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Subsoil moisture levels a concern for 2013 crop production

November 13, 2012
From ISU Extension , Estherville Daily News

SPENCER - Iowa State University has completed their fall survey of subsoil moisture in northwest Iowa, says Paul Kassel, ISU Extension Field Agronomist located in Spencer. Subsoil moisture levels are checked in the fall in many northwest Iowa counties.

The amount of subsoil moisture is well below average. The level of subsoil moisture at the soil moisture sites in Emmet, Dickinson, Clay, Buena Vista, Pocahontas and Sac county ranges from 1.4 inches to 5.8 inches of plant available moisture.

Soil moisture has been a concern since July of 2011. Rainfall has been below to much below normal since mid- July 2011. Subsoil moisture levels were below normal at most of the locations when subsoil moisture levels were checked in late April of 2012.

However, most of the area produced excellent corn and soybean crops on limited summer rainfall. Corn and soybean crops appeared to produce root systems that went deeper than the expected five foot depth. Deeper rooting may have been a result of good planting time conditions and a relatively dry spring that encouraged early season root development.

This example is illustrated by the data from the Schaller location. This location had 6.2 inches of subsoil moisture on April 23. Rainfall was between 8.1 and 10.5 inches of rainfall from April 23 to September 1. The subsoil moisture and rainfall total is about 15.0 inches for this location. That is well below the 20 to 22 inches of moisture that is considered a minimum to grow a normal corn or soybean crop. However, corn and soybean yields in this area were near normal with corn and soybean yields in the range of 170 bu/a and 50 bu/a, respectively. This moisture deficit also likely illustrates the fact that the corn and soybean crop accessed moisture below the normal five foot rooting depth.

The larger concern may be that this will be the third year with extended dry conditions. The conditions going into the 2013 crop year may represent the largest crop production risk in terms of the effects of a long-term drought conditions.

The subsoil moisture that is below normal five-foot rooting depth is also likely depleted and therefore would not be available to carry the crop through an extended dry period in the summer.

Rainfall during November, March and April will also contribute to subsoil moisture.

Typical rainfall for those months is 4.9 to 5.7 inches. About 80 percent of that rainfall to contribute to subsoil moisture reserves.

County Subsoil moisture –fall 2012.
Plant available
County FallMoisture, inches
CountyAve. inchesLocation2012 cropNov 9, 2012
Dickinson5.7Spirit Lakecorn3.9
Buena Vista6.0Newellcorn4.3



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