Soil and Nutrient Erosion Risk in Organic and Conventional Cropping Systems.
V. Steven Green1, Michel A. Cavigelli1, Thanh H. Dao2, and Dennis C. Flanagan3. (1) USDA-ARS-SASL, 10300 Baltimore Ave., Beltsville, MD 20705, (2) USDA-ARS, BARC-East, Bldg. 306-102, Beltsville, MD 20705, (3) USDA-ARS-NSERL, 275 S. Russell St., West Lafayette, IN 47907
Organic farming, which is growing in popularity, has been proposed as a sustainable alternative to conventional farming practices. However, it is not known how organic farming systems affect soil erosion risk and sediment-bound nutrient transport. Our objectives were to compare soil erosion risk and sediment bound nutrient transport potential for grain based conventional and organic cropping systems by determining selected soil physical properties and distributions of carbon (C), nitrogen (N), and phosphorus (P) in soil aggregates of the 0–5 cm depth of a Christiana-Matapeake-Keyport soil association (silt loam Hapludults) located at the Beltsville Farming Systems Project in western Maryland, USA. We measured soil bulk density, aggregate stability, aggregate size distributions, and total C, N, and P of the bulk soil as well as total C, N, and P associated with five soil aggregate size classes in conventional no-till (NT) and chisel till (CT) systems and in an organic tilled system (ORG). The plots had been in a corn, soybean, wheat rotation for 8 years at the time of sampling. No-till soils had lesser bulk density and greater aggregate stability than did CT and ORG soils. Carbon, N, and P concentrations were greater in large (>2.00 mm) and small macroaggregates (0.21 to 2.00 mm) than in microaggregates (<0.21 mm) regardless of cropping system. When nutrient concentrations were combined with aggregate distribution data, the quantity of aggregate associated nutrients was greatest in microaggregates in ORG and CT soils but greatest in macroaggregates in NT soils. These results indicate an increased risk of sediment associated nutrient transport from ORG and CT soils compared with NT soils, since microaggregates in these soils are preferentially lost through sediment transport. Using the Water Erosion Prediction Project (WEPP) model, however, risk of sediment associated nutrient transport was in the order NT<ORG<CT. Although the physical properties of CT and ORG were very similar, the ORG system utilizes cover crops during a greater portion of the rotation than the CT system and provides much needed soil protection resulting in predicted sediment losses of 66% of that of CT. The NT cropping system promoted macroaggregate formation and stability and reduced the risk of particulate nutrient transport in this warm, humid region soil. Some organic cropping systems, including the one tested in this study, need implementation of additional soil conservation management practices in order to be more environmentally sustainable.