Spring and fall are the best times to broadcast nitrogen, but what about winter?
Generally speaking, fertilizer should not be applied over deep snow and frozen soil, but if it must happen producers should remember there are economic losses and environmental considerations.
Producers may apply fertilizer over snow less than 10 centimetres deep only if there is no ice layer. The fertilizer granule needs to go through the snow, contact the soil and dissolve. Another option is to apply it to snow in warming conditions when the granules will be “driven” into the soil.
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Economically, if producers expect that ammonium nitrate or urease inhibitor fertilizers will be 15 percent more expensive in the spring, winter application of urea may be viable. An additional 15 to 20 percent cost advantage is required if urea is applied in the winter to account for the potential loss from runoff, leaching or volatile loss from warm weather.
Agriculture Canada conducted experiments on productivity following two types of nitrogen fertilizer applications in Lacombe, Alta., which showed that ammonium nitrate applied at 40 kilograms of nitrogen per acre doubled productivity over unfertilized forage fields in most cases, regardless of the fertilizer type or timing.
Productivity with fertilizer applied early in the winter dropped by as much as 15 percent 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 the snow had melted.
The efficiency of broadcasting nitrogen is affected by the type of fertilizer, soil properties, application timing and environmental conditions. Surface-applied nitrogen is susceptible to volatilization.
Several conditions increase volatilization potential: less than 12 millimetres of rain after application; high soil temperature; moist soil surface; high wind speed; coarse soil texture; low organic matter and soil with a high lime content.
There are also conditions that decrease volatilization potential: greater than 12 mm of rainfall after application; low soil temperature; dry soil surface; low wind speed; fine textured soil; high organic matter content and soil with a low lime content.
Ammonium nitrate is not recommended for fall application because the nitrate portion is subject to potential loss through leaching or denitrification, which is generally the largest way it is lost.
Fall nitrogen sources should be in the form of anhydrous ammonia, urea or urea with a urease inhibitor. The idea is to keep the nitrogen in an ammonium form.
