Subsoil moisture in Iowa has recharged with consistent heavy rainfall

By Jared Strong

Despite drier-than-typical conditions last week in Iowa, the abundant rainfall of preceding weeks has continued to percolate into deeper soil that can be important for crop growth, according to the U.S. Department of Agriculture.

About 92% of the state’s subsoil has adequate or surplus moisture for growing crops. That is a modest increase from the USDA’s report last week and is more than double the percentage of a year ago.

Further, while the state recently pulled out of drought after nearly four years, some areas have subsoil that is close to its maximum water saturation.

A recent Iowa State University Extension and Outreach survey of subsoil in northwest Iowa — which it has done twice a year for seven decades — shows that there was more than 10 inches of moisture in the soil near Calumet, Ireton, and Sibley. Iowa soil typically holds a maximum of 10 to 11 inches of moisture in the first 5 feet of depth.

Each of those areas has about five times the amount of soil moisture they did less than two years ago.

Corn and soybeans can grow roots that are many feet deep, and although most of their water is typically absorbed closer to the soil’s surface, deeper water is more stable and can act as a safety net against streaks of dry weather. Topsoil moisture can fluctuate more quickly and is susceptible to wind, heat, and low humidity.

A U.S. Drought Monitor report on Thursday shows that for the second straight week there is no area of Iowa suffering from drought. However, about 23% of the state — mostly in the northeast quadrant — is abnormally dry. That is a slight decrease in area from last week’s report.

There was an average precipitation of about 0.74 inches last week, compared with a normal of 1.08, according to a USDA report. But rainfall varied greatly: Orange City had about 4.35 inches and Pella had 0.03.

A recent report from the federal Climate Prediction Center projects that none of Iowa will develop drought again through at least the end of August.

As of Sunday, about 92% of the state’s corn crop had been planted — about five days behind schedule — along with about 84% of soybeans.

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