Ways of adjusting soil pH

  Ways of adjusting soil pH

a) Changing pH from alkaline to acidity (Lowering soil pH)

Addition of acidic organic matter e.g. organic matter from pine needles.

Addition of acidic fertilizers e.g. sulphate of ammonia

Changing pH from acidic to alkaline (Increasing pH)

Lower pH can be corrected by addition of agricultural lime, in a process called liming.

Examples of lime include:

Calcium carbonate ( calcite)

Calcium Magnesium carbonate ( dolomite)

Calcium Oxide ( Quick lime)

Wood ash

Paper mill

Qualities of a good liming material

It should be cheap

It should be easy to handle, store and apply

It should have a mild effect on pH

It should last long in the soil

It should be able to improve the soil structure

It should easily dissolve in the soil solution.

It should contain desirable cations e.g. Calcium

Factors to consider before liming

The pH of the soil

Type of crop to be grown

Economic returns in relation to the cost of lime.

Percentage base saturation.

Fineness of limestone or carbonate used.

Amount of manganese present

Loss of lime from the soil

Soil erosion

Crop rotation


Importance of lime

It improves the soil structure

It prevents certain fungal diseases which are common in acidic conditions.

It fastens decomposition of organic mater.

It neutralizes acidity in the soil

It supplies calcium in the soil.

It improves root nodulation and hence nitrogen fixation.

 It makes nitrogen and phosphorus available to plants.

Methods of determining soil pH

There are mainly three methods of determining soil pH:

Use of Universal indicator solution.

Use of litmus paper

Use of the pH meter

Use of universal indicator solution


Test tube


Barium sulphate

Dry soil sample


pH meter


Put a small quantity of soil in a test tube using a spatula

Add to it an equal volume of Barium sulphate. This will help to break soil particles and settle them at the bottom of the test tube.

Shake the test tube end to end to mix the two thoroughly well.

Add distilled water and shake vigorously.

After a few minutes, compare the colour in the test tube with the colours on the pH chart.

Read off the pH value of the colour that corresponds to the colour of the clear solution in the test tube.

Observation /deduction

  • Red colour indicates acidic pH ( 1-2)
  • Pink colour indicates moderately acidic pH ( 3-4)
  • Yellow colour indicates weakly acidic (5-6)
  • Green colour indicates neutral (7)
  • Deep blue/ Violet/ indigo colour indicates ( 9-14)

Determination of pH using litmus paper


Test tube

Litmus paper

Distilled water

Dry soil sample



  • Fill a test tube up to ¼ with soil sample and distilled water.
  • Cover the open end of the test tube with your thumb and shake vigorously.
  • Place the test tube in a rack and allow the contents to settle.
  • Obtain a strip of litmus paper (blue and red) and dip them into the soil solution. Make sure they don’t touch each other.
  • Observe the colour changes on the litmus paper

Conclusion and deduction

  • Acidic soil turns blue litmus paper red.
  • Red litmus paper remain red if the soil is acidic
  • Red litmus paper turns blue if the soil is alkaline
  • Blue litmus paper remains blue if the soil is alkaline
  • No colour change on both blue and red litmus papers if soil is neutral