Soil pH

Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. pH is defined as the negative logarithm (base 10) of the activity of hydronium ions (H+ or, more precisely, H3O+aq) in a solution. In soils, it is measured in a slurry of soil mixed with water (or a salt solution, such as 0.01 M CaCl2), and normally falls between 3 and 10, with 7 being neutral. Acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare.The pH is measured in soil-water (1:1) and soil-salt (1:2 CaCl 2 {displaystyle {ce {CaCl2}}} ) solutions. For convenience, the pH is initially measured in water and then measured in CaCl 2 {displaystyle {ce {CaCl2}}} . With the addition of an equal volume of 0.02 M CaCl2 to the soil suspension that was prepared for the water pH, the final soil-solution ratio is 1:2 0.01 M CaCl 2 {displaystyle {ce {CaCl2}}} .A 20-g soil sample is mixed with 20 mL of reverse osmosis (RO) water (1:1 w:v) with occasional stirring. The sample is allowed to stand 1 h with occasional stirring. The sample is stirred for 30 s, and the 1:1 water pH is measured. The 0.02 M CaCl 2 {displaystyle {ce {CaCl2}}} (20 mL) is added to soil suspension, the sample is stirred, and the 1:2 0.01 M CaCl2 pH is measured (4C1a2a2). Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. pH is defined as the negative logarithm (base 10) of the activity of hydronium ions (H+ or, more precisely, H3O+aq) in a solution. In soils, it is measured in a slurry of soil mixed with water (or a salt solution, such as 0.01 M CaCl2), and normally falls between 3 and 10, with 7 being neutral. Acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils (pH < 3.5) and very strongly alkaline soils (pH > 9) are rare. Soil pH is considered a master variable in soils as it affects many chemical processes. It specifically affects plant nutrient availability by controlling the chemical forms of the different nutrients and influencing the chemical reactions they undergo. The optimum pH range for most plants is between 5.5 and 7.5; however, many plants have adapted to thrive at pH values outside this range. The United States Department of Agriculture Natural Resources Conservation Service classifies soil pH ranges as follows: