Types Of Soil
Soil is a mixture of minerals, organic remains, humus, water and air. It also contains many living organisms such as bacteria, fungi and worms. The composition of soil depends upon the parent rock from which it has formed. Soil composition keeps changing due to pollution, decay of organic matter and by addition of manures and fertilisers.
Sandy soil: It contains more sand (90%) and less clay (10%). It is permeable to air and water due to large pore spaces and dries up too easily. It is suitable for growing fruits and vegetables.
Clayey soil: It has high portion of clay. It becomes sticky in water. It is not aerated and hence roots find difficulty in penetration. It gets water logged in much moisture and becomes suitable by adding sand and lime and usually not preferred for plant growth.
Loamy soil: It is a mixture of sand and clay together with silt and humus. It is most suitable for plant growth.
Soil should have the following characteristics:
Water-holding: The soil should have proper water-holding capacity, but should not be water-logging.
Air: Soil should be well aerated. Good air-holding capacity helps the roots to respire.
Texture: Soil texture should be such that water and air can pass through its particles.
Acidity and alkalinity: Excess of acids and alkalies in the soil is harmful.
Nutrients: Soil must have both macronutrients and micronutrients in their proper quantities. C, H, N, P, K, Ca and Mg are macronutrients, while Mn, Cu, Zn, Cl, Fe and Mo are some micronutrients. These are needed for the fertility of soil. All these nutrients are found in soil in the form of salts.
If the same field is used for growing the same crop again and again, then the soil fertility reduces. Thus, either the field should be left unused for one or two seasons for the activity of microorganisms to maintain the soil nutrients or manures or fertilisers can be used to enrich the soil. Crop rotation is also a method to replenish soil nutrients. In this method, leguminous plants are grown in rotation alternately between the two cereal crops. Leguminous plants contain nitrogen-fixing bacteria in the root nodules which help in fixing free nitrogen in the soil absorbed from the atmosphere into soluble nitrates.