A relatively early harvest throughout most of Illinois should allow enough time to get wheat planted and well established before it gets cold, says Fabian Fernandez, University of Illinois Extension specialist in soil fertility and plant nutrition.
To ensure adequate nutrient availability and successful establishment, he offers a few suggestions for growers.
Nitrogen (N) is important for vegetative growth, but the amount taken up by roots and vegetative tissues does not exceed 30 lb. to 40 lb. of N per acre before it gets too cold. While concern about lodging under high N rates has decreased considerably, it is best not to apply too much N in the fall to minimize lodging risks, Fernandez says.
Also, because N applications will promote excessive vegetative growth, the crop may be prone to disease problems later, he adds. If the soil has large potential to supply N, fall applications prior to planting may not be necessary.
"Corn fields should have some leftover N in the soil this year, as the corn crop probably did not use all the N during dry conditions in July and August," Fernandez says. "Normally, a 20 lb. to 30 lb. pound per acre application of N in the fall is all that is needed to establish wheat. This amount can be supplied in the form of di-ammonium phosphate, which should also supply what is needed for phosphorus fertility."
The total amount of N required for a wheat crop is dependent on the capacity of the soil to supply N. Dark soils that are high in organic matter require less N than light-colored soils with low organic matter. For soils with organic matter greater than 4%, 70 lb. to 90 lb. of N per acre is typically sufficient; soils with organic matter between 2% and 4% often maximize yields with a rate of 100 lb. to 120 lb. of N per acre; and soils with low or less than 2% organic matter will require 150 lb. of N per acre.
"While the full amount can be applied with anhydrous ammonia and a nitrification inhibitor in the fall, the preferred method is to apply most of the needed N by topdressing with fertilizers that do not contain free ammonia in the spring right before the crop greens up and starts to take N," Fernandez says. "Applying N at this later time minimizes the potential for N loss and provides needed N that might not be available from the soil due to slow mineralization during cool springs."
In high organic matter soils, spring application timing is not as critical. In low organic matter soils in southern Illinois, it is possible to reduce N rates by 10% by delaying application to late tillering (Feekes growth stage 5 to 6), splitting the application between early green-up and late tillering to early jointing, or using a nitrification inhibitor or slow-release N source.
While most wheat is planted after soybeans, if wheat is planted after corn, one potential concern is the temporary tie-up of N that can occur as microorganisms break down corn stover. Fortunately, most of this tie-up takes place in the spring once soils warm up, which is often after wheat has taken up most of its N. For these reasons, additional N beyond the recommendation is not needed for wheat grown after corn.
Phosphorus (P) is very important to stimulate early growth, help with tillering and improve winter survival. The amount of P to be applied depends on the soil test levels as well as the P-supplying power of the soil. It is recommended that the soil test level be at 40 lb., 45 lb. and 50 lb. per acre for the high-, medium- and low-P-supplying soils, respectively.
If the soil test is below the desired level, it is recommended to apply sufficient P to build up the soil as well as supplying what the crop will remove. If test levels are adequate, it is recommended that sufficient P be applied at planting time to replace 1.5 times the amount to be removed by the crop. This large amount is needed to meet the high P requirements of wheat.
"In many fields, a typical rate of 150 lb. of DAP (18-46-0) per acre supplies not only P, but also sufficient N for the establishment of the crop," Fernandez says. "Sometimes it might be tempting to reduce or eliminate P application in soils testing at or just above the critical level. If your finances do not allow for a full application, it is strongly suggested that 80 lb. to 100 lb. of DAP per acre be applied to ensure a good supply of readily available P to help adequate establishment of the crop."
Potassium (K) is also an important nutrient, but wheat normally does not respond to applications of K unless soil test levels are extremely low (less than 100 lb. per acre). Since soybean and corn are grown in the rotation with wheat and are more responsive to K than wheat, it is recommended to manage K to maximize yield of corn and soybean, Fernandez says. This will automatically take care of the K needs of wheat.
For More Information
Read more wheat news.