LATE SEASON N APPLICATIONS FOR IRRIGATED HARD RED WHEAT PROTEIN ENHANCEMENT. S.E. Petrie*, Oregon State Univ, B.D. Brown, Univ. of Idaho. Introduction The higher market prices and the premiums associated with high protein hard red wheat (winter and spring) have sparked considerable grower interest in these market classes of wheat. Unfortunately, we do not have the management tools to consistently produce hard red wheat with acceptable protein levels. The use of high pre-plant N application rates increases the likelihood of acceptable protein levels but also increases the potential for unacceptable N losses due to leaching and may increase lodging. Mid-season and late season N applications in sprinkler irrigation systems have been used to increase grain protein levels but N applications in surface irrigation systems (flood, furrow, etc.) are problematic. Non-uniform water application due to differences in infiltration rates, tailwater runoff and system inefficiencies all contribute to non-uniform N applications and subsequent differences in N availability and grain yield and protein responses. The objectives of this work were to (1) determine the most effective N application rate for mid-season applications, (2) compare foliar and soil applications, (3) compare foliar urea and solution 32, (4) and the time of application (tillering, jointing, heading, flowering). Materials and Methods A series of field trials were conducted between 1985 and 1996 at the Southwest Idaho Research and Extension Center near Parma, ID examining the effects of N rate, source, method of application and stage of wheat development on hard red winter and spring wheat grain yield and protein. The tillage, planting, variety, crop management, fertilizer (except N), weed control and irrigation practices varied between years but was typical for recommended Best Management Practices for the area. Winter wheat was furrow irrigated and spring wheat was sprinkler irrigated. The trials were seeded using a double disk drill with 7 inch row spacing and the plots were harvested using a small plot combine. The treatments in all trials were arranged in a randomized block design with four or five replications. Grain samples were cleaned, weighed and test weights determined. Leaf injury, when measured, was estimated by visual observation. Grain protein was determined using NIR at the University of Idaho Aberdeen Wheat Quality Lab. Abstract Nitrogen fertilizer is frequently applied late in the growing season to enhance hard red wheat (Triticum aestivum L.) protein to avoid low protein discounts. Both furrow and sprinkler irrigation are used for hard wheat production but N management options are limited when using furrow irrigation. Several furrow or sprinkler irrigated studies ( ) were conducted in southwestern Idaho to evaluate late season N manage-ment practices for increasing wheat protein. Treatments evaluated included N rates (0-67 kg/ha), sources (urea, uran), timing (tillering, jointing, heading, flowering), and application methods (foliar, soil). Late season N generally increased protein but the protein increase was not affected by N sources or application methods when soil applied N was adequately incorporated with subsequent moisture. The protein response to late N was limited if protein in untreated wheat was already high. Urea was less phytotoxic than uran as a foliar N source. N applied at tillering or jointing was less effective at increasing protein than heading or flowering growth stage applications. Late season N did not consistently increase hard red wheat protein to market-acceptable levels if the previously applied N was inadequate for maximizing yield N Rate (kg/ha) Leaf Injury (%) Urea UAN Sol'n Figure 1. Furrow irrigated winter wheat leaf injury from boot stage applied foliar urea and UAN at different N rates. Preplant N was 224 kg ha-1. Parma, Leaf injury varied among years and was worse in 1985 than the other two years. Leaf injury was significantly related to yield reduction in individual years but not when all years were combined (data not shown). Figure 2. Hard red spring wheat flag leaf injury from boot stage applied urea or UAN as affected by N rate and solution pH. Parma, Summary N applications made later in the growing season tend to increase grain protein. Late season N applications did not consistently increase grain protein to market acceptable levels if the previously applied N was not sufficient to maximize yield. There were no yield or protein differences between foliar and dry N if the topdressed N was incorporated by irrigation following application. Foliar applications of urea caused less leaf injury than UAN solution Slightly acidic spray solutions caused less leaf injury Figure 4. Hard red winter wheat protein as affected by N rate and foliar N source and year. Parma, Results Timing---Hard red winter wheat yielded higher and had higher protein when N was spring topdressed rather than preplant incorporated. Late season applied N generally increased winter wheat protein and the protein increase with late N depended on the timing of N previously applied. Late season N also increased spring wheat protein from low protein values and the protein increase was generally linear with N rate. The protein increase from late N was limited if protein otherwise exceeded 14%. The protein increase with N tended to be greater the closer the application was made to flowering. N Sources--Late season urea and UAN N sources did not generally differ in their effectiveness in increasing protein in three years of testing. UAN caused more leaf burn than urea solutions. Appreciable leaf burn was associated with significant yield reductions in some years. Solution pH--Solutions with higher pH generally caused more leaf burn than solutions closer to pH 7. Soil vs Foliar Late N--Soil and foliar applied late N did not differ in two years of testing in their effectiveness for enhancing protein provided there was no leaf burn from foliar applied UAN and topdressed N was sufficiently incorporated with subsequent sprinkler irrigation. Figure 3. Hard red spring wheat protein as affected by urea and UAN solutions and equivalent dry N sources and N rates. Dry N sources were incorporated with sprinkler irrigation. Foliar N sources were applied the day after the sprinkler wetting. Parma, Table 1. Irrigated hard red winter wheat yield and protein response to late season N as affected by fall and spring applied N. Table values are three year means % --kg/ha kg/ha TotalHeadingSpringFall ProteinYieldN Application Rate and Time