Every year the Dawson County Extension Service conducts hundreds of soil samples. One of the main things that a soil test will determine is soil pH. Soil pH strongly influences plant growth, the availability of nutrients and the activity of soil microbes.

Garden soil falls into one of three broad categories; 1) acid, 2) neutral or 3) alkaline. On the pH scale, which goes from zero to 14, seven is defined as neutral (neither acidic nor alkaline), below seven is acidic and above seven is alkaline. Each unit change in the scale represents a ten‑fold change in acidity or alkalinity. For example, a pH of 5.0 is ten times more acid than a pH of 6.0.

Many gardeners know that productivity of the vegetable garden decreases as the pH falls from the range of 6.0 ‑ 6.2 to 5.5 and below. The productive potential of soil is not determined solely by its sand, clay and silt composition, but also by the interactions of its mineral, organic, chemical and biological components. Reduced productivity of low pH soils is primarily due to its effects on these complex soil processes.

Over a period of time, Dawson County soil tends to become more acid. Rainfall, irrigation, soil erosion, crop removal and the use of the ammonium form of nitrogen all contribute to a gradual lowering of the pH. Routine applications of liming materials will prevent and/or correct low soil pH.

The amount of lime to apply can be determined by a routine soil test. Liming recommendations indicate the number of pounds of lime needed to bring your soil pH up to the satisfactory range for crop production. As a general rule of thumb, a pH in the range of 6.0 ‑ 6.2 is best for growth of vegetables. Usually four to eight pounds of lime will be required for each 100 square feet of garden; however, the exact rate will vary depending on soil type, fertilization practices and previous liming history. I will be happy to help you determine how much lime you need for your soil.

There are a number of different types of liming materials available. Most liming materials, in addition to neutralizing soil acidity, also supply calcium and/or magnesium. The most common liming materials used in Georgia is dolomitic limestone. Dolomitic limestone sold in Georgia contains more than six percent elemental magnesium in addition to calcium. Since Georgia soils are often deficient in magnesium, dolomitic limestone is usually recommended.

For additional information on lime and/or conducting a soil test, call the Dawson County Extension Office at (706) 265‑2442.