Subsoil moisture levels improved for 2021 crop production
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ISU Extension's subsoil moisture sample location near Rossie was an outlier among five other drier sites in Emmet, Dickinson, Buena Vista, Pocahontas and Sac counties.
Iowa State University has completed its spring survey of subsoil moisture in northwest Iowa.
The amount of subsoil moisture is sampled in the fall and spring in six northwest Iowa counties. Soil moisture is sampled to a depth of five feet in one-foot increments at six different pre-determined locations. The soil moisture samples are weighed wet, dried for 48 hours and weighed dry. Then soil moisture is reported in inches of plant available moisture after calculations account for plant available and plant unavailable moisture.
The amount of subsoil moisture is well below the spring average in every location except Rossie. The amount of subsoil moisture at the soil moisture sites in Emmet, Dickinson, Clay, Buena Vista, Pocahontas and Sac counties ranges from 4.1 inches (Spirit Lake) to 8.2 inches (Rossie) of plant available moisture. Soil moisture at these sample locations increased by 1.9 to 5.0 inches since early November.
Precipitation since Nov. 8, including snow and rain, ranged from 5.8 to 8.8 inches, and was above normal for all but one of these locations. This amount of rainfall would have been expected to increase the level of subsoil moisture to a greater extent than is observed by these spring sample results. About 80 percent of the precipitation is expected to contribute to subsoil moisture. It is possible that there was more evaporation in the late fall, early winter and early spring precipitation that limited subsoil moisture recharge.
According to Paul Kassel, ISU Extension and Outreach Field Agronomist located in Spencer, subsoil moisture levels are considered to be adequate at the sites near Rossie, Newell, Rolfe and Storm Lake.
The amount of subsoil moisture at the sites near Spirit Lake and Estherville is somewhat of a concern. A corn or soybean crop needs about 20 inches of moisture from rainfall or subsoil moisture to produce a normal crop. Therefore, the sites near Spirit Lake and Estherville will require about 15 to 18 inches of timely growing season rainfall to reduce the likelihood of soil moisture as a limiting factor in 2021 crop production.
