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N loss due to heavy rains may be less than you think

rain gauge
ASSESS N LOSS POTENTIAL: You’re more likely to see yellow corn after big rains like the one that filled this rain gauge if you applied 28% N rather than if you injected anhydrous ammonia.
The determining factors are what form you applied and when you applied it.

Heavy rains blanketed most of Indiana during the last few days of April through the first week of May. Amounts based on farmer reports vary from 2 inches in northern Indiana to over 6 inches in central and south-central Indiana to as much as 8 to 9 inches in southwest Indiana. Those numbers represent rainfall amounts observed by May 6.

If you applied nitrogen this spring before those heavy rains, your first reaction is likely that a sizable percentage of it will be lost. However, Bob Nielsen, Purdue University Extension specialist, says that may not be true in every case. It may boil down to when you applied it and what form you applied.

“If you applied anhydrous ammonia within a couple weeks before the rains, for example, there really may not be much loss,” Nielsen says. That’s because most of the nitrogen will still be in a form that isn’t easily lost.

“If soils are saturated and stay saturated, you’re not going to lose much N, even if it warms up,” he says. Once soils dry out enough that there is oxygen in the zone where the ammonia was applied, and it warms up, then conversion from one form to another can occur.

At that point, other factors may come into play. If corn was already planted before the rains, young corn may begin using nitrogen before much loss occurs.

“If you applied 28% liquid nitrogen within two weeks before the rains hit and soils became saturated, then the nitrogen will convert to the form that can be lost much faster,” Nielsen notes. “A fourth of it is already in the nitrate form which is more subject to loss when liquid 28% is applied.”

The bottom line is that if you applied 28% N ahead of large rains this spring, there may be a relatively high risk for loss. It would certainly be much higher than if you applied anhydrous ammonia, he concludes. 

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