Determination of soil PH

Determination of soil pH of 1:1 soil: water suspension

Significance of soil pH

Soil pH is very important indicator of soil health. It is defined as the negative log of the hydrogen ion activity. It is the measure of acidity or alkalinity of soil which is determined by the pH meter. It influences availability of soil nutrients, solubility of toxic elements, CEC and biological activity in soils. At high pH values, availability of P, and most micronutrients, except B and Mo, tends to decrease. The pH range normally found in soils varies from 3 to 9. Most of the Pakistani soils have >8 pH. On the basis of pH, soils can be categorized as;

 Strongly acid (pH < 5.0)

 Moderately to slightly acid (5.0-6.5)

 Neutral (6.5-7.5)

 Moderately alkaline (7.5-8.5)

 Strongly alkaline (> 8.5)

Objectives:

To determine the pH of soil saturated paste and different soil: water suspensions for evaluating the sodicity hazards of soil.

Principle:

pH is the measure of acidity or alkalinity of any medium determined by the pH meter. The basic principle of the pH meter is to determine the activity of hydrogen ions (H+). Higher H+ activity will indicate higher pH value and vice versa.

Materials/Reagents and Equipments Required

 Plastic beaker (250 ml)

 Spatula or mixing spoon

 Weighing balance

 Deionized water (DW)

 pH meter

 Buffers of pH 4.01 and 10.01 for pH meter calibration

 Wash bottle

 Glass rod

Procedure:

Preparation of 1:1 soil: water suspension

 Weighed 100 g air-dry soil (< 2-mm) into a 250 ml plastic beaker.

 Added 100 mL DI water using a graduated cylinder.

 Mixed well with a glass rod and allowed to stand for 30 minutes.

 Stirred the suspension every 10 minutes.

 Finally, pH was measured with the help of portable pH meter.

Observation:

The pH of the soil was ----------. According to measured pH, soil is categorized as-------------.

Determination of soil pH of 1:1 soil: water suspension

Significance of soil pH

Soil pH is very important indicator of soil health. It is defined as the negative log of the hydrogen ion activity. It is the measure of acidity or alkalinity of soil which is determined by the pH meter. It influences availability of soil nutrients, solubility of toxic elements, CEC and biological activity in soils. At high pH values, availability of P, and most micronutrients, except B and Mo, tends to decrease. The pH range normally found in soils varies from 3 to 9. Most of the Pakistani soils have >8 pH. On the basis of pH, soils can be categorized as;

 Strongly acid (pH < 5.0)

 Moderately to slightly acid (5.0-6.5)

 Neutral (6.5-7.5)

 Moderately alkaline (7.5-8.5)

 Strongly alkaline (> 8.5)

Objectives:

To determine the pH of soil saturated paste and different soil: water suspensions for evaluating the sodicity hazards of soil.

Principle:

pH is the measure of acidity or alkalinity of any medium determined by the pH meter. The basic principle of the pH meter is to determine the activity of hydrogen ions (H+). Higher H+ activity will indicate higher pH value and vice versa.

Materials/Reagents and Equipments Required

 Plastic beaker (250 ml)

 Spatula or mixing spoon

 Weighing balance

 Deionized water (DW)

 pH meter

 Buffers of pH 4.01 and 10.01 for pH meter calibration

 Wash bottle

 Glass rod

Procedure:

Preparation of 1:1 soil: water suspension

 Weighed 100 g air-dry soil (< 2-mm) into a 250 ml plastic beaker.

 Added 100 mL DI water using a graduated cylinder.

 Mixed well with a glass rod and allowed to stand for 30 minutes.

 Stirred the suspension every 10 minutes.

 Finally, pH was measured with the help of portable pH.