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