In many areas of the Midwest, less fertilizer was applied last fall and winter than normal and applicators have many unfilled orders.
Nitrogen application for winter wheat is urgent. Spring topdress applications should be completed by April 15 or prior to jointing. In other words, there's a lot of fertilizer to be applied.
Broadcast application of phosphorus for corn is behind schedule. However, unless soil test phosphorus is very low and a choice must be made, Charles Wortmann says nitrogen application should have priority over phosphorus application.
The University of Nebraska fertility specialist says low nitrogen availability is likely to constrain corn yield much more than low phosphorus availability. Given the 2009 high yields and current wet conditions, he says soil nitrates are likely low.
If we have a wet spring, Wortmann says you consider the following seven points regarding nitrogen application for corn.
- Delay applying most or all nitrogen to fields that are prone to flooding and/or waterlogging until after planting, then sidedress.
- For other fields, apply 20% to 40% of the nitrogen pre-plant or at planting and the remainder in-season to get the most efficient use of nitrogen, especially in wet springs.
- The advantage of in-season application is expected to be greatest in wet springs and on sandy soils since loss is minimized.
- Sidedress application allows for more accurate assessment of actual crop nitrogen need than a pre-plant application.
- Surface application of urea or UAN on crop residues creates a risk of significant nitrogen loss and could result in having less than the economically optimal nitrogen supply for the crop. Consider using an effective urease inhibitor or controlled release nitrogen fertilizer if you’re surface applying on good residue cover and you don’t expect more than 0.6 inches of rain or irrigation in the 4 days after application. Injection of UAN eliminates risk of nitrogen loss to volatilization.
- There is a risk that a field may be too wet for sidedress application this year, but that risk appears to be much more of a concern in the eastern Corn Belt than the western Corn Belt. A controlled-release nitrogen source applied pre-plant or at planting is an alternative to sidedressing.
- Similiarly, with a wet spring, there is a risk of needing to fertigate for the sake of nitrogen application before the crop needs irrigation.