University of Kentucky
UKnowledge
Soil Science News and Views
Plant and Soil Sciences
7-1980
Effects of Soil Erosion on Productivity
Wilbur Frye
University of Kentucky
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Frye, Wilbur, "Effects of Soil Erosion on Productivity" (1980). Soil Science News and Views. 47.
http://uknowledge.uky.edu/pss_views/47
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Unlversity of Kentucky, College of Agriculture
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Vol. 1 No. 3 July 1980
EFFECTS OF SOIL EROSION ON PRODUCTIVITY
W. W. Frye
About 75 percent of Kentucky's agricultural land is sloping enough that potential
erosion losses must be considered in its management. In addition to the effect of soil
erosion on water pollution is the question of its effect on the productivity of the soil.
This is a complex question due to the interactions of the many factors that affect crop
growth. Furthermore, the. same degree of erosion has a greater adverse effect on some
soils than on others. The kind of erosion that has taken place or is taking place is a
major factor in making land use decisions for crop production.
Of the three major kinds of accelerated soil erosion--gully, rill, and sheet--gully
erosion is the most spectacular, and where extensive it is the most damaging. The
second kind, rill erosion, can be thought of as the formation of small gullies which can
be concealed or repaired by normal tillage operations such as plowing or disking. Gully
and rill erosion are both caused by concentrated surface flow of water downslope. Sheet
erosion, the third major kind, is the removal of thin layers of soil from a wide area of
a field by water or wind. While sheet erosion is the least noticeable, nationwide, it
is probably the most damaging form of soil erosion. In sheet erosion, the impact of
raindrops detaches the soil particles and sheet flow of water moves them downslope where
most are deposited. Although not important in Kentucky, wind can cause similar losses
of topsoil. As the topsoil gets thinner from erosion losses, the subsoil is mixed into
the plow layer by tillage. This process has the greatest effect on sloping upland
positions where the soils are usually mature. These are soils in which the clay content
is considerably higher in the subsoil than in the topsoil or in which a pan has formed.
Where sheet erosion has occurred on such soils and the subsoil has been mixed with the
topsoil, the clay content of the topsoil is higher than normal. In some cases, it is
nearly as high as in the subsoil. If the color of the subsoil is much different from
that of the topsoil, it can be seen as a part of the plowlayer, and eroded areas are
easily recognized in freshly plowed fields by the color of the soil at the surface.
An experiment conducted on a Maury soil near Lexington revealed different degrees
of past sheet erosion. The experimental site was on a rather uniform slope of about 5
percent. It is thought that the site had been in bluegrass pasture without tillage for
50 - 60 years and that most of the erosion observed probably occurred over a period of
The Collt@/·. o:-~~gricu~Iurc is an_ Equal Opp or_( un'.ly~rgunization WJ lh respect to education and employmcnland is authorized to provl(k resNirch, educarional infornwlioii
dnd oL_l_ie~.senH ~s o,ily !o 11~_1v1duals and rnsnt~1twns that fu~cl'.?n w!Ihout n>gard to raty, color. national ongin, owx. religion, age and handicap. lnquiiies re 'a:rdin
f1lle VI. and l 1\k VJ! of the Ci:'ll Rights Ad of 1964, l ille IX of (be EduuJ.tional Amend men ls. Secrion 504 of the EehabililalionAcl and other related
"hould be· GH"cctcd w Equal Opp01ium(y 01f1<'e, Kernucky Cooperative Extension Senicc. University of Kentucky, Room S-105, Agriruli urnl Scirnre B .,,. '-N
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UN!VERSITY OF KENTUCKY, KENTUCKY STATE UNIVERSITY, U.S. DEPARTMENT OF AGR!CULTURE, AND KENTUCKY COUNTIES, COOPERATING
several years before the pasture was established. We sampled the soil in 0-3, 3-6, 6-12,
and 12-18 inch depths and analyzed for clay content. The clay content in the 0-3 inch
layer was the best indicator of the degree of past erosion. On this basis, the plot area
was separated into three sections. The section of plots with clay content greater than
30 percent in the top 3 inches was designated as "eroded" and the section with 26 percent
or less clay content was designated as "uneroded. 11
There was a narrow strip of soil be-
tween those two sections where the clay content was between 26 and 30 percent, and these
plots were excluded from subsequent comparisons.
The effects of erosion on the yield of corn grown by the no-tillage method and on
the available water holding capacity for the 6-12 and 12-18 inch layers of soil were
as follows:
Uneroded
99
Eroded
87
6-12 inches
23.7
17.3
12-18 inches
19.4
13.6
Yield of corn (3-yr. average, bu/A)
Available water holding capacit),_!/ (%)
1/ Data is incomplete on 0-3 and 3-6 inch depths.
On the eroded section average yields were 12 percent less than on the uneroded section
and the available water holding capacity of the upper subsoil (6-18 inches) was more
than one-fourth lower.
In summary, removal of topsoil by erosion decreases the soil organic matter, which
decreases the nitrogen supplying capacity and lowers the water supplying capacity of the
soil. Mixing clay from the subsoil into a silty topsoil by plowing as the topsoil becomes thinner also lowers the water supplying capacity and results in less desirable
physical characteristics in the plow layer of strongly developed soils such as the Maury.
Thus, erosion generally diminishes some of the most important yield-determining soil
properties. With a yield difference of the magnitude shown above in spite of the past
history of a long period in sod, it appears that the damage caused by erosion to the
productive capacity of the Maury soil is long-lasting, i f not permanent.