Soil pH

Soil pH measures acidity or alkalinity from hydrogen-ion activity in soil solution. It influences nutrient availability, chemical reactions, and the organisms that can thrive in soil.

Hydrogen-ion activity: The effective concentration of hydrogen ions in a solution, accounting for interactions among ions. Soil pH is defined by hydrogen-ion activity in soil water.
Soil testing: The analysis of soil samples to assess chemical, physical, or biological properties. Laboratory pH tests guide decisions about amendments and crop suitability.
pH: A logarithmic measure of hydrogen-ion activity in a solution. Soil pH applies this chemical scale to water extracted from or equilibrated with soil.
Soil salinity: The concentration of soluble salts in soil, often assessed through electrical conductivity. Salinity measures dissolved salts, not hydrogen-ion activity, though both affect plant growth.
Soil buffering capacity: The ability of soil to resist pH change when acids or bases are added. Clay minerals, organic matter, and carbonates can make pH resistant to change.
Agricultural lime: Ground limestone applied to soil to neutralize acidity and supply calcium or magnesium. Its application is commonly prescribed when soil pH is too low for a crop.
Soil solution: The water in soil containing dissolved ions and organic compounds. Its hydrogen-ion activity is the immediate basis for soil pH.
Soil sodicity: A condition in which excessive exchangeable sodium damages soil structure. Sodicity is not equivalent to alkalinity or a high pH reading.
Cation-exchange capacity: A measure of a material’s capacity to hold and exchange positively charged ions. Exchange sites help regulate acidity by holding hydrogen and aluminum ions.
Sulfur amendment: Elemental sulfur or sulfur compounds added to soil to lower pH. Acidifying amendments can correct alkaline soil for plants that require lower pH.

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