Discern nitrogen requirements to maximize yield, protein

Nitrogen lacking

A major hamburger chain once popularized the saying: “where’s the beef?”

This fall, I have heard a similar refrain from farmers. They are asking: “where’s the protein?”

There have been few disappointments with this year’s harvest, but protein levels may be one. 

Higher protein wheat almost became a liability last year. Premiums all but disappeared and the specs for a lot of wheat that was being sought was below 13 percent. 

Many people thought that growing protein in the post CWB monopoly era was going to be of much less importance than it had once been. This belief has been shown to have been a market reaction to the drought in the United States.

This year, the market is once again asking for high protein wheat and offering premiums for it. 

Thus the cry of “where’s the protein” from producers and grain buyers when wheat is delivered to the elevator. 

Now is a good time to review protein and the factors that result in high and low protein wheat.

Many factors go into determining wheat’s yield and the protein content: soil type, soil nitrogen distribution, soil moisture at seeding, growing season moisture, application of phosphate and sulphur fertilizers, variety and organic matter. 

Any factor that increases yields usually lowers protein content because a fixed supply of nitrogen is diluted over a larger amount of crop.

The first demand of the wheat plant on nitrogen is for yield. Once yield requirements for nitrogen are satisfied, the surplus nitrogen is converted to extra protein. 

If we could predict moisture availability, we could use models developed by Geza Racz at the University of Manitoba to predict the amount of nitrogen required to achieve a specified protein content for wheat.

Unfortunately, we cannot predict growing season weather and moisture. 

However, moisture supply is least variable in the Prairies’ black soils. As a result, we can more reliably predict the effect of extra nitrogen on protein content in areas of higher rainfall such as Manitoba than in lower rainfall regions such as southwestern Saskatchewan.

The results that were achieved in studies I was involved in follow a predictable path:

  • Protein increased from 12.5 to 16.1 percent with the addition of nitrogen. Nitrogen maximized yield when applied before seeding and maximized protein when top dressed at flowering time.

  • Seventy percent of the plant’s nitrogen requirements are taken up when only 30 percent of plant growth has occurred.

  • The largest portion of the nitrogen is taken up by the plant early in the growing season. This nitrogen is later trans-located to the seed portion of the plant as it matures. Potential yield is set by the late tillering stage and is determined by available moisture and nutrient supply up to that point in time.

  • Nitrogen taken up after the yield has been set will generally contribute only to protein. Conversely, the early season nitrogen taken up by the crop will be distributed over fewer bushels if a large amount of nitrogen is consumed by the crop early in the growing season followed by an environmental stress that reduces yields. This will result in high protein concentration, which has often been the case in Saskatchewan’s brown soil zone, well known for its production of high protein wheat.

According to Racz’s research, unless wheat’s protein content is in the range of 13.2 to 13.5 percent, chances are not enough nitrogen is being applied to maximize yields based on available moisture. Protein content cannot be effectively raised until crop yield nears its maximum potential. 

Organic matter and its mineralization also play an important role in protein. 

Mineralized nitrogen from organic matter moves into the soil throughout the season, which means some of it will transfer after the optimum yield has been set. As a result, this nitrogen will go towards protein.

There can be a significant effect on protein if enough nitrogen is mineralized. Estimates have been made that, under normal precipitation, 10 pounds of nitrogen are mineralized for every percent of organic matter in the soil. 

For example, soil with five percent organic matter will produce 50 lb. of nitrogen through mineralization in an average year. Unlike fertilizer nitrogen, almost all of this nitrogen is available to the crop and would be equal to 75 to 100 lb. of fertilizer nitrogen.

An annual application of 90 to 110 lb. of nitrogen in the black soil zone for 10 to12 years in a continuous no-till program may increase organic matter mineralization enough to ensure good protein levels in wheat when fertilized to reasonable 

Adjacent fields that have had lower nitrogen applications or where the soil has been continually tilled may not attain similar protein levels when fertilized at similar levels.

There have been stories of increasing protein by adding sulphur to wheat. This has been duplicated in research trials but occurs only where sulfur is deficient in the soil. 

Adding sulfur to fields that already had sufficient levels did not increase protein.

  • CWRS wheat protein is directly proportional to available nitrogen during the growing season.

  • Increasing the nitrogen rate higher than what is needed for maximum yield will continue to increase protein content.

  • Top-dress nitrogen applied during flowering may increase protein if rainfall occurs shortly after application.

  • A soil test, along with a sound fertility program, is the first step in achieving maximum yields and protein premiums. 

  • Long term no-till and aggressive fertilizer applications will improve mineralization of nitrogen from organic matter and lead to higher protein levels.

  • A protein level of 13.5 percent in hard red spring wheat indicates that nitrogen levels and moisture availability were in balance. Levels higher or lower than 13.5 percent indicate nitrogen levels were higher or lower than the level of available moisture.

Thom Weir is an agronomist with Farmer’s Edge. He can be reached by emailing [email protected]


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