Here is a compilation of term papers on ‘Soil’ for class 6, 7, 8, 9 and 10. Find paragraphs, long and short term papers on ‘Soil’ especially written for school students.
Term Paper on Soil
Term Paper Contents:
- Term Paper on the Definition of Soil
- Term Paper on the Constitution of Soil
- Term Paper on the Functions of Soil
- Term Paper on the Properties of Soil
- Term Paper on the Composition of Soil
- Term Paper on the Classification and Distribution of Soil
- Term Paper on the Aspects of Soil
- Term Paper on Salt Efflorescence in Soil
- Term Paper on Suitability of Soils for Crop Production
- Term Paper on the Improvement of Soil and Crop Rotation
- Term Paper on Soil Water
- Term Paper on Root-Zone Depth for Soil
Term Paper # 1. Definition of Soil:
Soil is a cap or covering on the solid crust of the earth’s land mass. It is made up of broken-down rock material of varying degrees of fineness. Rock disintegration takes place due to the action of different natural agencies e.g. wind, temperature changes, flow of water etc.
Hence we can define the soil as “a heterogeneous mixture of loosely packed broken rock together with some organic matter and minerals forming topmost portion of the earth’s land mass of varying depths”. It is responsible for supporting the plant life.
Term Paper # 2. Constitution of Soil:
Soil mass is essentially formed of three main constituents, the soil particles, air and water. Fig. 2.1 shows the three phases of the soil mass.
The solid matter of the soil mass is seldom very thoroughly packed as shown in Fig. 2.1. There are always some open spaces or voids between the solid particles. The soil pores may contain either water or air or both in different ratios.
Term Paper # 3. Functions of the Soil:
The soil mass acts as a store of the plant nourishing food. Plants derive water, which is the most important requirement of plant life, through the medium of soil. The soil crust makes it possible for growing plants to secure their bracings and anchorages through the roots below the surface of the earth.
In the presence of air and water plant nourishing foods are set free in the soil after completion of chemical reactions. Some harmful products present in the soil are also neutralized during the chemical reactions. Soil is the home of multiplying bacterial life which together with other forms of life are busy in making the soil richer in organic matter and suitable for healthy growth of the crops.
Term Paper # 4. Properties of Soils:
Some of the properties of soil are as follows:
It is an important property and gives fairly correct information regarding type of a soil. Colour of the soil depends upon its composition, porosity and also its age. Soil containing organic matter has grey, black or brown in colour. Diffusion of iron oxide gives red and yellow colour.
The sizes of particles of soil and their ranges show the texture of the soils. The soil particles are classified according to their sizes into three main groups so far as agricultural engineer is concerned. The groups are sand, silt and clay.
Sand has a gritty feel to the fingers. Silt has a feel of flour to eyes whereas clay particles cannot be distinguished by naked eye.
The soil is never fully made up of only one group. Depending upon the percentage of clay, it is termed as light, medium or normal and heavy.
The arrangement of soil particles in a soil mass is known as a structure of the soil. Many types of soil-structures are recognized and very common of these are granular, prismatic, columnar, laminar etc.
(iv) Void Ratio:
Void-ratio is defined as the volume of voids per unit volume of solid particles in a given soil mass and is variable with the soil density.
It is that property of the soil which allows water to move through the soil mass. The permeability of the soil is defined as the velocity of flow under unit hydraulic gradient. Permeability of a soil is affected by its texture, structure, and temperature changes. Fine textured soils are impermeable to water.
(vi) Acidity and Alkalinity or pH Value of Soils:
pH value is the chemical term which shows acidity or alkalinity of the matter. The pH value is the logarithm of the reciprocal of the hydrogen-ion concentration, measured in grammes per litre. The pH value for all practical purposes, range from 0 to 14. If the pH value is less than 7 it indicates acidic soil mass and if it is more than 7 it indicates alkaline soil mass. When the pH value is exactly 7 it shows that the soil is neutral.
