Last year several soybean fields exhibited potash deficiency. As potash prices have climbed over the years many producers have cut back on applications. So, although we experience a good growing year, these potash deficient fields are not going to yield their full potential. Potash deficiency shows up as yellowing along the leaf edges. Soybean cyst nematode can cause the same symptoms.
A 120-bushel corn yield removes 35 pounds of potash. Forty-five-bushel soybeans remove 65 pounds of potash. So, if you are rotating the two crops and only applying before the corn, you’d have to apply 100 pounds of potash just to replace what was removed. If the soil needed potash to be built up or the yields were higher, even more would be needed.
If producers are converting pastures or hayfields to crops, these may be very low in potash and will need large amounts applied to produce good crops. Three tons of fescue hay remove 100 pounds of potash. So, it is not surprising to find old hay fields that are nearly depleted of available potash. A soil test will tell you where your levels are and if you need yearly potash applications to get your fertility back in shape.
Contact your local University of Missouri Extension Agronomy Specialist if you have questions.