Erosion & Water Quality

Soil Erosion
& Water Quality
Soil erosion is a gradual process that occurs when the impact
of water or wind detaches and removes soil particles, caus-
ing the soil to deteriorate. Soil erosion by water, and the impact of
Conservation Quiz
sediment-attached nutrients (i.e., phosphorus) on lakes and streams,
1. What's the difference between
creates problems for both agricultural land and water quality.
ephemeral and gully erosion?
Preventing the topsoil from eroding must be an integral part of any
2. How does soil erosion by water
soil management system if water quality is to be improved. Several
contribute to poor water quality?
conservation management practices can be used to reduce or
3. How can surface water
control soil water erosion, but the factors that accelerate or control
quality be improved?
soil water erosion need to be understood.
(Answers located on page 3.)

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Types of soil erosion
(As de?ned by Glossary of Soil Science Terms, 1996, Soil Science Society of America)
1. Sheet erosion—The removal of a relatively uniform thin layer of soil from the
land surface by rainfall and largely unchanneled surface runoff.
2. Rill erosion—An erosion process on sloping ?elds in which numerous and
randomly occurring small channels of only several inches in depth with steep sides
are formed by running water.
3. Ephemeral erosion—Small channels eroded by concentrated ?ow that can be
easily ?lled by normal tillage, only to re-form again in the same location by
additional runoff events.
4. Gully erosion—The erosion process whereby water accumulates and often repeats
in narrow channels and, over short periods, removes the soil from this narrow area
to considerable depths, in terms of channels too deep to easily ameliorate with
ordinary farm tillage equipment.
Soil Erosion
& Water Quality
Conservation and best management practices
• Crop rotations
The Effects on Water Quality

Extended crop rotation and permanent cover crops effectively protect the

soil from the impact of raindrops. The thick, ?brous root systems associated
Water quality is affected signi?cantly by

with cover crops also bind the soil particles together (Table 1).
soil erosion. Increased levels of nitrogen
• Residue management
and phosphorus, along with higher sedi-

Plant residue controls soil erosion by intercepting raindrops, blocking wind
ment loads, are the leading contributors

erosion, reducing surface water runoff, and preventing soil detachment.

to reduced water quality. Nitrogen and

When using a combination of conservation tillage practices and surface

phosphorus move from ?elds to surface

residue management, it is critical to maintain the highest amount of residue

cover possible (Figure 1).
water when sediment is transported through
• Tillage practices
runoff and soil erosion. As a result of the

Whether using no-till, conservation tillage, or conventional tillage systems,
nitrogen- and phosphorus-enriched sedi-

harvest is the best time to begin the next year’s residue management. For
ments, eutrophication—the growth of algae

effective soil erosion control, try to maintain residue cover of 30 percent or
and other aquatic plants—occurs, decreas-

more during the off-season and at planting time.
ing dissolved oxygen levels.
• Grassed waterways

Wide, shallow, sod-lined waterways reduce the speed of water by providing

a grass cushion and preventing gully formation. They also act as a ?lter by
Preventing Erosion and Improving

trapping sediment and protecting covered soil from being detached and

Water Quality

transported (Figure 2).
Surface water quality can be improved by
• Terraces
using best management practices to reduce

Terraces break up slope lengths and reduce steepness to reduce surface ?ow
soil erosion. Those practices include conser-

and sediment transport. They are easily adapted to producers’ needs, soil

type, and equipment (Figure 3).
vation tillage, residue management, grassed
• Conservation buffers
waterways, terraces, conservation buffers,

Buffers (areas or strips of land in which permanent vegetation is established
crop rotations, and contour farming. A single

near row crops) are designed to intercept sediment ?ow and protect the soil
management practice typically can control

from detachment (Figure 4).
soil erosion; however, multiple practices are
• Contour farming
required where complex topography exists.

Planting rows on the contour helps channel small runoff streams across,

rather than down, the slope and creates a speed bump for larger ?ows


(Figure 5).
Plant residue management is another way
of controlling erosion by intercepting rain
drops thereby reducing surface runoff and
protecting soil surface particle detachment.
2

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Crop residue can provide an excellent
soil cover after harvest and enhance snow
harvesting during the off season, improve
40
soil water intake by preventing soil surface
sealing due to rain drop impact, and conse-
quently, reduce surface runoff. Also, equally
30
Soybean after corn
important in minimizing soil erosion, is
Corn after soybean
the adoption of a cropping system along
20
with conservation tillage practices such as,
s
s

(
T
/
a
c
r
e
)
no-till, strip-till, ridge-till, etc. The degree
of effectiveness of different tillage practices
i
l

Lo
o 10
depends on the degree of soil manipulation,
S
which effects the residue distribution on the
soil surface. Table 1 shows combinations of
0 0 10 20 30 40 50 60 70 80 90 100
different cropping systems and the relative
scale of erosion hazard associated with each
Residue Cover Percentage
system.
Figure 1. Soil loss due to water erosion in relation to percent residue cover for Iowa,
Table 1. Relative erosion hazards
based on the Universal Soil Loss Equation.
of selected cropping systems.
Cropping System
Relative Erosion (%)
Fallow
244
C-S
120
C-C-S
112
Continuous Corn
100
C-C-C-Ox
73
C-C-Ox
68
C-Ox
59
C-C-C-O-M
46
C-C-O-M
32
C-C-O-M-M
27
Figure 2. Grassed waterway.
C-C-O-M-M-M
22
Figure 3. Contour terraces.
C-O-M
17
C-O-M-M
12
C-O-M-M-M
10
Continuous Meadow
0
C, corn; S, soybean; O, oats; Ox, oats with green
manure crop; M, meadow.
Quiz Answers: 1. Ephemeral channels are
easily ?lled in by tillage passes; gullies are
not. 2. Runoff water carries nitrogen- and
phosphorus-enriched sediment to water
bodies, causing algae and other aquatic
plants to grow, which decreases dissolved
oxygen levels. 3. By using conservation till-
Figure 4. Conservation buffers.
Figure 5. Contour farming.
age, conservation buffers, grassed waterways,
etc. to reduce soil erosion.
All photographs are from the NRCS website photo gallery (http://www.nrcs.usda.gov).
3

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Resources Conservation Practices:
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Soil Erosion
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Soil Erosion and Water Quality is published by
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Iowa State University Extension, with funding
& Water Quality
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Conservation Service through Cooperative
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available in alternative formats for ADA clients. To ?le
a complaint of discrimination, write USDA, Of?ce of
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Civil Rights, Room 326-W, Whitten Building, 14th
Professor, Department of Agronomy; Mark
and Independence Avenue, SW, Washington, DC
Hanna, Extension Agricultural Engineer,
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Issued in furtherance of Cooperative Extension work,
Program Specialist, Department of Agron-
Acts of May 8 and June 30, 1914, in cooperation with
the U.S. Department of Agriculture. Stanley R. John-
omy. Edited by Tracy S. Petersen. Design by
son, director, Cooperative Extension Service, Iowa State
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