Term Paper # 5. Composition of Soil:
A good soil is made up of mineral matter, organic matter water and air in following proportion:
(i) Mineral matter = 50-60%
(ii) Organic matter =7-10%.
(iii) Soil water = 15-25%
(iv) Soil air = 25-35%
(i) Mineral Matter (Fig. 13.15):
It forms about 50- 60% of the soil. It occurs in the form of particles with numerous interspaces between them. These are formed by the weathering of parental rock and include about 25 elements out of which 16 elements are essential.
These are divided into two categories:
a. Macronutrients or Major Elements:
These are required in large amounts and are fundamental building blocks of body tissues. These are nine in number and include C, H, O, N, P, S, Ca++, and K+ Mg++. Out of these carbon, nitrogen, hydrogen and oxygen are supplied by au and water of soil. Phosphorus and sulphur are derived from the soil as phosphates and sulphates respectively.
b. Micronutrients or Minor or Trace Elements:
These are required in small quantities. Some of these are required by most of organisms and are seven in number and include Iron, Manganese, Boron, Molybdenum, Copper, Zinc and Chloride.
Term Paper # 6. Classification and Distribution of Soils:
Classification of soils cannot be given in a rigid framework.
On all India basis following six broad soil types are recognised for agricultural and irrigation purposes:
(i) Indo-Gangetic Alluvium:
This type of soil is the most important and the largest of all soil types of India.
(ii) Black (Cotton) Soils (Regur Soils):
They are very typical soils of Maharashtra and the adjoining areas. The colour of the soils is black and hence the name.
The black soils have been derived by decomposition and decay of two types of rocks:
(1) Basalt (Maharashtra), and
(2) Ferruginous schists and gneisses (Tamil Nadu).
(iii) Red Soils:
Red soils have been formed by decomposition of the ancient crystalline rocks like acid granites and gneisses and also from rock types rich in iron and magnesium minerals. The soils are named red soils due to prevalence of iron oxide.
(iv) Laterite Soils:
This type of soils is also red coloured. It occurs in tropical regions which have heavy rainfall during wet season succeeded by dry season. Laterite soils contain hydroxides of aluminium and iron, silica, various carborates and sulphates. Laterite soils do not from well-defined groups as other soils.
(v) Forest and Mountain Soils:
They are formed in depressions within the mountains, in valley basins, and on the mildly inclined slopes. These soils are of heterogeneous nature, varying with parent rocks, climate and local conditions. They have high percentage of organic and vegetable matter.
(vi) Desert Soils:
The main agents which give rise to desert soil are the wind and temperature changes. The desert soils are mostly sandy soils.
Term Paper # 7. Aspects of Soil:
For practical purposes, the following aspects of soil studies must be considered:
i. Soil Composition:
Weathering processes carried out by rain, sun, wind or frost/ice break down rocks to form soil. Since rocks are so varied in their chemical composition, including such minerals as calcium, potash, phosphorus, iron, aluminium, silica and soda, the soils which result from the weathering of these rocks will also differ greatly. For instance, the weathering of rocks rich in iron may produce soils rich in iron oxides.
On the other hand the weathering of limestone usually produces a soil with little lime content because the lime (calcium) is dissolved and carried away by rain-water. Thus the composition of the soil is greatly dependent on the nature of the parent material, i.e. the rock on which it was developed.
Other factors are also important. Soil is either sedentary, that is the soil may be found near the parent rocks from which it is derived; or it is transported. Soil may be carried to distant lands by winds e.g. loess; by ice, e g. boulder clay; by running water, e.g. silt; or by volcanic eruptions, e.g. volcanic ash.
Apart from their mineral constituents soils also contain organic matter derived from the decomposition of plants and animals. This is known as humus and is renewed by leaf-fall and root decay. The fertility of the soil is often determined by the amount of humus present, for humus improves soil structure, yields plant food and assists in retaining soil moisture.
