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Potentially contaminated soils may occur at old landfill sites. Particularly those that accepted industrial wastes at one time.
These could include old orchards that used insecticides containing arsenic as an active ingredient.
Possible fields that had past applications of waste water or municipal sludge, areas in or around mining waste piles and tailings. Or industrial areas where chemicals may have been dumped on the ground, or in areas downwind from industrial sites.
(Source: United States Department of Agriculture)
Trace Minerals: The selenium content in soils may vary by a factor of 200 in the United States.
A kilogram of wheat may contain from 50mcg to 800mcg of selenium depending on where it is grown.
Fertilizers: Farmers normally only replace the minerals that are crucial to crop growth, such as phosphorus, potassium and nitrates.
Soil Nutrient Deficiency
Chromium and zinc are also critically deficient in the soil. This problem has been under extensive study by the UDSA.
Note: Studies performed at Rutgers University by Dr. Firman E. Bear show that some carrots tested for nutrient potency were almost completely without nutrients. This reduction in nutrient potency occurred in carrots from different farms all over the United States.
Dr. William Albrecht at the University of Missouri has shown that over a 10 year period the protein content of grains in the Midwest has declined by 11 percent.
The use of nitrogenous fertilizers is causing copper deficiencies and the overuse of potash fertilizers is creating magnesium deficiencies.
Managing Contaminated Soil
Soil is composed of inorganic particles (sand, silt and clay), organic matter, air and water. The quality of soil is judged by the proportions of these ingredients and the level of activity by earthworms, fungus and microorganisms.
Soil and crop management methods can help prevent uptake of pollutants by plants, leaving them in the soil. The soil becomes the sink, breaking the soil-plant-animal or human cycle through which the toxin exerts its toxic effects (Brady and Weil, 1999).
Research has demonstrated that plants are effective in cleaning up contaminated soil (Wenzel et al.). Phytoremediation is a general term for using plants to remove, degrade, or contain soil pollutants such as heavy metals, pesticides, solvents, crude oil, polyaromatic hydrocarbons, and landfill leacheates For example, prairie grasses can stimulate breakdown of petroleum products.
Phytoextraction is the process of growing plants in metal contaminated soil . Plant roots then translocate the metals into aboveground portions of the plant. After plants have grown for some time, they are harvested and incinerated or composted to recycle the metals. Several crop growth cycles may be needed to decrease contaminant levels to allowable limits. If the plants are incinerated, the ash must be disposed of in a hazardous waste landfill, but the volume of the ash is much smaller than the volume of contaminated soil if dug out and removed for treatment.
Plants are available to remove zinc, cadmium, lead, selenium, and nickel from soils at rates that are medium to long term, but rapid enough to be useful.
Nutrient Depeleted Soil History
In the 1930s, farmers in the sountern United States began planting kudzu, a fast-growing, deep rooted Asian vine, to prevent nutrient depelted soil. While the nitrogen fixing bacteria that live on kudzu roots help enrich the soil, kudzu can grow up to sixty feet high and spreads so rapidly that it is virtually impossible to control. This caused havoc on the farmland.
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