Keeping soil in its place

Question: What are some things that farmers do to keep soils from eroding?

Answer: What a great question, but let’s not limit it to farmers!

Erosion is a natural process; it is the reason we have valleys, mesas, sand dunes, and the Grand Canyon. There are three processes in erosion:

1) Detachment of soil particles from the surface

2) Transportation of the detached particles

3) Deposition of the particles

Erosion control methods address one or more of these processes.

Keeping a blanket on the soil

The best protection a soil has is a blanket of living vegetation on the surface. Dead plants and plant parts (a.k.a., residues) on the surface and mulches also help.

rye-cover-crop-nrcs

A cover crop, like the rye grass sprouting between harvested rows of corn in this photo, helps protect the soil from erosion until the next corn crop is planted. Photo: Natural Resources Conservation Service

Farming and construction often remove or decrease the amount of vegetation (both living and dead) on the soil surface, and so increase the potential for erosion. But work activities are not the only danger to soil. Recreational vehicles, hiking off-trail, military drills, and other activities also can destroy vegetation and decrease the plant cover on the soil surface. After the vegetation is gone, the soil is susceptible to blowing in the wind, being pounded by raindrops, and washing away in runoff.

How do farmers keep the surface covered? When possible, they have a growing crop on the field, though not all crops are equally effective at decreasing erosion. Wheat and hay crops cover most of the soil surface, and so limit erosion better than crops like soybeans or cotton. These latter crops are often planted in wide rows, leaving bare soil exposed for a longer time.

After a crop is harvested, farmers in wet and humid regions may plant a cover crop to protect the soil surface until the next growing season when they plant another crop they will harvest. Some farmers use irrigation to plant a cover crop, but in many areas the water available for irrigation is becoming more limited.

Tilling the soil less

Traditional tillage systems turn and mix the soil, much like a rototiller that gardeners often use. When I was a child, my dad and I would turn our garden soil to about 30 centimeters (1 foot) deep with a spade. Then we’d run a rototiller to make the soil nice and fluffy. Intensive tillage systems like these break soil aggregates (natural clumps of soil particles) into smaller chunks.

contour_farming-wi-by-darin

In hilly areas, such as this landscape in Wisconsin, USA, farmers often plant along contours running parallel to the slope of the land. This keeps water from running downhill, and encourages infiltration of water into the soil surface. Photo by Darin, http://www.flickr.com.

In semiarid and arid regions, the soil can dry as deep as it was tilled. The powdery soils on the surface are also easily washed away by rain or blown away by wind.

In contrast, more modern tillage systems involve plowing less often, mixing the soil less, creating and leaving large aggregates at the soil surface, and/or leaving plant residues on the soil surface.

Slowing the downhill flow of water

When water erosion is a problem on sloping lands, farmers may plant on contours so that the plant rows follow lines of equal elevation. This limits water from running downhill, and increases infiltration of water into the soil surface. Terraces, grassed waterways, and diversions are other tools used on sloping lands to limit the amount of water running downhill across bare soils.

Similar techniques are used on hiking and biking trails, and on ditches in the roadside right-of-way to slow water movement or divert it away from the trail or road.

What about off the farm?

Construction projects often strip away all the vegetation and much of the surface layer of soil. Heavy equipment compacts and disturbs the soil surface even more. When it rains, water cannot permeate the ground, so there is more runoff. Moving water then carries soil particles with it: The soil goes where the water goes. In some areas, construction projects are also subject to wind erosion.

erosion-control-washington-dot

Farmers aren’t the only ones who should be concerned with preventing erosion. Erosion control measures are also needed during construction projects. Photo: Washington State Department of Transportation

During a project, special fences, compost, detention ponds, and other techniques are used to protect the soil surface, slow runoff, and limit the amount of water that leaves the construction site. After the project, vegetation is planted, often in two phases. The first phase provides quick ground cover (if there is rain to get the seeds to germinate and grow). The second phase establishes perennial plants that will protect the surface in the future.

