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Erosion is a natural process by which the soil is worn away by wind, water, and other forces. It becomes a problem when human activity causes it to occur at a much more rapid pace than under natural conditions. Soil erosion is at once the greatest threat to the Nation's soil productivity and the largest source of pollutants in our waterways.

Why control erosion?

Excessive erosion by wind and water reduces soil productivity and contaminates air and water. Erosion increases the cost of farming and contributes to lower profits for farmers and higher food prices for consumers. On farm damage from erosion includes lower yields of crops or forage, higher fertilizer costs, increased fuel costs to till the tougher subsoil and higher bills for equipment maintenance. Sediment from erosion in urban areas is also costly. It clogs storm drains and drainage channels causing increased costs for street and drain maintenance.

Off the farm and downstream from urban development, sediment from eroding areas clogs rivers and decreases reservoir capacity. This restricts navigation, reduces recreation potential and scenic value and increases the hazards and severity of flooding. A side effect of erosion and sedimentation is the movement of plant nutrients, pesticides and other chemicals off the land. This causes a loss of fish and wildlife habitat and polluted water supplies. An often-overlooked effect of sedimentation is a very serious safety hazard when the sediment covers road surfaces.

When did we first recognize soil erosion as a problem?

We have dealt with soil erosion since the early days of our nation. Settlers of the United States grew cotton, tobacco and corn, which they tilled to control weeds. That practice promoted erosion and loss of organic matter because the fields were partially or completely bare for much of the year. Many farmers also grew the same cash crop in the same field every year until the all the nutrients and organic matter were robbed from the soil. Then they moved on. Land was cheap and seemingly limitless.

It wasn't until the 1930's and the Great Depression, however, that soil erosion was brought to the forefront. In May 1934, a dust storm that originated in the southern Great Plains carried an estimated 200 million tons of soil to the northeastern United States and out to sea. A year later, in the midst of a major dust storm which blew into Washington, D.C., Congress passed a bill that created the Soil Conservation Service. Land across the nation was then divided into conservation districts to provide help directly to land users. Today, erosion remains a serious problem, although much headway has been made to control it.

Classifying erosion

Wind erosion occurs when the soil surface is bare and dry. Sandy soils are especially supceptible to wind erosion because particles do not stick together. Wind also erodes organic soils (such as peats and mucks) and soils from volcanic ash, when they are dry, because the dry particles are very light and noncohesive.

Water is the culprit of most of the erosion in Indiana. Water erosion begins when a raindrop hits an unprotected soil surface...

	splash erosion Raindrops splash soil particles short distances. These particles are then much more vulnerable to erosion by water flowing over the surface.
	sheet erosion When rain falls faster than the soil can absorb it, water begins to collect and flow over the ground surface. Sheet erosion begins when this surface water begins to carry along particles that were detached by raindrops.
	rill erosion Flowing water will soon establish paths. If the soil is unprotected, some of these paths become rills, small eroding channels. Water flowing through a rill easily detaches soil from its sides and bottoms . As it moves further downslope, flow in rills becomes more erosive, causing the rills to enlarge and join with others.
	concentrated-flow erosion The topography of some areas is such that water will collect in f few major waterways before leaving the fields. Concentrated-flow erosion is erosion by water flowing in channels that may range from a large rill to a small gully. Rills can be erased by tillage, however, channels tend to reform in the same location every year. If allowed to continue, a gully can form.
	gully erosion In a gully, soil is rapidly removed by water gushing over the "headcut" (the uphill end) of the gully, water removing soil material that has slumped from the gully's sidewalls. The slope at the headcut is nearly vertical, causing the runoff flowing over it be highly erosive so that the gully advances upslope.
	mass erosion or slumping This type of erosion occurs where a hillside becomes so saturated by water that large areas of soil slide or creep downhill.

Water erosion may move tons of soil per acre during one storm, or barely a ton over several decades. It may carry particles a few feet downslope, or thousands of miles to the ocean. Factors which affect the erosion rate of water are: (1) the type and amount of rainfall, (2) the length and steepness of slope, (3) the erodibility of soil, and (3) the management of the land.

What determines a soil's erodibility?

In our opening article for this series (see Pat's Page "What is Soil...and why is it so important?"), we discussed the factors that effect soil formation and the properties the soil takes on as a result. Four soil properties are instrumental in determining a soil's erodibility:

Texture -	Generally the most important factor, it refers to the proportions of particles of sand, silt and clay in a soil. Water moves detached clay particles more readily than particles of silt or sand, but clay particle bonds are stronger than those of silt and sand, therefore clay soils can be quite resistant to erosion.
Slope -	As slope steepness increases, so do the erosion effects of water runoff. The runoff then exerts more force on soil particles, breaking their bonds more readily and carrying them farther before deposition.
Structure -	Soil particles are clustered in aggregates held together by physical and chemical bonds. The aggregates in turn form clumps called peds. Peds of a given undisturbed soil have a consistent appearance and size range, but intensive use of a soil can alter the natural soil structure. Excessive tillage tends to break down peds and aggregates, lowering the erosion resistance of soil particles and the volume of air space in the soil.
Organic matter content -	Organic matter is the decomposed remains of plants and animals. It helps soil fertility, water infiltration and storage and soil structure. Farming a field year after year without an interval of a soil-building crop such as alfalfa depletes nutrients and organic matter in the soil. Increasing the content of organic matter is a principal means of improving soils that have been damaged by erosion.

Who is responsible for controlling soil erosion?

Most of the burden of maintaining the health of our soil is in the hands of private landowners who own 70 percent of our nation's lands. We must rely on their land use and management decisions to provide us with clean air and water, enhanced fish and wildlife habitat, and visually pleasing rural landscapes.

And, so far, they've done a pretty good job! The decade between 1985 and 1995 saw remarkable improvements in soil conservation by America's agricultural producers. Soil erosion has been cut by nearly one-third due to their adoption of practices such as conservation tillage, terraces, and contour farming.

More than two million acres of conservation buffers have been installed by landowners in recent years, and about 30 million acres of fragile cropland are now enrolled in the Conservation Reserve Program and seeded to grass or planted to trees for periods of 10 to 15 years.

Most erosion problems can be economically solved by using proven technology and methods that are available today. If you are a landowner and feel you have an erosion problem on your land, contact your local Soil and Water Conservation District office. They can provide technical help and explain programs available to assist you in creating a healthier soil and cleaner water. In the next edition of Pat's Page, I will highlight some of these programs.