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Spring Brought Notable Subsoil Moisture Benefit in Western Corn Belt

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Root-zone moisture in the Western Corn Belt is almost entirely recovered to normal levels compared with April 1, when dryness covered much of the region. (NASA GRACE project graphics)

The Western Corn Belt has seen a big turnaround when it comes to soil moisture this 2024 spring season. That turnaround is evident not only in topsoil moisture, but also in the subsoil levels.

For example, the Iowa crop progress and condition report for the week ended Sunday, June 2, 2024, shows subsoil moisture rated "adequate" or "surplus" totaled 92%. That is sharply higher than the rating total for those categories when the weekly crop progress report cycle began this year. The Iowa report on April 1, for the week ended March 31, 2024, noted subsoil moisture in the "adequate" to "surplus" categories totaled just 24% -- a big drop from 73% at the end of March in 2023. April rains improved the subsoil moisture level to 73% adequate to surplus in early May, and May precipitation advanced those categories to a total of 92% adequate to surplus in early June.

That level of improvement is evident in reviewing graphic maps of root-zone soil moisture from the NASA Gravity Recovery and Climate Experiment (GRACE) satellite-based global moisture analysis project. Back in early March, much of the Western Corn Belt was very dry, with root-zone wetness levels in the 20th percentile or below according to the GRACE analysis. But at the end of May, root-zone wetness levels had mainly changed to the 30th to 70th percentile levels. That is not surprising looking at precipitation over the past two months. The past 60 days have brought precipitation totals which range from 150% to more than 200% of normal in large parts of the Western Corn Belt, according to the High Plains Regional Climate Center.

This additional moisture is located in the top five feet of the soil profile, and it's here that crop roots will focus during their reproductive stages. Research on crop moisture use by the University of Nebraska-Lincoln notes that early in the season, the majority of corn root development and moisture use is concentrated in the top foot of the soil profile. The story is different once the corn plant reaches its silking stage. At that point, the plant begins to search out more and more of its moisture from two to three feet below the surface. And from silking all the way through maturity, more than 90% of the moisture needs for the corn plant are taken up in the top three feet of the soil profile. So, moisture that is in the soil bank now will be called upon significantly in the space of around six weeks.

The improved subsoil moisture does not guarantee a problem-free growing season from here on. But it does suggest crops will have some useful reserves for development when moisture use ramps up in the middle of summer.

Bryce Anderson can be reached at


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