LAND VALUE
AND PURCHASE
Prepared by: Michael D. Duffy, extension economist, Iowa
State University, Ames, Iowa.
Lesson 2: Using Soils Information
Overview
Understanding the soils information on a parcel
of farmland is very valuable in making the land
purchase decision. Once a farm is located, the
next task is to obtain a detailed soil inventory
as to what different soils are on the farm and
how they can be used. The soil inventory
should include the physical resources such as
topography, drainage, degree of erosion, slope
and climate. Intended use, such as permanent
pasture, should be distinguished from cropland
acres.
The soils map should include slope variation,
degree of erosion, and details about the
drainage system. These are important features
to note on the map as they have a definite effect
on the long-term productivity of the farm. In
fact, the purpose of the soils map is to present a
picture of all significant physical features
which enhance or limit the producing ability of
a tract of land. This is especially true in
regards to conservation compliance
requirements.
Soils map
Topography
Productivity of land represents the key reason
behind the soil inventory as it transfers the
contribution of the different physical resources
into a land value. Productivity is one of the key
factors which makes one farm more valuable
than another. A soils map can be used as a
systematic evaluation of the whole farm.
Remember, attention should be given to all
parts of the farm.
Topography deserves a large share of the
evaluator’s time. Besides being a key to the
water erosion hazard, topography gives an
indication of soil and drainage conditions and
determines the appropriate farming practices.
The amount of information on the soils map
will vary with the importance of the different
features of the farm. A desirable method of
making the map is to divide a farm into soil
areas of uniform crop producing ability. Each
of the soil areas may then be evaluated by
rating them in terms of the most important crop
grown. Two steps are involved: the first,
determining the boundaries of the soil areas;
and the second, estimating the yields for each
area.
Topography, in many instances, will help in
identifying the soil type. A study of soil survey
maps indicates that many soils are formed and
exist only under certain topographic conditions.
There are, for example, soil types that occur
only on level upland, and others that occur only
on terraces or bottom land.
It is desirable to follow a definite and uniform
system of measuring topography. The usual
divisions are level, undulating to gently rolling,
rolling, strongly rolling and steep. This
classification is subjective as the term “rolling”
to one person may mean “gently rolling” to
another. A classification system using
“percentage of slope” can eliminate
misunderstandings between individuals.
Percentage of slope is the number of feet rise in
100 feet of horizontal distance. A slope of zero
percent is level or horizontal. A 20 percent
slope is a 20-foot rise in 100 feet of distance.
Soil maps are available on the Iowa State
University extension website.
Erosion
Erosion consists of two main types, erosion by
water and erosion by wind. Water erosion is
divided into the three subtypes of sheet, rill and
gully erosion. Sheet erosion is described as the
removal by water of more or less an even
amount of soil surface from an area of land.
Instead of the soil washing away in spots, it is
carried away as a sheet from the surface area.
Unfortunately, this type of erosion is not
readily noticed and much damage may occur
before the producer is aware of what is
happening. Rill erosion produces rills or small
channels as the soil is carried away by water.
Usually, rill erosion results from a heavy rain,
particularly in the spring when soil is being
tilled. During the spring, there are few, if any,
plants with extensive root systems and
protection from crop residue has been reduced
by tillage.
Gully erosion is where water cuts a small rill or
channel into a ditch that is difficult to cross
with farm machinery. Gullies usually are
formed in a natural drainage way. Although
gully erosion does not cover as much area as
sheet or rill erosion, the gullies themselves can
be viewed as an obstruction resulting in a
substantial decline in the value of the land.
When they become numerous in a field, it may
restrict cropping use and could in time require
permanent seeding into grass.
Wind erosion is, as its name indicates, the
removal of soil by the action of wind. The
action of wind can affect the productivity of
land. Wind erosion usually carries the smallest
particles for many miles, but may move the
large participles only a short distance. Thus, a
loam soil can through time actually be changed
to a sandy loam if the wind blows away enough
silt and leaves the heavier sand particles
behind.
Drainage
Topography and erosion can be easily seen by
the eye, while drainage, although just as
significant in many cases, is often hidden in
such a way as to escape the eye of the potential
buyer. The evaluator’s first concern about
drainage is to determine how much water the
farm is likely to receive annually. Attention
should be given to the amount of rainfall during
the entire year as well as that likely to come in
any one month. Also make note of the amount
of water that will drain onto the farm from
adjacent farms.