In short, the basic principles for controlling erosion are similar regardless of who uses the soil. These include:

1) Keeping the soil surface covered with vegetation or residues to protect it from wind or raindrops. This limits detachment.

2) Slowing down flowing water or wind speeds at the soil surface. This limits detachment and transportation, while encouraging deposition of soil.

3) Improving soil physical conditions at the surface so that it holds together better. This also limits detachment.

–Answered by Clay Robinson, a.k.a., Dr. Dirt

Have a question for Soils Matter? Post it in the comments section below or email us at soils-matter@soils.org

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One response to “Keeping soil in its place

  1. Hi,

    I am writing this to ask for your help to keep the organic standards honest. Please sign a petition demanding that the USDA follow the recommendation of their advisory committee to not allow the hydroponic growing of vegetables to be certified organic. This only takes one minute, and will help show the USDA that the organic community does not support their weakening of the organic standards.

    Please sign our petition:

    http://www.ipetitions.com/petition/keep-the-soil-in-organic-growing

    For more information on this, please visit this website:

    http://www.keepthesoilinorganic.org/

    Why are we doing this?
    We are doing this because of our deep concern about a failure to maintain the integrity of the national organic standards. The way that the national standards work is that a group of federal bureaucrats (called the National Organic Program, or NOP) are responsible for defining and administering organic standards for the United States. There is also an advisory committee of 15 people (called the National Organic Standards Board, or NOSB) representing organic farmers and consumers who make informed recommendations to the USDA. The USDA has sometimes taken a long time to respond to a recommendation, but never before have they actually reversed a recommendation of the advisory committee (NOSB), which is charged with the mission of representing the organic community. The NOSB is a balanced group of very committed and knowledgeable people, who have taken their responsibility of guiding the federal organic standards very seriously. They do a great deal of good research and hold public hearings to hear all points of view, before making a recommendation. They only make recommendations on subjects requested by the USDA. They are meant to be the “experts” on organic to the USDA.

    The recommendation
    In 2010 the NOSB (National Organic Standards Board) submitted a recommendation to the USDA that soil-less vegetable production NOT be certified as organic. Until that time, the issue of soil-less growing had never been addressed by the NOP, so the USDA asked the advisory committee to come up with a recommendation. The NOSB voted 12 to 1 (with 2 abstentions) to prohibit soilless production. They wrote out a carefully worded, well thought-out document, making their arguments clear. The recommendations of the NOSB are usually eventually accepted by the USDA, but in this case the USDA has not acted on the NOSB recommendation, and three years later, the USDA continues to ALLOW hydroponic vegetable production to be certified as organic. The USDA has not offered any guidance to certifying agencies on this matter, nor any explanation. They have not held public hearings. Many certifying agencies in the US are now refusing to certify hydroponic operations as organic.

    Now
    Presently, the vast majority of the “hydroponic organic” produce sold in this country is grown in either Mexico, Canada, or Holland. ALL THREE OF THESE COUNTRIES PROHIBIT HYDROPONICALLY PRODUCED VEGETABLES TO BE SOLD AS ORGANIC IN THEIR OWN COUNTRIES. Mexico, Canada, Japan, New Zealand, and 24 European countries, (including Holland, England, Germany, Italy, France, Belgium, and Spain) all prohibit hydroponic vegetable production to be sold as organic in their own countries. There is no labeling to announce that these vegetables are hydroponically grown. Many consumers and produce managers have no idea.

    The USA is alone
    The NOSB has formally recommended that the United States join the international community in this common definition of organic produce. The USA is virtually isolated in the world in its decision to allow “soilless organic.” In essence, a small committee of the USDA is redefining “Organic”. The consequences of this will go far beyond the US, creating pressure from hydroponic growers in other countries to redefine organic there as well. Please let the USDA know that we won’t allow this.

    There is also a petition for consumers supporting us on the website, as well as letters from members of the organic community. Please forward this letter to your friends and family.

    Thanks,

    Dave Chapman
    Long Wind Farm
    East Thetford, VT 05043

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