Properties of Soil
Soil is a complex mixture of minerals, organic matter, liquids, gases, and microorganisms that all work together to support life. It is the top layer of the earth’s surface made up of organic remains, clay, and rock materials on which plants grow. It promotes plant growth and life. It is constantly evolving due to a variety of physical, chemical, and biological processes such as Weathering and erosion. Soil has a density of 1.6 g/cm3.
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Structure of the Soil
Soil is composed of four main components: minerals, organic matter, water, and air. These components are arranged in distinct layers, or horizons, which make up the soil profile. The top layer of soil is called the topsoil, which is rich in organic matter and supports the majority of plant life. Below the topsoil is the subsoil, which contains more minerals and less organic matter. The deepest layer of soil is called the parent material, which is composed of weathered rock fragments and minerals. The specific composition and arrangement of these layers depend on various factors such as climate, vegetation, and geology.
Soil structure describes how soil particles are organised into a block, layer, or different structure. For example, during the summer, clay soil becomes blocky, and thus its structure is blocky.
The sandy soils found in Rajasthan have a grainy structure. Columnar structure; black soils have a columnar structure due to verticle cracks that developed during the dry season. Horizontal space between particles in a plate structure. River valleys in the flood plains form the layer structure of khadar deposits every year.
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Physical Properties of Soil
Colour, texture, structure, porosity, density, temperature, and air are all physical Properties of Soil. Soil colours vary greatly from place to place and indicate properties such as organic matter, water, and redox conditions. The types of soil particles and their arrangement influence soil texture, structure, porosity, and density.
1. Soil Texture
The proportion of sand, silt, and clay-sized particles that make up the mineral fraction of the soil (such as loam, sandy loam, or clay) is referred to as soil texture. Sand and silt are unimportant to the soil because they contribute nothing to the soil’s ability to restore water and nutrients. Clay is an active component of soil texture because of its small size and large surface area per unit mass, and it aids in the storage of water and ions. The texture of soil can tell you how much water it can hold, how quickly water moves through it, and how workable and fertile it is.
2. Water Absorption
Because of its porosity, soil can absorb water. The capacity of different soil types to hold water varies. Sand absorbs significantly less water than clay. Sandy soil has a lower water-holding capacity than clay and loamy soil. Clay soil is more water-retaining than sandy soil.
3. Soil Color
The colour of soil varies depending on whether it contains oxidised or ferric iron compounds (brown, yellow, or red). The darker the colour of the soil, the higher the organic content. The presence of iron oxide causes the soil to be red, and the soil to be black is rich in minerals and humus.
- Porosity refers to the space between particles in the soil.
- Pores aid in the retention of air, water, and microorganisms.
- Porous soil is soil that has a large pore.
- Because sandy soil has half the porosity of clay soil, clay soil has a higher water or air-holding capacity than sandy soil.
- More porosity means more capacity to hold water or air.
5. Soil Permeability
Permeability refers to the rate at which moisture or air passes through the soil. Water flows easily through sandy soil but not clay soil; thus, sandy soil is more permeable than clay soil. The soil with the most pores is the least permeable.
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Chemical Properties of Soil
The chemical properties of soil are determined by the presence of various minerals, organic matter, and nutrients. These components interact with each other and with the surrounding environment to affect soil pH, nutrient availability, and the chemical reactions that occur within the soil. Soil pH is a measure of soil acidity or alkalinity and is an important factor in determining which plants can grow in a given soil. Soil pH is influenced by the presence of minerals, organic matter, and the activities of soil organisms.
- pH is determined by the relative concentration of hydrogen(H+) ions. Acidity increases as H+ concentration increases and pH values decrease.
- If the pH of the soil is less than 6.5, it is said to be acidic.
- If the pH of the soil exceeds 7, it is considered alkaline.
- Plants receive the most nutrients when the pH of the soil is between 6.5 and 7.
- Podzol and Forest Soil from the Taiga region are examples of acidic soil, with pH values ranging from 3 to 5.
Biological Properties of Soil
Many organisms and microorganisms live in the soil and help to enrich the air, water, and humus. The presence of bacteria in soil indicates the soil’s neutrality. The presence of fungi in the soil indicates that the soil is acidic.
Soil is a dynamic and complex environment that supports a diverse array of living organisms, including bacteria, fungi, insects, worms, and small mammals. These organisms play important roles in soil health and fertility by breaking down organic matter and releasing nutrients that are essential for plant growth.
Additionally, they create channels and burrows that allow for water and air movement through the soil. This increased porosity improves soil structure and aeration, which benefits root growth and overall plant health. Soil microorganisms also play a crucial role in maintaining soil fertility by converting nitrogen from the air into a form that plants can use, known as nitrogen fixation. The Biological Properties of Soil are also influenced by human activities, such as land use changes and the application of fertilizers and pesticides, which can affect soil biodiversity and ecological balance.
