Most wheat fields in North Dakota are in the 3-5 leaf stage and have some yellow in them, especially in areas receiving near record May rains. Now is a good time to stream UAN and maybe a little ammonium thiosulfate or ammonium sulfate solution to avoid a large protein dockage and perhaps protect yield. Application of N/S would best be done sooner rather than later. Stream nozzles can also work, but greater wind speeds break up the stream pattern sooner with nozzles than stream bars. Adding ammonium thiosulfate to the mix increases the severity of any leaf splash under high wind conditions. Be sure the yellowing isn’t due to disease or another condition. This is another case where a crop consultant can be a great benefit and help confirm the probable causes of a poor crop.
Corn is yellow mostly because the soil is still cold (put your hand in the soil- it feels like an icebox), the wind is beating the young plants up, and the lingering effect of frost(s) still takes a toll. Growers should be patient with the corn until it approaches V-5, then assess whether N/S is a problem and take remedial action. Until then, patience should be the rule.
In both conditions, it makes no difference to the plant what form of N is used as long as the plant can get to it. Avoid low-rate slow-release products on wheat, not because the products are not effective if used at similar N rates to UAN or urea, but because they are no more efficient in wheat uptake than UAN or urea and can be as much as 8 times higher in cost. The smart money is on more traditional products for yield and protein increases.