Section 1 - Stand Establishment, Fertility & Water Use

Topdressing N in Wheat for Protein

The first question is whether there will be an economic benefit to higher protein this year – consult with a grain market advisor or local grain handler to see what they think about prospects for premiums. With N prices hovering around 30 cents/ lb N or more, the cost of N plus application would be somewhere around $15/acre. That means that the ½ % protein enhancement possible with 30 lb N/acre would have to cover at least those costs to be profitable.

With 40 bu/ac wheat, that means a protein premium of about 38 cents/1/2 point.

Another consideration is weather; if hot temperatures and dry conditions may have chipped away at yield potential, the N already applied may be sufficient to produce higher protein without help from added N.

Topdressing from jointing through the watery ripe stage of grain development will often serve to increase protein content of grain, but will have little if any effect on yield. Applications of N past the watery ripe stage would have no real effect on grain protein content. By the time the wheat crop starts heading out, it has accumulated nearly all of the nitrogen that will eventually show up in either grain yield or protein. It is also logical to conclude that since leaf area decreases as the plants mature, especially with disease and natural senescence, foliar fertilization efficiency will decrease thereafter. Thus, once the grain is in the dough stage, the grain is basically drying and uptake of nutrients is over.

Consequently, it’s generally recommended that nitrogen applications for enhancing protein be made as soon after tillering as possible and before flowering and pollination. (A foliar N application is not recommended before pollination at flag leaf emergence or at pollination, because of leaf burn potential. The need to protect the flag leaf is crucial, and pollination is also a critical time to protect sensitive anthers). Topdressing N before the first joint extends will not leave wheel tracks in fields. Traffic across fields later breaks the stem below the joint and will leave tracks visible through harvest.

Leaf burning in trials conducted in N.D. have shown little if any decrease in yield when precautions are taken. Still, this is an art, not a science, and there is no guarantee against leaf burn. Sometimes despite best efforts there is some leaf burning, although if precautions are taken, the effects will not normally be severe. Make sure not to apply streamer N in a high wind which breaks up spray particle stream into a broadcast application. This will result in a high leaf burn risk. Leaves that are burned do not recover; however, bushels lost due to burn are usually low following pollination, and if protein premiums are expected to be high, a modest protein increase may be worth more than a slight loss in bushels due to superficial burning.

For the most consistent results, use a foliar application, not streamer bars unless it will rain about a half inch within 24 hours of application. Do not apply the 28% with fungicides. Put the fungicide on first when the label suggests. Apply the 28% directly after flowering at the watery-ripe stage of kernel development (right after pollination, but before starches have formed). Apply the 28% mixed half and half by volume with water and spray during the cool of the day. Unless the day is cloudy and cool, this means towards evening. Some growers have good success with application at night, but stop early in the morning. Application made late morning when the dew is burning off has resulted in burn similar to mid-day to afternoon applications. Applications of 10 gal 28% (30 lb N/ac) has resulted in protein increases from ½ to 1%, with ½ % being the more common.

There are some slow release N products that claim higher efficiency than 28%. Although these products have less burn potential, research at NDSU has not shown higher efficiency in protein enhancement. It appears that similar rates of N need to be applied with these products to increase protein to the levels achieved with the recommended rates of 28%.

A good choice for nozzles would be flat fans, not forward/back. The forward and back nozzles used for scab fungicide application are meant to cover the head. We don’t want to cover the head. This fertilizer application is meant to cover the leaf, so flat fans are better. It is highly recommended that no fertilizer N be applied during small grain heading. Often, scab fungicides are applied at this time for maximum effect. However, fertilizer should not be applied during a heading application.

Topdress Dry or Liquid N?

Both dry and liquid N products can be used for topdressing wheat. Dry products may be less expensive, while liquid products may offer the advantage of being used as a herbicide carrier. Urea solutions offer an added advantage of reduced leaf burn. Dry granular products can be applied at any rate. If dry urea is used, it might be wise to also have it coated with Agritain®, which is a tried, tested and proven urease inhibitor, and gives about 10 days of protection from volatility.

The amount of liquid N that can be applied without leaf burn diminishes as temperatures rise and crop growth accelerates. Forty lb N/ac as liquid N is a relatively safe rate when temperatures are cool and small plants provide 40-60% ground cover. With high temperatures and a ground covering crop canopy, safe rates drop to 10-25 lb N/ac with increased margins of safety for urea solutions.

If topdressing applications using liquid N (UAN, 28-0-0), it’s recommended to use streamer bars to minimize and reduce leaf burning and crop injury. Streamer bars concentrate the application into bands, which tend to drive most of the fertilizer to the soil surface rather than coat the leaves, where it could damage the leaf tissue. A concentrated band also slows the rate of urea volatilization from the urea portion (the N in UAN is about 50% urea) of the UAN.

Leaf burn potential when applying liquid N increases as the wind increases. Under windy conditions, the wind breaks the stream apart and converts it into a poor broadcast application, coating leaves and increasing burn. Do not broadcast UAN; the burn will be great and may cause a yield reduction in some cases.

Whichever source is used, rain is needed (about ½”) to move the N into the soil so that roots can utilize it.

Topdressing N in Wheat for Yield

Some spring wheat growers may consider topdressing with another 30 to 60 lb N if preplant N rates were based on conservative yield estimates, and growing conditions are favorable for wheat.

Topdressing N deficient small grains from emergence to the 6-leaf stage may serve to increase yield, provided a timely rain incorporates the application prior to jointing. The application and its incorporation by rainfall needs to be completed before jointing for yield enhancement. The interval between 3-5 leaf is best; NDSU data indicates that wheat yield response to topdressing is greatest through tillering. Topdressing after the 3-leaf stage and before the 6-leaf stage may help head size, spikelet number and kernel number decision, all of which are yield component decisions that the wheat plants make.

To top dress, use of stream nozzles or stream-bars and liquid fertilizer is strongly recommended. Sometimes, 28% has been known to result in foliar burn; one alternative is 25-0-0, a manufactured urea solution. Some studies have shown this material to be less likely to burn foliage than 28%. However, it is often more expensive to use, so the pros and cons of using this product should be weighed.

On taller wheat, stream nozzles are preferred because the stream-bars have a habit of catching on foliage and breaking off sometimes. However, they do work well and with care can last a long time. Because the stream application is not a foliar treatment, rather a concentrated soil band in effect, it needs rain to work it into the soil. If rain doesn’t fall before the wheat reaches jointing, the N may help boost protein, but will do little to increase yield.

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