What is a soil extractant?
A soil test utilizes an extractant to determine the amount of plant nutrients in the soil. A soil extractant is a solution made up of water and a certain concentration of chemicals which is thoroughly mixed with the soil and then filtered for analysis. The Mehlich-1 extractant works very well as a soil extractant but some states in the Southeast have switched to the Mehlich-3 extractant. These states have significant acerages of calcareous soils with pH values greater than 7.0. For these soils, the Mehlich-3 extractant performs much better than the Mehlich-1 extractant.
The Mehlich-1 extractant is used by the Southeastern state supported labs in Alabama, Florida, Tennessee, Virginia, Georgia and South Carolina as well as some private labs. The Mehlich-1 extractant (implemented in 1953) was developed by Dr. Adolph Mehlich for the North Carolina Department of Agriculture Soil Testing Division. It is a versatile soil extractant that is used for determining the amounts of phosphorus, potassium, calcium, magnesium, zinc, manganese, copper and boron. It is made up of a dilute solution of hydrochloric and sulfuric acids, thus it is often referred to as the "double acid" extractant. It works well for acidic, low cation exchange capacity (CEC) soils which encompasses essentially all of the soils in the Southeast.
The Mehlich-3 extractant is used by the Southeastern state supported labs in Kentucky and North Carolina as well as some private labs. In an attempt to make a universal extractant that could be used for any soil in the world, Dr. Mehlich developed the Mehlich-2 extractant which was used for about 2 years. The Mehlich-2 contained 4 different chemicals but the chloride in the extractant was causing laboratory instrument problems. Subsequently, Dr. Mehlich developed the Mehlich-3 extractant by changing the chemical composition of the Mehlich-2 extractant slightly to exclude the chloride component. In addition, he added a chelating agent to increase the amount of micronutrients extracted, particularly copper. The Mehlich-3 extractant was adopted in 1984 and is being used throughout the world.