Soil- Definition, Composition, Properties, Types and Uses

Soil is a natural resource that covers most of the land surface of the Earth. It is a complex mixture of organic and inorganic materials, living organisms, water, and air. Soil is essential for life as it supports the growth of plants, provides habitat for animals and microorganisms, regulates the flow of water and nutrients, participates in biogeochemical cycles, and serves as a basis for human activities.

Soil formation is a slow and continuous process that results from the interaction of five factors: parent material, climate, topography, biota, and time. Parent material is the original rock or sediment that is weathered and eroded into smaller particles. Climate influences the rate and type of weathering, erosion, and deposition. Topography affects the movement and accumulation of water and sediments. Biota includes all living organisms in the soil, such as plants, animals, fungi, and bacteria. They contribute to soil formation by adding organic matter, recycling nutrients, and modifying soil structure. Time is the duration of soil development, which can range from decades to millions of years.

Soil is a dynamic and heterogeneous system that varies in space and time. Soil can be classified into different types based on its physical, chemical, and biological properties. Soil classification helps to understand the characteristics and functions of soil in different regions and ecosystems. One of the most widely used soil classification systems is the USDA Soil Taxonomy, which divides soil into 12 orders based on diagnostic features such as soil horizons, texture, color, pH, and organic matter content.

Soil is a valuable and finite resource that faces many threats from human activities and environmental changes. Some of the major threats to soil include erosion, compaction, salinization, acidification, contamination, loss of organic matter, loss of biodiversity, and climate change. These threats can degrade soil quality and reduce its ability to perform its functions. Therefore, it is important to conserve and manage soil sustainably for the benefit of current and future generations.

Soil is a complex mixture of living and non-living things that support life on Earth. Soil contains both biotic and abiotic components that interact with each other and influence various soil properties and processes.

Biotic Components

The biotic components of soil are the living and once-living organisms that inhabit the soil environment. These include plants, animals, and microorganisms that play important roles in decomposition, nutrient cycling, soil formation, and soil health.

Some examples of biotic components of soil are:

• Plants: Plants are the primary producers of organic matter in soil. They use photosynthesis to convert light energy into chemical energy stored in carbohydrates. Plants also take up water and nutrients from the soil through their roots and release oxygen and carbon dioxide through their leaves. Plants influence the physical structure of soil by creating pores and channels with their roots and by stabilizing soil aggregates with their root hairs and exudates. Plants also affect the biological activity of soil by providing food and habitat for soil organisms and by altering the soil pH and temperature with their litter and canopy.

• Animals: Animals are the consumers of organic matter in soil. They feed on plants, other animals, or dead organic matter and release carbon dioxide, water, and nutrients through their respiration and excretion. Animals also influence the physical structure of soil by burrowing, digging, or crawling through the soil and by mixing and transporting soil particles and organic matter. Animals also affect the biological activity of soil by stimulating or inhibiting the growth and activity of soil microorganisms and by altering the soil pH and temperature with their waste products and body heat.

• Microorganisms: Microorganisms are the decomposers of organic matter in soil. They include bacteria, fungi, protozoa, algae, nematodes, and viruses that break down complex organic molecules into simpler compounds that can be used by plants or other microorganisms. Microorganisms also participate in various biogeochemical cycles that transform elements like carbon, nitrogen, phosphorus, sulfur, iron, and manganese between different forms and states. Microorganisms also influence the physical structure of soil by producing sticky substances like polysaccharides, mucilage, or hyphae that bind soil particles together into aggregates. Microorganisms also affect the biological activity of soil by competing or cooperating with other microorganisms or plants for resources and by altering the soil pH and temperature with their metabolic processes.

Abiotic Components

The abiotic components of soil are the non-living factors that affect the soil environment. These include minerals, water, air, and organic matter that determine the physical and chemical properties of soil.

