When best to apply fertilizer?

By Gary Sliworsky
Ag rep, Emo

Every year there are questions about whether it is better to apply fertilizer in the fall, or wait until spring.
The answer, as in most things, is that it depends.
The one nutrient where the answer is clear is nitrogen (N). With Ontario conditions, there is too much risk of N loss over winter for this practice to be acceptable, either economically or environmentally.
Phosphorus (P) is not subject to losses the way nitrogen is. But when phosphorus fertilizer is applied to the soil, it immediately begins to react with minerals in the soil to form less soluble compounds.
This is not a particular problem on a high testing soil, where you are applying nutrients to maintain soil test rather than for immediate crop response, since the tie-up is balanced by the release of previously-applied phosphorus.
On very low testing soils, however, 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 will help to reduce the rate of tie-up. But if you are going to the trouble of banding P, it may as well be applied as a starter.
As a general rule, fall P applications should be banded with winter cereals, but most of this fertilizer should be applied in the spring.
Potassium (K) is not as reactive in the soil as phosphorus. In light-textured soils that are no-tilled, a fall application can be an advantage by allowing winter precipitation to move the potassium down into the root zone.
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.
Of course, there will be some loss of both phosphorus and potassium if soil is eroded off the field.
Time is one of the chief advantages of fall application. There is never enough time in the spring, so applying the fertilizer now could mean getting the crop in two or three days earlier.
Application equipment also is easier to find at this time of year. You should, however, check the equipment over carefully when you get it.
Most blenders do equipment overhauls during the winter, so the spreader you get will have had a full season of hard use since the last thorough going-over.
The financial aspects of fall application are the hardest to predict, and are most affected by your individual circumstances. There often is a price spread from fall to spring, but the amount of this spread is quite variable.
If you are borrowing money at prime, you still need a three percent increase in fertilizer prices to cover the interest costs from now until spring—even assuming the availability of the nutrients does not decrease.
If you simply are trying to protect yourself against fertilizer price increases, you also should investigate pre-payment options, where you can lock in the fertilizer price for spring delivery.
There is no single right answer to whether you should apply fertilizer this fall.
You will have to balance your own factors in making the final decision.
Dates to remember
•Sept. 28–Calf sale, Stratton sales barn

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