Not all soils are easily drained and drainage
problems can make the difference in land value
between two soil types in the same area. To
determine whether a soil is easy or difficult to
drain, examine the texture of both the surface
soil and the subsoil. A subsoil with a tight,
impervious layer will, of course, prevent water
from going down or coming up. A sandy
subsoil, on the other hand, usually allows the
water to pass through too fast for the good of
the plants.
Climate
Only those factors which might vary on an
individual farm have been considered up to
this point. The climate’s effect on yields is not
likely to vary within a farm, but the effect
between farms is often of consequence and
over a wide territory it could be decisive. The
climate includes items such as precipitation,
evaporation, length of day, length of frost-free
season, temperature variation, hail and winds.
Each of these items can be further subdivided.
For example, precipitation could be divided
into annual average rainfall, distribution by
month, variability from year-to-year, frequency
of hard rainfall, and average rainfall during the
crop season.
soil survey report. Listed are soil mapping
symbols, soil type, degree of erosion, Corn
Suitability Rating (CSR), and yield potential
for the most often grown crops. Using this
information will help evaluate the expected
productivity of the farm.
Rainfall is probably the most important climatic
factor influencing yield in the Midwest. The
amount of rainfall during the critical months of
the crop season in some cases may be more
significant than the total annual precipitation.
Historical weather records can be used in
reviewing the influences of the climate on crop
production. The danger of unfavorable weather
occurrences is one of the major concerns in
crop production.
Using Soil Surveys
County soil survey reports will provide much
of the information needed in making a soil
inventory. These published reports provide a
systematic approach to classifying soil
properties and characteristics as they occur in
nature. The soil survey represents an effort to
communicate soil facts and land use
alternatives as viewed by soil scientists. In the
reports soil scientists delineate soil boundaries
on aerial photo sheets and show the distribution
of different soils across a landscape. These soil
maps represent an inventory of the soil
resources of the area surveyed. An example
soil map of a 110.7-acre farm is shown in
Figure 1.
The soil inventory is recorded on the map
sheets as soil mapping units. For example, the
soil map unit symbol 394C2 identifies the soil
type, the slope and the erosion phase. The 394
identifies the Ostrander Loam soil type, the C a
slope of 5 percent to 9 percent and the 2
represents a moderately eroded soil.
Table 1 lists some of the soils information
which can be gathered about this farm from the
It is important to remember that the average
yields apply to average conditions. These may
or may not be reflective of yields the individual
producer could expect. The average yields are
useful for relative comparisons but for income
determination individual producers may want
to adjust them to reflect their own management
capabilities.
County soil survey reports contain a wealth of
information concerning specific soil properties
and characteristics of each kind of soil in a
survey area. Information about soil texture,
percent organic matter, permeability ratings,
soil structure and potential soil erodibility
factors are examples of soil characteristics
described in these reports.
Corn Suitability Rating
The Corn Suitability Rating (CSR) is an index
procedure developed in Iowa to rate each kind
of soil for its potential two-crop productivity.
Soil profile properties and weather conditions
are the dominant factors which affect soil
productivity. The CSR index provides a
relative ranking of all soils mapped in Iowa
based on their potential to be used for crop
production. This index can be used to rate the
potential yield of one soil against that of
another over a period of time.
The CSR considers average weather conditions
as well as frequency of use of the soil for rowcrop production. The ratings range from 100 for
soils that have no physical limitations, occur on
minimal slopes, and can be continuously rowcropped to as low as 5 for soils with severe
limitations for producing row crops.
The CSR index assumes: (a) adequate
management, (b) natural weather conditions (no
irrigation), (c) artificial drainage where
required, (d) soils lower on the landscape are
not affected by frequent floods, and (e) no land
leveling or terracing. The CSR for a given field
or farm can be modified by sandy spots, rock
outcroppings, field boundaries, wet spots, and
other special soil conditions.
Calculating Average CSR Value
Corn Suitability Ratings can be used with soil
maps to calculate a weighted average CSR
value for any sized tract of land. A soil map of
a 110.7-acre farm located in Northeast Iowa is
shown in Figure 1. Calculation of a weighted
average CSR value for the tract can be made by
multiplying the CSR value for each soil type by
the number of acres of each. For example, the
84, Clyde Soil, has a 75 CSR index rating
which is multiplied by 17.0 acres to give 1,275
index points. The CSR values for the other soil
types are multiplied by their corresponding
acreages to yield a composite score of 8,299
points. The total points are then divided by the
number of acres to give the weighted average
CSR value of 75 for the farm (8,299 ÷ 110.7).
