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The Importance of Soil pH
December 31, 1969
Maintaining proper soil pH is crucial in crop production and keeping a healthy soil.
All soil activity in some way is regulated, or affected, by soil pH. Soil pH is the overall health of a soil. Raising or lowering soil pH produces an immediate affect on the productivity of a soil through microbial and chemical changes.
So what is soil pH, really? pH is the measurement of acidity or alkalinity of soil solution.
In short, pH is measuring hydrogen (H+) ions in a soil solution. The more H+ ions in a solution the more acidic, or lower the pH of the solution.
The values of the pH scale are 1 - 14. Neutral is considered 7. Any value above 7 is considered basic, or alkaline, and any value under 7 is acidic. For crop production, 6.4 - 6.5 pH is generally considered neutral.
Most crop production prefers a pH within a neutral range because when pH is in the neutral range, most nutrients are readily available to the plant. At the extremes nutrient availability decreases and other side effects may occur.
For example, acidic soils usually contain free aluminum, which is toxic to many plants. In alkaline soils, excess lime causes some plants to have trouble utilizing iron. Also, triazine herbicides become more phytotoxic to the plant in alkaline soils.
However, for some agricultural or horticultural plants, a soil slightly on the acidic or basic side of the scale is preferable.
On most soil test reports, a value for both soil pH and buffer pH is recorded. The soil pH value is an approximation of the soil pH when the soil is saturated with water. It is a measurement of the H+ ions in solution and does not give a value for the H+ ions attached to the cation exchange sites.
The buffer pH is used to determine how much lime is needed to neutralize soil acidity. It measures the reserve acidity of a soil, or its buffering capacity. The buffering capacity is the soils ‘resistance to change'.