Effects of Low Soil Moisture on Survival of Red Clover (Trifolium pratense L.) Under-Seeded to Winter Wheat.

Red clover (Trifolium pratense), when included in corn-soybean-winter wheat rotations in relay cropping with wheat, has been shown to increase organic matter and soil tilth, yield and productivity of all crops in the rotation, decreased soil erosion, nitrate leaching and synthetic nitrogen fertilizer requirements.  In spite of these benefits, red clover inclusion into crop rotation has declined, in large part, due to non-uniformity of red clover stands.  In Ontario, causes of heterogeneous red clover stands have not been conclusively determined although the effects of tillage and shifts in competition for light and nutrients between wheat and clover during relay cropping have been investigated. As suggested by the high year effect across those studies, variation in soil moisture during relay cropping may have a large effect on red clover stand uniformity. We are conducting a two-year field experiment to test the impact of different early soil moisture deficits on the establishment of clovers with different growth habits (single-cut and double-cut). Differences in traits associated with survival to extreme drought conditions are also being investigated in growth room studies. By conclusively demonstrating that red clover non-uniformity is due primarily to drought mechanisms, effective strategies for the development of improved varieties through breeding efforts can be identified.