What are the benefits of fertilizing in the fall instead of the spring?
Some producers feel that fertilizing in the fall has some advantages. These include reduced fertilizer prices and a workload that is more evenly spread out throughout the year.

What are the concerns with fall fertilization?
If not managed properly, there can be nitrogen losses with fall fertilization. Denitrification is the primary loss mechanism of fall-applied nitrogen. This occurs when nitrate is converted to nitrous oxides or nitrogen gas, which is then lost to the atmosphere. Denitrification can happen quickly in water logged soils, which typically happen in the spring after the snow melts.

What can I do to limit denitrification?

  • Use ammonium-based fertilizers such as urea or anhydrous ammonia.
  • Band the fertilizer. Concentrated bands of urea or ammonia will inhibit nitrifying bacteria, and can delay the conversion to nitrate (nitrification).
  • Fertilize in cool temperatures. The soil temperature at fertilization depth should be less than 10°C during mid afternoon.

Can you use anhydrous ammonia in the fall, even if it is dry?
Ammonia retention is not totally dependant on soil moisture. Clay and organic matter in the soil will retain ammonia in dry conditions. As long as the soil flows around the opener and seals, losses to the atmosphere should be minimal, even in dry conditions. In dry, sandy soils with low organic matter, anhydrous ammonia may need to be applied deeper than usual to help prevent losses to the atmosphere.

Can I use ammonium sulphate fines as a nitrogen source for fall fertilization?
Ammonium sulphate fines can be used as a source for nitrogen as long as the amount of sulphur being applied is taken into consideration. Using ammonium sulphate as the sole source of nitrogen can overload the soil with sulphur. Apply no more sulphur than the requirements for the next three years of cropping.

Is fall really the best time to apply elemental sulphur?
Yes, fall is a good time to surface apply elemental sulphur. Fertilizer pastilles need to be exposed to precipitation and freeze/thaw cycles to be physically broken down. Spring field operations will further degrade and disperse the particles so microbial oxidation to sulfate can occur.

Fall Applied Nitrogen

Prepared by Lisa Adam, Ag-Info Centre, Alberta Agriculture and Rural Development.