FOR IMMEDIATE RELEASE
FRIDAY, AUG. 20, 2004
||Brenda Cleveland, agronomist
Heavy rains increase need for lime
RALEIGH — Soil acidity has always been the most important soil fertility concern in North Carolina, and it probably always will be. Last year, nearly half of the 280,000 soil samples analyzed by the N.C. Department of Agriculture and Consumer Services showed a need for lime. This year's relatively frequent rains have increased that need in many areas of the state.
David H. Hardy, NCDA&CS soil testing section chief, wants people to be more aware of this problem. "In North Carolina, most soils are acid because the rocks and sediments from which they are formed tend to be acid," said Hardy, "but add to that several years of above normal rainfall, and you have a set of conditions that really promotes soil acidity. In our area, soil acidity is a recurring concern. It never goes away forever."
The best way to manage soil acidity is through periodic soil testing. The NCDA&CS Agronomic Division offers free soil testing for state residents. The tests not only measure soil acidity and levels of plant nutrients but also provide specific lime and fertilizer recommendations for the crop being grown.
Although soil samples can be submitted any time plants look stunted, deformed or discolored, it is a good idea to soil test on a regular schedule. Once every two or three years is appropriate for sandy coastal plain soils. Once every three to four years is sufficient for fine-textured soils of the piedmont or mountains.
Soil pH values in North Carolina typically range between 4.0 (acid) and 7.0 (neutral). A soil with a pH of 4.0 is 1,000 times more acid than a soil with a pH of 7.0. Most plants in the Southeast grow best in soils that are slightly acid (i.e., pH 5.5–6.5). The optimum pH, however, depends primarily on the crop being grown and soil organic matter content.
"When you put out enough lime to raise the soil pH by one unit, you've decreased acidity by a factor of 10," Hardy said. "That's a significant change."
Plant growth and yield depend on the balanced uptake of all essential plant nutrients. Soil acidity upsets that balance. It causes major nutrients (nitrogen, phosphorus, potassium, etc.) to be less available to plants and most minor nutrients (iron, manganese, etc.) to be more available. As a result, acidity often causes double trouble: deficiency of major nutrients combined with toxicity of minor nutrients.
In acid soils, plants may exhibit poor root growth, stunting, distorted leaves, yellowing or reduced yield. Root growth is limited partly because toxic elements, such as aluminum, are more available. At the same time, phosphorus, which is essential for good root development, is less available. To make matters worse, acid soils cause plants to be less drought tolerant and more susceptible to attack by pathogens and insects.
"Lime is the simple answer to soil acidity problems," Hardy said, "but applying lime properly requires advance planning. People really need to think ahead. It is not a last-minute, quick fix."
Lime moves into and reacts with the soil slowly. It takes months for it to be fully effective. Therefore, the best way to apply lime is to mix it thoroughly into the soil several months before planting. For shallow-rooted plants, such as turf or no-till crops, however, surface application of lime can be effective.
The two most commonly used liming materials are calcitic lime (calcium carbonate) and dolomitic lime (a mixture of calcium and magnesium carbonates). Cost, quality (particle size, calcium carbonate equivalency) and the need for magnesium are factors to consider when choosing a lime product.
Lime application is a good investment that improves yields for years to come. However, contrary to what some people will tell you, it is possible to apply too much lime. If the soil pH becomes too high, micronutrient deficiencies can occur. It is much more difficult to lower the pH level than it is to raise it. Therefore, be sure to apply only as much lime as needed.
Start thinking about soil testing now. It is the best way to manage soil fertility and optimize yields for the next growing season. Soil testing is a service of the N.C. Department of Agriculture and Consumer Services. For information on how to collect and submit soil samples, visit the NCDA&CS Agronomic Division Web site www.ncagr.com/agronomi or call (919) 733-2655.