Corn growers can cut back on nitrogen rates, Ohio expert said

If Ohio growers are just now getting their corn crop in the ground, they may be able to get away with slightly reducing their nitrogen application rates.

Robert Mullen, an Ohio State University soil fertility specialist, said growers may not have to supply as much nitrogen because of the lost top-end for yield potential typically observed for late planting situations.

"If growers have planted, say within the past five days, and they have yet to sidedress, they should consider cutting back nitrogen rates a little," Mullen said.

Growers can reduce their nitrogen rates by about 10 percent from current OSU recommendations for either a corn/soybean rotation or a corn-after-corn rotation, Mullen explained.

"Cutting back on nitrogen rates might be a good thing, assuming producers don’t have any nitrogen loss from this point forward," he said. "Producers might be a little concerned about cutting back, but our research suggests that as long as we do not get into a period of high loss potential from this point forward, they should be able to get away with a slightly lower nitrogen rate."

Warm temperatures coupled with wet weather have many producers concerned that they may have experienced loss from nitrogen already applied to their crop. The good news, said Mullen, is that soil temperatures have been cooler than normal, preventing anhydrous ammonia from rapidly converting to nitrate.

"We've been behind on our soil growing degree days, to the tune of about 100 days behind on average," Mullen said. "So these cooler soil temperatures and getting the crop in late have actually been a good thing for us as it relates to nitrogen loss potential."

However, the weather could change very rapidly with warmer air temperatures, warmer soil temperatures and the question mark of more rain, Mullen said.

"From this point forward, if we get into some really wet weather, then I'd be concerned about nitrogen losses," he said. "Producers just need to be more vigilant about watching their fields and documenting any nitrogen stress."

Mullen said there is no sure way of predicting how much nitrogen loss a field experiences, because of the number of contributing factors such as soil temperature, drainage issues and organic matter content. But he does promote a low-tech technique that may be helpful in estimating nitrogen loss.

"Essentially, it's establishing a reference area in a field and removing nitrogen as a limiting factor in that area," Mullen explained . "Then adding an additional 50-60 units of nitrogen to that reference area and monitoring it against the rest of the field. If the area looks different than other areas in the field, then it could be that nitrogen was lost during the season. It's not easy to implement, but it's one way of monitoring nitrogen losses."

Guidelines, recommendations and sampling strategies are helpful, Mullen said, but ultimately it's up to the producer to proactively scout fields, identify any potential issues or problems and implement the learned information.

According to the Ohio Agricultural Statistics Service, during the past week corn has been planted at a rapid pace. Seventy-six percent of the crop is now in the ground, a 37 percent increase from the previous week and 14 percent higher than this time last year. However, planting is still 12 percent behind the five-year average.

Corn is Ohio's most valuable field crop commodity. According to the Ohio Department of Agriculture, corn production contributes $2.1 billion to agriculture. Feed grain serves as a main component of corn production, but the crop is also becoming an integral source for ethanol.

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