Fall-applied nitrogen fertilizer
With El Nino conditions increasing the chances of a dry spring, fall fertilization might be a good idea.
But the decision to fall band nitrogen depends on soil moisture, the form of nitrogen used and how it is applied.
“Fall fertilization can improve time management and allow earlier planting,” said Ross McKenzie, soil fertility specialist with Alberta Agriculture.
“Producers often find that fertilizer prices and payment schedules are more favorable and the availability of product is often better in the fall. Drier soil conditions in the fall can also mean that application equipment is less likely to cause soil compaction.”
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Nitrogen can be applied to soil in several forms: as urea, anhydrous ammonia (NH3), ammonium (NH4) and nitrate (NO3).
“Urea and anhydrous quickly convert to ammonium. It’s the NH4 and NO3 that are taken up by plants. If the soil is warm, moist and well-aerated, ammonium is rapidly oxidized to nitrate through the nitrification process performed by highly specialized soil bacteria.”
Banding slows nitrification by inhibiting bacteria activity near the band. Generally, spring banding is the most effective method and fall broadcast the least. However, fall-banded nitrogen can be as effective as spring-banded if there is no extended period of saturated soil conditions in the spring.
When fall-applied nitrogen converts to nitrate before freeze-up, large losses can occur when soils are water saturated during and just after snow melt in early spring, said McKenzie.
In drier regions, nitrogen losses through denitrification, a process that converts nitrate to nitrogen and oxygen gases, are usually small and fall banding is equal to spring banding.
Where spring banding causes significant loss of seedbed moisture, fall banding can be superior.
Before fertilizing this fall, consider several agronomic factors:
- If soils tend to be saturated for long periods in the spring, the land is not suited for fall fertilizer applications.
- Test soil to determine the best fertilizer application rates.
- Apply a conservative rate of nitrogen fertilizer. An application of 75 percent of soil test recommendation is a hedge against high soil test nitrogen levels, poor spring soil moisture or low crop prices.
- Select the right fertilizer formula for your conditions.
- Avoid nitrate-containing products such as 34-0-0 and 28-0-0 on soils that tend to be saturated in the spring.
- Apply nitrogen in late fall after the soil temperature has dropped below 7 C and the nitrification process has slowed.
- Finally, band, don’t broadcast.
No soil type or region is completely safe when it comes to losses of fall-applied nitrogen. Producers should discuss their options with their fertilizer dealer or agronomist or a provincial crop specialist.
– Alberta Agriculture
