Farmers in the U.S. Corn Belt are showing increasing interest in winter cover crops. The known benefits of winter cover crops include reduced nitrate leaching, soil erosion, and weed germination, but evidence of improvements in soil productivity would provide further incentive for famers to implement winter cover crops. On the high organic matter soils that are typical of central Iowa, it is often difficult to show an increase in soil carbon with cover crops. The objective of this experiment is to determine the effects of a rye (Secale cereale L.) winter cover crop on particulate organic matter, potential nitrogen mineralization, and total organic carbon in a no-till corn silage/soybean rotation in central Iowa. Soil properties were measured on four treatments and at two depths, 0-5cm and 5-10cm. Treatments included no rye (control), rye following soybean [Glycine max (L.) Merr.], rye following corn silage (Zea mays L.), and rye following both soybean and corn silage. Plots were established in 2001 and results from the first year of sampling (2010) will be presented. Preliminary data suggest that potential nitrogen mineralization is increased in the treatment that has a rye cover crop each year.