In urban settings, heavy metals tend to rise to high levels because of settling of urban dust, air ...

Methods of controlling water erosion are based on four actions:1.
Reducing raindrop impact to lessen detachment (growing vigorous crops that canopy
quickly, leaving crop residues on the surface, mulching or growing a total vegetative
cover)
2. Reducing or slowing runoff (lessens detachment by scouring and reduces the amount of
soil that can be transported). Avoiding compaction, maintaining organic matter levels,
and subsoiling help water infiltrate the soil. Contour practices and conservation tillage
both reduce runoff.
3. Carrying excess water off the field safely by use of grass waterways or tile outlets.
4. Filtering soil particles out of running water.
In practice, soil conservation measures may be classified in the seven following categories.
1. Soil Improvements
Practices that improve infiltration of water into the soil reduce runoff and diminish erosion rates.
Practices that increase soil organic matter content and improve aggregate stability are crucialorganic
agriculture, conservation tillage, cover cropping, and other practices. Meadow crops effectively
improve aggregate stability to help save soil. Avoiding or treating compaction by subsoiling also
improves infiltration.
2. Vegetative Cover
Vegetative cover protects soil from raindrop impact, standing vegetation impedes overland flow, and
root systems help bind the soil together. A standard erosion control practice is simply selecting a crop
suitable for a site's erodibility. Other forms of erosion control practices such as strip cropping and
conservation buffers also use vegetative cover. Crop rotations that involve small grains and forages,
along with row crops, reduce erosion over continuous row crops. Other forms of vegetative cover
include cover crops, roadside vegetation, and turf grass lawns.
3. Conservation Tillage or Mulching
Conservation tillage sharply reduces sheet and rill erosion. It is the lowest cost conservation method
per ton of soil saved and carries other benefits. Conservation tillage is the most widely accepted Best
Management Practice for controlling soil losses. Conservation tillage effectiveness depends on a rough
soil surface and surface residues. The definition of conservation tillage states that residue coverage be
adequate to bring erosion below T30 coverage as a minimum.
4. Contour Practices
Contour practices include tillage and planting across slopes, on the contour, rather than up and down
slopes. A contour is an imaginary line across a slope that remains at constant elevation.
Contour tillage means tilling on the contour, then planting following the same contour. Rainfall ponds
form behind the small ridges created by tillage, providing more time for water to infiltrate and
impeding downhill flow. Areas of moderate slope and low intensity rainfall benefit most from contour
tillage. Combining contour tillage with conservation tillage layers two technologies for greater
protection.
Strip-cropping takes advantage of the fact that close-growing small grains and forage provide a dense
vegetative cover. Strip cropping adds another layer of protection to contour tillage and can be more
effective in areas of moderate rainfall. Adding conservation tillage adds yet another layer of protection.
5. Grassed Waterways
A grassed waterway is a shallow, sodded, wide ditch that runs down a slope. It is designed to carry
excess water off the field safely. Waterways are also designed to carry excess water off the field
safely, and may be used to collect water from tillage contours or terraces. Grassed waterways are also
a version of conservation buffer.
6. Conservation Buffers
Strips of permanent vegetation that retard overland flow and act as living filters to remove sediment,
nutrients, and pesticides are called conservation buffers. They reduce erosion, preserve water quality of
nearby bodies of water, and enhance wildlife habitat.
Conservation buffers work by slowing runoff while improving soil physical properties so infiltration is
improved. Examples include enhanced structure, improved macroporosity, higher organic matter
content, and lower bulk density. Microbial activity is also improved, and some buffers, especially
riparian buffers, remove nitrates from water by exposing the water to enhanced denitrification.
Contour buffer strips are strips of permanent vegetation planted on the contour between strips of
cultivated crops. They are permanent, not cropped, and slow water flow, permitting more time for
infiltration, and filter the flow. The strip should be made of a vigorous, stiff-stemmed grass that will
not fall over when water flows through it.
Filter strips lie along the downhill edge of a field, and work to filter sediment out of runoff from a field
before it can enter a receiving area. They can also filter out some nutrients and pesticides. Like contour
buffer strips, a dense, stiff-stemmed grass works best.
Riparian buffers are strips of permanent vegetation along streams, wetlands, and other bodies of water,
to protect water quality from field runoff. Riparian buffers include versions with herbaceous plants like
stiff grasses, and woody plant buffers with trees and shrubs or some combination. A residential
form of riparian buffer is planting dense vegetation along the shore of lakeside homes and cabins,
rather than mowing right to the shore.
7. Terraces
Terraces are required on long or steep slopes on impermeable soil. They are expensive and used most
commonly for valuable crops or where there is a shortage of good land. In general, two kinds of
terraces are used.
Level terraces parallel the slope and do not empty into a waterway. This
type of terrace is used where soil is permeable enough so water can seep in
once captured in a terrace.
Graded terraces are needed where water cannot soak in enough. These may
slope gently toward a waterway or be drained by an underground tile outlet.
Terraces are accounted for in the USLE by the LS factor. Terraces break up a slope into several shorter
slopes. Depending on terrace design, the slope factor may or may not change. It is assumed that most
of the eroded soil within the cropped part of a terrace is deposited in the terrace channel and that a
smaller amount leaves the field in waterways or outlets.
Diversions are large-capacity terraces that divert runoff from higher elevations. Diversions are not
farmed but are covered with grass. Their uses include:Protecting
fields from runoff flowing from higher elevations.
Directing water away from active gully heads.
Directing water from feed lots, farmsteads, or other sensitive areas.
Directing water away from homes.