Question

The principal cation in alkaline soil is
A) $Na^+$
B) $K^+$
C) $Ca^{2+}$
D) Any of the above

Answer 1

Soil is known to be a mixture of minerals, organic matter, liquids, gases and organisms. The major function of soil is promoting the growth of plants and serving as a habitat for organisms.

Complete answer:
Soils are of four main types- sandy soil, clay soil, loamy soil and silt soil. Sandy soils are those which consist of small particles of rocks and due to poor water holding capacity are not suitable for the growth of plants. Clay soil comprises very small particles with very little airspace and have good water holding capacity but air does not penetrate through it because of its sticky nature as a result plants cannot grow very well in them.

Loamy soil consists of sand, clay and silt and is the most suitable for the growth of nutrients. Silt soil is made up of particles smaller than sand but larger than clay and holds water better than sand and are considered to be fertile. Alkaline soils are clay soils that have a pH greater than 8.5. The basicity of alkaline soil is mostly due to the presence of large quantities of sodium carbonate that causes the soil to swell.

So the correct answer is option (A) $Na^+$.

Note: Alkaline soils are not suitable for agricultural purposes due to the low infiltration capacity as a result of which rain water stagnates making cultivation really difficult. Agriculture in alkaline soils is limited only to crops that can tolerate water logging such as grass and rice.