Prioritizing Phosphorus and Potassium Fertilizer Applications

Prioritizing Phosphorus and
Potassium Fertilizer Applications
The increase in crop input prices has many growers concerned about what might happen if commodity prices drop. The cost of phosphorus and potassium fertilizers has increased dramatically and are at record highs. Swings in crop yields and prices provide a great amount of risk into the profitability of the operation. The need for sound planning is more important than ever.
The use of fertilizers should be used to obtain the greatest return on investment rather than to maximize yields. First, prioritize what nutrients are limiting crop yields. This is addressed by using a good soil testing program across your row crop, pasture and hay acres.
Yes, this is simple but often overlooked. We often see growers applying fertilizer rates that have traditionally been applied in the past. Our suggested strategy is to apply phosphorus and potassium fertilizers by using soil testing to determine the soils ability to supply nutrients to the crop. There may be one or more nutrients limiting yields. Also, soil tests will help us identify areas where we need to apply fertilizers maximize yields.
Once you determine what nutrients limit the crop yields, next step is to correct this limitation by developing a strategy that meets the needs of crop that you can afford.
For example, if phosphorus levels are low and all other nutrients are adequate, then adding potassium would not help to increase yield. This is simple but this often ignored. If both nutrients are limiting, then it is better to apply at least a portion of every limiting nutrient rather than focusing on one.
If soil test values are well above a point where a response will not be expected, one may eliminate the nutrient and use the fertilizer dollars in a field or portion of field that will generate a return on investment.
So the strategy is to apply nutrients to portions of the field that have the highest likelihood of yield response rather than applying an average amount across the entire field. We are maximizing the greatest return on investment while maximizing yields.
Another strategy would be to focus different fertilizer applications on different fields. Often fields vary in phosphorus and potassium levels. This may provide an opportunity to prioritize different fields for phosphorus and potassium applications.
For more information contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists with the University of Missouri Extension.