Crops require varying amounts of the different mineral nutrients in the soil. For example cotton requires soils rich in nitrates, rubber does best on deep, slightly acidic soils and cocoa grows well on soils rich in iron and potassium.
It is necessary to replace the worn-out soil nutrients from time to time if a high level of productivity is to be maintained. Manuring, crop rotation and fallowing are some of the methods used by farmers to keep their soils fertile.
ii. Soil Structure:
The physical texture of the soil, depending on the size of the soil particles, may be coarse, medium or fine. All soils possess some particles of all these groups but the proportions vary. Thus sandy soils have more coarse particles than fine ones; loams have equal proportions of coarse, medium and fine grains and clays have a large proportion of fine particles (Fig. 3.1; Table 3.1).
The texture of the soil governs such vital aspects of agriculture as ease of ploughing, root penetration and aeration. Clayey soils are very moisture-retentive and are thus heavy to work. They are best suited to wet crops like lowland padi.
On the other hand sandy soils, comprising mainly the coarser grains, lack coherence and are much easier to work. They are better suited to crops like groundnuts, which need greater aeration and cannot tolerate stagnant water.
Soil structure is also affected by the presence in the soil of various materials which bind the individual soil particles together. These binding materials act as a kind of weak cement and their presence makes soil different from loose sand, for example, which would simply run through the fingers. Soil is loosely cemented into small or large crumbs, or lumps.
The greater the tendency to adhesiveness in the soil, the larger these lumps will be so that clay, for instance, is very sticky and lumpy while sandy soils are drier and form only small crumbs. Several materials such as carbonate of lime and oxidized iron (which gives many soils a reddish colour) act as cementing agents. But more important are colloids.
These are very fine particles of clay and humus, less than 1/60,000 cm (1/150,000 inch) in diameter, which bind together the larger grains in the soil. They are most numerous in clays and loams. The presence of colloids in soils also increases their retention of water. The texture of the soil determines the size of pore spaces between particles and lumps in which air and water can circulate.
Factors such as the work of worms, micro-organisms and soil bacteria, or the action of frost can affect soil structure. The constant cultivation of the soil including ploughing, removing large stones and applying mineral fertilizers or organic manure can both change and improve the qualities of soils.
iii. Aeration and Water Supply:
All plants need both air and water to survive. Water is absorbed through the roots and must therefore be present in the soil. It may be supplied by rain-water which sinks into the earth or by irrigation water applied with a hose or sprinkler or led to the fields by means of ditches and canals.
In soils, water is present as a thin film around the particles. This is known as hygroscopic water. It is more abundant in humid than arid regions, more in fine than coarse soils. Water absorption by plants through their root hairs is easiest in well flocculated soil where the pore spaces for air and water penetration form between 35 per cent and 50 per cent of the volume of the soil.
If there is insufficient water in the soil this will prevent the plants taking in mineral nutrients which are dissolved in the groundwater. On the other hand, completely saturated soil or waterlogged conditions may rot the roots of plants. It will also impede the free circulation of air in the soil which is vital for crop survival.
In waterlogged conditions all the pore space is occupied by water so that air cannot move freely in the soil and cannot be absorbed by plants. Waterlogging may result from the formation of a hard pan. This is caused by the accumulation of certain cementing materials such as iron in the sub-soil. Alternatively, in low-lying areas natural drainage may be impeded.
Waterlogging can be relieved by the digging of drainage ditches to allow excess water to escape. Heavy soils can be improved by the addition of lime. Light soils which dry out quickly on the other hand are improved by manuring and by ensuring an adequate supply of water.
iv. Soil Temperature:
The soil is heated by the sun during the day and the effectiveness of this heating varies considerably between tropical and temperate lands and between the ‘sunny’ and the ‘sheltered’ slopes of mountains. All plants need a sufficient amount of heat to be able to germinate and grow. The minimum temperature for plants to grow is 6°C (42° F).
