By Gary Sliworsky
Ag rep, Emo
Applying fertilizer as close to the time the crop needs it generally provides the greatest benefit.
The longer the fertilizer sits in the soil, the greater the chance it either will be lost to the environment or get tied up in less available forms.
There are exceptions, however, where the advantages of fall application out-weigh the risks.
Time availability is one of the chief advantages of fall application. There is never enough time in the spring.
Applying the fertilizer in the fall could mean getting the crop in two or three days earlier.
Application equipment also is more available in the fall.
Fertilizer price savings from fall application are much more difficult to predict. Last fall, the market signals all pointed to significant price increases over winter.
This year, the signals are much less clear.
In any case, you can manage the tax implications by pre-paying fertilizer for spring application, rather than taking delivery now.
Potassium can benefit from fall application on light-textured soils which are no-tilled by allowing winter precipitation to move the potassium down into the root zone.
Where very high rates of K are being applied on sandy soils, fall application can reduce the risk of salt injury to the crop by allowing the chloride to leach over winter.
In heavy clay soils, there can be some tie-up of potassium between the clay layers, and fall application allows more time for this process to occur.
Phosphorus immediately begins to react with minerals in the soil to form less soluble compounds. On a high testing soil where you are applying nutrients to maintain soil test rather than for immediate crop response, this is not a problem because the tie-up is balanced by the release of previously-applied phosphorus.
However, on very low testing soils and if the fertilizer is broadcast, by the time crop growth begins next spring, most of the fertilizer you applied could be tied up in unavailable forms.
Banding to reduce the contact with the soil would help to reduce the rate of tie-up. However, if you are going to the trouble of banding P, it may as well be applied as a starter.
The one nutrient where the risks of fall application clearly outweigh the benefits is nitrogen. With Ontario conditions, there is too much risk of N loss over winter for this practice to be economically or environmentally acceptable.
There is no single correct answer as to whether you should apply fertilizer this fall. You will have to balance your own factors in making the final decision.