Fertilizing Winter Wheat

Winter wheat fertilization recommendations in North Dakota previously were similar to spring wheat and durum. As a larger research base was developed for spring wheat and durum, separating winter wheat from other wheats became necessary due to their unique nutrient requirements.

Nitrogen rate cannot predict yield. Previous recommendation formulas forced a grower to predict a yield and then apply the yield prediction to a formula. This strategy resulted in underfertilization in some years due to less than ideal growing conditions at the time of fertilization.

Weather in the region is unpredictable, and growing conditions can improve and better yields are possible than those planned for initially. Recent N-rate research on several crops indicate that no relationship exists between yield and N-rate and the environment.

A similar optimum N rate is appropriate in a low-yielding environment as in a high-yielding environment due to differences in N mineralization release from the soil, probability of N loss due to leaching and/or denitrification, and N uptake efficiency of roots in different soil moisture environments. In wheats, some consideration of historic soil productivity is necessary due to the economics of the application, and not necessarily the yield response of the application itself.

Our research indicates that the following productivity ranges are appropriate for consideration of optimum economic N rate for winter wheat:

• Low – yields below 40 bushel per acre

• Medium – yields between 40 and 70 bushels per acre

• High – yields greater than 70 bushels per acre

For areas of low productivity, total available N (fertilizer + soil test nitrate 2 feet) = 100 pounds of N/acre

For areas of medium productivity, total available N (fertilizer + soil test nitrate 2 feet) = 150 pounds of N/acre

For areas of high productivity, total available N (fertilizer + soil test nitrate 2 feet) = 200 pounds of N/acre

Adjustments to N Rate

Applying banded phosphate (P) to winter wheat at seeding is extremely important. Phosphate helps the plants establish good root systems and crowns going into winter and helps winter survival. Broadcast P may be better than no P, but the difference in efficiency between the two applications in winter wheat is very pronounced.

When banding granular or liquid fertilizer with the seed, do not exceed rates of N + K2O as provided in Tables 3 and 4. If fertilizer must be applied at rates exceeding those in the tables, some change in fertilizer delivery must be made on the seeder so that the seed and fertilizer application is separated by at least 1 inch, and preferably 2 inches.

The potassium (K) recommendations have been changed. Finding responses to K is difficult when soil test K levels are greater than 100 ppm. Nearly all of the higher soil test K responses are related to a chloride response.

Most soils in North Dakota have high enough potassium (K) levels to support excellent wheat production. Exceptions might be sandier soils or soils with a history of many years of continuous soybean.

Current K fertilizer recommendations are displayed below. If chloride levels are adequate and other crops in the rotation regularly receive K fertilizer, then fertilizer rates in the high range of soil tests may not be needed.

• Soils with smectite-to-illite ratio greater than 3.5 (Figure 2)

Soil test K > 150 ppm, no additional K required. KCl (0-0-60-50Cl) may be applied if Cl levels are low.

Soil test K 150 ppm or less, apply 50 pounds/acre KCl (30 pounds/acre K2O)

• Soils with smectite-to-illite ratio 3.5 or less (Figure 2)

Soil test K > 100 ppm, no additional K required. KCl (0-0-60-50Cl) may be applied if Cl levels are low.

Soil test K 100 ppm or less, apply 50 pounds/acre KCl (30 pounds/acre K2O)

Figure 2. Smectite-to-illite clay chemistry for soils in North Dakota from a soil sampling survey conducted in 2017.

Sulfur is becoming more important than potassium or chloride in the state as a third major nutrient. Environmental regulations on fossil fuel emissions have put more stringent restrictions on sulfur emissions in recent years. This has resulted in less sulfur through rainfall.

The sulfur soil test is not a good predictor of possible sulfur deficiency. Sulfur deficiency has become so prevalent in small grains and corn that for spring wheat/durum, a base application of 10 pounds of S/acre would be prudent, particularly if the fall, winter or early spring before seeding has received normal to above normal precipitation. Soils with sandy loam or coarser textures, and less than 3 percent organic matter on higher landscape positions are most at risk, but most soils are at risk in wetter seasons.

Sulfur fertilizer application is a spring operation. The spring fertilizer application should consist of a soluble sulfur fertilizer. Ammonium sulfate at rates of about 10 pounds of S/acre or gypsum at 20 pounds of S/acre would be excellent sources of sulfur. Elemental sulfur, even premium bentonite-blended forms, would not be nearly as useful in correcting a deficiency.

Composite blended granules of phosphate fertilizers that include sulfur could be used, but rates need to be high enough to supply the 10 pounds of S/acre needed as the ammonium sulfate portion of the fertilizer, or the application should be supplemented with a sulfate containing fertilizer. Gypsum or ammonium sulfate may be blended with a urea top-dress application, while ammonium sulfate solutions or ammonium thiosulfate may be applied with stream-bars (not broadcast nozzles), along with 28-0-0.

Increases in yield and decreases in fusarium head blight (scab) have been documented in North Dakota with the application of copper (Franzen et al., 2008). The responses to copper were seen mostly on low-organic matter, sandy soils. However, only about 15 percent of the sites that fit these criteria in the study responded.

Predicting whether wheat grown on these soils would respond to copper would be difficult. Copper application is a site-specific nutrient at best. Applying it on loam or heavier soils, or in soils with between 3 and 8 percent organic matter, would provide no benefit. An application of copper sulfate at a rate of 5 pounds of Cu/acre would last many years.

Chloride responses are well-documented in wheat. In studies in the state and the region, wheat tends to respond positively to chloride about half the time, with yield increases in the 2- to 5-bushel/acre range. Studies in consecutive years that investigated varietal responses to chloride provided inconsistent results.

Yield increases from chloride arise from increased resistance to certain root and leaf diseases and an increase in kernel size. The critical level of chloride is 40 pounds/acre in the surface 2 feet of soil. If the soil test is less than 40 pounds pf Cl/acre, fertilizing with 5 to10 pounds of Cl/acre with or near the seed at planting should sufficiently supply the crop for the year.

The most common source of Cl is KCl (potash, 0-0-60). When adding Cl to fertilizer, refer to Tables 3 and 4 so critical levels of N + K2O are not exceeded.

No evidence indicates that supplemental zinc, iron, manganese and boron are needed in North Dakota. Although numerous reports exist in the US and around the world of these nutrients being required as fertilizer, our soils apparently supply enough and our wheat is adapted to our soils enough that these nutrients do not need to be supplied artificially.

Franzen, D.W., 2015. Fertilizer application with small grain seed at planting. NDSU publication SF1751.

Franzen, D.W., M. McMullen and D.S. Mossett. 2008. Spring wheat and durum yield and disease responses to copper fertilization of mineral soils. Agronomy Journal 100:371-375.

January 2018