When is the best time to broadcast fertilizer, spring or fall?
The best timing will depend on the environmental conditions and the seasonal growth patterns of the plant. There are advantages to both spring and fall fertilizing, but early season N supply is critical. Fall applications tend to more favorable field conditions, lower costs and offset time constraints in the spring. Spring applications may be subject to fewer losses of nitrogen and allow producers the option of adapting to the conditions (for example: wet conditions verses dry conditions).

Can I apply nitrogen over the snow?
Fertilizer should not be applied over deep snow or frozen soils. However, if it has to be applied over the snow producers should keep in mind that the fertilizer granule needs to go through the snow, contact the soil and dissolve. It is also important to recognize there are economic losses and environmental considerations. Growers may apply fertilizer over snow that is less than 4" deep only if there is no ice layer. Apply to snow when warming conditions are such that the granules will be "driven" into the soil. Economically, if you expect that fertilizers will be 15% more expensive in the springtime, winter applications of urea may be viable. An additional 15-20% cost advantage is required if urea is applied in the winter to account for the potential loss from run-off, leaching and volatilization loses that can occur with Alberta chinooks. (Source: Dowbenko, 2005)

How much production will I lose by broadcasting over the snow?
Experiments on productivity following two types of nitrogen fertilizer applications were conducted by Agriculture and Agri-food Canada in Lacombe. They showed that ammonium nitrate applied at 100 kg N/hectare doubled productivity over unfertilized forage fields in most cases, regardless of the fertilizer type or timing. Early winter applications of fertilizer appeared to be the worst. However, productivity with fertilizer applied early in the winter dropped by as much as a 15% over the same application occurring in early spring. Applications before fall snowfalls appeared to produce more than winter applications on top of the snow. Forage yields were still the best when fertilizer was broadcast in the spring after snowmelt.

What conditions effect volatilization?
Type of fertilizer, soil properties, application timing and environmental conditions influence the efficiency of broadcasting N. Surface applied nitrogen is susceptible to volatilization and the efficiency comes from reducing this gassing off.

High Volatilization Potential Low Volatilization Potential
Less than one half inch of rainfall Greater than one half inch of rainfall
High soil temperature Low soil temperature
Moist soil surface Dry soil surface
High wind speed Low wind speed
Coarse soil texture Fine textured soil
Low organic matter High organic matter content
High lime content (calcium carbonate) Low lime content
(Source: Sherritt Fertilizers)

What form of nitrogen fertilizer is the best to broadcast in the fall?
Fall nitrogen sources for broadcasting should be in the form of urea or urea with an urease inhibitor. The idea is to keep the nitrogen in an ammonium form. (Source: Dowbenko, 2005)

Fall-applied Nitrogen: Risks and Benefits