Spring subsoil moisture improves in northwest Iowa

April 21, 2021 10:10 PM
Blog Post

Subsoil moisture levels have improved for 2021 crop production.

Iowa State University has completed their spring survey of subsoil moisture in northwest Iowa, says Paul Kassel, ISU Extension and Outreach Field Agronomist located in Spencer.  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 foot in one-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. This soil moisture information is based on actual soil samples.  

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 county ranges from 4.1 inches to 8.2 inches of plant available moisture (table 1).    Soil moisture at these sample locations increased by 1.9 to 5.0 inches since early November (table 2).

Precipitation since November 8 - including snow and rain - ranged from 5.8 to 8.8 inches - and was above normal for all of but one of these locations.  This amount of rainfall would have been expected to increase the level of subsoil moisture at a greater degree than is observed by these spring sample results.  About 80% of the precipitation is expected to contribute to subsoil moisture.  It is possible that there was more evaporation of the late fall, early winter and early spring precipitation that limited subsoil moisture recharge.

Subsoil moisture levels would be considered to be near normal 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 of the likelihood of soil moisture as a limiting factor in 2021 crop production. 

Expected rainfall for these locations is about ten inches from mid-April to June 30 and about 18 inches from mid-April to August 30. 

Table 1. County subsoil moisture – spring 2021.                                                                                      

                                                                                                                                                                                                                                             spring                                                                         

County            average, in.     location                       2020 crop        11/3/ 20           4/17/21

                                                                                                           plant available H2O, inches

Dickinson        7.8                   Spirit Lake                  corn                 2.2                   4.1

Emmet            7.9                   Estherville                   soybean           2.5                   5.4

Clay                7.5                   Rossie                         corn                 3.2                   8.2

Buena Vista    7.5                   Newell                        soybean           2.9                   7.3

Pocahontas    7.6                   Rolfe                           soybean           3.4                   6.1

Sac                 7.7                   Schaller                       corn                 1.8                   6.8

 

Table 2.  subsoil moisture gain from November 8, 2020 to April 17, 2021                                                                                                    

County            .           location                      Moisture gain since fall, inches

Dickinson                    Spirit Lake                  1.9

Emmet                        Estherville                   2.9

Clay                            Rossie                         5.0

Buena Vista                Newell                        4.4

Pocahontas                 Rolfe                          2.7

Sac                             Schaller                      5.0

 

Table 3.  Rainfall November 8, 2020 to April 17,2021.

                        Actual  normal  difference

                        ------------ inches -----------     11/7/20 - 1/30/21   3/1-4/17/21

Milford             5.8       6.4.       -0.6                  1.7                             3.5

Estherville        7.0       6.8       +0.2                 2.4                              3.8

Spencer            6.7       6.3       +0.4                 2.4                             3.9

Storm Lake       8.4       6.9      +1.6                 3.9                              3.8

Pocahontas       8.8       7.4      +1.4                 3.7                             4.4

Sac City           8.2       7.3       +0.9                 3.2                              3.7

 

Table 4. Location of moisture in the soil profile, April 17, 2021.

Location           Spirit    Esther   Ros-     New-    Rolfe    Schal-

                         Lake     -ville     sie         ell                     ler       

Depth, ft.          ----------------------------inches --------------------

0- 1                  1.3       1.5       1.9       1.8       1.7       1.8

1-2                   1.2       1.2       1.7       1.7       1.0       1.7

2-3                   0.5       1.1       2.0       1.1       1.1       2.0

3-4                   0.2       0.8       1.6       1.2       0.8       0.9

4-5                   0.9       0.8       1.0       1.5       1.5       0.4

Total                4.1       5.4       8.2       7.3       6.1       6.8

 

Table 5.  average expected growing season rainfall. 

                        April 17 to June 30        April 17 to August 30

                        ----------------------- inches -----------------------

Milford             9.9                                 17.1

Estherville        10.0                              17.1

Spencer            9.6                               17.1

Storm Lake       10.9                             19.2

Pocahontas       10.3                            18.4

Sac City           10.7                              18.5

 

 

 

 

 

 

 

 

 

 

 

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Paul Kassel Field Agronomist in NW Iowa

Paul Kassel provides research based crop production information to area farmers and agribusiness. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include soil survey, crop production, soil fertility, so...