The best time to broadcast fertilizer depends on environmental conditions and the seasonal growth patterns of plants. Both spring and fall fertilizer applications have advantages.
Fall application is most common and tends to have more favourable field conditions and lower costs and can help offset time constraints in the spring. However, spring application has fewer losses and the option of adapting to the conditions. The critical factor is early season nitrogen supply.
“Fertilizer should not be applied over snow or frozen soils,” said Karla Bergstrom, an Alberta Agriculture crop specialist.
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“In situations where there is no alternative to applying over snow, producers should understand that there can be considerable economic losses depending on environmental conditions.”
For winter applications to be considered economically wise, a 15 to 20 percent cost advantage is required if urea is applied.
To be environmentally responsible, broadcasting is only recommended in late fall or early winter if fields are not frozen and snow cover is minimal: less than five centimetres.
Bergstrom said productivity experiments at Agriculture Canada’s research centre in Lacombe, Alta., using two types of nitrogen fertilizer applications found 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 done in early spring,” she said.
“Applications before fall snowfalls were more beneficial than winter applications on top of snow. Yields were the best when fertilizer was broadcast in the spring after snow melt.”
The type of fertilizer, soil properties, application timing and environmental conditions influence the efficiency of broadcasting nitrogen. Surface applied nitrogen is susceptible to volatilization and efficiency comes from reducing this gassing off.
When loss potential is low, urea (46-0-0) will produce satisfactory results. When loss potential is high, it is important to select a fertilizer with lower susceptibility to volatilization, such as ammonium nitrate (34-0-0), or use a urease inhibitor.
When there is a potential for high volatilization, losses typically range between 10 and 15 percent over one to seven days and may be greater if rain does not move nitrogen into the soil. If fertilizer is applied in the fall, ammonium nitrate or urea with a urease inhibitor is the best form of nitrogen to apply.
Further information is available in the fact sheets Fall-applied Nitrogen: Risks and Benefits (Agdex # FS542-11) and Native Range Fertilizer Guide (Agdex # FS130/541).
