Soils
C. Enright D. Hulse D. Richey
Land Use Planning and Resource Management
Data Sources
The map at right represents soils of the Willamette River Basin (WRB)
ranked by land use capability classes, a general measure of the suitability of
soils for agricultural field crop production. Data from two of the United
States Department of Agriculture (USDA) soil geographic data bases were
used to create the map: the Soil Survey Geographic data base (SSURGO)
and the State Soil Geographic data base (STATSGO). The most detailed
information about soil properties is contained in SSURGO, data appropriate
for use with areas ranging in size from an individual agricultural field up to
entire counties. SSURGO data are compiled using field observation methods
or are based on aerial photography. STATSGO maps are designed for use in
planning and natural resource management at a multistate or regional scale.
As shown in Figure 9, Map 2 contains data from both sources. STATSGO
data are coarser than SSURGO data, and are used only where SSURGO data
are unavailable.
The Oregon Department of Land Conservation and Development uses
soil capability classes to define Agricultural Land and High-Value Farmland
in Administrative Rule #660-033-0010-20 for implementation of Goal 3 in
Oregon’s Statewide Planning Goals (see p. 72). In western Oregon, Agricultural Land is defined as being soils predominantly in capability classes I-IV.
High-Value Farmland includes all soils in capability classes I and II, and
soils in subclasses IIIe, IIIw, IVe, and IVw. Land within acknowledged urban
growth boundaries (UGBs) is not considered Agricultural Land and is
exempt from Goal 3. Figure 12 and Table 2 show acreages of soil capability
classes within the WRB and its 1995 UGBs.
Salkum
Class II
Group B
0.28
Class VIII
2%
Class I
Class II
15%
Class VII
13%
Class II
Class VI
6%
Class V
< 1%
Class III
Class IV
ClassV
Class VI
46%
Class IV
14%
Class VI
Class IV
8%
Class VII
Class VIII
Unknown
Class V
<1%
Class III
21%
Soil Classification
UGB
Portland
Metro
Salem
51,781
24,930
53
15,966
2,911
40,809
10,218
1,333
24,441
10,733
4,170
0
1,013
227
38
1,687
900
6,505
3,785
7,547
0
1,188
52
0
584
1,741
6,799
3,550
3,554
0
145
0
490
629
10,686
13,788
6,558
10,603
0
3,501
304
2,038
1,374
Subtotal
18,809 123,310
76,406
50,804
53
21,813
3,495
43,375
14,492
42,207
18,334
9,648
0
5,752
181
1,827
2,805
25,718 165,517
94,740
60,451
53
27,566
3,676
45,202
17,297
6,909
Other UGBs
UGB Total
ac
3
ac
13
9,
22
53
7
100%
Percentage
of soil class
outside 1995
UGBs
80%
60%
Percentage
of soil class
inside 1995
UGBs
40%
Class VII
Class VI
Class V
Class IV
Class III
Class II
Unknown
20%
Class I
Maps represent soils as uniform areas with well-defined boundaries. As
with other land features such as vegetation and geology, soils can be heterogeneous complexes without distinct boundaries. Soil map delineations
represent the dominant soil type in an area, but, like all maps, may include
errors in classification and boundary position.
ac
ac
20
0,
3,
41
96
ac
3,
0
4
36
2,
26
61
1,
65
9
ac
ac
5
81
7,
0,
91
3,
71
4
39
5
ac
ac
Table 2. Acres of soil capability classes inside 1995 urban growth
boundaries within WRB.
Note: 2.47 acres equal one hectare.
0%
Soil Maps and Representation
10
75,777
12
Map 2 at right depicts soils based on an interpretive classification
system designed to indicate the suitability of soils for agricultural crop
production. This system assigns a land use capability classification from I to
VIII (this is also known as soil capability classification). Figures 10 and 11
show the percentage of these capability classes within the WRB and its 1995
urban growth boundaries. Class I soils present the fewest limitations and are
the most suitable for agricultural crop production. As the capability classification number increases, soil limitations increase and suitability for agricultural crop production decreases. Soil capability is further described with the
addition of subclass and unit labels. The most complete description of a soil
capability class is in the form IVe2. The Roman numeral indicates the degree
of limitation, the lower case letter (subclass) describes the type of limitation
(e- erosion potential, w- wet soil, s- shallow soil) and the Arabic number
(unit) characterizes appropriate crops and management practices.
4,149
CorvallisPhilomath
AlbanyMillersburg
EugeneSpringfield
Percentage of Soil Class in WRB
The scientific classification system used by the USDA National Cooperative Soil Survey has six hierarchical levels of taxonomic classification:
order, suborder, great group, sub group, family, and series. A soil order, the
most general level, contains soils that have similar processes and degrees of
formation. A soil series, the finest level of description, comprises soils with
similar composition and major soil horizons.
