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Dirty facts
Slag may look like dirt, but that doesn’t make it soil. According to Purdue soil mineralogist Darrell Schulze, soil is made up of four main chemical elements: oxygen, silica, aluminum and iron. In addition, there are lesser amounts of other elements like calcium and magnesium. Depending on how these elements are combined, soil may contain minerals that release nutrients to plants or minerals that hold on to nutrients and make them unavailable. Slag lacks certain plant nutrients, the vital ingredients that make soil a good growing medium.
While good soil is a blessing for farmers, Schwab says it’s not necessary to grow things. “You don’t need soil, but you do need something to jump-start the process,” he says. “For plants, that’s usually water, and if the seeds are waiting, they will grow when water’s applied.”
Getting plants to grow in the slag will not only improve the appearance of the industrial area, but also will improve the environment. As plants grow, die and decay, they add organic matter to the slag. The decaying plants also add nutrients to the sterile substance that will improve the quality of the material to eventually help turn it into soil.
“While it won’t be soil during our lifetime, the effort will accelerate the biological process,” says Schwab.
It’s no gyp
At the other end of the state, about 250 miles directly south of the U. S. Steel plant, is Petersburg, Ind., home of an Indianapolis Power and Light electric generating station. At this coal-burning facility are beige mounds of a very fine substance similar to cosmetic powder. However, the beauty of this product is its potential to benefit soil.
The mounds are synthetic gypsum, a byproduct of the scrubbing process used to meet clean air standards in coal-fired generators. Unlike mined gypsum that can contain many other minerals, synthetic gypsum is 95 percent pure. It can be used to produce wallboard for construction or as a fill material for roads. It also contains calcium and sulfur, both essential plant nutrients.
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USDA soils researcher Darrell Norton shows samples of unfiltered (left) and filtered water in a study to use gypsum to control farmland erosion. |
Sulfur used to be plentiful in Indiana fields, freely added to the soil by acid rain. Since 1970, when the Clean Air Act was passed, some areas experience sulfur deficiencies. Synthetic gypsum, removed from the smoke stacks to improve air quality, is about 15 percent sulfur. The calcium in gypsum can also replace calcium lost from fields due to decreasing use of lime and acidic fertilizers.
Darrell Norton, a U.S. Department of Agriculture researcher with the National Soil Erosion Research Laboratory located at Purdue, studied the use of gypsum from the Petersburg plant to control farmland erosion in Sullivan County. An agronomy adjunct faculty member, he worked with Purdue graduate students and researchers, and found that soil loss was minimized when gypsum was added. “Gypsum is easy to apply and helps to reduce crusting and soil erosion on soils with a lot of clay,” he says. “It’s also a good way to beneficially recycle a waste product.”
Norton, who has studied the agricultural benefits of gypsum for a few years, says it can also increase yields. “It improves water infiltration and promotes better rooting, which helps the plant to take up nutrients,” he says.
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