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Don't lime withouta soil test

All about lime and soil pH levels

Date published: 11/10/2006

ANSWERING QUESTIONS is part of an extension agent's job. Today I'll answer some recent questions about lawn and garden activities in November.

QWhy do you recommend soil testing? Can't we just buy lime and fertilizer and skip the soil test?

ASoil tests provide us with key information on the health and general condition of our soils. We need to think of soil as the growing medium for our turf and landscape plants. All plants have a desirable range of growing conditions. These growing conditions include an ideal pH range and nutrient requirements. A soil test tells us the soil's pH and provides information on the level of minerals or nutrients in the soil.

Soil pH measures the acidity of the soil's water. As soil pH changes, the availability of the soil's nutrients changes. To be absorbed by plant roots, the minerals or nutrients must be dissolved and in solution. Soil pH has a direct effect on the nutrients' solubility and availability. A pH range of 5.8 to 6.5 provides optimum nutrient availability to plants.

When soil pH is below 6.0, the primary plant nutrients nitrogen, phosphorus and potassium become less available to plants. In soils with a pH above 7.5, iron, manganese and phosphorus are less available.

You might note that phosphorus availability is reduced both by a pH below 6 and by a pH above 7.5. When soil pH is maintained at a level to keep phosphorous available to plants, other plant nutrients--nitrogen, potassium, calcium, magnesium, sulfur, zinc and manganese--also are highly available to the plants.

In highly acid soils (low pH), aluminum and manganese can become more available and more toxic to plants. On the other hand, soils with a low pH can have high levels of some plant nutrients that are not in solution and not available to plants. Simply adding more fertilizer does not make plant nutrients more available.


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JOHN E. HOWE is an agent in Virginia Cooperative Extension's Spotsylvania County office who specializes in animal science. Direct questions to him at 540/ 507-7571, or by e-mail to jhowe@vt.edu.



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Date published: 11/10/2006