Farmers frequently ask Ross McKenzie about the effectiveness of fall versus spring nitrogen applications.
“Fall fertilization can range from very effective to disastrous, depending on soil moisture conditions, the form of nitrogen fertilizer and how it’s applied,” said the Alberta Agriculture agronomy research scientist.
McKenzie said problems can occur even if everything is done correctly.
The three main considerations are waiting until the soil temperature is less than 7 C, using the right form of nitrogen fertilizer and banding it to minimize soil-fertilizer contact to slow the nitrogen conversion.
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“In terms of fertilizer management, no soil type or region of the province is completely safe when it comes to losses of fall-applied N,” McKenzie said. “In most years, N losses through denitrification in southern Alberta are relatively small and fall banded N is usually 90 to 100 percent equally effective to spring banded N.
“In cases where spring banding causes a significant loss of seed bed moisture, fall banding can be superior to spring banding.”
However, McKenzie cautions that fall application puts nitrogen at risk, depending on localized moisture and temperature.
He said general guidelines about nitrogen timing and application methods should be considered:
• Spring banded is generally the most effective method.
• Fall banded nitrogen can be as effective as spring banded if there is no extended period of saturation in the spring.
• If lack of seed bed moisture is a concern, fall banding may be more effective because spring banding dries the soil.
• Fall application is probably not a good option on soil that tends to be saturated with water for extended periods in the spring.
• Soil test to determine optimum fertilizer rates. Producers should sample zero to six, six to 12 and 12 to 24 inches to determine cumulative nitrogen down to two feet.
• Select a formulation that is right for your conditions. Generally, under low risk conditions, such as those in southern Alberta, anhydrous ammonia (82-0-0) or urea (46-0-0) perform equally well when fall banded. However, soil in southern Alberta tends to be alkaline, and losses through ammonia volatilization can occur if the bands are too shallow or soil is dry and cloddy.
• Avoid products that contain nitrates on soil that tends to be saturated in the spring to avoid leaching losses.
• Apply fall nitrogen after the soil temperature has dropped below 7 C and the nitrification process has slowed down.
• Always band nitrogen. Don’t broadcast it. Banding restricts the contact between soil and fertilizer so over-winter losses are lower. McKenzie said applying fall nitrogen has several benefits:
• A field operation is eliminated in the spring allowing earlier planting.
• Availability of product and application equipment is often better in the fall. Fertilizer prices and payment schedules tend to be more favourable as well.
• Soils tend to be drier in the fall, so nitrogen application equipment is less likely to cause compaction.