The various soil types and CSR ratings for the
example are found in Table 1.
Special soil symbols can be added to identify
soil areas less than two acres in size which vary
significantly from the soil mapping unit in
which they occur. Many of these symbols
indicate hazards or features that detract from
the optimum use of the land and must be
considered in evaluation of the tract. For
example, the D symbol (Figure 1) indicates
there are severely eroded spots on this farm.
CSR Versus Yields
Crop yields for a given soil type are expected to
change while the CSR values should remain
relatively constant in relation to one another
through time. The CSR’s are based upon soil
properties, average weather, and the inherent
potential of each kind of soil for corn
production. The Corn Suitability Ratings are
specified for average management and assume
that technological advances are applicable to all
soils.
The yield estimates listed in Table 1 are based
on a high or an above average level of
management. This level of management
includes an implicit assumption that soil
conserving activities on sloping lands are part
of the management practices used to obtain
these high yields. Factors that determine crop
yields for a specific crop are soil properties,
topography, weather and management. Yields
are usually normalized for a five- or ten-year
average.
A comparison of the CSR values and estimated
corn yields for different slope and erosion
phases of the Kenyon soils is shown in Table 1.
Note the differences in the CSR value and corn
yield on the Kenyon soils, 2 to 5 percent slope,
(83B) and the 5 to 9 percent slope moderately
eroded (83C) land. The CSR value changes
from 85 to 70 while the estimated corn yield
changes from 159 to 149 bushels.
The difference in CSR implies fewer inputs
will be required to achieve an average yield of
159 bushels per acre on the 2 to 5 percent slope
land compared to the inputs required to achieve
149 bushels per acre on the 5 to 9 percent slope
land. The additional inputs required on the
steeper sloping soil may include agronomic and
engineering practices such as conservation
tillage, contour farming, a crop rotation that
includes a grass or legume crop with row crops,
conservation structures, and above average
application of fertilizers.
The changes in CSR value by 15 points implies
a need to conserve the soil on steeper slopes for
maintenance of its long-term productivity.
Also, when CSR and yields are compared, do
not expect a linear one-to-one relationship
among different slope classes and erosion
phases for the same kind of soil.
The task of establishing weighted average
CSR’s, soil types, etc. can be rather laborious.
Today there are other options available to the
potential buyer. Most County Assessors have
detailed maps available. There are also
commercial services available that can provide
the information for a fee. And, there are real
estate brokers and appraisers who can provide
this information.
Soil Productivity Approach to Yields
Establishing realistic yield levels for a tract of
land is very important in the land purchase
decision. A yield level too high leads to
overoptimistic returns, thus overstating the long
run earning potential of the farm. Likewise, too
conservative of yield levels understates the
earning potential of the farm and raises the
possibility of a missed purchase opportunity.
Using the soil productivity approach is one
method of determining potential yield
expectation for a tract of land. This approach
requires three critical pieces of information for
calculation of a weighted acreage yield of the
land being evaluated. First, a soil map is
essential with the various soil map units
outlined.
Next, the yield potential for each different soil
map unit must be determined. These estimates
can be found in the soil survey reports,
however, yields in older soil surveys may need
to be updated. Estimated yields for major crops
grown in Iowa have been established for more
than 1900 soil map units which are identified in
the modern soil survey reports. These yield
estimates are available at the various County
Extension Service and Soil Conservation
District Offices.
Third, the acreage of each soil in the field must
be estimated or measured and recorded on a
worksheet. A dot grid transparent overlay can
be used to estimate acreage for each soil
delineation. The estimates of acreages for the
110.7-acre farm are included in Table 1.
The final step is calculation of the weighted
average yield for the various crops to be grown
on the farm. This is accomplished by
multiplying the various yield potentials and the
corresponding acreage for each soil map unit.
The sum of these products is divided by the
total acres in the farm to give the weighted
average yield for each crop. The calculated
weighted average yields for the 110.7-acre farm
are: Corn, 145.2 bushels; soybeans, 44.3
bushels; oats, 86.9 bushels; and alfalfa, 5.6 tons
(see Table 1).
A. Calculate the weighted average yield for the
field listed below.
