Archive for Sunday, November 30, 2003

Nutrient management vital to gardens

November 30, 2003


One of the most important keys to gardening success is nutrient management.

The biggest influence on nutrient availability is soil pH. Around here, soils naturally have a high pH and that can mean less nutrients are available for plant growth. The most common of these problems is caused by a lack of iron called iron chlorosis. Often times, simply lowering soil pH can eliminate this condition. If you have had problems with plants that are yellow, weak or just unhealthy looking, maybe it is time to adjust your pH.

Here's how:

Begin by taking a soil test. A good soil test sample represents the entire gardening area -- not just one or two spots. Take small samples, four to six inches deep, from eight to 10 different areas in the garden, lawn or flower bed. Mix them together and submit two cups for testing.

If the pH is too high, it will be recommended that sulfur be added to help lower the pH. Unfortunately, adding sulfur is not a clear-cut solution. For example, some soils have free calcium carbonate, actual particles of limestone mixed in the soil. These "calcareous" soils normally have a pH of 7.3 to 8.5. To lower the pH, all of the free calcium carbonate must be neutralized first. You would need to apply enough sulfur to neutralize the free lime, then make additional applications to actually lower pH. Adding this much sulfur at one time would not be good for the soil. It may take several years and many applications to achieve the desired lower pH.

Likewise, elemental sulfur does not lower pH directly. It must be oxidized to the sulfate form with the result being sulfuric acid. The sulfuric acid produces hydrogen, which acidifies the soil and lowers pH. The oxidation takes place primarily through microbial activity. Unfortunately, oxidation takes time. Microbial oxidation of elemental sulfur is slow and can depend on the number of sulfur oxidizing bacteria present, the temperature (75-104 degrees is optimum), moisture content of soil (too wet or too dry will slow the process), and the size of sulfur particles (the smaller the better). For the most part, a single application normally takes at least two years for the sulfur to react and form sulfuric acid.

So, how much sulfur should be applied? Different textures of soil require different amounts of sulfur to lower the pH. A sandy soil needs 7 pounds of sulfur per 1,000 square feet to lower the pH one point. A loam soil needs 11 pounds and clay needs 17 pounds to do the same. For example, if you need to lower the pH from 8.5 to 6.5 on a loam soil, you would need 22 pounds of sulfur per 1,000 square feet.

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