Conservation Reserve Program effects on soil quality indicators

Soil quality indicators may be useful for evaluating public policies such as the Conservation Reserve Program (CRP). The objective of this study was to determine how CRP affected several physical, chemical, and biological indicators of soil quality. Soil aggregate stability and size distribution, bulk density, total organic C and N, nitrate-N, ammonium-N, pH, cation exchange capacity, microial biomass C and N, soil respiration, fluorescein diacetate hydrolysis, fungal hyphal length, and ergosterol concentrations were measured in paired CRP and cropland sites in Iowa, Minnesota, North Dakota, and Washington. CRP sites in Iowa generally had a higher percentage of water stable soil aggregates than cropland sites. In Minnesota, the mean aggregate diameter was significantly higher in CRP than cropland samples, but differences in North Dakota were not significant. In all states, microbial biomass carbon was 17 to 64% higher at CRP sites than at cropland or fallow sites. Nitrate-N was 18 to 74% higher in cropland than CRP sites. Soil respiration values were greater (but not significantly different) in CRP than cropland sites in all four states. Hyphal length, measured only in Iowa, increased 26 to 62% under CRP. CRP samples had higher ergosterol only in Henry County, Iowa, where cropland was chisel plowed and disced each year. Overall, soil biological indicators showed more significant differences than either chemical or physical indicators. This multi-state project shows that several soil quality indicators were improved by placing highly erodible cropland into perennial grass, and that with refinement, those indicators could be used to assess long-term impacts of agricultural management practices.