The optimum temperature is the temperature at which plants grow best; temperatures higher or lower either retard growth or make cultivation impossible. The effect of soil temperature on plants is most profound in the temperate lands where the farming year is governed by seasons.
Winter wheat, sown in late autumn, lies through the long, cold winter and germinates when the ground thaws in spring. The crop is ready for harvest in the bright, sunny summer. But further polewards or towards the continental interiors the winter cold is so severe that no wheat can be sown in winter. Sowing can only begin in spring, when the weather conditions are milder, and the crop is harvested in late summer.
A quarter of the world’s wheat comes from such areas and is known as spring wheat. In the northern hemisphere, more fruits and vegetables are grown on the south-facing slopes which receive more of the sun’s heat. The north-facing slopes in the European Alps may be colder by as much as 3° to 6°C (5°-10°F).
Apart from the heat received from the sun, soil temperature is influenced by several other factors. The decay of vegetative matter, when acted on by the microscopic bacteria within the soil, liberates heat. This is one reason why compost or manure is added to the soil. The rate of absorption and radiation of solar energy in different types of soil over different parts of the globe also differs.
Generally speaking, dark-coloured soils absorb more of the sun’s heat than light-coloured ones. In temperate lands this may make a difference of between 3.5° and 5°C (6° and 9°F.) in the soil temperature. Soils also lose heat at night through radiation when the air temperature drops. Bare soils lose heat much faster than those covered with vegetation.
This explains why night frosts do not penetrate so deeply in the grass-covered Steppes as they do in the sandy deserts of the Sahara. The presence of air and water in soil, both of which are poor conductors of heat, also affects soil temperatures.
Thus differences in temperature exist between wet and dry soils, and between compact clay and porous sand. For many garden crops and the more delicate fruits, farmers have to take soil temperature into consideration if the maximum benefit is to be attained.
Term Paper # 8. Salt Efflorescence in Soil:
For good crop growth soil should be neutral, i.e. the pH value of the soil should be about 7.
An alkali soil is one which contains alkali salts, usually sodium carbonate, to an excessive degree of saturation, either with or without appreciable amounts of soluble salts and has a pH value higher than 8.5.
A saline soil is one which contains excessive amount of soluble salts of sodium, magnesium, calcium and potassium. The salts are usually chlorides and sulphates. The percentage of these salts is more than 20 percent and sodium carbonate less than 15 percent. The pH value of the saline soil is between 7 and 8.5.
Accumulation of excess salts resulting in saline and alkali soils is caused by upward capillary movement of the soil moisture and evaporation at the ground surface. When ground water-table is high and ground water carries heavy loads of dissolved salts, the soil solution soon becomes so concentrated that the salts are precipitated in the root-zone and at the soil surface.
When irrigation water also carries such salts and if drainage facilities are not adequate salt accumulation will be still more. The process of bringing in injurious salts in the root-zone of the crops and at the soil surface is called salt efflorescence.
Symptoms of Salt Injury:
A first symptom of salt injury in crop production is small reduction in plant size and crop yield. This evil effect may not be noticed during early stage of salt accumulation. As the salt content of the soil gradually increases plant growth becomes more plainly stunted and the crop yield more definitely decreases.
Plant leaves at this stage dry out, turn brown, curl at edges and become yellow, mottled or otherwise discoloured. When salt accumulation becomes excessive leaves drop off, small twigs die, plants gradually loose their foliage and finally growth ceases. The above mentioned symptoms of the salt injury may develop in crops grown on both alkali and saline soils.
If sodium salts are present they tend to deflocculate the soil. As a result permeability of the soil is reduced and land becomes water-logged.
Alkali and Saline Soils Curation:
Temporarily the salt trouble on irrigated land is removed by one or more of the following procedures:
(i) Ploughing salt surface crusts very deep.
(ii) Scraping the salts which have accumulated on the field surface.
