CENTERVILLE, S.D. - Farmers are concerned about crop loss and denitrification of fertilizer due to flooding after Mother Nature dropped several inches of rain on portions of Iowa, Minnesota and South Dakota the last two weeks. Craig Andersen farms near Centerville, S.D. and says starting the week of June 18, rain totals in his area have exceeded eight inches. This resulted in flooding along the Vermillion River and adjacent cropland.

Several of the fields in his operation now look like lakes and it's nearly impossible to determine what was planted. "Between the boys and I, 400 acres are completely under water," Andersen says.

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However, there are also many other fields that have areas of ponding that will have lower production potential. "As for yield loss and everything, we'll probably say 25 percent without much trouble," he says.

Southwest Minnesota and northwest Iowa were also hit hard with heavy rains and flooding, especially along the Floyd and Rock Rivers. Steve Abma farms near Rock Valley, Iowa. He says rain totals the last week have been nearly 11 inches on his farm and there is more rain in the forecast. He and other farmers in his area have a few hundred acres of cropland under water and there is more throughout the county.

Where the water has receded, Abma anticipates a yield hit. "I would expect somewhere the water did flow, as it's going to knock down the corn plants," he says. In his soybean fields, disease will also be an issue. "It's always a concern. When the beans are stressed a little bit they're more vulnerable," he adds.

Both Andersen and Abma says this isn't the first time they've experienced flooding on their farms, mainly due to their proximity to area rivers. "We go through this it seems like more and more. We just get some of these big rain events," Andersen says.

Abma says he has lived on his farm since he was a kid and has rarely seen the flooding this bad. "This is the second worst flooding I've ever seen only surpassed by four years ago," he says.

The losses will be partially covered by crop insurance or the farm program, but to what level is yet unknown. "Insurance maybe will cover some of it, depending on how you have it structured," Andersen says. He says those with enterprise units may do better than those with individual coverage because enterprise units are figured on the county yield. "It depends on what level of crop insurance you had and what percentage of your full operation it is, or if you have each individual field covered," Abma says. He says insurance will be the most helpful in the areas where the entire farm is under water.

The main questions farmers are asking agronomists include: How long can crops stay submerged in water before they die, and once the water recedes, how much nitrogen will be lost? Pioneer Field Agronomist Curt Hoffbeck says while soybeans can remain underwater longer than corn, neither crop can stay submerged for more than a few days without a complete loss. "For corn I have rule of thumb of two to four days, but it's highly dependent on the air temperature and the amount of direct sunlight," he says. "If it's really high temperature and direct sun, it will be more to the two days. If it's cloudy and cool, more to the four days."

Hoffbeck says soybeans can tolerate flooding better than corn. The biggest problem with soybeans after being under water is the increased likelihood of soil-borne diseases like pythium and phytopthera.

The other issue is the loss of nitrogen, but Hoffbeck says just because a field is flooded doesn't mean total denitrification. He says if farmers just got done applying urea or UAN at 28 percent, it will not all be converted to the nitrate form. "Only about 50 to 60 percent of those are in the nitrate form three weeks after application and about three-fourths of it is in the nitrate form and susceptible to leeching six weeks after application," he says.

So, not all recent applications are completely vulnerable. He says the amount of nitrogen loss also depends on soil temperature and the number of days the field is saturated. Hoffbeck says if a soil test comes back with nitrogen levels at less than 20 parts per million, farmers need to add 5 to 7 pounds per part to get back to the required level for optimum yield.