Sidedress in a Drought (06/17/21)
There is a wide range of soil moisture and corresponding corn health across the state. In a tour today (Tuesday June 14, 2021) across the eastern 1/3 of the state, good soil moisture and excellent corn growth was observed in Richland County, but nowhere else. Further north, the drier the soil became and the more distressed the corn appeared. Corn growth stage was generally from V4 to V7. Corn that received the full N rate before/at planting has enough N to complete the season. There have been no excessive rain events that would lead to leaching or denitrification. The extremely dry soil this spring would lead to little N release from surface application of urea, so unless the soil actually blew away with the N, N should be sufficient to yield whatever the corn would be capable of with whatever moisture is available.
There are fields that in normal/wet springs perform best when side-dress is applied. Those fields may have received half to 2/3 of the total N preplant/planting this spring. The question is whether to apply the remaining half to 1/3 of the total N, reduce the rate, or abandon the side-dress totally.
If the field has moisture to a couple feet in depth, then application of the remaining N would make sense. If the soil is dry, then some N application might be warranted, but probably not the entire amount from the original recommendation. The corn N calculator assumes a corn yield response with a side-dress response of about 60% efficiency. However, in dry soil my field studies indicate that side-dress, especially if dribbled on the surface or otherwise surface applied would have an efficiency of as low as 16%. That makes the cost of side-dress N in relation to yield gained almost 4 times the N cost per bushel of the original N application. As a result, a side-dress of perhaps 30 pounds of N/acre would be the maximum under these conditions that would make economic sense. An application of 100 pounds of N/acre may increase the yield another 10 bushels per acre, but the cost to do so would exceed the cost of N applied.
Certainly, unless it rains in excess late summer or into the fall, the residual soil N would be high. However, so much corn ground gets planted the next year to soybean or other legumes that these subsequent crops would not benefit from the N left over. Also, I think that in many operations there is not an over-abundance of excessive operating funds that one might risk this season, so reducing the side-dress rate in all but the most ideal circumstances would be the prudent course of action.
Corn under irrigation with fertigation capabilities should fertilize as planned, since water should not be a limiting factor if properly managed.