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Corn Belt rains fueling soil erosion

Another storm system that brought spotty heavy rainfall and severe wind will again push back planting progress in central and western parts of the Corn Belt. But, it could be doing more than that.

According to the Iowa Environmental Mesonet, overnight storms dropped rainfall amounts up to 2 inches in parts of Nebraska and Iowa, with the system rapidly moving east Wednesday morning. Parts of Indiana and Ohio also saw rainfall amounts in excess of 1 1/2 inches Tuesday night.

"There were numerous reports of .50" to .75" rains in southwest Minnesota and northwest Iowa. A fast-moving squall line brought brief heavy rains to portions of central Iowa early this morning," said Craig Solberg, meteorologist with Freese-Notis Weather, Inc., in Des Moines, Iowa, Wednesday morning. "This weakening squall line is pushing heavy rains over south-central and eastern parts of Iowa this morning and is also covering parts of western Illinois. During the past 24 hours, many stations in central Illinois reported .25" to .75" rainfall amounts with some locally heavier rains. There were severe storms reported around Monticello, Illinois, moving into west-central Indiana yesterday afternoon and evening."

And, more is expected. In fact, Solberg says the wet trend looks to continue through the weekend, likely stalling most or all fieldwork, much to many farmers' chagrin.

"Three and a half inches in an 18-hour period has put water over the roads, big ponds in all fields and tiles now running full," says Marketing Talk contributor bullrider685114, who farms in west-central Indiana. "So much for the early start. Replanting is now a real possibility."

And, the rain isn't just keeping the planters stalled. It could be creating more trouble in the form of erosion in fields without much of last year's crop residue left on or near the surface. That danger's been higher than normal this spring because of the combination of early fieldwork progress and spotty heavy rains, according to Iowa State University agronomist and Iowa Water Center director Rick Cruse.

"I think early spring in itself has not caused more erosion," he says. "The opportunity for farmers to till sooner (apply anhydrous, for example in January or February) existed and that activity if coupled with heavy rains (and we have again had some) does open the door for accelerated soil erosion rates."

And, it's not just rainfall. "The other question to address is the increased risk that one encounters with the early warming period," Cruse adds.

Unprotected land -- like those acres prepared to plant or that have already been planted -- can be changed dramatically by rainfall, according to Iowa State University Extension field agronomist Mahdi Al-Kaisi.

"In a normal rainfall, raindrops range in size from 1 to 7 millimeters in diameter and hit the ground going as fast as 20 miles per hour. The impact of millions of raindrops hitting the bare soil surface can be incredible, dislodging soil particles and splashing them 3 to 5 feet away," Al-Kaisi says. "A heavy rainstorm may splash as much as 90 tons of soil per acre. However, the majority of the soil splashed is not immediately lost from the field. Most of the splashed soil particles don't leave the field; they clog surface pores which in turn reduces water infiltration, increases water runoff, and increases soil erosion."

If you get a rain immediately after you've planted, crusting could get in the way of emergence and early growth, too. Add that to erosion potential and it's a recipe for poor, uneven emergence.

"When rapid drying occurs, a hard crust layer can form in the top 2 inches of the soil. Soil crusting is troublesome when it develops prior to seedling emergence," Al-Kaisi says. "Additionally, soil crusts create conditions that are extremely conducive to soil erosion during following rainfall events."

So, is there anything to do at this late juncture to avoid erosion? The best thing is to avoid any additional tillage, if at all possible, until your crop's planted and emerged. If you do have to perform tillage, take a closer look at the landscape and try to avoid any major trouble spots in your fields were erosion is most likely.

"Farmers should consider the effect of any additional tillage on remaining crop residue. If residue cover should fall below 30%, adjust your field operations to minimize potential soil erosion due to early spring rain. Options for steep slope areas include cover crops, permanent vegetation, strip cropping, and planting on the contour, all of which can reduce the speed of water runoff and slow soil erosion," Al-Kaisi says. "If soil crusting occurs, consider using a rotary hoe to allow seedling emergence to occur unrestricted. The faster the crop is growing, the sooner a crop canopy will develop; a partial crop canopy is better than none at all."

Looking further ahead, Al-Kaisi recommends examining your tillage practices and, starting this year, make adjustments if you're facing a lot of erosion potential. He advises asking these question:

  • Was surface residue enough to prevent soil erosion?

  • Is the surface residue cover distributed evenly across the field?

  • Is there enough residue cover left after winter decomposition?

"If these questions can be answered no, then fall tillage passes and fall manure or anhydrous application need to be considered based on the amount of residue and the residue distribution in the field," he says. "Remember that spring is the best time to evaluate conservation systems for their impact on improving soil and water quality."

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