Several calls have come in about adding 28% UAN with glyphosate to kill weeds and also provide a source of nitrogen to crop plants that are yellow and chlorotic from excess rain.
This is a less effective practice based on two reasons:
#1 – UAN at 1 gallon per acre does not provide enough N for restore optimal N levels for crop growth. A better strategy would be to stream UAN between roles at 10 to 30 gallons per acre.
#2 – 28% UAN does not contain sulfur to remedy antagonistic cations in spray water that can reduce the activity of glyphosate. Ammonium sulfate is required to remedy hard water. AMS and 8.5 to 17 lbs/100 gallons of water will not supply sufficient N for optimum crop growth.
For weed control from glyphosate, AMS is the preferred product. To feed N to crop plants, it is recommended to stream UAN between crop rows and 10-30 gal/A.