Answers are from the Indiana certified crop adviser panel: Betsy Bower, Purdue Extension senior research associate, West Lafayette; Abby Horlacher, Nickel Plate Consulting, Frankfort; Brian Mitchem, Farmer 1st Agronomy Consulting Services, Decatur; and Dan Quinn, Purdue Extension corn specialist.

 

My son’s agronomy professor says more folks are making late-season nitrogen applications. How do I determine if it is worth it?

 

Bower: The professor is correct. The Y-drop applicator has improved placement of late-season nitrogen near roots. However, even with the Y-drop applicator, it still takes rainfall to move nitrogen into the soil.

 

Some advantages to splitting nitrogen applications into a starter, sidedress and late-season application would include improving nitrogen use efficiency and providing less exposure to soil nitrogen loss from leaching and ponded soils after heavy rainfall. When we apply layers of nitrogen through the growing season, we reduce the total nitrogen load at any given time, reducing the amount of nitrogen subject to loss.

 

Late-season nitrogen fits soils prone to loss, like excessively drained and poorly drained soils. One inch of rainfall can move nitrogen 12 inches in excessively drained soils. In sandy irrigated fields, farmers apply upward of five layers of nitrogen and are typically rewarded with high yields.

 

There is no hard-and-fast rule on when to make the additional application, but typically it would be within two weeks of tassel to early after tassel. Layer in nitrogen right before the plant would need it. Consider 30 to 40 pounds per acre for the late split.

 

Horlacher: The first step is to assess current nitrogen availability. Conduct soil tests for nitrate and organic nitrogen, as well as a plant tissue analysis to evaluate nitrogen content within the crop. If results indicate low nitrogen levels in the soil, proceed with a nitrogen application. Leave a few untreated control blocks across different soil types. At harvest, these control plots can be compared with treated areas using yield data. This allows for evaluation of economic benefit derived from late-season nitrogen.

 

Mitchem: Modern corn hybrids utilize nitrogen in greater quantities starting during the rapid growth phase around V10 through reproduction. We should use as low amount of nitrogen at planting as we are comfortable using and apply the balance later. At planting, a minimum of 20 pounds of nitrogen or 7 gallons of UAN per acre is adequate for early growth and development in corn rotated from beans.

 

Rapid uptake begins at V12, with leaf concentration maximizing at tassel. Total in-plant nitrogen maximizes at R5. To make midseason nitrogen applications available at V12, apply at V10. Applications with a Y-drop system have shown promise in delivering nutrients with this timing.

 

In my experience, we only show consistent returns when we apply nitrogen late if we have experienced nitrogen loss. However, I see more consistent returns when we include other nutrients along with nitrogen at V6 through V10. Consider including boron, sulfur and water-soluble potassium.     

 

Quinn: We typically do not see any additional benefit from a late-season nitrogen application in V10 through V14 beyond just a typical sidedress application of nitrogen at V3 through V5. If we run into scenarios where we have excessive rainfall and expect nitrogen was lost, then a late-season application can be beneficial. However, it typically does not provide any additional benefit.

 

We often see the most benefits from split applications of nitrogen beyond just a single application prior to planting. Many folks have moved away from late-season nitrogen applications in recent years, except for those with the ability to fertigate and where a late application is warranted.