Class II Class III Class IV Class V Class VI Class VII Class VIII Unknown
Class I
06
land uses and management practices such as agricultural production, building
development, and wildlife management. These are developed by experts in a
specific field through interpretation of the comprehensive taxonomic system.
Figure 11. Percentage of soil
capability classes inside 1995
urban growth boundaries within
WRB.
Figure 10. Percentage of
soil capability classes
within WRB.
1,
Soil science provides a comprehensive taxonomic classification for
soils. This scientific classification is based on underlying geology, and the
formation processes, composition, physical structure, and chemical properties of soils. Technical or interpretive classification systems consider specific
Class II
38%
,9
Figure 9. Areas of WRB described by SSURGO and STATSGO data. Each
SSURGO soil unit (polygon) represents a component that is associated with
60 properties and 84 data elements such as hydrologic group and erodibility
factor.
Class III
12%
11
5
SSURGO Data
STATSGO Data
Unknown
4%
Class I
Class VIII
6%
Class VII
10%
1%
Unknown
2% Class I
2%
Class VIII
Component Name
Capability Class
Hydrologic Group
Erodibility Factor (kffact)
Soil properties and characteristics are important considerations in
determining how land is used. Choices arise when land is well suited for
many uses. For example, attributes such as gentle slopes, availability of
water, and adequate drainage characterize many agricultural soils in the
Willamette Valley and also make them valuable for building and urban
development.
Soil Capability Class
Figure 12. Percentage of soil capability classes within and outside 1995
urban growth boundaries in WRB. The numbers at the top of the chart
represent the total number of acres for each soil capability class within WRB.
PNW Ecosystem Research Consortium
LANDFORMS
123°45’00"
123°37’30"
123°30’00"
Map 2. Soils
123°22’30"
123°15’00"
122°45’00"
123°07’30"
122°30’00"
122°37’30"
122°15’00"
122°22’30"
122°07’30"
122°00’00"
121°52’30"
121°45’00"
45°52’30"
45°52’30"
Saint Helens
Projection UTM Zone 10
0 mi
0 km
Scale 1:750000
10 mi
45°45’00"
10
km
45°37’30"
20 km
20 mi
45°45’00"
Scappoose
30 km
45°37’30"
Banks
North Plains
Portland
Fairview
84
Troutdale
Forest Grove
45°30’00"
Gresham
45°30’00"
Beaverton
205
Happy Valley
Milwaukie
Gaston
Tigard
Sandy
Tualatin
45°22’30"
45°22’30"
Sherwood
Yamhill
Oregon City
5
Wilsonville
Newberg
Carlton
Estacada
Dundee
Canby
Lafayette
45°15’00"
45°15’00"
Aurora
Dayton
Donald
McMinnville
Hubbard
Woodburn
Molalla
45°07’30"
Sheridan
Gervais
Amity
Willamina
Mt Angel
Scotts Mills
45°00’00"
Silverton
45°00’00"
Keizer
Salem
Dallas
44°52’30"
44°52’30"
Falls City
Independence
Aumsville
Monmouth
Turner
Sublimity
Lyons
Gates
44°45’00"
44°45’00"
Mill City
Detroit
Jefferson
Idanha
Scio
Millersburg
Adair Village
44°37’30"
44°37’30"
Albany
Corvallis
Lebanon
Tangent
44°30’00"
44°30’00"
Waterloo
Sodaville
Brownsville
Halsey
Sweet Home
44°22’30"
44°22’30"
Monroe
Harrisburg
44°15’00"
44°15’00"
Junction City
Coburg
44°07’30"
44°07’30"
Eugene
Veneta
44°00’00"
Class I
Class II
Springfield
44°00’00"
Few limitations
for agriculture
Moderate limitations
for agriculture
Creswell
Lowell
Reduce choice of plants or require
moderate conservation practices
43°52’30"
Class III
43°52’30"
Severe limitations for
agriculture
I5
5
Reduce choice of plants and/or require
special conservation practices
Class IV
Cottage Grove
Very severe limitations for
agriculture
Westfir
43°45’00" Reduce choice of plants and/or
43°45’00"
require very careful management
Class V
Class VI
43°37’30"
Oakridge
Limitations for agriculture
Use limited by considerations, other than
erosion, that are impractical to remedy
Severe limitations for agriculture
Generally unsuitable for cultivation
43°37’30"
Class VII Very severe limitations
for agriculture
Unsuitable for cultivation
Class VIII Unsuitable for agriculture
Limitations nearly preclude use for cultivation
Water
43°30’00"
N
43°30’00"
Unknown
5
Interstate Highways
S
199543°22’30"
Urban Growth Boundary
123°45’00"
123°37’30"
123°30’00"
43°22’30"
123°22’30"
123°15’00"
123°07’30"
123°00’00"
122°52’30"
122°45’00"
122°37’30"
Willamette River Basin Atlas
2nd Edition
122°30’00"
122°22’30"
122°15’00"
122°07’30"
122°00’00"
121°52’30"
121°45’00"
11