Some examples of abiotic components of soil are:

• Minerals: Minerals are the inorganic substances that make up the solid fraction of soil. They originate from the parent material (the rock or sediment from which the soil is derived) or from atmospheric deposition (the dust or ash that falls from the air). Minerals vary in size, shape, color, composition, and crystal structure. The most common minerals found in soil are quartz (silicon dioxide), feldspar (aluminum silicate), mica (potassium aluminum silicate), calcite (calcium carbonate), gypsum (calcium sulfate), iron oxides (hematite or magnetite), clay minerals (hydrous aluminum silicates), and humus (a complex mixture of organic compounds). Minerals provide a source of nutrients for plants and microorganisms as well as a buffer for pH changes in soil.

• Water: Water is the liquid fraction of soil that fills the spaces between soil particles or aggregates. Water is essential for life as it transports nutrients, gases, wastes, hormones, and enzymes within and between organisms. Water also dissolves minerals and organic matter in soil and facilitates chemical reactions and biological processes. Water also influences the physical structure of soil by creating capillary forces that hold soil particles together or apart depending on the moisture content. Water also affects the biological activity of soil by providing a medium for microbial growth and activity as well as a regulator for temperature changes in soil.

• Air: Air is the gaseous fraction of soil that occupies the spaces between soil particles or aggregates that are not filled with water. Air consists mainly of nitrogen (78%), oxygen (21%), carbon dioxide (0.04%), water vapor (variable), and trace amounts of other gases like methane, nitrous oxide, ozone, ammonia, hydrogen sulfide, etc. Air is essential for life as it provides oxygen for aerobic respiration and carbon dioxide for photosynthesis. Air also transports gases between organisms and between different layers of soil. Air also influences the physical structure of soil by creating pressure differences that cause soil particles to move or settle. Air also affects the biological activity of soil by providing a source or sink for gases involved in biogeochemical cycles as well as a regulator for temperature changes in soil.

• Organic matter: Organic matter is the dead or partially decomposed remains of plants, animals, and microorganisms in soil. Organic matter consists of various compounds like carbohydrates, proteins, lipids, lignin, cellulose, hemicellulose, etc. Organic matter provides a source of energy and nutrients for soil organisms as well as a buffer for pH changes in soil. Organic matter also influences the physical structure of soil by increasing the water holding capacity and cation exchange capacity of soil and by stabilizing soil aggregates with its humic substances. Organic matter also affects the biological activity of soil by stimulating or inhibiting the growth and activity of soil microorganisms and by altering the soil pH and temperature with its decomposition products.

A soil profile is a vertical cross-section of the soil that reveals the different layers or horizons that make up the soil. A soil profile can be used to identify and classify the soil type, as well as to understand its formation and characteristics.

Soil horizons are distinct layers of soil that have different properties, such as color, texture, structure, mineral content, organic matter, and biological activity. Soil horizons are formed by various processes of weathering, leaching, accumulation, and decomposition that occur over time.

The major soil horizons are O, A, E, B, C, and R. The O horizon is the organic layer that consists of decomposing plant and animal material. The A horizon is the topsoil layer that contains a high amount of organic matter and microorganisms. The E horizon is the eluviation layer that is leached of minerals and nutrients by water. The B horizon is the subsoil layer that accumulates minerals and nutrients from the upper layers. The C horizon is the parent material layer that consists of partially weathered or unweathered rock. The R horizon is the bedrock layer that is not part of the soil.

The soil profile and soil horizon can vary depending on the location, climate, vegetation, and parent material of the soil. Some soils may have more or less horizons than others, or some horizons may be thicker or thinner than others. The soil profile and soil horizon can also change over time due to natural or human-induced factors.

The soil profile and soil horizon are important for understanding the fertility, quality, and function of the soil. The soil profile and soil horizon can affect the water retention, drainage, aeration, nutrient availability, and erosion resistance of the soil. The soil profile and soil horizon can also influence the plant growth, crop production, and biodiversity of the soil.

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Soil moisture is the water, including the water vapor, in the spaces between soil particles, generally in the upper 10 cm of soil. It is not the water in rivers, lakes, or groundwater. It depends on factors like soil type, vegetation, and weather conditions. It affects the exchange of water and heat energy between the land surface and the atmosphere, and the development of weather patterns and precipitation. It also influences groundwater recharge and soil chemistry.

