What is in this article?:
- Plan for Phosphorus and Potassium Fertilization
- Fall and spring application effective
- Wait until mid-October
- Applying P and K annually or biennially is debatable
- Fall and spring applications have proven to be effective
- Know the test level of the soil
With a promising harvest under way, it’s a good time to replenish fields with phosphorus (P) and potassium (K), says Fabian Fernandez, University of Illinois Extension (U of I) specialist in soil fertility and plant nutrition.
“High fertilizer prices for a few years were followed by a wet fall and late harvest last year,” Fernandez says. “This resulted in many fields not receiving all the P and K needed to maintain optimum test levels. Since many fields have already been harvested and soil conditions are ideal for tillage or to drive equipment over the field, now’s a great time to plan for P and K applications.”
Fernandez says how P and K are applied does not matter as long as you apply it so test levels are adequate for crop production.
For farmers interested in strip-till this fall, Fernandez recommends waiting until at least the middle of October to avoid heavy rains that can flatten the berm created during the tillage operation.
Applying P and K annually or biennially is debatable. U of I research indicates that as long as needed fertilizer is applied, there is no yield benefit hinging on whether the application is done every year or every other year.
“However, we have seen that for biennial applications it is better to apply fertilizer before the corn crop and have soybean as a residual feeder,” he said. “Research has shown that having corn in the second year after fertilization can cause yield reductions, especially in no-till systems. Conversely, soybean yields were not affected in response to the time of fertilization. Even if a biennial application results in time saving and one less pass over the field, if your experience tells you that your soil does not build up, I would suggest always applying on an annual basis.”