Nitrogen management of spring milling wheat underseeded with red clover

The benefits of underseeding cereals with legumes and grasses have been established. However, research is required to determine the effects of underseeding spring wheat with red clover on yield and milling quality. The objectives of this study were: (1) to determine the rates of supplemental N required to obtain 13.5% or greater grain protein of three spring milling wheat (Triticum aestivum L. em Thell.) cultivars underseeded to red clover (Trifolium pratense L.); (2) to determine the effect of supplemental N on establishment of red clover , and (3) to relate the N status of the soil after harvest to grain protein. Field experiments were conducted from 1998 to 2000 on three sites: Hartland, New Brunswick; Truro, Nova Scotia; and Harrington, Prince Edward Island. Grain yield and protein content increased with increasing amounts of supplemental N. In most years, supplemental N above a base application of 55 kg N ha-1 applied at 52.5 kg N ha-1 at Zadoks GS 30 resulted in 13.5% protein in the grain of Grandin and AC Barrie, but 70 kg N ha-1 was r equired for AC Walton. Based on the N content of the straw, Grandin was less effective in partitioning N into the grain than AC Barrie and AC Walton. Increasing rates of supplemental N caused a reduction in red clover establishment. Soil pH decreased with increasing rates of supplemental N. Nitrate N in the soil at 0-5 and 0-20 cm depths increased with supplemental N, but there was no effect on ammonium N. Differences in pH or levels of soil N after harvest did not account for differences in grain protein. In the Maritime provinces, to reach a desirable milling protein level in spring wheat of 13.5%, producers will need to add supplemental N at a rate of at least 100 kg N ha-1 over and above background levels; however, this will be at the risk of reducing red clover establishment and increasing levels of soil N available for leaching.