Soil pH

Why timely pH measurement is required in Soil?

Soil pH value is measure of acidity and alkalinity in the soil. It is also the measure of hydrogen ion concentration. As hydrogen ion concentration varies over a wide range, a logarithmic scale (pH) is used: for a pH decrease of 1, the acidity increases by a factor of 10.

The pH value of the soil depends upon the location or region of the country.

 The pH value ranges from 0 to 14 with 7 being neutral, 7 below acidic and 7 above alkaline. Most plants have the pH from between 5.5 to 7.

Below are suitable pH ranges.

  • 5.0 – 5.5 – Blueberries, Potatoes etc.
  • 5.5 – 6.5 – Barley, Peanuts, Wheat, Corn, Cotton, Rice etc.
  • 6.5 – 7.0 – Clovers, Beets etc.

Now let’s see the factors which affect the soil acidity:


  • When water (H2O) combines with carbon-dioxide (CO2), it forms a weak acid called carbonic acid (H2CO3). The weak acid ionizes, releasing hydrogen (H+) and bicarbonate (HCO3). The released hydrogen ions replace the calcium ions held by soil colloids, causing the soil to become acidic.

Nitrogen fertilizers

  • Nitrogen fertilizers, manures and legume plants contain and form ammonium. This causes acidification because the plants absorb the ammonium ions directly. The greater the nitrogen fertilization, the greater the soil acidification.

Now let’s see the different acidic ranges:

  • 4.5 pH – Extremely acid –
    • Nitrogen -30%
    • Phosphate-23%
    • Potash-33%
    • Fertilizer wasted-71.34%
    • Fertilizer used-28.66%
  • 5.0 pH – Very strong acid –
    • Nitrogen-53%
    • Phosphate-34%
    • Potash-52%
    • Fertilizer wasted-53.67%
    • Fertilizer used-46.33%
  • 5.5 pH – Strongly acid –
    • Nitrogen-77%
    • Phosphate-48%
    • Potash-77%
    • Fertilizer wasted-32.69%
    • Fertilizer used-67.31%
  • 6.0 pH- Medium acid-
    • Nitrogen-89%
    • Phosphate-52%
    • Potash-100%
    • Fertilizer wasted-19.67%
    • Fertilizer used -80.33
  • 7.0 pH – Neutral –
    • Nitrogen-100%
    • Phospate-100%
    • Potash-100%
    • Fertilizer wasted-00.00%
    • Fertilizer used-100.00%

Measurement of soil pH value

The soil pH value is measured by a meter or a chemical test kit. The soil pH value meter costs about Rs. 400-500. The pH value is also measured in laboratories.


Now let’s talk about some manures and organic fertilizers which help to gain neutral pH value for the plant:


Limestone is available in 2 varieties which are as follows:

  • Calcitic Limestone
  • Dolomitic Limestone

Now let’s talk about these 2 lime stones in brief:

  • Calcitic limestone: Calcitic limestone contains mostly calcium carbonate and less than 1-6% of magnesium.
  • Dolomitic limestone: Dolomitic limestone is a mixture of calcium carbonate and magnesium carbonate. In some states, it must contain at least 6 percent Mg to be classified as dolomitic lime.

Hydrated lime

  • Hydrated lime (Ca (OH) 2) is calcium hydroxide, sometimes called slaked or builder’s lime. The neutralizing value ranges between 120 and 135 compared to pure calcium carbonate. Fifteen hundred pounds of hydrated lime with a neutralizing value of 135 is equivalent to 2,000 pounds of agricultural lime with a neutralizing value of 100.

Agriculture lime

  • Agricultural lime is also known as aglime and garden lime is a soil additive. The component of this lime is calcium carbonate.


  • These are deposits of calcium carbonate mixed with clay and sand that are mostly found in the Coastal plain section of the eastern states. Marls are usually low in magnesium as their reaction with the soil is the same as calcitic lime.

Basic Slag

  • Basic slag is a product of the basic open-hearth method of making steel. The calcium contained is in the form of calcium silicate, and reacts with soil acids in a manner similar to ground limestone. Its neutralizing value ranges from 60 to 70, but since basic slag generally has smaller particles than agricultural lime, it tends to change soil pH more rapidly than conventional agricultural lime. It also contains P2O5 ranging from 2 to 6 percent and some micro-nutrients and magnesium.

Ground Oyster Shells

  • Oyster shells and other seashells are largely calcium carbonate. They make a satisfactory liming material when finely ground and have a neutralizing value of 90 to 110. Since they are composed of primarily calcium carbonate, they contain little or no magnesium.


4 thoughts on “Importance of soil pH in Organic Farm”

  1. Very good information about organic farming.i have been doing zero budjet natural farming based on Shri Subhash Palekar Guruji’s zbnf to test the pH of a soil by our self ? Please give me the name of instrument to be used to determine pH value of soil . phone number of supplier .Last from five years I have been using only liquid jivamrut as a manure and for spray also.I have three Gir gau whose cow dung and gaumutra I am using for my farm,fodder,mango plantation,haldi crop etc.
    Ravi Marshetwar
    At Washim district Washim Maharashtra

    1. Ravi, Glad you like our site informative!
      For test pH you can use pH test papers or you can use pH meter, you can find these materials from Amazon or any other online sites. We have installed pH, Moisture, Humidity, Temperature and EC sensors will update you about how accurate its giving reading. Thanks

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