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College of Food, Agricultural, and Environmental Sciences


New Test Simplifies Soil Quality Assessment

July 1, 2002

PIKETON, Ohio - Assessing soil organic matter for overall soil quality can now be done in an agricultural field, a greenhouse and even a homeowner's backyard garden.

Ohio State University researchers have developed a method for measuring soil quality that involves mixing the soil with a non-toxic solution and measuring active carbon content by matching the color of the solution to a color-coded chart. The work is in association with Ray Weil, a soil scientist with the University of Maryland.

Rafiq Islam, a soil and water specialist with Ohio State's South Centers at Piketon, said the simplified test would enable users to measure soil quality directly on site and make soil management practices based on the results. The study will be published in the American Journal of Alternate Agriculture.

"With this test anyone can monitor the quality of their soil right in the field and measure it over time based on what management practices they've applied," said Islam. "It's not meant to replace the commercial soil tests, but it's just another tool for farmers who can then conduct additional soil tests or consult professionals if they do have poor soil quality." Islam and Ohio State horticulturist Shawn Wright said the test is so simple that farmers could not only use it, but greenhouse professionals, landscape consultants and even home gardeners could take advantage of its efficiency.

Soil organic matter is a core indicator of soil quality, and soil quality is usually characterized by high levels of active carbon. Active carbon includes microbial biomass, amino acids, soluble carbon and soil carbohydrates. Any changes in the levels of active carbon changes the level of organic matter, resulting in either a degradation or improvement in soil quality.

Islam said that current commercial soil tests do not measure active carbon content. Total soil organic matter tests can be calculated in the lab, but are time consuming, not user-friendly and do not give an accurate measurement of active carbon since the results also include passive carbon, the bulk of soil organic content that changes little when soil properties are altered.

"Most organic matter is not active," said Islam. "So acquiring results from a test that also accounts for inactive carbon is not a very accurate assessment of soil quality. We needed a test that separated the active carbon from the rest of the soil content." The result is a method that can accurately identify active carbon in field and lab situations on soils around the world. For example, soils tested in South and Central America, the mid-Atlantic, North Dakota, Kansas, New Jersey, Africa, and Asia measured for active carbon 98 percent of the time.

Researchers were also able to test for active carbon between plowing and no-till production systems compared to methods that tested for total carbon content. They found that while neither system showed any significant difference in total carbon levels, the no-till system produced a higher active carbon content under the new testing method.

"The test gives you an idea of soil structure either for the type of soil you are planting in and even for the type of production system you are using," said Islam.

The simplicity behind the test involves its active ingredient - potassium permanganate and some other components. Islam said the non-toxic deep purple solution reacts with the active carbon in the soil when the soil is mixed with the solution and shaken. The higher the active carbon levels, the lighter in color the solution becomes. Users can then compare the result to a chart that ranges from deep purple, indicating poor soil quality, to light pink, indicating excellent soil quality.

The researchers equate the test to soil pH kits. "It's simple and cost effective, requires no elaborate equipment and can be tested on a wide variety of soil types," said Wright.

Researchers plan to develop a data bank of active carbon analyses on thousands of soils around the world.

Candace Pollock
Rafiq Islam, Shawn Wright