Corn yield following a delayed application of nitrogen

Delaying some of the N supplied to the corn crop is considered a way to increase N uptake and yield and to limit N losses, but the length of the delay may increase the risk of yield loss. We conducted a 3-year experiment at Urbana, Illinois in which half of the N (112 kg N ha-1) was injected as UAN at planting and the other half or all (224 kg N ha-1) of the N was dribbled UAN next to the row, at each of eight stages ranging from V3 to R3. In corn following soybean, when half of the N was applied at planting, the other half could be applied as late as R2 without significant yield loss, and application at R3 produced 92% of yield that the treatment with the second application at V3 did. Delaying application of all 224 kg N ha-1 through V15 did not decrease yield significantly, but yield declined by 12, 19 and 37% with application at VT, R2 and R3, respectively. In corn following corn, delaying the second half of the N to R3 produced 96% of the yield that the second application at V3 did, and none of the delayed timings lowered yields significantly. Delaying all the N to V9 did not significantly decrease yield, but yield thereafter decreased as the delay increased, from 11% less at V12 to 42% less at R3. Without N at planting, N needed to be applied by mid-vegetative stages to prevent yield loss, but when half the N was applied at planting, there was surprisingly little yield loss from delaying application until past pollination. SPAD readings showed that the split-N treatments were able to recover their healthy leaf color no matter how late N was applied, but with no N at planting, plants could not regain their full leaf color (or yield) if N was applied later than mid-vegetative stages. Our results indicate that even a lengthy delay in application of N can result in full yields, especially when half of the N is applied early. This application window is shortened if all of the N is delayed, in which case application should be made before plants reach mid-vegetative growth stages