Nitrogen on winter wheat

Cereals are very responsive to nitrogen. However, over-application of nitrogen causes lodging resulting in reduce yield, quality, and harvestability. The optimum rate of nitrogen for a particular field will depend on the type of wheat grown, past applications of manure or fertilizer, soil type, and crop rotation. Use general recommendations as a starting point but combine them with observation of crop growth and lodging tendency. The idea is to ensure nitrogen is available early and consistently though the major uptake period (node development though booting).

Timing

Time single applications for late April. This avoids significant N loss from wet soil conditions that might occur earlier, while providing N when the crop demand goes up. Large single applications increase lodging potential.

Split application are preferred. The main benefits are reduced concerns over N loss, greater weed control due to increased crop vigor, more uniform heading, and less lodging. Yield benefits are secondary. Apply 50-80 lbs/ac N as early as possible (on frost any time after March 15-20), with the balance at 1st – 2nd node. Nodes can be easily seen or felt on the stem above ground level.


Rates

Without fungicides, 90 lbs/ac N. It is not recommended to grow wheat without applying fungicides, as you will not achieve the highest yield potential that could be available with fungicides.

With fungicides, use 120 to 150 lbs/ac N depending on past field history, organic inputs, soil organic matter and nitrate levels, and economics. Beware of lodging when going with high rates. Try strip trials of different rates in the field to experiment and learn how to keep rates high, while avoiding lodging.

Application

To maximize yield, nitrogen must be applied uniformly across the field. Uniform application is more critical than the form of nitrogen fertilizer applied.

Urea-Ammonium Nitrate Solution (UAN) (28-0-0 or 32-0-0) applied with streamer nozzles gives excellent, uniform nitrogen application and has shown small yield advantages (2.5 bu/acre). UAN applied through streamer nozzles causes little or no leaf burn. Applying 28% nitrogen (UAN) as an overall broadcast treatment (using flood jet or tee-jet nozzles) to emerged cereal crops is NOT RECOMMENDED. The addition of 28% to a herbicide application, especially contact herbicides, will greatly increase leaf injury and yield loss.

Urea, calcium ammonium nitrate or ammonium sulfate can be applied using airflow technology, thereby improving uniformity – although uniformity is not guaranteed. Be sure to maintain clear hoses to achieve a uniform spread pattern. Spinner spreaders often have the greatest inconsistency in spread pattern. If spinners are employed, consider double spreading the field (i.e., 6-m or 20-ft centres at half the rate, instead of 12-m or 40-ft centers) to overcome this.

Sulfur

When sulfur deficiency occurs, crop response stops at 10 lbs S/ac. The best general recommendation is to add 10 lbs S/ac as an “insurance” policy and do trials on each farm to find responsive and non-responsive fields. Generally sandy and low organic matter fields are the most responsive. If you have high yield goals and are using high nitrogen rates (100+ N/ac), include sulfur.

Urease/Nitrification Inhibitors

These products reduce the loss of nitrogen through natural processes such as ammonia volatilization, denitrification, and leaching. They are highly recommended to protect your nitrogen after applications from difficult weather conditions. These products would be very beneficial in wet springs, on sandy and poorly drained soils, where leaching is prevalent, and when urea/28% UAN is surface applied.

Controlled Release Nitrogen

These products do not prevent nitrogen loss directly. Instead they control the release of nitrogen so that all is not available immediately. This is commonly done through sulfur coating on urea or more recently with superior polymer technology like in the product Environmental Smart Nitrogen (ESN).