By Dave Franzen
With the logistics of the planting season and wetness of fields, getting anhydrous when needed may be a problem for some growers.
In some years, alternative N sources are very costly in comparison. This year they are not as much. Differences between in-season purchased anhydrous and urea, for example, are likely only 5-7 cents per pound of N. Differences between anhydrous and UAN may be as little difference as 12 cents per pound of N. If a grower purchased anhydrous prepay, they may be stuck with that as their only choice unless the retailer is flexible enough in their purchasing that they can allow trading out pre-pay dollars for anhydrous for another product. Sometimes this is possible, but at other times due to what the retailers paid and when it is not possible. Keep in mind that side-dressing is always possible in row-crops if the soils are suitable. This year, soils may not be suitable in the high clays for anhydrous side-dressing, but they would be with streamed or coultered UAN.
Timing between anhydrous application and seeding
There is no really safe time to seed following anhydrous application. The old rule-of-thumb was to wait a week. I have seen seed injury from shallow-applied fall anhydrous in the spring to small grains in some years. The best strategy is to apply the anhydrous at a slight angle to the intended planting direction and then seed whenever you have the opportunity. Anticipate a small loss in stand, so increase seeding rate about 10% to compensate.
Soybeans on land with N applied
In some fields, soybeans may be seeded to land with N applied last fall. High residual soil nitrate can increase the incidence and severity of iron deficiency chlorosis (IDC). In these fields with high residual nitrate, consider seeding the soybeans in wider rows (22", 30") rather than solid seeded. In addition, or in the lack of a wider row option, consider a companion oat cover crop. Oats will help to dry the soil, which itself decreases IDC, but oats will also take up some N. Trial results in trials in South Dakota, North Dakota and Minnesota have shown a decrease in IDC when an oat cover crop is used. This strategy works best with glyphosate-resistant soybeans. Kill the oats out no later than the 5-leaf stage. If the weather turns dry (we can only hope) then kill the oats out earlier. Planting about one bu/acre of oats should be enough.
-- Franzen is a NDSU Extension soil specialist.
Source: ND Crop Pest Report