How does our soil moisture balance sheet look?

June 14, 2021 12:56 PM
Blog Post

The following is a view of the moisture status for six locations in northwest Iowa where the soil was analyzed for spring subsoil moisture.  This discussion may or may not reflect the current soil moisture conditions in your area.  This article does attempt to account for stored soil moisture, 80% of spring rainfall and expected average rainfall for the rest of the growing season.

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. 

The concern is that the current levels of soil moisture plus 80% of expected total rainfall is below  the needed 20 inches of rainfall to produce normal corn and soybean grain yields (table 2).

Table 1. crop moisture use balance sheet as of June 11, 2021.                                                                                            

                                    plant                                                    crop                 current

                                    available                                              moisture          soil moisture

                                    moisture          rainfall                         use                  status - inches

                                    inches              since                           since               plant available

location                       4/17/21            4/17/21 (dep)              5/31/21            moisture 6/11/21

Spirit Lake                  4.1                   3.6 (-3.2)                     1.9                   5.1

Estherville                   5.4                   3.2 (-3.5)                     1.9                   6.1

Rossie                         8.2                   4.7 (-2.1)                     1.9                   10.1

Newell                        7.3                   3.9 (-3.6)                     1.9                   8.5

Rolfe                           6.1                   3.2 (-3.8)                     1.9                   6.8

Schaller                       6.8                   3.6 (-3.8)                     1.9                   7.8


Table 2. Expected average rainfall - for June 11 to September 1, inches.  The last column is the total- or the first column plus the info in the last column in table 1.

                        expected        total

                        rainfall            potential

                        6/11- 9/1         moisture

Milford            10.5                 13.5

Estherville       10.5                 14.5

Sioux Rapids   11.0                 18.9

Storm Lake     11.8                 18.0    

Pocahontas      11.6                 16.0

Sac City          11.4                 17.0

Plant available moisture - subsoil moisture levels - sampled by April 17, 2021

rainfall - ISU Mesonet

            location           weather station used

            Spirit Lake      Milford

            Estherville       Estherville

            Rossie             Sioux Rapids

            Newell            Storm Lake

            Rolfe               Pocahontas

            Schaller          Sac City

Crop moisture use - from University of Nebraska Lincoln - data from Concord NE which is based on the evapotranspiration from the past seven days from the table, or 0.17/inches of moisture/day.

Current moisture status

            - subsoil moisture as 4/17/21 plus 80% of the rainfall that has occurred since 4/17/21 minus crop moisture use.  Rainfall is considered to be about 80% efficient since evaporation may reduce the total amount of moisture supplied to the crop.