Write short notes on the following: (a) soil pH; (b) soil texture; (c) soil organisms; (d) soil profile.

Answer Details

(a) Soil pH

Soil pH is a measure of the degree of acidity or alkalinity of the soil, expressed on a scale of 0 to 14. A pH of 7 is neutral, values below 7 are acidic, and values above 7 are alkaline. Most crops grow best in slightly acidic to neutral soils (about pH 6 to 7). Acidity can be corrected by liming, while alkalinity may be reduced by adding sulphur or organic matter. Soil pH affects the availability of nutrients and the activity of soil organisms.

(b) Soil texture

Soil texture refers to the relative proportion of the different sizes of mineral particles (sand, silt and clay) in a soil. It determines whether a soil is sandy, loamy or clayey. Texture influences water-holding capacity, drainage, aeration and nutrient retention. Loamy soil, which is a balanced mixture of sand, silt and clay, is the best for most crops.

(c) Soil organisms

Soil organisms are the living things found in the soil. They include micro-organisms such as bacteria, fungi and algae, and macro-organisms such as earthworms, termites, millipedes and rodents. They help to decompose organic matter into humus, release and recycle nutrients, fix nitrogen, and improve soil structure and aeration. A few of them are harmful as pests or disease-causing organisms.

(d) Soil profile

A soil profile is the vertical section of the soil from the surface down to the parent rock, showing the different layers called horizons. The main horizons are the top soil (A horizon), the sub soil (B horizon), the weathered parent material (C horizon) and the underlying bed rock (D or R horizon). It is studied to know the depth, fertility and suitability of a soil for crop production.