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

Achieving high grain yields and crude protein (CP) standards in organic winter wheat ( Triticum aestivum L.) is challenging because ensuring that adequate nitrogen (N) is available at key periods of wheat growth is difficult in organic systems. Split application regimes and in-season N management tests may improve organic production. In field trials conducted over four site-years in Maine and Vermont, USA, N application regimes were analyzed for their effects on organic winter wheat, N uptake, grain yield, and CP. Tiller density and tissue N tests were evaluated as in-season decision tools. Eight treatments arranged in a non-factorial design differed in terms of N application timing (pre-plant (PP), topdress at tillering (T1), and topdress at pre-stem extension (T2)) and N rate. Treatments were: (1) an untreated check, (2) pre-plant N at a low rate of 78 kg N ha − 1 (PP L ), (3) pre-plant N at a high rate of 117 or 157 kg N ha − 1 (PP H ), (4) T1 78 , (5) PP L + T1 39 , (6) PP L + T2 39 , (7) PP H + T2 39 , and (8) PP L + T1 39 +T2 39 . Responses to N treatments were variable among site-years, however some common results were identified. The PP-only treatments increased grain yields more than they increased CP. The T1 78 and PP H + T2 39 treatments were the most effective at increasing yield and CP, compared with the PP-only treatments. Tiller density and tissue N tests were good predictors of grain yield (r = 0.52, p < 0.001) and CP (r = 0.75, p < 0.001) respectively. Future work should test in-season decision tools using a wider range of tiller densities, and topdress N rates against tissue N measurements.