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Corn+Soybean Digest

More H20=Less N

If measuring nitrogen (N) loss or denitrification during an ideal growing season proves challenging, then judging the effects of extreme moisture on N loss is an even greater challenge.

And, if any corn producer can speak to extremely wet growing conditions, it's Cal Dalton, a first-generation farmer with approximately 2,200 acres of corn, soybeans, wheat, oats and hay that stretch from Pardeeville to Endeavor, WI.

His season began wet as his area received 122 in. of snow — five times the regular amount. “All the snow recharged the water table before the rain started,” he says. “We started out slow in planting because we were getting stuck, even on high ground. One day in June, it rained 8 in. over three hours.”

When the rain hit, Dalton says the corn was up with about two leaves, and he had most of his fields sprayed. “Luckily, the 25 gallons of 28% (N) that I sprayed in the early spring had been absorbed by the corn crop by the time the rains started,” he says.

Normally, he would have applied a sidedressing from mid-June to July, but with the wet fields he was forced to wait. “We went in the fields in July and faced tall, green corn. Normally, we try to get in when the corn is about knee high with seven leaves,” says Dalton.

“We couldn't get to some fields because of washouts. We were surprised to see live, yellow sprouts when the water receded from fields where it stood for five to seven days,” he says.

Judging his fields in early August, he hoped to average 40 bu./acre.

Joe Lauer, corn agronomist with the University of Wisconsin, has worked in Dalton's area for 15 seasons. “Any time you have plants underwater for longer than 48 hours, you can start to have a basic lack of oxygen,” says Lauer.

He continues to explain that poor aeration causes cell death and eventually root death. Short-term reductions for root and leaf growth rate begin immediately within 1-12 hours, but tend to recover within a few days.

In his recent piece, “Flooding Impacts on Corn Growth and Yield,” Lauer cites Ashraf and Rehman who wrote, “Almost immediately leaf elongation ceases and N, P (phosphorus) and K (potassium) concentration in leaves decrease, but in roots N, P and K concentrations increase. Flooding restricts root growth in the upper 18 in. of soil, but root elongation continues in deeper horizons.”

DESPITE ALL THE moisture, the 2008 season has been the second wettest and coolest season on record behind 1993. By late summer, Lauer reported the corn was doing well, and it was too soon to know the effects of denitrification. “While the plants can stand the water for a short time, this year the water just hasn't receded.”

Meanwhile, the picture down south looks different for farmers like Don Glenn. Even with all the rain in his north Alabama area, which is considerably wetter than last year, Glenn says only one month has recorded above-normal rainfall. June and July were dry.

Glenn, a fifth-generation farmer who currently serves on the Alabama Soybean and Corn Association board, farms 2,000 acres in partnership with his brother Brian. He reports that his 450 corn acres will yield 75% of average due to dry conditions.

Glenn reports that the plants aren't absorbing N as much as during wetter times, and after last year's severe drought, he expected some carry-over. “We look at yield history to determine future application rates. We cut back on the wheat this year expecting carry-over from last year.”

Trying to judge N levels has been difficult for Dalton, who believes that his no-till/minimum-till practices and his multiple-application process helped save some of the soil fertility. Going into harvest, he predicts the uneven moisture rates will make combining the corn even more difficult.

And Joe Lauer agrees. “Growers need to be concerned with the unevenness of the corn crop at harvest. Crops are very uneven from the moisture, and now the concern is drydown and uniform moisture,” says Lauer.

Another problem Lauer predicts involves the amount of soil that has splashed onto the plants. “They are more predisposed to diseases,” he says.

As the season winds down, producers in extremely wet areas may not know the full effects of the moisture until next season.

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