Soil moisture can be expressed in terms of volume or weight. The volumetric water content of soil is the ratio of the volume of water to the total volume of soil. The gravimetric water content of soil is the ratio of the mass of water to the mass of dry soil. Soil moisture measurement can be based on in situ probes (e.g., capacitance probes, neutron probes) or remote sensing methods.

Soil moisture is one of the factors that determine the availability of water for plant growth. Plants can only extract water from soil pores that are smaller than their root hairs. The larger pores drain quickly by gravity and are called macropores. The smaller pores retain water by capillary forces and are called micropores. The water in micropores is divided into two categories: available water and unavailable water. Available water is the water that plants can easily access and use. Unavailable water is the water that is held too tightly by the soil particles and cannot be extracted by plants.

The amount of available water in a soil depends on its texture and structure. Texture refers to the relative proportions of sand, silt, and clay particles in a soil. Structure refers to the arrangement and aggregation of soil particles into larger units called peds. Sandy soils have large pores that drain quickly and hold little water. Clayey soils have small pores that retain more water but also make it harder for plants to access it. Loamy soils have a mixture of pore sizes that provide a balance between drainage and retention.

The amount of available water in a soil also depends on its moisture status. Soil moisture status is described by two terms: field capacity and wilting point. Field capacity is the maximum amount of water that a soil can hold after excess water has drained away by gravity. Wilting point is the minimum amount of water that a soil can hold before plants wilt and die. The difference between field capacity and wilting point is called the plant available water capacity.

Soil moisture is an important indicator of soil health and crop productivity. It can also have significant impacts on climate change, natural disasters, and human activities. Monitoring and managing soil moisture can help improve agricultural practices, conserve water resources, reduce greenhouse gas emissions, prevent soil erosion, mitigate droughts and floods, and enhance ecosystem services.

Soil gas is the term used to describe the gases that are present in the spaces between soil particles or aggregates. Soil gas mainly consists of nitrogen, oxygen, and carbon dioxide, which are similar to the atmospheric gases. However, soil gas also contains other gases that are produced by biological and chemical processes in the soil, such as nitric oxide, nitrous oxide, methane, ammonia, and volatile organic compounds.

Soil gas plays an important role in various aspects of soil functioning, such as:

• Soil respiration: Soil gas provides oxygen for the respiration of plant roots and soil organisms, and also carries away the carbon dioxide that is produced by their metabolism. Soil respiration is an indicator of soil biological activity and carbon cycling.
• Soil moisture: Soil gas occupies the pores that are not filled with water in the soil. The amount and distribution of soil gas affects the soil moisture content and movement, which in turn influences the availability of water and nutrients for plants and soil organisms.
• Soil quality: Soil gas can reflect the presence of environmental contaminants in the soil, such as landfill wastes, mining activities, and petroleum products. These contaminants can produce harmful gases that can diffuse through the soil and affect the health of plants, animals, and humans. Soil gas can also be used to monitor the remediation of contaminated sites.

Soil gas is influenced by various factors, such as:

• Soil texture and structure: The size and arrangement of soil particles and aggregates determine the size and connectivity of soil pores, which affect the diffusion and movement of soil gas. Generally, coarse-textured soils (such as sandy soils) have larger pores that allow more air exchange with the atmosphere, while fine-textured soils (such as clay soils) have smaller pores that restrict air movement.
• Soil organic matter: The decomposition of organic matter in the soil by microorganisms produces carbon dioxide and other gases that contribute to the soil gas composition. Organic matter also affects the soil structure and water retention capacity, which influence the soil gas distribution.
• Soil temperature: The temperature of the soil affects the rate of biological and chemical reactions that produce or consume soil gases. Higher temperatures usually increase the soil respiration and gas production. Temperature also affects the solubility of gases in water and their diffusion coefficients.
• Soil moisture: The moisture content of the soil determines how much space is available for soil gas in the pores. Higher moisture content reduces the soil gas volume and increases the pressure gradient between the soil and the atmosphere. Moisture also affects the diffusion and solubility of gases in water.

