Proper pH of the soil is important to plants. If the pH is low, lime may be added any time of the year. However, since lime is slow to react, applying lime as soon as possible is important. 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: Acid, neutral or 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 10-fold change in acidity or alkalinity. For example, a pH of 5.0 is 10 times more acidic 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.
Poor vegetable performance in Georgia gardens with low pH is usually caused by aluminum or manganese toxicity (low pH “releases” excessive amounts of these elements which are usually “bound” in the soil) and/or nutrient deficiencies of calcium, magnesium, potassium, phosphorus or molybdenum (their availability in the soil decreases as soils become more acid).
Over a period of time, Dawson County soil tends to become more acidic. 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 should be determined by a well-calibrated, lime-requirement test (the pH part of 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 4-8 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. You may contact the Dawson County Extension Service Office to have your soil tested.
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 material used in Georgia is dolomitic limestone.
Dolomitic limestone sold in Georgia contains more than 6 percent elemental magnesium in addition to calcium. Since Georgia soils are often deficient in magnesium, dolomitic limestone is usually recommended.
Clark Beusse is the Dawson County extension agent. For more information, call (706) 265-2442.