Acidalkaline Soil

Soils are often acid (sour) or alkaline (sweet). This is expressed in terms of pH (the degree of alkalinity or acidity) on a scale of 1 to 14—7 is neutral, below 7 acid, above 7 alkaline. Most vegetables—with some notable exceptions like tomatoes—do best in neutral soils. (See Figure 2.03.)

Soils become acid by the leaching of calcium and magnesium ions and their replacement by hydrogen ions. This occurs naturally in regions of heavy rainfall.

Soils turn more alkaline as calcium, manganese, and sodium ions accumulate and replace hydrogen ions. This conditions occurs because of low rainfall and poor drainage. It is also prevalent in areas with native limestone deposits.

Sometimes you can tell whether the soil is too alkaline just by looking at it Symptoms of alkalinity are yellowing leaves on vegetation, stunted growth and burning of leaf margins. Often, alkaline soils are too salty. In extreme cases, heavy brown or white.salt deposits are left on the soil surface or on the edges of water ditches.

The surest way of telling whether or not your soil is too acid or too alkaline is with a pH test There are three ways to make this test First, take samples of your soil and have them tested by the State Cooperative Extension Service. Usually, the agent in your county can arrange to have this done free or for a small fee. Second, you can send these soil samples

Figure 2.05






A ground volcanic stone full of minute cavities

Holds apart massed clay particles


Useful when applied in large quantities


Exploded mica

Holds 3-4 times its weight in water



Naturally occurring calcium sulfate

The calcium in gypsum is capable of replacing the sodium ions in clay that make clay particles pack so hard; when the calcium ions replace the sodium, the particles group, forming large pore spaces

Lime sulfur

Sold as calcium polysulfide

Acts in a manner similar to gypsum; the most effective lime sulfur has a wetting agent that causes a deeper soil penetration

Soil sulfur

As the soil warms up, the sulfur breaks down into sulfuric acid and reacts with calcium carbonate in the soil to form soluble calcium sulfate

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