Preplant Slow Release N for Furrow Irrigated Hard Spring Wheat.

Producing furrow irrigated hard red wheat with acceptable protein is challenging because of limited N management options for increasing protein. Slow release N has potential for improving N use efficiency in furrow irrigated hard wheat by avoiding the effects of excessive early season N yet providing later N for protein enhancement.  A three year study (2005-2007) was conducted at Parma, ID to evaluate different N rates (134, 202 and 269 kg/ha) of polymer coated urea (ESN) and dry urea preplant N sources for furrow irrigated hard red spring wheat (variety WB 936).  Grain yield decreased in the absence of lodging with both preplant N sources when applied N exceeded 134 kg/ha in 2005, possibly due to exacerbated stripe rust.  With no stripe rust in the following years, yield increased more with ESN N than with urea N, unless the urea N was split applied.  Protein with ESN was often higher than with preplant urea and matched the protein of wheat topdressed with 67 kg urea N/ha at heading in five of six N rate comparisons, differing no more than 0.3% protein lower or higher from split urea.  Apparent N recovery (ANR) ranged from 6.5 to 9.9% higher for preplant ESN at the 134 kg/ha N rate, and 11.5 to 14.9% higher at the 202 kg/ha N rate.  Slow release N proved an effective preplant N source under the conditions of this study which included a minimum of 80 kg/ha of preplant residual N.