Northwest Iowa subsoil moisture survey results

November 10, 2020 12:17 PM
Blog Post

Iowa State University has completed their 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 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.

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 (table 1).   

Rainfall during the growing season was 3.6 inches below normal in Estherville to 8.3 inches below normal in Sac City (table 3).  Additionally, rainfall from September 1 to November 8 was 1.8 inches below normal in Pocahontas to 2.8 inches below normal in Estherville (table 2).  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 (table 4). About 80% of that rainfall will contribute to subsoil moisture reserves.

 

Table 1. County subsoil moisture – fall 2020.                                                                                           

                                                                                                            plant   

                                                                                                            available

                        County                                                                        moisture

                        Fall                                                                              inches

County            average, in.     location                       2020 crop        Nov. 3, 2020

Dickinson        5.7                   Spirit Lake                  corn                 2.2

Emmet            5.9                   Estherville                   soybean           2.5

Clay                5.7                   Rossie                         corn                 3.2

Buena Vista    6.0                   Newell                        soybean           2.9

Pocahontas      6.0                 Rolfe                           soybean           3.4

Sac                  5.9                  Schaller                       corn                 1.8

 

Table 2.  Rainfall from September 1 to November 8, 2020 (info from ISU mesonet).

                        Actual  normal  difference

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

Milford             2.8        5.5       -2.7

Estherville        2.7       5.5       -2.8

Spencer            2.8       5.4       -2.6

Storm Lake       3.7       5.7       -2.0

Pocahontas       3.7      5.5       -1.8

Sac City           3.9       5.8       -1.9

 

Table 3.  Rainfall from April 25 to September 1, 2020. 

                        Actual  normal  difference

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

Milford             10.8      16.3      -5.6

Estherville        12.8      16.4      -3.6

Spencer            11.2      16.3      -5.1

Storm Lake       13.5      18.3      -4.8

Pocahontas       10.7      17.6      -7.0

Sac City           9.4       17.7      -8.3

 

Table 3. Location of moisture in the soil profile, November 3, 2020.

Location           Spirit    Esther Ros-     New- Rolfe    Schal

                         Lake     -ville    sie        ell                    ler       

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

0- 1                  1.0       1.3       1.4       1.4       1.6       1.6

1-2                   0.0       0.5       0.8       0.0       0.7       0.2

2-3                   0.0       0.1       0.7       0.0       0.3       0.0

3-4                   0.3       0.3       0.3       0.3       0.1       0.0

4-5                   0.9       0.3       0.0       1.2       0.7       0.0

Total                2.2       2.5       3.2       2.9       3.4       1.8

 

Table 4.  average expected rainfall for November, March and April. 

 

                        November         March 1 to April 30       total

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

 

Milford             1.4                   4.5                               5.9

Estherville        1.3                   4.7                               6.0

Spencer            1.3                   4.7                               6.0

Storm Lake       1.5                   5.0                               6.5

Pocahontas       1.5                   5.0                               6.5

Sac City           1.5                   5.1                               6.6

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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 ferti...