(iii) Adding some other salts or acids to neutralize the effects of exchangeable alkali salts.
To cure alkali and saline soils permanently the following four steps are essential:
(i) Adequate Lowering of High Water-Table:
When water-table is lowered the alkali salts which are in solution with the ground-water also be go down.
(ii) Satisfactory Draining of Sub-Soil:
When the sub-soil water is drained out of the area the soluble salts also go out with the subsoil water.
(iii) Leaching of Land Surfaces by Good Water:
The soluble and to some extent insoluble salts can be washed off by flooding the area with good water. From the fields the excess water is then drained off.
(iv) By Adding Some Exchangeable Salts to the Soil:
From sodium salts sodium can be replaced by calcium of calcium salts be adding latter to the soil. Calcium sulphate may be added to the affected soil for this purpose.
Term Paper # 9. Suitability of Soils for Crop Production:
A crop cannot be grown economically on every type of soil. Selection of a particular crop depends on the texture, structure and chemical characteristics of the soil.
So far as possible soil under cultivation should be neutral. It means the pH value of the soil should be about 7. Soil should be rich in organic as well as inorganic matter. But the soil containing either chloride or carbonate or sulphate of sodium or magnesium or potassium is useless for cultivation.
A soil with less than 2% clay is useless for growing crops. Light soil (2 to 10% clay) is suitable for crops with less water requirement, e.g. millets (Jowar, Bajra), pulses, sesame, mustard, groundnut, fodder etc.
Normal soil (10 to 20% clay) is very good for cultivation of most of the crops with ordinary water requirement, e.g. cotton, wheat, maize, oil seeds, gram, peas, potato, vegetables etc.
Heavy soil (40% and above clay) does not allow quick drainage of water. Hence it is suitable for crops which require large quantity of water at regular intervals, e.g. rice, sugarcane etc.
Table 2.3 shows the distribution of various soils in our country and their suitability to various crops.
Term Paper # 10. Improvement of Soil and Crop Rotation:
The soil acts as a store house of nutriments required for crop growth. It is also clear that a particular type of soil is suitable only for particular crops.
The usual tendency of the greedy cultivators is to select a cash crop which is suitable on their soils and to grow the same crop for years together, to drive maximum benefit. By practicing the cultivation of the same crop for number of years, the same nutriments which are required for that crop are consumed.
Ultimately the soil becomes poorer as those nutriments get consumed. At such a stage even the same cash crop will start giving lesser yield as nourishment of the crop is not satisfactory and the soil is rendered useless.
The soil can be improved or cured by any of the following three methods:
(i) By giving rest to the land, (keeping land fallow),
(ii) By adding manures to the land, and
(iii) By crop rotation.
In the first method the field is ploughed but not cultivated for a period of full one or two years. Though this method is simple the culturable land is just wasted since no crop is grown.
Consumed nutriments can be restored back by adding manures to the land externally. The manure may be in the form of chemical fertilizer or green manure. The process of adding green manure to the land is as described below. On the land jute or some fodder is grown. When the crop is still green the land is ploughed to mix green plants with the soil.
The land is afterwards left uncultivated for a year. In this period green plants decay and finally from a part of the soil. Though this method is good it is costly.
Common manures are compost (which is compound mixture of animal waste, vegetable matter, etc.), ammonium sulphate, sodium nitrate, bone mill, etc. The manures are spread over the land in required dozes before sowing.
Third method of crop rotation is most natural and economical. Crop rotation means simply changing the crop grown every year on the same field. Every crop requires different nutriments in different proportion. By changing a crop every year in a way the soil is given rest as the same nutriments are not used next year.
At the same time land is not left idle. In this method only precaution to be taken is to select the crops properly for rotation. So far as crop rotation is concerned there is no distinction between Rabi and Kharif crops. Rabi crops can be brought in rotation with Kharif crops. For best and quick results manures may also be added to the fields.
