Northwest Iowa subsoil moisture survey results

Iowa State University <
p><p>Extension and Outreach

Iowa State University has completed its fall survey of subsoil moisture in northwest Iowa. The amount of subsoil moisture is sampled in the fall in six northwest Iowa counties.

Soil moisture is sampled to a depth of 5 feet in 1-foot increments at six different pre-determined locations. Soil moisture samples are weighed wet, dried for 48 hours and weighed dry. 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 average. The amount of subsoil moisture at the soil moisture sites in Emmet, Dickinson, Clay, Buena Vista, Pocahontas and Sac county ranges from 1.8 inches to 3.4 inches of plant available moisture.

Rainfall during the growing season was 3.6 inches below normal in Estherville to 8.3 inches below normal in Sac City. Additionally, rainfall from Sept. 1 to Nov. 8 was 1.8 inches below normal in Pocahontas to 2.8 inches below normal in Estherville. The water use during the growing season by the relatively good crop produced in 2020 and dry fall explains the current lack of subsoil moisture.

The concern now will be to recharge the subsoil moisture for 2021 crop production. However, these low levels of fall subsoil moisture and a dry early growing season would compromise crop yield potential for 2021.

Rainfall during November, March and April will also contribute to subsoil moisture. Typical rainfall for those months is about 6 inches. About 80% of that rainfall will contribute to subsoil moisture reserves.