Still Dry 4 Feet Down

Missouri's soil hasn't recovered from last year's drought

BucketThe heavy Midwest snowfall this winter wasn’t enough to recharge the soil with enough moisture for a bumper crop next season, a soil scientist says.

Randall Miles, associate professor of soil science at the College of Agriculture, Food and Natural Resources, University of Missouri, said soil in much of Missouri is still dry four to five feet down where the crop roots live. Without enough moisture and nutrients, crops produce poor yields.

Four to five feet down is an improvement from a year ago when two years of drought left many prime growing areas bone dry to almost six feet. Miles has been observing the depths of soil moisture around the Midwest.

Soil moisture recharge is a process where water from rain and snow moves downward from surface water and fills in the pore space found in soil. The soil is recharged naturally by rain and snow melt. Much of the recharge comes from winter snows and spring rains.

Randy Miles.Randy Miles.

Even with dramatic snowfalls, much of the moisture ran into streams and rivers and not into the earth. “We estimate that half of moderate or heavy rain or snow ran off and didn’t penetrate into the soil,” Miles said. “Ideally, we needed a long-term drizzly kind of rain or snow to replenish the soil for it to have enough residual moisture available for use at planting and harvest.”

Miles said moisture near the surface can evaporate with just a few days of high winds, higher than normal temperatures, low relative humidity or a combination of the three. This can also prevent moisture from having a chance to move deep into the soil where it is needed. He pointed out that when Hurricane Isaac in 2012 dropped large amounts of rainfall, the soil recharge only went down to a few inches.

“People think that if we get a few good rains or snows that the problem is solved,” said Miles. “We’ll need extraordinarily persistent rains for the moisture to get down five feet where the roots of mature plants live. It could take many weeks and months for water entering the soil surface to move into the three to five feet depth of the soil profile,” he said.

Miles said it could take another year of good rains and snows for the soil to get back to normal moisture levels. It will also take that long for beneficial microbes and insects to recover, Miles said. “The soil lives in a balance of water and biological activity,” Miles pointed out. “The deep drought has disrupted a comprehensive hydraulic recharge.”