Planting Date and Nitrogen Effects on Grain Yield and Protein Content of Spring Wheat

High grain yield with adequate protein concentration is an important goal for spring wheat (Triticum aestivum L.) production. A field experiment conducted at two sites representing sandy loam and clay loam soils in Ottawa during 2003 and 2004 examined the effects of planting date and nitrogen (N) management on grain yield and grain protein concentration (GPC) in spring wheat. Cultivar AC Brio was planted at three dates at about 10 d intervals starting from the last week of April. Five N treatments were 0, 60, and 100 kg N ha-1 applied as preplant, 60+40 (preplant + topdress at boot stage), and 60 + 40 kg N ha-1 (preplant + foliar spray at boot stage). Both planting date and N had significant effects on grain yield and GPC. When planting was delayed beyond mid-May, grain yield was reduced by 15 to 45% in three out of four site-years. However, GPC increased by 6 to 17% in all late planting dates than the early plantings. Grain yields were increased with N application, but there was no benefit due to split N application as topdress or foliar spray than a single application at 100 kg N ha-1. Regardless of application method, GPC was greater with 100 kg N ha-1 than with 0 or 60 kg ha-1, and GPC was more responsive to applied N in a sandy loam soil than in the clay loam soil. Results of this study suggest that it is likely to achieve the target GPC in spring wheat without a significant reduction in grain yield if wheat is planted before the middle of May, especially in clay loam soil.