The uppermost layer of the earth, called top soil, is formed through a continuous process of weathering actions of nature. The top soil contains rich nutrients. The mother earth is rich in soluble material and contains relatively higher proportion of organic matters. The top layer is also known as zone of aeration, where the activities of the roots of plant bodies are seen, besides several microbiological activities.
The zone is divided into two sub-zones (i) surface soil and (ii) sub-soil. The surface soil supports the plant kingdom and provides nutrition to the plant bodies. The sub-soil is not fully weathered and contains much less soil nutrients and fine earth. The sub-soil layer is present just below the surface soil.
The study of soil with regard to its various properties, relationship among themselves and naming and grouping is called classification of soil. The taxonomic unit of knowledge on every type of soil is essential to group them rightly for the purpose of agriculture, horticulture and forestry. The agriculturist, horticulturist and forester should know the taxonomic behaviour of each soil as well.
The scientific classification of soil can easily explain the behaviour of a particular soil. The soil structure and texture and proportions of different organs in a particular soil can help the crop growers to raise their crops. When a definite shape and size including the arrangement of soil particles in a particular soil relates to soil structure, the soil texture relates to fineness of the soil particles.
Various relative proportions of soil particles relate to texture of the soil. A plant grower should be aware of soil physics and chemistry.
Clay soil is sticky and is needed for manufacture of bricks and pottery. The soil aeration is very poor. Very limited species prefer to accommodate to this soil. Soil rich in clay is known as Decan soil, whose origin is igneous rocks. The soil is very much refractory. When wet, it is sticky.
The legume species of plants adapt with this soil as the water holding capacity is very poor in tropical and sub-tropical soil. Black cotton soil is very much suitable for cotton and ground nut etc.
Silt is very rich in soil nutrients achieved through biological as well as weathering actions of the nature. It is found in river mouths. Mangrove forests grow luxuriantly on this soil. The river mouths are also very much rich in bio diversity. Different kinds of flora, fauna and avifauna are noticed here.
The varieties of food grains and vegetables found in the mangrove forests, apart from the fishes and grasses found in river water provide a sound food chain for various animals and birds.
The ever-green plant species are commonly found in the estuaries with special adaptations to exist and multiply.
Find sand is poor in soil nutrients. The water holding capacity of the soil is also poor. This soil absorbs water very quickly and also releases the same quickly. Very limited species adapt with this soil.
The lower species of plant kingdom generally grow in this type of soil. The casuarinas grow luxuriantly in the soil. The coastal sands are generally brine sands, which carry salts. There are very limited species in plant kingdom, which thrive in coastal brine-sands. There are also certain creepers which grow in the brine sand and their roots help control soil erosions.
Coarse sands contain coarse particles. Its water holding capacity is very poor. It quickly absorbs rain waters, but releases the same to the atmosphere in a similar rate.
The soil needs ground coverage for conservation of moisture. The casuarinas, eucalyptus, cashew nut, bamboos and palms can be raised in this sand profitably.
Better soil mulching is seen in gravel. The water holding capacity of the sand is very poor but aeration takes place very efficiently. The root systems of plant species can travel better within the soil for collection of soil moisture and food materials.
A wonderful biological pyramid is noticed within gravelly lands. As the legumes and cereals are profusely found in the landmass and the soil morphology is very congenial, rodents and other predatory animals like lizards, reptiles and snakes are found within this land.
The predatory birds also perch in the land to hunt their daily intakes. But at present the gravels are mostly exploited for various constructional purposes. This picturesque land is losing its importance.
When we discuss about soil morphology, we cannot ignore soil chemistry.
The organic parts of the soil are formed by plant and animal residues in various stages of partially or fully decompositions. The soil contains cells and tissues of various organisms. Organic substances of flora and fauna enrich the soil particles, which provide perfect health to soil in natural conditions.
The application of unnatural, inorganic fertilisers to soil harms the soil rather than improves it.
So every plant grower should be proficient in soil science and soil technology, when dealing with soil for raising any crop. The plant growers should depend more on organic manures than inorganic, artificial manures.
(The writer is a former senior forest officer and an environmentalist)