Keeping Nitrogen in the Corn Root Zone

As growers prepare for spring nitrogen applications, it’s important to keep their investment in nitrogen fertilizer in the soil where plants can use it. Wilbur-Ellis agronomy experts like Robb Mohr help growers boost yields and get the most value from their fertilizer investment. He talks about the best ways to keep nitrogen in the root zone.

“We do the 4 R nutrient stewardship. Make sure we’re putting the right rate down. You know, the right source. How are you planning on applying it? Are you going to use liquid UAN? Are you using an anhydrous ammonia or a dried prilled urea? Application timing, we want to spoon-feed this crop, trying to put the nitrogen down as close to the time when that plant needs it. And you know we’ve got a long growing season, and sometimes just putting it all out early or putting it all out in the fall, is there enough that’s left there for that plant to take up? Of course, the right product which, again, we’ve talked a little bit there earlier with the source. Having the right product down for what you’re shooting for.”

A soil test is a great idea to determine how much of last year’s nutrients remain in the soil going into the new season. He says it’s important to make sure the nitrogen is available when the plants need it.

“When we talked about spoon-feeding nitrogen or giving it to the plant when it’s needed, depending on your soil CEC, your Cation Exchange Capacity, that soil is only capable of holding so much nitrogen. So, when you’re thinking about applying, and you look at your soil test, and you’ve pulled your soil tests for what was available in the spring, also look at that CEC number. And then you don’t want to over-apply nitrogen from what your soil is capable of holding. Soil can hold 10 times the amount of your CEC number can hold nitrogen. If your CEC is 12, you can hold 120 pounds of nitrogen. If you take a soil test and you took a nitrate test and you see there are 30 pounds of nitrogen out there, then that soil can only hold another 90 pounds. So, to try to go out there and apply 150 pounds, 200 pounds, a lot of times that soil can’t hold it, and that just leads to leaching or runoff of nitrogen.”

Other keys include split-applying nitrogen when the crop needs it most, such as corn during the ear-set and fill stages. It’s also a great idea to use nitrogen stabilizers. Mohr talks about where nitrogen losses are most likely to occur.

“If we apply nitrogen at the top of the soil and we don’t get it worked in, we can have volatilization and be losing all that. We can also have runoff. So, if you get big rains after you apply nitrogen, literally it can leave the field just by the water leaving the field and you can have quite a bit of runoff. When ammonium turns to nitrates, it’s a negative charge, and our Cation Exchange Capacity is negative as well, and so what you end up doing is it tracks and pushes it down into you know what could be into the groundwater or into your tile lines. And lastly, in saturated soils, you can have denitrification, and that gives that nitrogen off as a gas into the atmosphere.”

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