|Karlen, Douglas - Doug|
Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/25/1997
Publication Date: N/A
Citation: Interpretive Summary: Farmers, politicians, scientists, and the general public want to know if soil quality assessments can be used to evaluate the effectiveness of public policies such as the conservation reserve program (CRP). We conducted a two year field study in Iowa, Minnesota, North Dakota, and Washington state to compare several soil properties in side-by-side fields that were either enrolled in the CRP or still being cropped. To evaluate soil quality, indicators such as texture, pH, electrical conductivity (EC), cation exchange capacity (CEC), aggregate stability, bulk density, organic matter, microbial biomass, respiration, and fungal activity were measured. Increased soil organic matter, lower nitrate nitrogen concentrations, and greater microbial activity indicated that soil quality was improved by placing cropped land into perennial grass. Soil biological properties were affected more quickly than soil physical or chemical properties. This study also suggested that benefits gained by enrolling land into the CRP could be maintained for a longer period of time if no-till practices were used when the land was returned to crop production. Policymakers, resource conservationists, consultants, and land owners will benefit from this research by having information on how the CRP or similar soil and crop management practices can affect soil quality. The information can also be used to evaluate soil quality benefits of public investment in the CRP.
Technical Abstract: Soil quality assessments present a promising method for evaluating the environmental impact of public policies such as the Conservation Reserve Program (CRP). This 2-year comparative assessment evaluated changes in aggregation, bulk density, organic C and N, nitrate, ammonium, pH, CEC, microbial biomass, respiration, fungal activity within the surface (0 to 7.5 cm) of paired CRP and cropped or fallow soils in IA, MN, ND, and WA. Aggregate stability was 23% higher in CRP sites in Iowa, but no differences were found in North Dakota sites. Total organic C was 27% greater under CRP in MN, but not significantly different from cropland soils in the other states. Nitrate-N was 18 to 74% higher in cropped soils than those in CRP. Ammonium-N was 10% higher in cropped soils in ND, but not at sites in MN and WA. Soil pH was significantly lower in cropped soils in WA, but not in soils from CRP sites within the other states. Microbial biomass carbon was 17 to 64% greater under CRP than cropped soils. We conclude that soil quality was improved by placing cropped land into perennial grass. Soil biological properties were impacted most quickly and significantly by the CRP. This study also suggests that no-till management could maintain many of the benefits derived from CRP when the land is returned to crop production.