Spring Nitrogen Management in Winter Wheat

Crop Solutions That Work article by
Kent Wolfe, CCA-ON, 4R NMS
Crop Sales Specialist
AGRIS Co-operative - Dutton

Nitrogen management is a very critical part of winter wheat production. Spring N demand in winter wheat basically has two important functions, one is to help manipulate head count through tillers and secondly, it must supply nutritional needs to that plant through all stages of growth so that it can maximize both yield and protein content.

The next step is to determine rates of application and whether or not a split of a single application is warranted. Next is timing, based on planting date and plant density. Later planted thin stands may need an early application while early planted thicker stands can wait until Zadoks growth stage 30. This spring in our trading area field conditions did not allow us even the opportunity of considering that early application.

What is the right time, right rate, right source, and right place?

This approach is referred to as the 4Rs of Nutrient Stewardship. We always take these factors into account when making crop plans for your farm. The whole nitrogen system availability can be a very complex issue, so the more we look at these factors the more we learn, allowing us to make better recommendations.

What is the right time?

Nitrogen application timing should be aimed at green-up time with a one-time application by Zadoks 30-32 (stem elongation) which is typically in the latter part of April, basically now as field conditions allow without causing too much compaction. It is from this stage to Zadoks 58 (early flower) that the majority of N is required by the plant.

If going with a split application, oftentimes applying an initial amount based on tiller count at early green-up then taking a plant tissue leaf sample prior to stem elongation can assist in determining the final split application timing and rate. My general suggestion this year especially for both soft red and white varieties is to maybe skip the split application and apply it all in one pass. I really think that the extra job of cleaning out a spraying in three or four weeks for the second application is likely when there will be plenty of other jobs that will be needing to be addressed. The one exception might be with hard red winter wheat if you are really pushing for the higher protein premiums.

What is the right rate?

What's the right rate of N that I should be applying to my wheat this year? There are two parts to this question. Are you pushing for maximum yield? Then that means higher N rates and higher N rates, in turn, mean a fungicide application to maintain plant health and allow the plant to utilize the additional nitrogen. Higher N rates, high yield and fungicide need to be a coordinated effort. Another new consideration that we are having to work through this year is extremely high nitrogen prices and also allocations and balancing of where the nitrogen will benefit the most; looking at not only the wheat crop but also our corn planting intents.

We have conducted trials over the last number of years comparing rates of N. It would suggest that the average number is 120 lb/ac of actual N and 20 actual S in normal crop conditions. This value can be adjusted by (+ or – 15 lbs) when looking at some of the other factors like expected yield, plant stand, plant health, application timing and wheat prices and nitrogen prices. Last year we pushed those values up more to the 135 lb/ac rate and again adjusted by (+or – 15 lbs) mostly due to the wheat being a little more advanced from a warm April and much lower nitrogen costs.

What is the right source?

What is the right source of fertilizer to supply the wheat crop with its nitrogen requirements? In our territory basically, it comes down to one of two sources: dry urea plus ammonium sulphate, or liquid UAN, plus ammonium thiosulphate (ATS). Each product comes with its own advantages and disadvantages.

The first product is urea (46-0-0) which is a dry product that is popular in some areas because it is the most economical form of N. It can also be applied easily with pull-type spreaders or custom-applied with airflow units and can also have other dry fertilizer products blended with it for a one-pass program.

The main disadvantage of urea is that it can be subject to losses from volatilization, this occurs when the urease enzyme breaks apart the urea on the surface and ammonia is lost. These losses can be as high as 30% under the right conditions which are dry soil surfaces, higher pH soils, warmer soils, windy days and high trash cover. A half-inch rain within 12 hours of application can significantly reduce the loss, or, adding a urease inhibitor such as Anvol to prevent the loss for up to 14 to 21 days.

The other N source is UAN 28% which is a combination of urea and ammonium nitrate in a liquid form. This form of N has shown a slight yield advantage when compared to the dry forms of N over the last couple of years. It does however require special sprayer tips to apply the product (jet or streamer tips are what they are referred to). These tips get less product on the leaf surface of the plant which greatly reduces the leaf burn that we would see with traditional fan or flood jet nozzles.

UAN can also be subject to volatilization losses in dryer conditions, however, it is only half urea so losses are less than straight urea when conditions for loss exist. Again Anvol can be added to reduce losses if dry weather persists after application ( likely a rare event this spring).

Whatever the N source always remember to add sulphur at 20 lbs/ac actual. Field trials conducted by your co-operatives over the past four years show on average a 6 bushel per acre yield response.

What is the right place?

For the majority of us, a spring top-dress application of N at green-up is the only option. Make sure application equipment is calibrated to ensure uniform application. This is very important in maintaining uniformity, consistent maturity, reduced lodging and maximizing the yield.