|USDA-Soil Conservation Service|
cooperative publication . . .|
Water is a finite resource essential to life. Water sustains Idaho's fish and
wildlife, agriculture, industry, mining, forestry, hydropower generation,
recreation, and growing population. Idaho's rivers and lakes are renowned for
their water sports and provide some of the most spectacular natural scenery in
the world. Water is precious, and its management determines the quality of
Today, Idaho is in the enviable position of having abundant water and water
quality much better than the national average. Yet water use will increase. As
that occurs, Idaho's water can be managed thoughtfully or abused and degraded. As
Idahoans make decisions about preferred uses for their limited water, conflicts
are inevitable. The challenge for all of Idaho's water users will be to cooperate
in managing water efficiently, maintaining its quality and conserving its
Sediment from eroding croplands is the largest nonpoint source pollutant in
Idaho's surface water (rivers, lakes, streams, reservoirs). Some facts:
Solutions to Erosion and Water Pollution
- Idaho has 6.5 million acres of cropland producing over 27 million tons of
sheet and rill erosion per year.
- Sediment from this eroding cropland is the largest nonpoint source pollutant
in Idaho's surface water.
- Not all eroding soil ends up in Idaho's surface water. The average sediment
delivery rate is about 20 percent, or about 5 million tons per year.
- Sediment from cropland has nutrients attached to the eroding soil particles.
Each ton of sediment contains about 3 pounds of nitrogen and 2.8 pounds of
- Based on sediment delivery rates, about 9,000 tons of nitrogen and 8,500 tons
of phosphorus are delivered into Idaho's surface waters each year.
To reduce erosion and protect surface waters we should use best management
practices (BMPs). Best management practices can be defined as implemented
strategies that reduce pollution and at the same time maintain farm
profitability. Idaho has a full compliment of BMPs farmers can use to reduce soil
erosion and nonpoint source pollution. BMPs are most effective when applied in
combinations that work together for erosion control and reducing sediment. Use of
a single BMP will seldom solve all conservation problems. BMPs best suited to any
individual field depend on site characteristics such as:
Specific types of BMPs for erosion control that should be employed in many areas
of Idaho include:
- rainfall and snowmelt,
- soil erodibility,
- land slope and slope length,
- crops and soil cover, and
- presence of supporting conservation practices.
Specific Erosion Control BMPs:
- Conservation Cropping Sequence
- Crop Residue Management and Conservation Tillage
- Contour and Cross-Slope Farming
- Contour Strip Cropping and Divided Slopes
- Deep Chiseling and Subsoiling
- Cover Crops
- Grassed Waterways
- Vegetative Filter Strips
- Water and Sediment Control Basins
Conservation Cropping Sequence
Use to reduce soil erosion by 40 to 50 percent.
Crop Residue Management and Conservation
- Remember the cardinal rule for reducing erosion: keep the land
- Start with crops that protect the soil.
- A good conservation cropping sequence contains a high
percentage of crops that are soil hugging, produce heavy canopy cover, and
produce large amounts of after-harvest residue.
- Do not grow crops producing low residue more than one year in a row.
- Use crops that provide protective cover during normal high erosion
Use to reduce soil erosion by 60 to 70 percent and prevent surface
Crop residue management is any tillage system leaving 30 percent
of the soil surface covered with crop residue after planting.
Contour and Cross-Slope Farming
- Use crop residue management to protect the soil not covered
by a growing crop.
- Crop residue management begins with selection of high
- Use conservation tillage systems such as no-till and mulch
till to plant crops while maintaining crop residue on the soil surface.
- No-till uses a one-pass drill with openers that places seed and fertilizer
in narrow bands without disturbing the area and residue between the drill
- Mulch tillage uses equipment that disturbs the full soil surface but does not
invert the soil or bury excessive amounts of crop residue.
- One important aspect of mulch tillage is using chisels, conservation plowing,
and/or uphill plowing as the first tillage operation.
- For conservation plowing and uphill plowing, remove trash turners from
moldboard plows so a row of residue is left sticking out along the edge of each
furrow. The goal is to leave the soil rough with about 1,500 pounds of crop
residue (60 percent surface cover) on the soil surface after primary tillage.
Surface straw intermixed with the soil will rapidly wick moisture into the
Use to reduce erosion 30 to 40 percent, depending upon size of ridges and
closeness to contour.
