Fall 2004 Subsoil Moisture Survey Results
- Counties: Carroll, Calhoun, Sac, Crawford, Monona and Ida
- Date Sampled: October 27 and 28
The ISU Extension Fall 2004
subsoil moisture survey has been completed for Carroll, Calhoun, Crawford,
Monona, Ida, Sac and Pocahontas counties. Results form this fallís sampling
indicate a sharp contrast in stored soil moisture between counties, yet
west-central IA is going into the winter season in relatively good shape with a
greater than average amount of moisture stored in the areaís sub-soil.
Results from the soil
moisture survey taken in late October indicate that west-central IA had on
average 5.0 inches of plant available water (PAW) in the 60-inch soil profile or
43% of capacity. This was 108 % of the last 6-year fall average and much above
the last fallís total of 2.6 inches PAW. Soils with the most stored moisture
were found in Carroll, Sac, Pocahontas and northern Ida counties with an average
of 7.9 inches PAW. In contrast, Calhoun, Crawford and Monona county soils were
holding only 2.6 inches PAW.
West-central IA has
received between 2.0 to 4.0 inches of precipitation since the sampling period;
therefore an additional 1.5 to 3.0 inches could be added to the location totals.
began the cropping season in very good soil
moisture condition with the areaís soils holding on average 8.5 inches of
plant available water (PAW) which was 73% of capacity. Precipitation was mostly
adequate through early July, but then became short during late July through
September in many areas. Yet because of the below normal temperatures, soil
moisture demand was less and moisture stress was not a problem in most areas.
Late summer and early fall precipitation recharged soil moisture in Ida, Sac
and Pocahontas counties.
The maximum amount of plant
available water (PAW) in the top five feet of soil is around eleven inches for
most northwest Iowa soils. The subsoil moisture samples are taken to a depth of
five feet in one-foot increments. Five feet is the normal depth that corn,
soybeans and alfalfa can extract moisture. On average, a corn and soybean crop
requires 26 inches of water to produce a normal yield. Timeliness and intensity
of the rain events greatly effects water infiltration into the soil and the
plant's ability to utilize the moisture. Keep in mind that rainfall has been
variable across the region and the samples capture only a snapshot of time and
location of actual subsoil moisture status. Rainfall has occurred since the
samples have been taken so moisture levels in many areas may have improved since
the sampling period.
Soil Profile Graphs
State-wide map and
Commentary by Elwynn Taylor (coming soon)