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

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.