Despite snow and rain, deeper soil remains too dry for crops

Friday, March 8, 2013 | 6:00 a.m. CST; updated 6:56 a.m. CST, Friday, March 8, 2013

COLUMBIA — Rain and snow this winter have provided much-needed moisture to central Missouri topsoil, but scientists say the above-average precipitation hasn't reached the deeper soils that crops and plants depend on.

A layer of soil in Central Missouri called a clay pan, which is hidden two to 10 inches beneath the topsoil, provides a reserve for plants in the toughest days of summer. MU soil scientists say these deeper soils have been running a water deficit since the winter of 2011-2012.

Tim Reinbott, superintendent of MU's Bradford Research and Extension Center, said the rain and snow this winter will help the topsoil but haven't been enough to permeate the clay-pan subsoil.

Reinbott said the top three feet of the subsoil in Central Missouri, which he uses to measure for moisture, is fully charged when it contains six inches of water. At this time, he said, that moisture content is only about two inches. 

The 6.29 inches of precipitation recorded at Columbia Regional Airport since Jan. 1 was 1.6 inches above normal. But Reinbott said the rain and snow arrived so swiftly in central Missouri that it will create a "perched water table" above the clay pan where the upper layers of soil will be so full of water that additional rain will run off.

MU soil professor Randall Miles said that to overcome the dry conditions, it would take more than two years of 10-plus inches of precipitation above Columbia's annual average of 42.6 inches from 1981 through 2010. It would be ideal, he said, for rains to continue this spring before "the faucet is turned off for about six to eight weeks" in early July.

Jason Hubbart, a forest hydrology professor at MU, agreed the recent moisture won't be enough to replenish moisture deeper in the soil. He said plants and crops in Central Missouri stretch their roots three to six feet and can depend on the deeper reserve to make it through the heat of summer.

The latest U.S. Drought Monitor showed the recent moisture has improved conditions in Boone County. The severe drought classification for the southern half of the county was removed, leaving the entire county in moderate drought.

"Snow water equivalent of the snow pack is in the two to three inch range, so warmer temperatures should yield considerable benefit to well depths and pond/lake levels in the days and weeks ahead through melting," the drought monitor summary for the Midwest reads.

A seasonal drought outlook from the Climate Prediction Center for March 7 through the end of May shows no drought in roughly the eastern half of the state with improved conditions for the western half.

Making predictions about the future of soil moisture can be as difficult as forecasting the weather.

The land and the soil work on their own schedule, Reinbott said. “Nature doesn’t know when one year ends and another begins, but it’s amazing to see how to keeps itself going," he said. "We’re here trying to see what we can do to help it along.”

Supervising editor is John Schneller.

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