Nutrient applications for wheat
While most wheat is planted after soybean, if it is planted after corn, one potential concern is that N can be temporarily tied up while 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, N beyond the recommended amount is not needed for wheat grown after corn.
On soils with higher organic matter, spring application timing has little impact on yield. On the other hand, N rates can be decreased by 10% in soils low in organic matter in southern Illinois when one of the following applies:
- Spring application is delayed due to late tillering (Feekes growth stage 5.0-6.0).
- Spring applications are split, with one at early greenup and one at late tillering or early jointing.
- Nitrification inhibitor or a slow- or controlled-release N source is used.
Research has also shown that a spring-split N application, with one-third early and two-thirds at late tillering to jointing, can increase yields by about 10% compared to a single spring application at greenup, especially when conditions favor N loss. Delaying all of the application to late tillering or early jointing usually produces the same yield as splitting applications in the spring.
Phosphorus (P) is very important to stimulating early growth, helping with tillering (which eventually determines the number of seedheads), and improving winter survival. The amount of P to be applied depends on soil test levels as well as the P-supplying power of the soil. It is recommended that test levels for high, medium, and low P-supplying soils be at 40, 45, and 50 lb per acre, respectively.
If P is below the desired level, it is recommended that you apply enough to both build up the soil and supply what the crop will remove. If test levels are adequate, it is recommended that you apply enough 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 establishment of the crop (discussed earlier). It might be tempting to reduce or eliminate P application in soils that test at or just above the critical level. If your finances do not allow for a full application, it is strongly suggested that you apply 80 to 100 lb of DAP per acre to ensure a good supply of readily available P to facilitate 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 (<100 lb per acre). Since soybean and corn are grown in the rotation with wheat and are more responsive to K than is wheat, it is recommended that you manage K to maximize yield of corn and soybean. Doing so will automatically take care of the needs of wheat.