Acid sulfate soils occur in areas where soil has been disturbed, either by human activities such as construction or by the natural weathering of susceptible terrain such as wetlands and tidal basins. Soil disturbance exposes sulfide-containing matter to the atmosphere. When exposed to the atmosphere, chemical reactions take placed transforming the sulfides into sulfates, which then transform neutral soil into highly acidic soil. Adding lime and other alkaline soil amendments can improve acid soil, bringing its pH balance back into a neutral zone. Testing the soil will help to determine the specific treatments necessary to reduce acid levels.
Tests
A variety of tests can be conducted to determine the amount of sulfate in soil. The results of these tests help determine the amount of lime needed to reduce the acid levels of the soil. Other methods of soil remediation are also considered.
Acid sulfate soils can be the result of mining and other industrialized land use. In circumstances such as this, where exact amounts of sulfate may need to be measured, tests are conducted in the lab. Government employed environmental scientists in Queensland, Australia, use the following tests to determine the amount of sulfates present in severely damaged soils: the Suspension Peroxide Oxidation Combined Acidity and Sulfate method test (SPOCAS) and the Chromium Reducible Sulfur method (SCR).
The Crop and Soil Environmental Sciences division at Virginia Tech tests soil using the Patented Peroxide Acidity Test, which is a common field test used to measure overall soil acidity. Highly acidic soil likely contains high quantities of sulfates, which can be countered with the application of lime. The Patented Peroxide Acidity Test provides scientists with the information necessary to provide prescriptive amounts of lime. It is essential that lime is added to this soil in specified quantities as over-liming soil is detrimental to soil.
Treatments
There are two ways to treat acid sulfate soils. The first is to simply not disturb the soil. Lack of disturbance prevents the sulfides from becoming exposed and oxidized. The second treatment is the addition of lime to the soil. Many gardeners are familiar with liming. Lime, or calcium carbonate, helps decrease acidity and bring soil back into a neutral pH allowing more vigorous plant growth.
Acidic soils do not support lush vegetation. If you are having difficulty growing crops and notice your soil has reddish patches and a yellow tinge, then the soil most likely contains sulfates. In order to confirm your suspicions, you should submit a soil test to a local testing agency, such as your Master Gardener Extension.
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