INFLUENCE OF PLANTING DATE AND SEEDING RATE ON WINTER-WHEAT GRAIN-YIELD AND YIELD COMPONENTS

Winter wheat (Triticum aestivum L.) is commonly seeded over a 60-d per iod in the Midwest depending on crop rotation options, weather, and ot her farm operations. This study was conducted to determine whether win ter wheat seeding rates should be altered depending on planting date a nd cultivar. Seeding date and planting rate responses of the cultivars , Merrimac and Cardinal, were evaluated at the University of Wisconsin Arlington Research Station during the 1988 to 1991 growing seasons. E ight planting dates ranged from 24 August to 3 November and seeding ra tes were 14, 28, 42, and 56 seeds/sq ft. Grain yield and yield compone nts were influenced by all variables and specific interactions. Heads per square feet and kernel weight, two primary yield components, decre ased as seeding was delayed after 12 September. Maximum grain yield oc curred when planting Cardinal on 3 September using 28 seeds/sq ft. Del aying Cardinal planting to late September required a seeding rate of 4 2 to 56 seeds/sq ft to maximize yield. When planted in September and e arly October, Cardinal had higher yields than Merrimac due to heavier kernel weight. Changes in yield components allowed plants to adjust to varying conditions as planting was delayed. As grain yield decreased with a planting delay into October, kernel weight and heads per square feet continued to decrease for both cultivars. When planting was dela yed past 3 October in 2 of the 4 yr, Merrimac had greater kernel weigh t, which translated into higher Merrimac grain yields than Cardinal. G rain yields of wheat planted in late October decreased due to yield co mponent response to environment and to stage of plant development when growth ceased. These results can be used to improve establishment and yield of winter wheat, especially when planting at dates that are not always optimum.