For rotation some crop groups are given below:
(1) Wheat—Great millet—Gram.
(4) Cotton —Wheat—Sugarcane.
(5) Cotton—Great millet—Gram.
In most crop rotations it may be seen that gram completes the cycle. It is because of the fact that gram is a leguminous crop and when sown on the field gives nitrogen to the soil. It makes soil rich in nutriments.
Term Paper # 11. Soil Water:
The soil water may be divided in the following two main groups:
i. Soil moisture, and
ii. Gravitational water.
i. Soil Moisture:
Soil moisture is the water retained in the pore spaces in the unsaturated zone of a soil mass.
Further, soil moisture is subdivided into two following groups:
(a) Hygroscopic Water:
The particles of water forming a very thin layer on the soil grains or as minute particles of water wedged between the smallest soil grains are known as hygroscopic water. This water is not capable of any movement by gravity or capillary forces. It is held in static state with atmospheric water vapour.
(b) Capillary Water:
They are also water particles which exist in the pore spaces of a soil mass. The particles are retained in their position by virtue of surface tension against the force of gravity. Capillary water permits drainage almost unobstructed.
ii. Gravitational Water:
Gravitational water is that water in unsaturated zone which is in excess of hygroscopic and capillary water which moves downward due to gravity if favourable drainage conditions are existing.
The proportion of each type of water in the soil depends upon the soil texture, structure, organic matter content and the temperature.
With reference to plant needs soil-water is also classified as:
(i) Unavailable (Hygroscopic water).
(ii) Available (Capillary water).
(iii) Superfluous (Gravitational water).
Hygroscopic water is not available for crop growth because it cannot be moved by capillary or gravity forces. During extreme drought, however, it is used by trees and desert vegetation.
Capillary water of the soil mass readily contributes water to the plant roots for use. The water after circulating through the plant structure is returned to the atmosphere in the form of vapour. This process is termed transpiration.
If the rate of transpiration is more than the rate at which water is absorbed by the roots, the plant structure will not get adequate amount of water for growth and the leaves will drop down. This drooping down of plant leaves due to shortage of water is called wilting point. Wilting coefficient is the percentage of moisture left in the soil when the plants wilt permanently.
Gravitational water drains down to such a depth that the plant roots cannot derive water from gravitational water storage. It is the reason for calling it superfluous water.
Every soil mass has a definite capacity to hold the water as soil moisture at a specified time after irrigation water is applied to it. It is called field capacity of the soil mass. It is expressed as a percentage of moisture retained as soil moisture. Thus field capacity is a line of demarcation between capillary water and gravitational water.
Field capacity depends on the initial moisture content, moisture transmission property of the soil, its moisture retaining capacity and depth of water applied.
Naturally when irrigation water is applied to the land care is taken to ensure that the field capacity of soil mass is not exceeded. The reason being any extra quantity of water applied goes down as gravitational water and thus wasted.
Term Paper # 12. Root-Zone Depth for Soil:
Root-zone depth is the maximum distance below the surface of the soil from which particular crop derives water for use and develops its root system.
Root-zone depths in irrigated fields are usually dependent on soil type, subsoil formation, kinds of crop grown, distance of water table from the ground surface, and amount of water supplied during irrigation.
For clayey soils depth of root-zone is less. Clayey soils do not permit crop roots to penetrate to considerable depths. When other limitations do not exist root-zone depths may be determined by plant characteristics or by the soil-moisture characteristics.
For medium soils the percentages of the total seasonal water requirement of the crop are shown in Fig. 2.2 with respect to depths below the soil surface.
Depth of the root-zone is 1.25 metres. It is divided in four parts. The first quarter depth contributes 57 percent of the total water required by the crop. The percentage decreases with increase in depth and the last quarter of root-zone depth contributes only 7 percent.
In general plants develop most of their roots and derive most of their moisture supplies from the upper portions of the root-zone depths.