Wet spring and fertilizer
Flooded fields are forcing some farmers to re-evaluate their fertilizer options because of potential losses from fall-applied nitrogen fertilizer.
John Harapiak, manager of agronomic services with Westco, said many farmers have questions regarding risk of fertilizer loss under flooded or extremely wet conditions.
“The risk of loss with fall broadcast fertilizer is the most serious,” said Harapiak. “If the fertilizer was broadcast applied, most of the ammonium will have been converted to nitrate which can readily be denitrified under flooded conditions, and a significant portion of the fertilizer nitrogen could be lost to the atmosphere.”
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The cooler the conditions, the slower the denitrification process; conversely, the warmer it is, the faster the conversion to gas.
Harapiak said it is possible to lose two to three pounds of broadcast fertilizer a day in very wet conditions. In the worst-case scenario, more than half of fall broadcast fertilizer can be lost. Under these conditions, soil nitrogen (i.e., the portion detected by soil testing) is also very vulnerable to serious denitrification losses.
Westco studies show that in the case of ammonia or urea fertilizer banded late in the fall, the conversion process is much slower and as a result, losses are minimal. A higher degree of conversion to nitrate with early fall-banded urea fertilizer resulted in losses in the 10 percent range under very wet soil conditions.
“In the case of flooded fields, these losses are worth noting because they can cause significant loss of yield potential. In many cases they need to be corrected at seeding or with top dressing after the crop has been seeded,” said Harapiak.
Not enough time
A separate but related concern arises from the fact that cooler spring temperatures have delayed seeding and compressed the growing season. This may force some farmers to directly proceed with seeding rather than first applying the usual spring band application of fertilizer.
Harapiak suggested applying extra N fertilizer in the seed row can be effective for cereal crops providing the safe rate is not exceeded.
Cereal farmers need to take into account the influence of seedbed use when determining how much fertilizer can be applied in the seed row. The wider the opener and the narrower the shank spacing, the more N can be applied in this manner.
Harapiak cautioned that canola and flax have lower tolerance for seed row nitrogen than cereals, and extra nitrogen should not be applied at all in the seed row with peas.
If enough fertilizer can’t be applied at seeding, Harapiak said one option worth considering is using narrow openers to band ammonia after seeding, providing the crop has not emerged. If the crop has emerged, it is too late to use this approach.
For most farmers whose field operations are significantly delayed, the most practical option is to simply broadcast N fertilizer just before seeding.
Fertilizer N can also be broadcast after the crop has emerged up to the late tillering stage. However, this option will be most effective if some of the nitrogen has been placed with the seed and the balance top-dressed later.
Help is available for farmers who need to determine a safe rate of seed row N for cereal crops under their specific soil conditions and type of seed opener being used. Westco has published guidelines for determining a safe rate of seed row N.
– Westco Fertilizer
