ISSUE 8    June 23, 2005


Topdressing for Protein

For protein enhancement, extra N applied before heading using stream technology not incorporated into increased yield will be used for protein. Also, aerial application of urea might also be attempted. These strategies, although there is little burn risk (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!) need rainfall to work. A ˝ inch rain is needed to move the fertilizer into the soil. With the wet leaves and heavy dew we have experienced, high levels of urea can convert within a week after application using this method. 28% will be better able to hang in there due to its ammonium nitrate component. Dry urea will not.

An approach not dependent on rainfall is a foliar application of 10 gal/a (30 lb N) as 28%, mixed with 10 gal/a water, and applied just after pollination at the watery-ripe stage of kernel development This application risks leaf burn, which is why I do not recommend it before pollination at flag leaf emergence or at pollination. The need to protect the flag leaf is crucial, and pollination is also a critical time to protect sensitive anthers. Although some leaf burn with a foliar application is expected, it will be minimized when the fertilizer is applied during the cool of the day. In years with night temperatures in the 40's and daytime temperatures in the 60's and low 70's, low levels of burn have been reported. Lately, with daytime temperatures in the high 80's and 90's, the best times would be early in the morning from 4AM until perhaps 9 or 10 AM, then again in the evening after 7-8 PM. This is an art, not a science, and there is no guarantee against leaf burn. Leaves that are burned do not recover, however, bushels lost due to burn are usually low following pollination, and if the protein premiums remain high this fall, the protein increase will probably be worth more than any lost bushels due to superficial burning.

Topdressing distressed wheat fields for yield?

In most years, the possibility of increasing yield with applications of N later than jointing will not be successful. However, in areas with extreme rainfall, the plants may be so deficient that there is not enough N in the plants to adequately fill kernels. In this situation, application of supplemental N may increase yield through better kernel fill and increase in test weight. This increase would be accomplished with about 30 lb N, applied with stream-bars, or aerial urea, both with rainfall helpers, or a foliar application as described previously for protein enhancement. The best to expect would be about a 10% yield increase.

Side-dressing corn

With saturated soils, it might appear that time is slipping by to apply side-dressed N on row crops. However, the weather has cooperated so far in bringing cool conditions along with the deluge. Corn growth has been slow, so it is possible that the soil will dry up enough to allow a side-dress application before it becomes too tall. Corn yield decisions are made later in growth than in small grains. Corn can be 8-10 leaves and still have close to full yield potential if N application is delayed until then. Corn yields can be increased with N applications all the way to tasseling if conditions completely fall apart, although I wouldn’t wait that long on purpose. It is best to try to get the N on before 10 leaves show.

If the corn becomes too tall for injecting with anhydrous or liquid, set up a boom on a high-clearance sprayer with drop nozzles placed between the rows. The nozzles should be weighted or braced so they don’t ride above the canopy. Don’t broadcast N either dry or liquid. Remember that corn isn’t like wheat. Wheat sheds dry and liquid fertilizers to some extent, while corn gathers most of what lands on it into the whorl, which concentrates the fertilizer, resulting in significant and often serious burn and yield reduction potential.

Successful post-N applications with drop nozzles are possible until the corn is taller than the high-clearance sprayer platform. The taller the corn, the more damage will be done turning on the field ends and corn breakage from crowding rows (especially in 22 inch rows).

Soybean/Flax chlorosis

It is probably no surprise that after the heavy rains soybeans in the first trifoliate stage or older are showing chlorosis. Saturated soil, with high pH, carbonates and especially higher soluble salts are ideal conditions for chlorosis to develop. The adoption by growers of more chlorosis/salt tolerant varieties has resulted in more soybean fields withstanding this stress. However, work by Dr. Goos as NDSU suggests that even fields that recover quickly probably have had 5 bu/a taken off the top due to the condition. To date, iron sprays have not been effective in increasing yields from this condition. The best thing to have happen is for dry weather to move back into the region.



During the last few weeks, much of the state has experienced substantial, and often excessive rainfall. Rainfall is good to a point. However, these rains have resulted in losses of N from leaching in center and west parts of the state and both leaching and denitrification in the east. As a result, we have good growth conditions in some fields, but lower available N than is needed to achieve good yields.

It is difficult even with soil testing and plant analysis to determine rates of N needed to supplement N loss. These losses are often very small scale in variability, so sample numbers need to be large to have a good chance to predict N status based on numbers alone.

The following decision chart was developed by Dr. George Rehm at the University of Minnesota. It appeared in last week’s Minnesota Crop News. With his permission, I reproduce it here for your use, with my comments.

Decision Table for the Need for Supplemental N

Question #1 When and how was the N applied?

A. In the fall, less the 4 inches deep and soil temperatures were above 50oF


B. In the fall, 4 or more inches deep and soil temperatures were above 50oF


C. In the fall, less than 4 inches deep and soil temperatures were below 50oF


D. In the fall, 4 or more inches deep and soil temperatures were below 50oF


E. In early spring (March/April)


F. Broadcast on the soil surface in the fall, unincorporated


G. Broadcast on the soil surface in the fall, incorporated, below 50oF


H. N applied in May, incorporated.


Question #2- What was the predominant spring (May/June) soil condition?
A. Normal or drier than normal


B. Wetter than normal


C. Standing water in low areas


Question #3- What does the crop look like?
A. Crop is tall and moving on in maturity, showing N deficiency*


B. Crop is short and early in maturity, showing N deficiency*


C. Crop is short and early in maturity, showing no N deficiency*


D. Crop is tall, moving on in maturity, green



* N deficiency symptoms vary for each crop. Generally, crops are yellow, more so in lower leaves, with upper leaves greener. Lower leaves on corn will become yellow from leaf tip in a V pattern following the mid-vein with the V-tip aimed towards the stalk.

Add the points for each of the three questions.

Total is 7 or less- Supplemental N for yield not necessary
Total 8-9- Supplemental N may or may not be necessary
Total of 10 or more- Supplemental N is suggested

Rates from 30-50 lb N/acre are suggested for most crops. High rates for crops with high yield potential and low down-size quality risk from application of N (any crops except flax, barley, sugarbeet, safflower).

Also, for canola, if N appears lost, assume that sulfur was also lost and include some in the supplement.

Sulfur supplementation

Although less common than N deficiency, if yellowing is seen, particularly in younger leaves on hilltops and eroded areas, S may have leached from the root zone and the crop may require supplementation if not too far advanced. Plant analysis may confirm a S deficiency. Ammonium sulfate or another available sulfate fertilizer would be suggested to correct a problem. Do not broadcast liquid ammonium thiosulfate on most crops, except through irrigation water or on canola. Canola has a heavy wax leaf layer after 5 leaves that prevents serious burning.

Dr. Dave Franzen
Extension Soil Specialist

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