Grain Protein Percentage, Kernel Hardness, and Grain Yield of Winter Wheat with Foliar Applied Ureal1

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Abstract
In the Pacific Northwest a major constraint to growing hard red winter wheat (Triticum aestivum L.) is the consistently low grain protein percentage observed. Foliar fertilization of winter wheat offers a potential for increasing grain protein percentage when applied around flowering. The main objective of this study was to determine the effect of foliar urea sprays on grain protein percentage, grain yield, and kernel hardness of 10 genotypes of winter wheat when grown in the field under four diverse environments. Also, immature spikes were analyzed after foliar treatments for percent protein, and optimal grain uptake of foliar applied N was measured under controlled conditions using 15N labelled urea. Foliar sprays of urea increased grain protein percentage by 16 and 10 % and yield by 8 and 3% over the control of no applied urea in two environments. Combinations of topdressing and foliar sprays produced yields equivalent to standard topdressed plots at all locations and increased grain protein percentage by 12 and 9% in two of the four environments tested. Foliar applications did not alter kernel hardness overall. Significant genotype X N treatment interactions were found for grain protein percentage, grain yield, and kernel bardness. Spike protein analysis at flowering showed N treatment effects 2 weeks after foliar applications in the field, and the ranking of treatments corresponded closely with that determined by grain analysis at harvest. Uptake of N from foliar sprays was also confirmed with a mean of 44.1 % of applied 15N recovered in grain samples. Genotypes differed for I5N recovery rates in the grain from 48.3% for ‘Stephens,’ a low protein soft white cultivar, to 39.9% for ‘Centurk,’ a higher protein hard red cultivar. Daylength after treatment also affected recovery rates with 41.4 and 46.9% of applied 15N being recovered for 12 and 18 hours respectively.