Soil pH
Soil pH is one of the indications of the
soil acidity or alkalinity. It can be measured by pH units. The pH is defined
as the negative logarithm value of the concentration of the hydrogen ion. It is
denoted the following equation:
pH =
-log[H+]
The pH varies from 0 to 14 with the neutral point pH 7.When the pH value
decreases thus the soil become more acidic; when the pH value increases the
soil become more alkaline. From pH 0 to 7 the acidic nature of the soil is decreases
and from pH 7 to 14 the alkaline nature of the soil is increases.
Soil pH ranges are:
Ø
Extremely acid.
Less than 4.5
Ø
Very strongly acid.
4.5–5.0
Ø
Strongly acid. 5.1–5.5
Ø
Moderately acid.
5.6–6.0
Ø
Slightly acid. 6.1–6.5
Ø
Neutral. 6.6–7.3
Ø
Slightly alkaline.
7.4–7.8
Ø
Moderately alkaline.
7.9–8.4
Ø
Strongly alkaline.
8.5–9.0
Ø
Very strongly alkaline.
More than 9.
Measuring of Soil pH
The values of Soil pH will give several clues about the properties of soil
and it can be determined easily. Using a pH meter is the most accurate method for
determining the pH of the soil. Indicators or dyes also can be used for this
purpose. In case of soil pH, may be variations occur in considerable amount from
one spot to another in a land. To determine soil pH of a land the samples of
soil to be collect from several locations and then the samples to be combined
into one sample is necessary.
Effect of pH
The solubility of nutrients or minerals is depending on soil pH. Most of
the essential plant nutrients are obtained by the plants from the soil. Before
a nutrient can be used by plants, it must be dissolved in the soil solution. These
nutrients are more soluble and should be dissolved otherwise cannot be absorbed
by the plants. More acidic nature or more alkaline nature of the soil will
affect the intake of the nutrients by the plants. Commonly the pH range between
6 to 7 is suitable for nutrient intake.
The beneficial microorganisms which decompose the organic matter from
soil also get affected by high acidic conditions. The activity of the concern
microorganisms will decreases in low pH conditions. The prevention of breaking
down of organic matter from soil will result the reduction of nutrients intake
by the reduction of solubility of plant nutrients through tie up with organic
matter.
Changes in Soil pH
The reasons soil becomes acidic are
·
Basic ions get leach
by water such rain water, irrigation water.
Eg – Ca, Na, Mg, K.
·
The acids like HNO3,
H2SO4 are will get formed from the organic matter
decaying.
·
The oxidation which is
takes place in the sulfur fertilizers and ammonium fertilizers also will
generate few, strong acids.
·
CO2 gas which
is generated by decomposition of organic matter and the respiration by root
will form a weak carbonic acid through dissolving in soil water.
v To improve the soil pH, lime also can be
added. By adding lime, the pH of the soil increases. The Lime addition will
give nutrients Ca and Mg to the soil and also increase the availability of nitrogen
& phosphorous to plants.
Common liming materials…
(1) Dolomitic limestone.
(2) Calcic limestone.
(3)Such as wood ash.