Characteristics of Soil
Soils are typically classified into six types based on their chemical composition, which determines how water and nutrients are retained and which crops grow best in them. Soil composition can be sand, clay, loam, chalk, peat, or silt-based, and many soil systems will have patches with higher concentrations of one component than another. Let us break down each soil type into its key features and characteristics, as well as how this translates in an agricultural context.
This includes herbs native to Mediterranean regions like rosemary, thyme, and oregano, as well as several species of trees such as bay laurel, fig, and olive trees. The loose texture and lightness of the soil also make it easy for root vegetables to grow and expand without being impeded, so carrots, beetroot, parsnips, radish, and turnips are also compatible with this soil type. Sandy soils, as you might expect, are densely packed with sandy particles, resulting in a grainy but light-growing medium. Water and other fluids drain quickly, it is easy to work with, and it is soft and malleable for digging.
These soils are often noted for their lower nutrient availability and tendency to heat up and dry out quickly because water drains efficiently through them. Sandy soils typically have a lower average pH, making them ideal for plants that prefer a slight acidity in their soil profile. Crops that thrive in sandy soils prefer well-draining soil and hot, dry conditions.
Clay soils are nearly the polar opposite of sandy soils, being extremely heavy and having poor drainage capabilities. Because clay particles are so small, the soil texture becomes firmer and more easily compacted, leaving few pathways for water to drain out. Although clay soils are often undesirable for agricultural purposes due to poor drainage, they do typically contain high levels of nutrients and minerals that can be beneficial to certain crops. Certain fruiting trees and vegetables in the Brassica family can tolerate clay soils, but they grow best in a mix of clay and loam soil, where they can absorb nutrients while also benefiting from improved drainage.
Silty soils have a silky and soft texture, are typically quite fertile, and have the ideal balance of good nutrient density and poor drainage. Most crops can be grown in silt soils, though drainage amendments may be required for optimal crop performance. Silty soils do not compact as easily as clay soils and are softer and lighter; however, they lack a robust structure in their soil profile, which can be improved by planting perennial crops whose roots hold them together. Perennial bushes and trees that thrive in moist, fertile conditions are frequently the best choices for silty soils.
Loamy soils are defined as a balance of the three soil types mentioned previously: sand, clay, and silt. This is one of the most desirable and fertile soil types because it has the ‘best of both worlds’ characteristics, which means it has the advantages of all three soil types. Loamy soils have good drainage, high nutrient availability, a well-structured profile, and are slow to heat up and cool, providing crops with a relatively temperature-stable environment.
Most fruits and vegetables thrive in loamy soils, but because its composition is a delicate balance of three other soil types, it must be well maintained to prevent one component from taking over and tipping the scales. Crop rotation is beneficial to this soil because it prevents the repeated planting of a single heavy feeder from depleting the soil of all of its beneficial characteristics.
Because of the high concentrations of calcium carbonate present, chalky or lime-rich soils have an alkaline pH. These soils and their characteristics are typically formed by being on top of limestone or chalk bedrock, and they are often most arable when amended with organic matter and sulphuric fertilisers to improve nutrition and lower pH. Because of the presence of larger particles and rocks, chalky soils have excellent drainage, but they can also impede the growth of certain root vegetables.
Peat soils have the opposite characteristics of chalk soils in that the presence of peat, which is decaying organic matter, creates acidic conditions that must be alkalized for most crops to grow successfully. Peat soil is light and fluffy, with a springy texture that absorbs water like a sponge. The main problem with peat soils is drainage, but they can be amended with lime or chalky soils (or vice versa) to balance out the acidity and improve drainage.
Determining Soil Types
Because the six soil categories are distinguished by particle size, determining where your soil falls on the spectrum is as simple as feeling its grittiness versus smoothness, how easily it falls apart or glues together, and leaving it in a medium of water to see how the particles settle. Soil test kits can provide detailed breakdowns of your soil profile, so if you want a conclusive diagnosis of your soil’s characteristics, you should buy a professional testing kit.
The colour of your soil can also indicate the type of soil you have; for example, peat soils are dark in colour and can be nearly black depending on the percentage of peat content. Chalk soils, on the other hand, have a white layer of dust or visible chalk particles in the soil that makes it instantly recognisable.
Properties of Soil UPSC
Soil is a combination of rock debris and organic materials that form on the earth’s surface. Relief, parent material, climate, vegetation and other life forms, and time are the major factors influencing soil formation. Aside from these, human activities have a significant impact on it.