Soil Type
Name
Nicolett
loam
Storden
loam
Harps clay
loam
Coland clay
loam
Clarion
loam
Soil Map #
Acres
20.7
Corn
Yield
156
Soybean
Yield
50
55
62C2
7.2
123
39
95
13.9
125
40
135
3.2
136
44
138B
10.5
145
46
Total Acres
55.5
Using Historical Yield Data
Records of actual farm yields or average county
yields can be helpful in establishing yield goals
for a farm. When using production records, a
minimum of five years of record data should be
used. Average historical records can be used as
a cross-check for the yields determined by the
soil productivity approach. Although
individual farm yield records are preferred, in
most cases they are not available, making
county yield information the best source of data
for estimating yields.
http://www.nass.usda.gov/ia/
Table 2 shows average yield data in Butler
County for corn, soybeans, and oats. The yield
data was obtained from the Iowa Crop and
Livestock Reporting Service. The five-year
and ten-year average yields are shown towards
the bottom of the table. Also included are the
median yields (middle) using the last eleven
years of yield data. There is little difference
between the five-year and ten-year average
yields for corn and soybeans. Note, however,
the median yields for all three crops are higher
than either the five-year or ten-year averages.
Yield losses in poor years are large than yield
bonuses in good years.
http://www.nass.usda.gov/ia/releases.htm histacrg
Table 2. Butler County Average Yields for
for Corn, Soybeans, and Oats
Year
Corn
Soybean
Oats
(bu./acre) (bu./acre) (bu./acre)
1989
94.3
33.9
72.3
1990
129.5
41.6
70.1
1991
125.6
40.0
48.3
1992
152.3
45.9
73.6
1993
73.9
29.9
33.5
1994
140.0
49.1
75.0
1995
125.1
49.2
82.7
1996
143.2
46.5
73.5
1997
137.7
45.2
76.9
1998
151.9
51.7
64.2
1999
145.9
45.0
70.6
2000
140.9
46.5
82.5
2001
157.9
44.6
62.1
5-year
average
10-year
average
146.86
46.6
71.26
136.88
45.36
69.46
Additional References
PM-1168
Corn Suitability Ratings – An
Index to Soil Productivity
PM-1268
Establishing Realistic Yield Goals
Yield Goals
When evaluating the expected returns for a
farm, the producer should establish crop yield
goals slightly above the historical average.
This would reflect an above average level of
management and implies the adoption of the
latest available technology for crop production.
This would include optimum management
practices of proper cultivar selection, seed
quality, planting dates, population rates, rowspacing, fertilization, insect control, and timely
harvesting practices. Keep in mind, however,
that in some years production will exceed the
established yield goal while in other years
yields will fall below the yield goal.
Remember that a conservation plan is required
for some farms and fields to remain eligible for
government program benefits. Before
purchasing a farm the buyer should check with
the local Natural Resources and Conservation
Service for any cropping restrictions that may
apply.
Figure 1.
Feet
Section 25, Township 93 North, Range 15 West
Iowa Interpretive Soils Map, ISU Extension 0 200 400
Layer Legend (soil feature descriptions are abbreviated)
5 Drain end
Section
Int. drain (2 dot)D Severe erosion
Regions
Short steep slope
Soil map unit
5
5
83C
198B
83D2 84
783B 198B
83B
D
83C
D
198B
83B
783BD 84
391B
399
394C2
198B
W
394B
25
198B
394C
394B
391B
399
83C
399
84
83D2
391B 83B
Table 1: Soil Survey Information.
A. Calculation of weighted potential yield.
Soil Type
Kenyon
Kenyon
Kenyon
Map
Symbol
83B
83C
83D2
Acreage
33.1
17.9
1.6
Clyde
Floyd
Clyde-Floyd
Ostrander
Readlyn
84
198B
391B
394C2
399
17.0
6.9
14.0
12.2
.2
Cresco Loam
783B
7.8
D
Erosion/
Slope
2-5%
5-9%
9-14%
None to
Slight
2-5%
2-5%
5-9%
None to
Slight
2-5%
?
110.7
acres
B. Slope and Gradient Symbols
No Letter = 0-2%
B = 2-5%
C = 5-9%
D = 9-14%
C. Erosion symbols
No Number = None to slight erosion
2 = Moderately eroded
3 = Severely eroded
CSR
85
70
58
Corn
154
149
136
Soybeans
47
45
41
Oats
92
89
82
Alfalfa
6.5
6.3
5.7
75
75
72
68
90
140
144
140
145
157
43
44
43
44
48
84
86
84
87
94
4.2
5.8
4.2
6.1
6.3
63
123
38
74
4.9
------ Severely Eroded Slope ------75
145.2
44.3
86.9
5.6