Late fall can present challenges when it comes to fertilizer application. Improper timing of fall fertilizer applications can lead to risk of nutrient loss through runoff.
Fabian Fernandez, extension nutrient specialist at the University of Minnesota (U of M), reminds growers to wait until soils have reached 50°F. and cooling before dropping anhydrous ammonia applications, but what if soils approach freezing temperatures?
As soil temperature approaches freezing, the risk of nutrients being retained in the soil decreases and the risk of loss increases, Fernandez says.
Here are five tips for best practices in late fall fertilizer management from a Minnesota university Crop News take-home article from Fernandez; Daniel Kaiser, U of M Extension Nutrient Management Specialist; and Paulo Pagliari, nutrient management specialist at U of M Extension.
1. Never apply on frozen or snow-covered ground.
Do not apply fertilizer if a hard frost is expected within a week of application and never apply fertilizer to frozen or snow-covered ground. To ensure that the nutrients in the fertilizer stay where they are applied, they need time to react with the soil. Phosphorus, for example, needs 7 to 10 days after application without rain to react. If the ground is frozen, these nutrients will not hold in the ground.
2. Cultivate the soil to avoid runoff.
If you plan to apply fall fertilizer to soybean stubble, you must also till the soil. Without tillage, you run a significant risk of losing nutrients from fertilizers through runoff. Tillage is a best management practice to prevent runoff, as long as tillage does not increase the risk of erosion. If tillage reduces the movement of water over land, you reduce the risk of nutrient loss. Whenever nutrients remain on the surface, there is a risk of loss.
3. Properly seal anhydrous strips to reduce the risk of nitrogen loss.
For anhydrous ammonia applications, ensure the floor is sealed behind the cutters. Cold weather will not prevent loss, and since anhydrous is a gas, it must be properly sealed.
4. Incorporate fall urea applications.
Urea must convert to ammonium to be retained by the soil. There is a significant risk that N will not have enough time to perform this conversion in frozen soils. Fall urea applications are acceptable in areas of western Minnesota, but be sure to incorporate them. This ensures that urea N is converted to ammonium N, a form retained by the soil. Volatilization of ammonia can occur even in cooler soils if it is not incorporated.
5. Remember the risk of spring loss.
All fertilizers are water soluble and will move with water during runoff events. If applied to frozen ground, there will be little reaction with the ground and greater potential for loss each time water moves through the ground. If fall fertilizer conditions are not conducive to fertilizer application, it is best to wait until spring rather than risk nutrient loss.