University of Idaho Water Quality Brochure

USDA-Soil Conservation Service
	BMPs for Erosion Control
	A cooperative publication . . .

Idaho's Water
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 Idaho's environment.

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 quantity.

Erosion=Water Pollution
Sediment from eroding croplands is the largest nonpoint source pollutant in Idaho's surface water (rivers, lakes, streams, reservoirs). Some facts:

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 phosphorus.
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.

Solutions to Erosion and Water Pollution
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:

rainfall and snowmelt,
soil erodibility,
land slope and slope length,
crops and soil cover, and
presence of supporting conservation practices.

Specific types of BMPs for erosion control that should be employed in many areas of Idaho include:

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
Terraces
Water and Sediment Control Basins
Mulching

Specific Erosion Control BMPs:

Conservation Cropping Sequence
Use to reduce soil erosion by 40 to 50 percent.

Remember the cardinal rule for reducing erosion: keep the land covered!
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 periods.

Crop Residue Management and Conservation Tillage
Use to reduce soil erosion by 60 to 70 percent and prevent surface runoff.
Crop residue management is any tillage system leaving 30 percent of the soil surface covered with crop residue after planting.

Use crop residue management to protect the soil not covered by a growing crop.
Crop residue management begins with selection of high residue-producing crops.
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 rows.
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 soil.

Contour and Cross-Slope Farming
Use to reduce erosion 30 to 40 percent, depending upon size of ridges and closeness to contour.

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.

Contour Strip Cropping and Divided Slopes
Use to reduce soil erosion 50 to 60 percent.

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 crop.

Deep Chiseling and Subsoiling
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 loss.

Cover Crops
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 winter.
Rapidly establishing small grains are the most popular cover crops.

Grassed Waterways
Use to reduce soil erosion 60 to 80 percent from the flow area.

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.

Vegetative Filter Strips
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 materials.
Plant filter strips in areas where water will pass over them as sheet flow.
Filter strips are most effective for removal of heavy particles.

Terraces
Use to reduce gully erosion and trap sediment.

A terrace is an earthen embankment constructed across a slope to trap and store water runoff or transport water to a non-erodible outlet.
Terraces are best adapted to rainfed croplands but can also be used on sprinkler irrigated croplands.

Water and Sediment Control Basins
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.

Mulching
Use to reduce soil loss by 60 to 70 percent.

Mulch the soil surface with off-site residue or other organic material to protect soil when vegetative or residue cover is not available.
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.

Summary of Best Management Practices for Erosion Control
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 practices.

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.

3M 5-94

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Revised: January 3, 2003

URL: http://www.uidaho.edu/wq/wqbr/wqbr27.html