Long Term Soil Water Improvements in Iowa Using a Winter Rye Cover Crop.

Our goal is to understand how cover crops impact soil water dynamics on a long term research site in Central Iowa and to see if soil water offers any explanation for differences in cash crop growth dynamics. We collected two years of cash crop growth, leaf area and C/N allocation data (soybeans in 2013, corn in 2014) to better understand if there are differences in cash crop growth dynamics with the incorporation of a winter rye cover crop.  No significant differences were found in soybean biomass, leaf area, N allocation or final yields between cover crop and no cover crop treatments.  Corn data will be analyzed following the growing season.  We also analyzed soil moisture data from 2008-2012 to determine how soil water storage varied from year to year and how winter rye growth impacted soil moisture at the start of the cash crop growing seasons.  Further, we sampled intact cores to 30-cm depth for a water retention curve analysis.  We measured volumetric water content at field capacity and permanent wilting point to determine if there were differences between treatments.  In the cover crop plots, we found neutral to positive effects of soil moisture in both wet and dry years at several soil depths.  We found minimal evidence that the growing winter rye cover crop depleted early season soil moisture; therefore it did not leave the cover crop plots in soil water deficit ahead of corn or soybean planting.  Further, the water retention analysis found significant differences in the plant available water where the cover crop plots had an average of 4mm additional water available.  Therefore when analyzed together, the crop growth and soil water dynamics from this long term site who neutral impacts on cash crop growth and positive impacts on soil water storage.