Carbon, Nutrient and Energy Budgets in the LTAR in Iowa: 10-year Comparison.

The Long-Term Agroecological Research (LTAR) site was established in 1998 on the Neely-Kinyon Research Farm near Greenfield, Iowa to evaluate agronomic and economic outcomes of certified organic and conventional grain-based cropping systems. The site was certified organic in 2000. This study evaluates changes in carbon and nutrients during and after transition from conventionally managed corn and soybeans to organically managed corn- and soybean-based rotations containing small grains and forage legumes amended with composted swine manure. Experimental design is completely randomized with 4 replications. Soil samples (0-15 and 15-30 cm) were collected after harvest from 1998 through 2007. We quantified soil organic and inorganic carbon and nitrogen pools, and Bray P, ammonium acetate extractable K, Mg, and Ca, electrical conductivity (EC), pH, and bulk density. After 10 years of organic management, the organic soils had more total and biologically active soil organic matter, higher P, K, Mg, and Ca concentrations, and lower soil acidity than conventional soils. The corn-soybean-oat/alfalfa-alfalfa organic rotation had more biologically active organic C and N and higher inorganic N concentrations than the corn-soybean-oat/alfalfa organic rotation due to the greater alfalfa cropping intensity (2 of 4 yrs).  Higher inorganic P and K concentrations in the 3-yr rotation were related to manure application intensity. Our data indicate overall soil quality is enhanced in organic rotations and suggest organic management may enhance soil function to maintain agronomic productivity and increase environmental buffering capacity of the soil.