As you plan your fertilizer programs, be sure to notice trends in your soil test nutrient levels identified in your soil tests. We have been finding soil test values in some grower fields declining. Sometimes it is phosphorus. Other times we see potassium and many times, it is both nutrients.
Adequate amounts of these nutrients are critical for high crop yields. Other inputs will not maximize yields if either of these nutrients are limiting. If one of these nutrients are limiting, then adding additional inputs such as increasing the rate of nitrogen that you apply will have a not have the desired impact.
If you are using variable rate fertilizer applications and see areas of your fields showing symptoms of poor growth, you should consider moving your soil sampling points to sample these areas to insure that adequate amounts of nutrients are being applied. Between grid soil test points, there may be lower testing soil nutrient levels. By moving points, this will allow you to more accurately find what is in your fields.
Another approach to calculate the crop removal of your nutrients per bushels of yield harvested. If you are applying less amounts of nutrients that you are removing during harvest of grain, soil test levels will be declining. I believe this is happening with the high cost of fertilizer materials.
Also, forage crop yields should be considered. Growers who are selling or buying hay should consider the price of nutrients that are contained in the hay. You may be exporting nutrients off your farm or bringing nutrients onto the farm if you are purchasing hay.
For more information, contact Wayne Flanary at 660-446-3724 or Heather Benedict at 660-425-6434, Regional Agronomists, University of Missouri Extension.
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