Topdress Nitrogen Effects On Organic Winter Bread Wheat Yield & Quality.

Wheat grain must have a protein concentration of 12% or greater to be considered suitable for bread flour.  The most critical factor controlling grain protein is the amount and timing of nitrogen (N) available to the wheat plant.  Supplying adequate N to winter wheat can be challenging, particularly for organic producers.  Nitrogen applied after stem elongation has been shown to increase grain protein under conventional production, whereas N applied earlier tends to increase yield.   The objective of this trial was to test the effects of two different OMRI-approved sources of top-dress N (Chilean nitrate (CN) and dehydrated chicken manure (DCM)) at three times of application (tillering, flag leaf, and boot) on soil N availability, winter wheat N uptake, grain yield, and grain protein. Duplicate trials in Maine and Vermont were conducted in 2010 and 2011.  All plots received approximately 78 kg available N ha^-1 as manure before planting wheat (c.v. ‘Harvard’).  Topdress treatments were applied at 22 kg available N ha^-1.  Results from 2010 were consistent over sites.  Ideal growing conditions resulted in relatively high grain yields and low grain protein; the no-topdress control treatment yielded an average 3.8 tonnes ha^-1 with a grain protein concentration of 8.1%.  Topdressing N did not affect yield except for the boot-stage application of CN (22% increase).  Both topdress N sources increased grain protein, but CN was more effective than DCM.  Averaged over application time, grain protein was 9.3 and 8.6% for these treatments, respectively.  Topdressing later in the season produced greater increases in grain protein.  Averaged over topdress source, grain protein was 8.6, 8.9, and 9.4% respectively for tillering, flag leaf, and boot stage applications.  Results from 2010 indicate that topdressing N can be an effective strategy for organic farmers to increase grain protein.  Results from 2011 also will be presented.