ISSUE 10 July 8, 2004
LATE SEASON N TO CORN AND SUNFLOWER
The week of June 23, temperatures finally favored warm season crops like sunflower and corn. Corn that looked yellow and terrible the week before suddenly shot up, turned green and acted like it was really summer. Yellowing is not always caused by lack of N. Corn that is scheduled to receive a side-dress application should receive it very soon. All supplemental N applications to standing corn should be made between the rows. Nitrogen applied over the whorl will concentrate in the whorl and result in undesirable burning, both esthetically and in lower yields. In taller corn where knifed-in applications are not possible, configure the spray boom so that the nozzles will be between the rows. Obtain a stiff drop extension and insert a straight-stream orifice nozzle into it, along with a hose that will drop the liquid further beneath the leaves. Nozzles are available that will apply most any practical rate of liquid. When figuring nozzle size, please realize that 28% is about 10.6 lb/gallon in density. The same recommendations apply to sunflower as well seeded in rows.
Some growers are concerned about the result of N leaching in certain fields where corn and sunflower are grown. Be sure that the N is really outside of the top 2 feet before spending more money on the crop. A few well-placed soil samples split into 6 inch increments and tested for nitrate will show where residual N is located. In corn, if the N is in the top 18 inches, and in sunflower, if the N is in the top 2 feet, the crop should hit the N before the critical yield. If the N has exited these depths, then supplemental N will need to be applied. During the last two weeks, rainfall to help incorporate these applications has not generally been a problem. Rainfall will again be necessary to incorporate any additional applications.
NDSU Extension Soil Specialist