Contour Strip Cropping and Divided
- Perform tillage operations on the contour or across the slope.
- Ridges left by the tillage implement will trap and store rainfall and
snowmelt, increase the amount of water that infiltrates into the soil and reduce
the amount that runs off the surface.
- Use cross-slope farming when the topography makes it impractical to stay on
the true contour, but still stay as close to the contour as possible.
Use to reduce soil erosion 50 to 60 percent.
Deep Chiseling and Subsoiling
- Divide fields into narrow strips so that strips containing higher erosion
crops are alternated with low erosion crops.
- Operate every other strip to trap surface runoff so it doesn't run downhill
to the next strip.
- Divided slope farming is a form of strip cropping used where the hill isn't
long enough to accommodate three normal strips. Divide the hill into two fields,
alternating the protective crop and trap strip with the less protective
Use to reduce surface runoff and soil erosion by about 20 percent.
- Deep chiseling and subsoiling consists of pulling chisels
or subsoil shanks through the soil below normal plow depths to fracture
compaction layers and improve water infiltration.
- For best results, perform deep chiseling and subsoiling in the fall after
crop harvest when the soil is dry.
- To avoid concentrating surface water and creating gullies, pull chisels and
subsoilers on the contour or across slope.
- Deep chiseling and subsoiling leaves open fissures to the soil
surface where rain and snow can infiltrate. Advantage: Greater amounts of
moisture stored in the soil for the next crop.
- Close chisel and subsoiler fissures the next spring to avoid moisture
Use to provide emergency or short-term soil protection.
- A cover crop is one that is planted especially to protect
the soil from erosion and may be harvested for commercial purposes or tilled out
once the erosion period is over.
- Plant vigorous, close-grown crops in the fall to provide soil protection over
- Rapidly establishing small grains are the most popular cover crops.
Use to reduce soil erosion 60 to 80 percent from the flow area.
Vegetative Filter Strips
- Most cropland fields have a variable topography, with normal water runoff
moving to the concave portions of the landscape known as waterways.
Erosion occurs in the waterway when the soil is loose or has been tilled.
- Shape the sides of waterways and plant to grass to provide
protection from erosion.
Use to reduce sediment 30 to 50 percent.
- Vegetative filter strips are strips of grass or other close
growing vegetation that slow water runoff and trap sediment and other solid
- Plant filter strips in areas where water will pass over them as sheet
- Filter strips are most effective for removal of heavy particles.
Use to reduce gully erosion and trap sediment.
Water and Sediment Control Basins
- A terrace is an earthen embankment constructed across a
slope to trap and store water runoff or transport water to a non-erodible
- Terraces are best adapted to rainfed croplands but can also be used on
sprinkler irrigated croplands.
Use to reduce suspended solids in runoff by 40 to 60 percent.
- Water and sediment control basins are earthen embankments
constructed across minor watercourses.
- These small basins are effective for preventing gully erosion, trapping
sediment, and reducing downstream peak flows.
Use to reduce soil loss by 60 to 70 percent.
Summary of Best Management Practices for
- Mulch the soil surface with off-site residue or other
organic material to protect soil when vegetative or residue cover is not
- Mulches improve water intake, absorb the impact of falling
raindrops, and trap water to slow its movement.
- Straw mulching is becoming a readily accepted way to reduce
irrigation-induced erosion in furrow irrigated fields.
Idaho has an adequate compliment of BMPs to reduce soil erosion and nonpoint
pollution of surface water throughout the state. Best management practices are
most effective when they are applied as a system or combination of practices.
Multiple practices usually have synergistic impacts that compliment each other so
the value of the whole is greater than the sums of the individual practices. For
this reason the greatest protection usually comes from a combination of
This brochure, WQ-27, was prepared by R. L. Mahler, F. G. Bailey,
S. Norris, and K. A. Loeffelman. Mahler and Loeffelman are in the Soil Science
Division, University of Idaho, Moscow, Idaho 83844. Bailey is the State
Agronomist for the USDA Soil Conservation Service, stationed in Boise, ID. Norris
is the Public Affairs Officer for the USDA-SCS, also stationed in Boise.
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College of Agricultural and Life Sciences, University of Idaho.
All rights reserved.
Revised: January 3, 2003