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Corn Suitability RatingsCorn Suitability RatingsAn Index to Soil Productivity
76th Annual Soil Management and Land Valuation Conference
Gerald “Jerry” MillerIowa State University
soil@iastate.edu
COLLEGE OF AGRICULTURE
Outline
Background and History
The algorithm
Index versus yields
Correction factors
Uses
Questions
“The aim of the appraiser, as he sets out to make a physical examination of a farm, should be to DETERMINE VARIATIONS IN THE SOIL which indicate DIFFERENCES in crop-producing ability.”
W.G. Murray, 1969, p. 291
The task of a soil scientist is to
identify soil variability across the
landscape and record these
differences to produce a soil
map.
North Central Iowa Landscape
N
Story Co NE ¼ Sec 14 T83N, R21W
5/21/76
Unit of Soil Interpretation A Soil Map Unit
Symbol on map
Soil Series Clarion ---
Soil Type Clarion Loam 138
Slope Class 5-9% slope gradient C
Erosion Class Moderately eroded 2
Productive Capacity of LandSoil differences
Weather differences
Response to technology
Corn Suitability Rating (CSR)History
Late 1940’s – Taylor county soil survey
Late 1960’s – refinement and CSR list developed for each completed county soil survey
1971 – special report 66 “Productivity Levels of Some Iowa Soils” defines the algorithm
1990’s – websitehttp://extension.agron.iastate.edu/soils
Corn Suitability Rating
Factors Considered in CSR System
Benchmark soil
Slope class
Erosion class
Drainage class
Depth phases
Native vegetation
Parent material
Precipitation
Temperature
Special soil conditions
Corn Suitability RatingsAssumptions
Adequate management
Natural weather conditions (no irrigation)
Artificial drainage where required
Bottomland soils protected from frequently flooding
No land leveling or terracing
Productivity IndexIndex Versus Predicted Yield
Accounts for predicted yields as well as frequency and intensity
Allows for ranking one soil map unit against other soil map units
Soil type Soil map unit symbol
CSR Est. corn yield
Est. soybean
yield
Muscatine sicl 119 100 170 57
Tama sicl 120 100 170 57
Tama sicl 120B 95 167 56Tama sicl 120C 80 162 54
Tama sicl 120C2 78 158 53
Tama sicl 120D2 68 149 50
Corn Suitability Ratings and Estimated Yields for Major
Soils in Eastern Iowa
Productivity IndexIndex Versus Predicted Yield
Should be fairly constant over time while technology may cause changes in predicted yields
Corn Suitability RatingsIowa system: for use with modern county soil survey maps
Supplements listing CSR’s available in most counties with modern soil survey reports
CSR’s included on crop yield table in published soil survey reports starting in 1995
Drainage (tile and surface)
Flooding (bottomland soils)
Contrasting soil inclusions within a map unit
Rainfall and temperature
Corn Suitability RatingsAdjustment Factors
Clarion-Nicollet-Webster Soil Association AreaClarion-Nicollet-Webster Soil Association Area
Reference: Clarion loam, A slope, CSR 87 Average annual precipitation, 30 inches Average annual temperature, 48oF
750.862
790.908
740.850
790.908
810.931
810.931
850.977
820.943
830.954
850.977
850.977
871.000
850.977
850.977
850.977
891.023
860.989
810.931
To83
0.954
871.000
850.977
850.977
891.023
881.011
911.046
911.046
881.011
911.046
891.023
911.046
781.040
740.987
751.000
710.947
720.960
751.000
761.013
730.973
761.013
801.067
781.040
791.053
Reference: Galva silty clay loam, A slope, CSR 75 Average annual precipitation, 27 inches Average annual temperature, 47.5oF
Galva-Primghar-Sac Soil Association AreaGalva-Primghar-Sac Soil Association Area
Marshall Soil Association AreaMarshall Soil Association Area
820.911
860.955
840.933
901.000
870.978
901.000
880.978
880.978
880.978
901.000
880.978
901.000
880.978
Reference: Marshall silty clay loam, A slope, CSR 90 Average annual precipitation, 30 inches Average annual temperature, 49.5oF
Ida-Monona Soil Association AreaIda-Monona Soil Association AreaWeather Adjustment Factor by CountyWeather Adjustment Factor by County
0.953
1.000
0.976
0.918
1.000
0.882
1.000
1.000
1.000
0.929
1.000
1.000
Soil map number
Soil type name Acreage CSR X Acreage CSR
55 Nicollet loam 5.9 90 531.0
62D Storden loam 6.4 45 288.0
62E Storden loam 1.9 35 66.5
95 Harps clay loam 8.0 63 504.0
107 Webster clay loam 13.8 85 1173.0
135 Coland clay loam 2.0 80 160.0
138B Clarion loam 36.1 82 2960.2
138C2 Clarion loam 3.9 65 253.5
201B Coland-Terrill complex
2.0 40 80.0
80.0 6016.2
Calculation of weighted average CSR from the 80-acre field shown.
6016.280.0
= 75.2 = weighted average CSR for field
Corn Suitability RatingsProvides for calculation of a quantitative value of crop productivity for a tract of land
Independent of size of tract
County Weighted Average Corn Suitability Rating
59.5 65.5 68.066.968.0
64.8 69.2 69.671.8
55.8 72.4 74.062.7
49.4 70.9 77.460.1
49.9 68.0 76.459.5
54.4 60.5 55.758.2
60.8 56.9 53.661.8
64.2 56.8 55.263.5
65.1 52.7 45.763.2
70.4 71.4 75.571.4
74.0 69.4 56.977.7
74.8 76.8 72.573.2
74.0 75.9 84.775.5
72.3 75.9 70.777.6 72.861.2
47.3
65.8
73.6 64.1 65.074.2
54.7 68.2 58.856.1
40.1 40.6 46.839.7
35.1 41.3 39.943.1
71.6 63.0 51.371.1
67.5 75.259.6
62.6
60.4
66.6
63.0
47.8
56.6
40.9
74.2
62.4
48.164.3
41.5
65.0
69.4
73.4
Weighted Average CSR
Under 60
60-70
70-75
Over 75
Calculated from acreages and CSR’s contained in ISPAID (Iowa Soil Properties and Interpretations Database)As of August 15, 2001Prepared by Gerald A. Miller and Thomas E. Fenton, Professors of Agronomy, and Brian Tiffany, System Support SpecialistDepartment of Agronomy, Iowa State University, Ames, Iowa 50011
Use of Corn Suitability Ratings
“No”
Are not equal to yields
Weighted averages not comparable among major soil areas
Use of Corn Suitability Ratings
“Yes”
Determining productivity potentials
Tax assessment of agricultural lands
Land values
Comparable land for estate taxes
“Prime Agricultural Land”
Questions
Thank you!
COLLEGE OF AGRICULTURE
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