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Soil pH     - A Basic Soil Property

Soil pH is a basic soil property that effects many chemical and biological activities in the soil. The degree of acidity or alkalinity in the soil is known as the “Soil Reaction” or soil pH are determined and measured by pH (potential Hydrogen ion, H+) concentration in the soil. Basically it is a measure of the amount of lime (calcium) contained in the soil and the type of soil. Generally, soils in moist climates tend to be acid and those in dry climates are alkaline.

Soil pH is expressed on a logarithmic scale between 0. 0 - 14.0 . A soil with a pH lower than 7.0 is an acid soil and one with a pH higher that 7.0 is alkaline. A pH of 7.0 is neutral. A soil with a pH of 6.0 has ten times as many hydrogen ions (H+) present as a soil pH of 7.0 and a soil with a pH of 7.0 is 100 times more alkaline than pH 6.0

Soil pH Range Soil Reaction

        3.0 - 4.0 Very Strong Acid 7.0 - 8.0 Slightly Alkaline
        4.0 - 5.0 Strong Acid  9.0 - Moderately Alkaline
        6.0 - 7.0 Slightly Acid 9.0 - 10.0m Very Strong 

See articles:  Nitrogen,  Iron Chlorosis,  Trees are Vital and Fertilizing Trees & Shrub

Most plants grow best in mineral soils with a slightly acid reaction. In this range, most plant nutrients are at or near their high solubility. Generally, plants take up nutrients only if they are dissolved in the soil solution, so if the nutrients are in the soil solution they are available for plant uptake. In Soils which are strongly acid (pH4.0 - 5.0), aluminum, is a compound of clay, is very soluble and dissolves more readily. As levels of dissolves aluminum increases, a chemical reaction occurs with phosphorus compounds, making them insoluble and unavailable to plants. If the dissolves aluminum levels become too high, toxic levels are reached and plants die.

When soil pH is moderately alkaline (pH> 8.0), the solubility of many nutrients decreases. Phosphorus as an example becomes less soluble as the pH increases. Iron, Magnesium, Zinc and Copper also become insoluble and unavailable to plants.

Soil pH can also influence plant growth by its effects the activity of beneficial soil based microorganisms that build soil structures, cycle organic matter or fix nitrogen in the soil.

Soil pH can also have a significant effect on the performance and breakdown of many pesticides. Bacteria that decompose soil organic matter are hindered in strong acid soils. This prevents organic matter from breaking down, resulting in an accumulation of organic matter and the tie up of nutrients particularly Nitrogen, that are held in the organic matter. Phosphorus, Potassium, Calcium and Magnesium also become insoluble in the high acid soils.

Some plants do well in moderate to high acid soils, while other plants are more tolerant in alkaline soils. Alkaline tolerant plants do not do well in acid soils and acid loving plants can not live in alkaline soils and in both cases they become chlorotic, the inability to absorb sufficient nutrients. It is usually best to use plants that grow well in your particular area, according to your soil conditions.

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                     Jim Rediker - Nurseryman -  Arborist  - TDA Certified

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