Soil pH Determination (Practical)

Soil hydrogen ion concentration may be a crucial soil indicator, and is outlined because of the negative log of the cation activity. Since hydrogen ion concentration is an index, the H-ion concentration in resolution will increase 10 times once its hydrogen ion concentration is lowered by one unit.

The hydrogen ion concentration varies usually found in soils varies from three to nine. numerous classes of soil hydrogen ion concentration are also at random delineated as follows:

  •  powerfully acid (pH < five.0)
  • Moderately to slightly acid (5.0-6.5)
  • Neutral (6.5-7.5)
  • Moderately basic (7.5-8.5), and
  • powerfully basic (> eight.5)

The significance of hydrogen ion concentration lies in its influence on the convenience of soil nutrients, the solubility of hepatotoxic nutrient parts within the soil, the physical breakdown of root cells, and CEC in soils whose colloids (clay/humus) area unit pH-dependent and biological activity.

At high hydrogen ion concentration values, the convenience of P, and most micronutrients, except B and Mo, tend to decrease (see Box No. a pair of for a lot of details).

Acid soils are unit rare in semi-arid, dryland areas of the world; they have the inclination to occur in temperate and tropical areas wherever precipitation is substantial; conversely, soils of drier area units are typically basic, i.e., above pH 7.0, as a result of the presence of CaCO3, and can visibly foam (fizz) once 100% hydrochloric acid (HCl) is additional dropwise to the soil.

Most soils within the WANA region have hydrogen ion concentration values of 8.0 – 8.5. carbonate soils with minerals have somewhat lower hydrogen ion concentration values, whereas those with excess sodium have values over eight.5 (sodic soils).


  • pH meter with combined conductor
  • Reference conductor-saturated KCl
  • Measuring cylinder
  • Glass rod
  • Glass beaker
  • Interval timer
  • Wash bottle, plastic
  • pH Paper

Procedure: I

1 . Weigh fifty g of dry soil (< 2 mm) into a 100-mL glass beaker.

2 . Add fifty cubic centimeters of DI water employing a graduate or 50-mL meter flask.

3. Combine well with a glass rod, and permit to face for half-hour.

4 . Stir suspension every ten minutes throughout this era.

5 . After one hour, stir the suspension.

6 . Calibrate the hydrogen ion concentration meter (see Box No. three for a lot of details).

7 . Put the combined conductor in suspension (about 3 cm deep). Take the reading when thirty
seconds with one decimal.

8 . Remove the combined conductor from the suspension, and rinse totally with DI water in a separate beaker, and punctiliously dry excess water with a tissue.

Procedure: II

  1. Weigh 50 g air-dry soil (< 2 mm) into a 100-mL glass beaker.
  2. Add 50 mL DI water using a graduated cylinder or 50 mL volumetric flask.
  3. Mix well with a glass rod, and allow to stand for 30 minutes.
  4. Stir suspension every 10 minutes during this period.
  5. After 1 hour, stir the suspension.
  6. Put pH paper in the Suspension and allow them to dry and match it with the pH chart to measure the pH.

Technical Remakes

  1. Make sure that the combined electrode contains saturated KCl solution and some solid KCl.
  2. At ICARDA, pH is measured in a 1:1 (soil: water) suspension. For special purposes, pH can be measured in a saturated soil paste, or in more dilute suspensions. In some laboratories, pH is measured in a suspension of soil and 1 N KCl or 0.01 M CaCl2.
  3. The pH measured in 0.01 M CaCl2 is about 0.5 units lower than that measured in water (soil: the liquid ratio of 1:2).
  4. For soil samples very high in organic matter, use a 1:2 or 1:5 (soil: water) ratio.
  5. The main advantage of the measurement of soil pH in the salt solution is the tendency to

    eliminate interference from suspension effects and from variable salt contents, such as
    fertilizer residues.

  6. Air-dry soils may be stored for several months in closed containers without affecting the pH measurement.

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