Soil is formed by the degradation of rocks. These rocks consist of salts called minerals. These salts are taken up by the plants, along with water, and are used by them for making food by the process of photosynthesis. These salts consist of two parts: one is positive and the other is negative. The positive part is generally metal ion. The salts, when dissolved in water, disassociate into ions and are absorbed by plants in ionic form.
Let’s understand what pH exactly means.
When salts are present in water, salt, as well as water, gets dissociated into their ions. The concentration of H+ ions in water is known as pH. It ranges from 0 to 14.0 to 7 is acidic and 7 to 14 is alkaline. 7 is neutral. pH of distilled water is 7. This H+ ion concentration helps in the taking up of salts by the plants. Most of the plants do well in the pH range of 6 to 7.5 i.e. slightly acidic to slightly alkaline.
There are certain plants, such as azaleas, rhododendrons and blueberries, which work well in acidic soil from pH 4.5 to 5.5.Some, such as ferns, lilac, asparagus , work well when pH is above 7, that is alkaline.
There are certain salts which are insoluble in acidic medium and hence are unavailable to plants. Example, leaves of some plants, like oak, turn yellow in alkaline soil because iron is insoluble in alkaline medium.
How to check the pH of soil
There are ways that we can check the pH of soil ourselves. One is by adding half cup of water to soil sample and mixing well and then adding half a cup of vinegar to it. If the soil shows bubbling or fizzing sound the soil is basic. Second, we can do it with pH metre or pH paper. The range of different pH is mentioned on the box of pH paper.
How to increase or decrease the pH of soil:
To increase the pH of soil we can add lime or lime stone and to decrease the pH we can add cow dung manure or wood ash to soil. We know organic compost is acidic in nature. Wood ash is rich in phosphorus, magnesium, aluminium, potassium and calcium.
At low pH, phosphorus, magnesium, calcium etc. are not available. At high pH, iron, boron, aluminium, manganese is unavailable.
We can learn the importance of pH to plants by the fact that hydrangea gives blue flowers at pH 4 to 5 and pink flowers at pH 6 to 7.
Acidic soil loving plants: – Azaleas, Rhododendrons, Hydrangeas, Daffodils, Blueberries
Alkaline soil loving plants: – Ferns, Asparagus, Lilac