|Karlen, Douglas - Doug|
Submitted to: Journal of Production Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1997
Publication Date: N/A
Citation: Interpretive Summary: Politicians, administrators, and scientists want to know if soil quality assessments can be used to evaluate the effectiveness of public policies such as the CRP. By reviewing the literature, we find that soil quality per se cannot be measured directly. It must be estimated by measuring indicators such as texture, pH, nutrient availability, electrical conductivity (EC), salinity, porosity, aggregate stability, water retention, bulk density, organic matter, microbial biomass, or respiration; observing soil conditions such as color, structure, topsoil and plant rooting depth, erosion, infiltration rates, earthworm populations, invertebrate populations or communities, or soil enzymes; or evaluating the efficiency of processes such as crop production or nutrient cycling. Soil quality can be assessed at point, plot, field, farm, watershed, or larger scales, but the indicators chosen as well as the precision and accuracy will vary. Comparisons between CRP and cropped sites made for several soil quality indicators in Iowa, Minnesota, North Dakota, and Washington showed that soil microbial biomass and respiration were affected more quickly and to a grater extent than organic carbon, organic N, nitrate-N, ammonium-N, and pH. We conclude that soil quality assessments can be useful for evaluating the natural resource effects of public policies such as the CRP.
Technical Abstract: Soil quality assessments may be useful for evaluating natural resource benefits of policies such as the Conservation Reserve Program (CRP). Several studies conducted to assess the impact of CRP on indicators of soil quality were reviewed to determine how this information could be used to assess soil quality at point, plot, field, farm, watershed, or regional scales. With respect to CRP effects on soil quality, critical soil functions include resisting soil erosion, sustaining production, and maintaining stability. Soil erosion potential was evaluated by measuring runoff from simulated rainfall studies. Paired comparisons for several soil quality indicators measured on adjacent CRP and cropped sites were reviewed. Those results showed that soil microbial biomass and respiration were affected more quickly and to a greater extent than organic carbon, organic N, NO3-N, NH4-N, and pH. Fewer indicators showed significant differences in comparisons where cropped sites were managed using reduced- or no-till practices than where more intensive tillage was used. Based on the soil quality impact of post-CRP management studies that were also reviewed, we conclude that if CRP land is returned to row-crop production, no-till practices should be used to preserve the soil quality benefits that have been purchased through a $20 billion public investment.