOC storage (Burke et al., 2008). However, low water availability limits the recovery of perennial vegetation (Coffin et al., 1996), and plant species in CRP fields may * Corresponding author. Current address: USGS e Southwest Biological Science Center, Canyonlands Research Station, 2290 S. West Resource Blvd. Moab, UT 84532, USA. Tel.: þ1 303 236 1404; fax: þ1 303 236 5349. E-mail address: smunson@usgs.gov (S.M. Munson). Contents lists available at SciVerse ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv 0140-1963/$ e see front matter Published by Elsevier Ltd. doi:10.1016/j.jaridenv.2011.11.027 Journal of Arid Environments 79 (2012) 25e31