Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2005
Publication Date: 5/15/2006
Citation: Karlen, D.L., Hurley, E.G., Andrews, S.S., Cambardella, C.A., Meek, D.W., Duffy, M.D., Mallarino, A.P. 2006. Crop rotation effects on soil quality at three northern corn/soybean belt locations. Agronomy Journal. 98:484-495.
Interpretive Summary: Increased farm size, specialization and separation of crop production and animal enterprises, and increased pressure to maximize short-term profit throughout the U.S. Corn/Soybean Belt have collectively resulted in a decreased use of long-term crop rotations that included both grain and forage crops. This study examined the effects of different crop rotations on soil quality indicators as well as potential profitability. Without government supported commodity payments, long-term rotations that included at least three years of forage crops in addition to corn and soybean had a higher soil quality rating and were more profitable than either continuous corn or a two-year corn-soybean crop sequence. Therefore, as government policies such as the Conservation Security Program are implemented, increased efforts should be made to develop markets and uses for forage crops so that producers will be encouraged to use more diversified crop rotations. Doing so could result in long-term economic, social, and environmental benefits for the region.
Technical Abstract: Extended crop rotations in the Midwest have been replaced by a two-year corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] sequence, but how is this affecting soil quality? Our objectives were to determine (1) how this change affected soil quality indicators, (2) if a soil quality index (SQI) reflected the changes, and (3) if the SQI values and profitability were related. Soil samples were collected from three long-term studies in Iowa and one in Wisconsin. Bulk density, soil pH, water-stable macro-aggregation (WSA), total organic carbon (TOC), total N (TN), microbial biomass C (MB-C), extractable phosphorous (P) and potassium (K), and penetration resistance were measured. The indicator data were scored using non-linear curves reflecting performance of critical soil functions (e.g. nutrient cycling, water partitioning and storage, or plant root growth). Profit was calculated by estimating costs of production and subtracting them from potential income based on actual crop yields and the 20-yr average non-government supported commodity prices from the National Agricultural Statistics Service (NASS) database. Extended rotations had a positive effect on soil quality indicators. Total organic carbon was the most sensitive, showing significant differences at all locations, while bulk density differences were significant at only one Iowa location (Kanawha). The lowest SQI values and 20-yr average profit were associated with continuous corn, while the highest ratings were found with extended rotations that included at least three years of forage crops. Our results suggest the Conservation Security Program (CSP) should reward more diverse and extended crop rotations.