Fertilizer costs for crop production have skyrocketed over the last couple of years. Nitrogen cost has doubled in the last five years.
The cost of phosphorus is three to four times more than just five years ago and the same is true for potassium. These are the major nutrients that corn, soybeans, wheat and hay need to grow and reproduce. So these are the nutrients that farmers need to supply in ample amounts.

Five years ago when prices were relatively inexpensive, a farmer could apply 100 pounds of 0-46-0 and 200 pounds of 0-0-60 to supply the phosphorus and potassium for the next year’s crop.
The days of applying a set amount on the assumption the soils needed it are gone. You can’t even purchase the 0-46-0 formulation these days.

As an example, I just got off the phone with a farmer who has, over the years, applied phosphorus and potassium to his fields each year. It’s like putting nutrient in the bank. If the crops did not use it, it didn’t matter as long as phosphorus did not get too high and soil sediment did not wash from the field. The nutrient would stay in the soil for later.

This year his soil test revealed the field with the lowest level of phosphorus was 40 PPM.

Ohio State University provides recommendations for both phosphorus and potassium in our Tri-State Fertilizer Recommendations.

The critical level of soil phosphorus is 15 PPM for corn or soybean production.

If the soils are below this level the soil will not be able to supply the needed nutrient and additional fertilizer should be applied. If the soil tests are above this critical level of 15 PPM the soil will be capable of supplying the nutrient to the crop and no response in yield would be expected from applying additional fertilizer to corn or soybeans.

If your soil test results are stated in pounds per acre instead of PPM, the critical level for phosphorus is 30 pounds per acre available. To convert pounds per acre to parts per million, just divide by two.

To calculate the critical level for potassium you need to know the Cation Exchange Capacity (CEC) of the soil from the soil test. The critical level for potassium is 2.5 x CEC + 75 in PPM. So if the CEC for your soil is 20 then the critical level for that field is 125 PPM. If you are above that level, no yield response to additional potassium would be expected.

Prices for fertilizer may moderate now that oil has come down some. It makes sense to soil test, soil test, soil test. Take the nutrient in the soil out of the bank.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Readers with questions or comments for Steve Bartels may write to him in care of this publication.