Serving O'Brien & Clay Counties
Serving O'Brien & Clay Counties
A cloud of dust trails a combine south of Hartley as the farmer harvests a soybean field in early October. According to ISU Extension & Outreach, autumn rains helped recharge subsoil moisture levels compared to spring totals.
Iowa State University Extension and Outreach field agronomists have completed their fall survey of subsoil moisture in northwest Iowa. Eighteen locations were sampled, according to Agronomists Gentry Sorenson and Leah Ten Napel.
"The sites were selected for being typical for the major soil type," Ten Napel said in a news release. "Each site that was selected has little or no water run-on and no ponding. A 40-foot by 40-foot area is designated for sampling at the locations, and GPS helps ensure sampling is done at the same location each spring and fall."
Results from the fall 2023 sampling indicate improved levels of subsoil moisture at 12 of the 18 locations compared to the spring sampling, and improvement at all locations compared to a year ago.
Fall sampling totals at area locations include: Calumet/Sutherland, 8.11 inches; Rossie, 9.10; Sanborn, 6.75; Sibley, 6.31; and Spirit Lake, 7.55. All totals are above fall 2022 levels and all but one (Rossie) are also above spring 2023 levels.
"The results show that there was some recharge of soil moisture this fall," Ten Napel said. "We confirm we are going into the winter months with much more moisture in the profile when we compare the fall 2022 and fall 2023 data. A full profile in northwest Iowa can hold about 11 inches of plant available moisture."
Soil moisture is sampled to a depth of five feet in one-foot increments at predetermined locations in the spring and fall. Moisture samples are taken to a depth of five feet as corn and soybeans can root to this depth.
"The drought monitor had significant changes from our sampling period this spring to our most recent sampling this fall," Sorenson said.
Rainfall received in northwest Iowa over the course of the growing season was variable but allowed some counties to be moved out of the D4 drought category, leaving most in the D0 to D1 categories.
Subsoil moisture levels across northwest Iowa have improved from last fall but winter conditions, like amount of precipitation and frost depth, will affect how much moisture is able to infiltrate the soil profile by spring.
Subsoil moisture can also be replenished by rainfall when the ground thaws in the spring through the months of March and April. Typical rainfall for those months is three to five inches, and about 80 percent of that rainfall will contribute to subsoil moisture reserves.
Corn and soybean crops require about 20 inches of moisture from rainfall and subsoil moisture to produce a crop. That number may increase to 25 inches per season when high temperatures and windy conditions are prevalent during the summer.
