Daniel Gill, Koske, Thomas J.
Acidic soils (low pH) cause more gardening problems in Louisiana than any other soil factor. They affect so many other soil factors in both pest management and soil fertility.
Soils become acidic naturally in our humid climate. Rainfall (over time) leaches out the basic minerals in soils. Fertilizers and organic matter from manure and compost tend to speed this acidulation process. Under very acid conditions (below pH 5.4), some minerals such as aluminum and manganese become very soluble and often are toxic to plants. These elements may cause foliage to yellow, pucker or burn. Plant nutrients such as calcium and magnesium often are deficient in acidic soils. The beneficial soil bacteria that fix nitrogen on the roots of legumes such as beans and peas cannot survive in acidic soils, and then those crops will suffer.
Many Louisiana soils require liming every three to five years to maintain the soil pH between 5.8 and 6.5. This pH range is adequate to ideal for most crops. Some soils may not need liming for acid reduction but may need extra calcium. In that case, we apply gypsum (calcium sulfate) to supply calcium without a change in pH. Many gardeners have quick pH testers that can identify serious problems in soil pH. A detailed soil test by a reputable laboratory, however, is the only way to determine the precise soil pH and any lime requirement.