In‐Season Nitrogen Effects on Organic Hard Red Winter Wheat Yield and Quality

Abstract

Ensuring adequate available N for grain protein development is a primary challenge for organic production of winter bread wheat (Triticum aestivum L.). Topdressing organic wheat in‐season may improve grain yield and quality. The objective of this study was to determine if supplemental N topdressing at key wheat developmental stages would improve organic hard red winter wheat yield and protein concentrations. Field experiments were conducted over 4 site‐years from 2009 to 2011 in Maine and Vermont, using the variety Harvard. Treatments were a factorial arrangement of two organic‐approved N sources (Chilean nitrate, CN, and dehydrated poultry litter, DPL) and three times of application (tillering, flag leaf, and boot stages). Plant N uptake, grain yield, and grain protein concentration were determined. Plant‐accumulated N was always higher in the CN treatments than in the DPL and manure‐only treatments. The CN topdress treatments yielded on average 11% more than the manure‐only treatment and 6% more than DPL treatments. Topdressing increased grain protein concentration in all cases, although none of the treatments reached the 120 g kg–1 milling standard, due in part to variety Harvard being a low‐protein, high‐yielding variety. Chilean nitrate was more effective at increasing grain protein levels than DPL, and for both N sources, later applications were more effective than earlier ones. Topdressing could be a cost‐effective strategy to boost grain protein levels for organic winter wheat production, but further work is needed to evaluate topdressing with higher protein varieties and identify additional rapidly‐available and economical organic approved N sources.

Evaluating Split Nitrogen Applications and In-Season Tests for Organic Winter Bread Wheat

“…These results are congruent with others who have found that applications at the pre-plant timing alone do not supply an adequate amount of late-season available N to enhance CP in winter wheat [3,45]. At the majority of site-years, it was possible that the amount or timing of mineralization from the organic N fraction of manure was insufficient to support protein production.…”

“…The timing of supplemental N applied in the PP L + T1 39 and PP L + T2 39 treatments had no influence on yield and CP results likely because the applications were too close in time to cause differences. The application at T2 was relatively early compared to other studies that showed topdress applied later, at flag leaf (GS39) and boot (GS45), were more effective at increasing CP than the T1 application [3].…”

“…On the bread wheat market, a grain CP of generally 120 g kg −1 or greater is desired because it gives dough strength and provides loaf volume [2]. Grain with lower CP can be sold as feed but typically receives a lower price [3].…”

“…The difficulty of ensuring late-season available N for winter wheat with pre-plant applications makes it challenging to achieve grain CP suitable for the bread flour market [12]. In an organic winter wheat study, Mallory and Darby [3] found that spring applied topdress N, in addition to preplant manure, increased grain CP by up to 2 percentage points. While no treatments reached the 12% CP milling standard in this study, had a variety with higher protein potential been used, that 2 percentage point increase might have increased CP to above 12%.…”

“…Few studies have analyzed split application regimes for organic winter wheat production [3] and to our knowledge none have used the in-season decision tools under organic conditions. The adoption of these practices by farmers has the potential to reduce N loss to the environment and increase the value of bread wheat through enhancing yield and quality.…”