High yields are being harvested from most of Iowa's fields this fall. However, due to low grain prices producers are considering to reduce their phosphorus and potassium fertilizer application rates. Before doing this it is important to consider different management options.
Soil Sampling: Soil Sampling is not a perfect tool but it is very useful when it comes to making decisions and your P & K. Producers should not reduce P & K application in soil samples that come back very low and only a low starter rate may be justified in high testing soils. Only removal based rates are recommended for optimum levels soils. For corn and soybeans, the optimum level for Phosphorus is 16 to 20 ppm. The optimum level for Potassium is 161 to 200 ppm.
Watch yield level and P & K removal rates: The yield levels and P or K removal should be determined by the application rate needed to maintain adequate levels. Often a removal based rate will maximize yield, but often the small yield increase does not offset the application cost, especially with the current lower prices. Producers are able to use the soil test with fields having high testing P and K and save money by withholding or reducing application rates of what you would of put on the begin with.
Use a good soil sample and variable-rate technology for application: Use of a variable- rate P and K fertilization is a good option to improve P and K management in fields that have significant variation in soil test and yield levels.
Do not reduce the recommended P and K rate for low testing soils with banding: Research has shown in many fields in Iowa that banding P and K fertilizer is seldom more efficient than broadcasting. Reducing the fertilizer rate for low testing soils when banding will increase the risk of yield loss, reduction of profits from crop production, and the future fertilizer rates will need to be increased.
Sources: ISU Extension & Google Image
