High amounts of aluminum in soil may be harmful for plants.
Aluminum, the most abundant metal in Earth's crust, makes up about 7 percent of the crust by weight. Aluminum occurs in various forms in the soil but is not essential for plants or animals. On the contrary, high aluminum content may be detrimental to plant growth.
Types
Not all forms of soil aluminum are harmful for plants. Growers mainly rely on two types of tests to determine the type and content of aluminum in the soil. The results of each test, known as Mehlich 3-Al test and Available Al test, may be converted to the other. If aluminum content is too high, the soil may be treated to control the metal.
Available Al
"Available Al" refers to excess amounts of easily soluble aluminum in soil. High amounts of available aluminum is toxic for plants and also reduces the amount of nutrients that plants can make use of, such as phosphorus and sulfur. As such, growers specifically target available aluminum by treating the soil.
Factors
The amount of available aluminum is influenced by certain soil factors, including pH, amount and type of clay in soil, presence of organic matter in soil, and amount of all forms of aluminum in the soil. In treating for aluminum, soil pH is the most important controlling factor to manage the soil.
pH Treatment
The easiest and cheapest measure to control soil aluminum is to treat the soil to maintain its pH within a certain range and make the soil less acid. Soil pH may be maintained by adding lime to decrease acidity and available aluminum.
Gypsum Treatment
Soils with highly acid subsoils may not be properly treated with surface application of lime. For such soil types, the best treatment is to apply gypsum. Neither lime nor gypsum neutralizes the soil right away; it may take up to 18 months for the soil to decrease its acidity and aluminum content.
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