Soil PH_1.pptx

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1. Determination of pH (Hydrogen Ion Activity) Soil pollution prac. Dilzheen sami Ronak A. Meshbaz

2. 2 The soil pH is a measure of the acidity or basicity in soils. pH is defined as the negative logarithm (base 10) of the activity of hydronium ions . It ranges from 0 to 14, with 7 being neutral. A pH below 7 is acidic and above 7 is basic . The pH range normally found in soils varies from 3 to 9.

3. 3 Classification of soil pH ranges Denomination pH range Ultra acid < 3.5 Extreme acid 3.5–4.4 Very strong acid 4.5–5.0 Strong acid 5.1–5.5 Moderate acid 5.6–6.0 Slight acid 6.1–6.5 Neutral 6.6–7.3 Slightly alkaline 7.4–7.8 Moderately alkaline 7.9–8.4 Strongly alkaline 8.5–9.0 Very strongly alkaline > 9.0

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5. 5 Importance of soil pH measurement Soil pH is considered one of the most common and important measurements performed in standard soil chemical analysis, as it affects plant through in many ways including:

6. 6 By affecting availability of plant nutrients At high pH the availability of Phosphoru s ( P) and most micronutrient except Molybdenum ( Mo) tend to decrease. At low pH the availability of Mo and most macronutrients (Mg, Ca , S, N, P) tend to decrease. Most mineral nutrients are readily available to plants and most plants grow best in soils with a pH of 6.0 or 6.5 to 7.5.

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8. 8 By affecting the activity of soil microorganisms, which in turn affects nutrient cycling and disease risk. The most numerous and diverse microbial populations exist in the middle of the pH range; fewer organisms are adapted to strongly acid or strongly alkaline soils. Nutrient cycling is slower in acid and alkaline soils because of reduced microbial populations.

9. 9 Soil pH also affects pathogenic microbes, and growers can adjust pH to manage some plant disease. Fungal diseases favored by acidic conditions - Control by liming Bacterial and actinomycetous diseases favored by neutral or alkaline conditions - Control by acidification

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11. 11 By affecting availability of toxic metals Aluminum is one of the most common elements in soil, but it is not a plant nutrient, and it is toxic to plants in high concentrations. Very little aluminum is in solution in soils above pH 6 and it causes no problems to plants but as pH declines (pH < 5), aluminum availability will increase and aluminum toxicity becomes a problem.

12. 12 Aluminum toxicity

13. 13 What Causes Soil to become Acidic or Alkaline? Parent Material: soil that originated from acidic rock like granite, creates acidic soil, while soil that originated from basic rock like limestone, creates alkaline soil.

14. 14 Rainfall: Rain leaches basic elements such as calcium and magnesium from the soil. Therefore you will find areas with high rainfall generally have acidic soil while dry areas tend to have alkaline soil.

15. 15 Root and microbial respiration produce CO 2 which react with water to produce carbonic acid CO 2 + H 2 O H 2 CO 3 H + HCO 3

16. 16 Use of fertilizer: that contain ammonium (NH 4 + ) like urea, unless specially treated, increase acidity due mainly to nitrification of ammonium by soil bacterial NH 4 + + 2O 2 NO 3 - + H 2 O + 2H H + is also released during the decomposition of organic matter as a result of nitrification of ammonium by soil bacterial

17. 17 Factors affecting measurement of soil pH: Soil type Organic matter The amount of materials needed to change soil pH. Fertilizers Rain affect soil pH. Soil microorganisms , Agricultural limestone normally is used to increase the soil's pH. Sulfur is normally used to lower the soil pH.

18. 18 Methods of pH measurement Colorimetric methods: - such as pH test paper.

19. 19 pH meter method

20. 20 Apparatus : pH meter with Combined Electrode. Glass rod. Glass beaker .   Reagents : A. Deionized water. pH meter

21. Determination of Soil pH by pH meter Procedure: Prepare a 1:2 soil: water suspension. Weigh 20 g air-dry soil (< 2 mm) into a beaker or conical flask and add 40 mL deionized water or distilled water. (Other amounts can be used e.g. 40 g:80 ml.) Mechanically shake for 15 - 20 minute.

22. 22 2.Then let the suspension to stand for 10 minutes Suspension Determination of Soil pH by pH meter

23. Determination of Soil pH by pH meter Rinse the pH meter electrodes in distilled water and dry gently with a tissue. 4. Measure the pH by immersing the electrode into the soil suspension.

24. 24 5. Then , rinse the pH meter electrodes again in distilled water and dry gently with a tissue.

25. Thanks for your attention