The Impacts of Inherent Soil Properties, Environmental Conditions, and Restoration Time on Ecological Benefits during CRP Restoration.

The Conservation Reserve Program (CRP) has numerous benefits including reduced soil erosion, increased C sequestration, and biodiversity through the conversion of highly erodible cropland to grasslands. The rate and magnitude of these changes varies and the factors that impact these changes are largely unknown. To address these knowledge gaps, we evaluated soil microbial community composition (fatty acid methyl ester profiles), a suite of dynamic soil C properties (DCPs) and C sequestration potential using δ¹³C values, abiotic variables (e.g. soil water content, temperature and daily temperature range (DTR)), and inherent soil properties (bulk density, soil texture, pH, calcium carbonate equivalent (CCE)). The DCPs included: soil organic C (SOC), microbial biomass C (MBC), particulate organic matter (POM-C), CO₂ flux, and three C cycling soil enzyme activities. In 2012 and 2014, soil samples (0-10 and 10-30cm) were collected from 16 CRP fields enrolled from 6-28 years, 7 annually cropped dryland fields (0 years restored), and 3 rangelands. The relative abundance of fungi (arbuscular mycorrhizal and saprophytic) increased and all bacterial groups decreased from 0 to 15 years under restoration (p<0.0001). An increase in the proportion of C from C₄ grasses from 0 to 15 years, with no further increase beyond 15 y, suggests C saturation in these sandy (>75%) soils. Soil temperature, water content, pH and texture were not significant drivers of shifts in FAME groups along the chronosequence. Higher bacterial abundance was associated with higher DTR. Microbial community composition was similar between rangeland and crop, despite higher overall DCPs in rangeland. DCPs also were positively affected with increasing restoration time (p=0.01). The increased DCPs were associated with higher silt and clay contents, but lower sand content and bulk density, temperature, and DTR. However, soil water content, pH, and CCE were not correlated with DCPs.