The Influence of Polymer-Coated Urea and Urea Fertilizer Mixtures on Spring Wheat Protein Concentrations and Economic Returns

Published in Agron. J. 105:1328–1334 (2013) doi:10.2134/agronj2012.0454 Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. R for the U.S. HRSW producer is determined by grain yield, protein concentration, and the market grain price. Often, discount and/or premium prices are associated with protein concentrations below and above 140 g kg–1, respectively. Discount and premium prices are not fixed and can vary both during the year and between years, depending on market demand. One of the factors that governs fluctuations in HRSW discount and premium prices is the production of other wheat types with low protein concentrations. Typically, HRSW is blended with wheat types with low protein concentrations that change the mixture’s characteristics as per the end user’s demand. Ideally, HRSW producers select cultivars with high grain yield potentials and rely on N fertilizer management to increase protein concentrations. It is not unusual for protein concentrations to decrease as grain yields increase (Bly and Woodard, 2003). To maximize economic advantage and minimize economic risk, strategic producer will estimate potential market grain prices and consider potential protein discount and premium prices. In soils with low N availability, fertilizer N management can be the most important factor determining HRSW grain yields and protein concentrations. Effective fertilizer N management is critical for optimizing grain yields and protein concentrations and for obtaining maximum profits. Fertilizer N management in rainfed HRSW production depends on environmental conditions such as temperature, precipitation, available N, and the ability of cultivars to use available N during the growing season (Daigger et al., 1976). Some cultivars enhance grain protein concentration by more efficiently translocating vegetative N accumulated earlier in the growing season (Bhatia and Rabson, 1976; Papakosta and Gagianas, 1991). However, general consensus states that N accumulated early in the growing season contributes mostly to grain yield while N accumulated later in the growing season, near and after anthesis (Zadok’s scale 60, Zadoks et al., 1974), contributes mostly to grain protein concentration (Banziger et al., 1994; Woolfolk et al., 2002). Therefore, N amount and timing when it become available during the growing season significantly impact grain yield and protein concentration. Several authors (Cassman et al., 1992; Boman et al., 1995; Bly and Woodard, 2003) have found that split N applications could increase grain yield and protein concentration but the costs associated with the additional applications can make split N applications economically unprofitable. In northwestern Minnesota, split N application management is also challenging because of unpredictable rainfall patterns and short intervals between HRSW growth stages (Wiersma and Ransom, 2005). Consequently, the current best management practices for HRSW production in the northern Great Plains of North Dakota and northwestern Minnesota dictate the application of pre-plant N in sufficient amounts (Wiersma and Ransom, 2005; Franzen, 2009). In recent years, research has been conducted to study whether different types of PCU (controlled-release N fertilizer) can increase wheat grain yield (Yang et al., 2011), protein ABSTRACT The economic benefit of using controlled-release N fertilizers on hard red spring wheat (HRSW, Triticum aestivum L.) depends on its cost/price ratio, grain yield, and availability of discount and/or premium prices for protein concentration. The objective of this study was to evaluate the effect of five different proportions (0, 25, 50, 75, and 100%) of polymer-coated urea (PCU) in the N fertilizer mixture applied at three different N rates on (i) HRSW grain yield and protein concentration and (ii) whole-plant dry matter and total N accumulation, and (iii) also to perform an economic analysis. As the proportion of PCU in the fertilizer mixture increased, the grain yield decreased in Environment 1 and remained the same in Environment 2. Cool dry conditions in Environment 1 delayed N release from PCU causing N deficiencies during the critical yield-development phase and resulting in lower grain yield as the PCU proportion increased. In contrast, this was not the case in Environment 2. As the proportion of PCU in the fertilizer mixture increased, protein concentrations increased in both environments indicating that PCU increases soil-N availability later in the growing season, regardless of the early season weather conditions. The proportion of PCU in the fertilizer mixture did not affect total N accumulation and post-harvest soil NO3–N concentrations. The results of this study suggest that adding a portion of PCU in the fertilizer mixture can increase HRSW grain protein concentration and provide economic benefits to producers if discount prices are around $20 per Mg or greater.