Identifying Causes of Non-Uniform Red Clover Establishment When Underseeded to Winter Wheat.
Adam A. Queen, Bill Deen, and Hugh J. Earl. University of Guelph, 50 Stone Rd., Guelph, ON N1G 2Z9, Canada
Red clover (Trifolium pratense L.) underseeded to winter wheat provides substantial nitrogen (N) credits to subsequent crops in a rotation. However, many growers have difficulty achieving uniform red clover establishment. The objectives of this study are to determine when red clover mortality occurs (leading to non-uniform establishment) and assess whether it is a function of soil moisture and/or light competition stress induced by the wheat canopy. A two-year study was conducted that evaluated six winter wheat field sites across Ontario. Main treatments were N rate applications on winter wheat (67 and 135 kg N/ha) and row width configuration (15 cm rows, 15 cm rows with every thrid row removed with an herbicide application). Treatments were established at four locations within a field, with two replications per location. Red clover stand, red clover biomass, wheat biomass, light penetration from the wheat canopy and soil moisture were assessed on a bi-weekly basis beginning in mid-May and extending to wheat harvest. End of season red clover biomass was also assessed. As wheat development progressed, red clover stands were reduced. Lowest red clover stand counts for all treatments were observed post wheat anthesis and prior to wheat grain maturity. Following wheat harvest, red clover populations generally increased. Red clover stand counts and biomass were consistently increased by removing every third row. Effects of nitrogen rate on red clover stand counts and biomass appeared less consistent. Adjusting row width configuration had a greater effect on light penetration and wheat yield than reducing N rate.