ST. LOUIS (DTN) -- December in Iowa isn't usually known for its flood warnings.
But with almost every river in the state swelling to near-record levels for this time of year, farmers are getting an unusually timed lesson on the dangers of exposed soils, Iowa sources told DTN.
The state had already seen more rain than usual since Veterans Day, Iowa state climatologist Harry Hillaker said. Then a slow-moving storm system dumped 5 to 6 inches across much of Iowa -- four to five times what the state normally sees in December -- in three days.
"It's the kind of rain that should open some eyes and make some people think maybe they shouldn't be doing so much fall tillage," said Iowa State field agronomist Mark Johnson.
SOIL AND NUTRIENT LOSS RISK
Fields will see varying levels of damage, depending on the farming practice, Johnson said. Recently tilled fields will be most at risk for soil erosion and nutrient loss.
Recent fertilizer applications are also a likely loss.
"Anyone that broadcast dry fertilizer on top recently and didn't get it worked in would certainly lose a lot," Johnson noted. Even those who did work it into the ground with tillage will see a lot of nutrients like phosphorus and potassium washed out of the field with topsoil. Any fall nitrogen applications that went on when soils were still warm and converted to nitrates will also be at risk of leaching, he added.
The greatest loss from the heavy rains is more permanent, however. "The biggest loss is topsoil, and unfortunately a lot of farmers probably don't realize how much they're losing," Johnson said. "And that's not replaceable in their lifetime -- it's naturally created at a much, much slower rate than it's lost."
Farmers who put down cover crops following the fall harvest will fare best, especially since mild conditions this year allowed for plenty of fall growth, both Johnson and Hillaker noted.
Not only will the root system of cover crops help keep soil in place, but the plant growth will also use any nitrogen left in the soil at the end of the growing season, Johnson said.
Cover croppers are still a small, albeit growing, percentage of the state's farmers. Johnson estimated that only 400,000 to 500,000 of Iowa's 25 million row-crop acres have cover crops planted on them.
"Maybe if farmers drive around and see damage from the last three days, that will speed up adoption," he said.
Another storm system next week promises to keep things damp in the Midwest, particularly over Illinois and Indiana, Hillaker said.
"We certainly have no worries about soil moisture going into the winter," he said. "But there's a tendency for the upper Midwest to have drier-than-usual springs on the tail end of El Nino events, so given our current situation, that would be a good thing."
But don't hold your breath. "We've had 10 consecutive wetter-than-normal Aprils until 2015, and even then, that month was just barely below normal," Hillaker added.
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