Nitrogen (N) top-dress can provide an economic return on investment, can improve N-use efficiency and can provide greater flexibility to adjust for changing growing conditions. Top-dressing N is often preferred over pre-plant applications, if:
– Changing growing conditions cause uncertainty in crop yield outlook;
– Excessive rain commonly causes high rates of N loss by denitrification or leaching; or
– Corn is showing signs of nitrogen deficiency.
Corn utilizes large quantities of N during the grand growth stage. From the 8 leaf stage through tasseling, N uptake is 4 to 8 pounds per day. Ideally the N should be applied just prior to and/or during this period of high N demand. While most of the N uptake occurs during this period of rapid growth, many new corn hybrids continue to take up significant amounts of N well into the grain-fill period.
Some primary advantages of a delayed N application are:
1. Applying N closer to the time of crop demand usually increases utilization of the fertilizer by the crop;
2. Delaying application of part or all of the N reduces the exposure of fertilizer N to loss mechanisms;
3. Less delay in planting by using the available time for planting when conditions are right. (This is especially important in wet springs where timing is critical and N loss may be high.); and
4. Flexibility to adjust for changing growing conditions and yield potential.
ESN & Use Recommendations…
Top-dress ESN applications can be used to supply the large mid-season N demand of corn and may provide better synchronization of N release with crop N demand of full-season hybrids.
Apply 10-25 per cent of the total recommended N before or at planting. Top-dress the remaining N as a blend of ESN and soluble N fertilizer (such as urea or ammonium sulfate). ESN should comprise about 50-80 per cent of the N in the blend for applications up to V6 growth stage. ESN may be applied up to the V10 growth stage. For applications at V8-V10 growth stage, ESN should not exceed 50-70 per cent of the total N in the blend.
Top-dress ESN applications can be used to supply the large mid-season N demand of corn.
Apply N at recommended rates in a blend with ESN comprising 50- 80 per cent of the total recommended N up to the V6 growth stage. Applications up to the V8 growth stage are possible with a small amount of soluble N applied before or at planting to reduce early N deficiency.