Nitrogen Rate and Timing Effects on Yield and Protein Concentration in Hard Red Spring Wheat in Northern California.

Achieving acceptable protein content is a continual challenge for wheat producers throughout California and proper nitrogen (N) management is key.  Field studies were conducted to evaluate the effectiveness of N management strategies for four prominent spring wheat varieties (Yecora Rojo, Hank, Fusion and Malbec).   Yield and protein content was evaluated under seven different nitrogen fertilizer regimes (different timings and total amount of N) over 3 years.  Fertilized plots yielded approximately 1.8 Mg/ha higher than the non-fertilized control plots.  Split applications tended to yield higher than a preplant application alone.  Yield and protein varied by site, and protein goals were especially difficult to achieve at the high-yielding site.  Acceptable protein levels were not obtained with a preplant application of N alone and a late-season N application was required.  Another trial with a single variety (Yecora Rojo) conducted over two years focused on N application timing and the optimum proportion to apply at different wheat growth stages.   Nitrogen was applied as urea at a total of 168 or 280 kg/ha over the season at eight different application timings for both rates.  Treatments varied in the proportion of total N that was applied preplant, at tillering, boot or anthesis.  Applying most of the N at tillering resulted in a higher yield than applying all N preplant.  Adequate N at tillering, ahead of the rapid uptake phase, was critical for maximum yield and yield declined when the majority of the N was applied at boot and later.  However, protein was significantly improved when more of the N was applied at boot or anthesis.  In terms of yield and protein, common producer practice of applying all of the N preplant was one of the least effective treatments, while applying 80 percent of the N at tillering and 20 percent at anthesis was the most effective.