How to Acidify Your Soil

Why acidify your soil?

Blueberries for example require lower soil pH, or acidity, then is required by crops such as raspberries, corn, forage grass and vegetables. Typically, highbush blueberries must have soil pH between 4.5 and 5.5. If your soil test shows a higher pH, what can be done to decrease it?

Luckily, you can reduce soil pH reasonably easily. The pH of your soil can be reduced with substances such as sulphuric acid, aluminum sulphate and iron sulphate, but elemental sulphur is the most efficient and cost effective. It is really the only practical option for blueberries and other crops requiring more acid conditions. In warm, moist soils elemental sulphur is oxidized by bacterial species of the genus Thiobacillus, resulting in the production of sulphuric acid. Since an acid is defined as a substance that tends to give up hydrogen ions when dissolved, sulphuric acid produced from the oxidation of elemental sulphur effectively lowers pH.

How much elemental sulphur must be used?

A reasonable approach has been chosen using data taken from a Michigan State University site. Following is a simplified table relating sulphur requirement to soil texture.

Elemental sulphur needed to lower pH to 4.5 (lbs/acre)

Alternatively, if soil texture is not known, the second table (from the same source) relates Cation Exchange Capacity (CEC) to texture, so a guess at texture can be made based on the known CEC. Look on your latest soil test to see what your CEC is.

General range of ECEs for different soil texture groups

In the event that your field has not yet been tilled and planted, an opportunity exists to apply much more elemental sulphur than after the crop is established. In this case cost is a limiting factor, and the sulphur would be broadcast and disced in about eight inches in depth. Where a crop is established, use the rates from the chart but reduce proportionally by topdressing in a band on each side of the rows.

Apply elemental sulphur once, then take a fresh pH test several months later. If more is required, apply sulphur again the same time the following year, then test again at the same time of year under the same weather and soil conditions as the previous year. According to the MSU website, no more than 400 lbs/acre of sulphur should be applied to established plants at one time. This way a benchmark is established the first time, and testing the same time every year under the same conditions removes the chances the test will be affected by other parameters such as soil moisture.

TerraLink Horticulture supplies elemental sulphur in a prilled form. For more information, contact us today.

REFERENCES: Longstroth, M. Michigan State University. Internet reference, downloaded July 26, 2011.  http://web3.canr.msu.edu/vanbu... Updated July 15, 2009. Use of sulphur to reduce pH.