Understanding the Causes of Non-Uniform Red Clover Overseeded to Winter Wheat.

Red clover (Trifolium Pratense L.) is a perennial legume that has been traditionally overseeded to winter wheat and grown as a cover crop in wheat-corn-soy rotation systems in North America.  As well as preventing soil erosion, retaining moisture, and building soil organic matter, red clover is an excellent soil conditioner and provides substantial nitrogen contributions to the subsequent corn crop. Unfortunately, red clover use has been declining as producers experience difficulties in maintaining uniform stands, and consequently, are unable to reliably reduce nitrogen fertilizer rates.  Existing research on red clover use in winter wheat has focused on management factors affecting overall biomass production, but the mechanism behind non-uniform stand densities is still not understood.  In a previous study, our research group observed that red clover appeared to establish uniformly across the field, but died during the season. We proposed that moisture stress, which can vary across soil types and topography, and by location and year, is the primary cause of red clover death that occurs inconsistently across fields.  To test our hypothesis, clover stand densities and soil moisture levels were monitored during the growing season across multiple locations in Southern Ontario over two years. Furthermore, topography and soil properties related to moisture, such as soil bulk density and soil texture, were characterized at these same sites to better estimate available water and to identify additional explanations for red clover non-uniformity. Overall, quantifying and affirming the cause of heterogeneity can help shape effective management practices for farmers to achieve resilient red clover stands.