Nitrogen Management to Improve Winter Wheat Grain Yield and Protein Content

Low grain protein content in hard red winter (HRW) wheat (Triticum aestivum L.) has been a serious challenge for rainfed wheat growers, particularly in years with elevated grain yield. Proper nitrogen (N) management with adequate N rate and time of application will be critical for optimizing both grain yield and protein content. In addition, crop canopy reflectance sensors (CRS), which have been widely used for precision N management in corn in Nebraska and explored in winter wheat in some other states, are yet to be explored in Nebraska. This 2-yr experiment evaluated the effects of different N rates (0%, 25%, 50%, 75%, 100%, and 125% of recommended rate) and application timings (fall, spring, and split between fall and spring) on grain yield and protein of HRW wheat. Field experiments were conducted at four different sites across Nebraska under rainfed conditions in 2018/2019 (Year 1) and 2019/2020 (Year 2). Nitrogen fertilization significantly increased grain yield in a year with above-average precipitation (Year 1). There was an increase in grain protein with increasing N rates at all sites in both years and the highest grain protein was always with the 125% N rate. Spring and split applied N was effective over fall application in the site-year when there was a risk of applied N loss via leaching or denitrification. Ruth, as a semi-dwarf most recently developed variety for greater adaptation in Nebraska and neighboring states demonstrated potential to benefit from spring or split N application given no disease pressure. Normalized Difference Vegetation Index (NDVI) obtained from active CRS at different growth stages had significant positive relationship with applied N rate, grain yield, and protein at certain growth stages and site-years, indicating its potential use for in-season N management in winter wheat. The results of this study suggest that an effective N management strategy for winter wheat should account for and be adaptable to weather variability to optimize grain yield and protein content in winter wheat. Advisor: Bijesh Maharjan