If your sprayer is equipped with Y-drops or a similar system to make nitrogen applications in tall corn, you could add more nitrogen even at R1. People have experimented with this approach in recent years. But just because you could do it, should you? Especially if corn is green and not showing signs of nitrogen deficiency?
Information provided by South Dakota State University Extension in its iGrow series indicates that corn typically takes up “a large percentage of its nitrogen from V6, or about 10 inches tall, to R1, or silking. During this stretch, studies indicate newer hybrids require as much as 8 pounds of nitrogen per day for maximum productivity.”
So, is there still enough need for nitrogen during grain fill to justify a late-season, planned application around R1? Dan Quinn, Purdue Extension corn specialist, and Mark Licht, Iowa State University Extension cropping systems specialist, provide insights while addressing this real-life scenario:
We’re in a high-yield environment with 180 pounds of N per acre down near planting. Corn is at R1. The preseason plan was to add 40 units of N now using Y-drops. Corn prices are still low. Will we lose any N applied now? Overall, will it pay?
Quinn: First, determine the recommended nitrogen rate for your region. In Indiana, find Purdue’s N management guidelines. Elsewhere, utilize the N recommendation guidelines for your state.
In many high-yield environments, especially those with high organic-matter soils with strong nitrogen mineralization potential, 180 pounds per acre of applied N is often sufficient to support high yields. If there are no visible signs of N deficiency, applying an additional 40 pounds of N per acre at R1 using Y-drops is unlikely to provide an economic return. That is particularly true with low corn prices.
However, if deficiency symptoms appear or if local recommendations suggest a higher economically optimum N rate than 180 pounds, a supplemental application at R1 could still be justified. Corn can still respond positively to additional N as it enters grain fill if additional N is required. The primary risk with a surface-banded application using Y-drops is N loss via volatilization, especially in warm, dry conditions. To minimize risk, consider using a urease inhibitor to help protect N until rainfall or irrigation facilitates uptake.
In summary, assess crop health, local N recommendations, and potential yield response before proceeding. If the crop shows no N stress, another application may not be warranted. But if there's evidence of deficiency or higher N demand, the planned application may still be economically viable.
Licht: N applications at pollination aren’t always required. While the plan may have been to add another 40 pounds of N per acre, looking for N deficiency symptoms and leaf color may be a good indicator of whether additional N is needed. If there is no leaf firing, and leaf N concentration and/or chlorophyll leaf index does not indicate a deficiency, there likely would not be a benefit from additional N application.
Look for some signs of N deficiency. These include traditional firing of leaves. If present, then another 10 to 20 pounds of N per acre may be warranted. Lower corn prices also justify a reduced N application rate.