Water and Nitrogen Effects on Winter Wheat in the Southeastern Coastal Plain: I. Grain Yield and Kernel Traits

Understanding how environmental factors affect winter wheat (Triticum aestivum L. emend. Thell.) responses to spring N application is an important component of economically and environmentally sound winter wheat production on the southeastern Coastal Plain of the USA. Increasing the amount of N applied to winter wheat grown in this region has been shown to result in a greater severity of drought stress during grain fill and lower individual kernel weights. This 2-yr field study was conducted to determine whether drought-induced reductions in kernel weight with high spring N rates are the result of decreases in the rate or the duration of kernel growth. Winter wheat was grown with different rates of spring-applied N (0, 45, 90, and 135 kg N ha⁻¹) under both irrigated and nonirrigated conditions. Increases in the rate of springapplied N resulted in a greater severity of soil water deficits under nonirrigated conditions. Quadratic increases in grain yield and kernel number per square meter occurred in response to increased spring N under both levels of soil water treatment. Grain yield and individual kernel weight responses to irrigation were greater at the higher N rates than at the lower N rates. Over both years, the average increase in individual kernel weight due to irrigation was 3.9 and 13.3% at the 0 and 135 kg N ha⁻¹ rates, respectively. Similar responses were found for the effective filling period (EFP), where irrigation increased the EFP an average of 3.2 and 14.5% at the lowest and highest spring N rates, respectively. Soil water treatment had no effect on kernel growth rate. Results indicate that high rates of spring-applied N increase the severity of drought stress in nonirrigated winter wheat grown on the Coastal Plain, resulting in reductions in the EFP and, consequently, kernel weight. South Carolina Agric. Exp. Stn. Technical Contribution no. 3552.