To measure and sample soil gas, various methods and techniques can be used, such as:

• Active sampling: This involves pumping or extracting a known volume of soil gas from a specific depth or location using a probe or a well. The collected sample can then be analyzed in a field or laboratory instrument for its concentration or composition.
• Passive sampling: This involves placing a device or a material that can adsorb or accumulate soil gas over a period of time at a specific depth or location. The device or material can then be retrieved and analyzed for its concentration or composition.
• Continuous monitoring: This involves installing sensors or probes that can measure and record soil gas parameters (such as concentration, pressure, temperature, etc.) continuously or periodically at a specific depth or location.

Some examples of applications or purposes of soil gas sampling and analysis are:

• Vapor intrusion assessment: This involves evaluating the potential risk of exposure to volatile organic compounds (VOCs) that migrate from contaminated subsurface sources (such as groundwater or soil) into indoor air spaces (such as buildings or homes).
• Landfill gas monitoring: This involves measuring and controlling the emission of landfill gases (such as methane and carbon dioxide) that are generated by anaerobic decomposition of organic waste in landfills.
• Soil carbon sequestration estimation: This involves estimating the amount of carbon that is stored or released by soils as a result of land use change, management practices, or climate change.

The soil matrix is the solid phase of soils, and comprises the solid particles that make up soils. Soil particles can be classified by their chemical composition (mineralogy) as well as their size. The particle size distribution of a soil, its texture, determines many of the properties of that soil, in particular hydraulic conductivity and water potential. The mineralogy of those particles can strongly modify those properties. The mineralogy of the finest soil particles, clay, is especially important.

The soil matrix consists of three main types of soil particles: sand, silt, and clay. These are further classified into different groups based on their size and shape. The following table shows the classification of soil particles according to the USDA system:

The soil matrix also contains organic matter, which is the decomposed or partially decomposed remains of plants and animals. Organic matter is mainly found in the form of humus, which is a dark-colored substance that improves the soil structure, water retention, nutrient availability, and biological activity.

The soil matrix determines various physical and chemical properties of soil like water retention capacity, nutrient content, and pH. The soil matrix also influences the biological properties of soil, such as the diversity and activity of soil organisms, the decomposition of organic matter, and the cycling of nutrients.

The soil matrix is not static, but dynamic and constantly changing due to various factors such as weathering, erosion, deposition, leaching, compaction, tillage, and human activities. These factors affect the composition, structure, and function of the soil matrix over time. Therefore, understanding the soil matrix is essential for managing soil health and fertility.

Soil is composed of various factors like air, water, minerals, and different living and non-living organic compounds. The entire composition of soil can be classified as biotic and abiotic components; the abiotic component includes the non-living things of soil while the biotic component includes the living organisms.

In general, the abiotic component of the soil accounts for about 40-45% of the soil volume followed by air and water that occupy 25% each with 5% covered by living things. The exact composition of the soil, however, might vary from place to place with the existing rocks of the area and the climate. Other factors like the quantity of vegetation, soil compaction, and water retention capacity also influence the composition of the soil of a particular area.

The following table shows the approximate composition of soil by volume:

The inorganic part of the soil is composed of rocks that are slowly broken down into smaller particles that might vary in size. The size and proportion of these particles determine the soil texture and structure. The most common minerals found in soil that support plant growth are phosphorus, potassium, and nitrogen. Other minerals include calcium, magnesium, sulfur, iron oxide, and carbonates.

The organic component of soil is called the humus, which is made up of living organisms like insects or microorganisms (dead or alive) and dead animals and plants in varying stages of decay. Humus might even form organic colloids with water and other inorganic substances. The organic matter provides nutrients and improves the water-holding capacity of the soil. It also influences the soil pH and cation exchange capacity.

The composition of soil affects its physical and chemical properties, which in turn determine its suitability for different purposes like agriculture, engineering, or ecology. Soil composition also influences the biotic factors like plant growth and soil organisms. Therefore, understanding the composition of soil is essential for its proper management and conservation.

The physical properties of soil are the characteristics that can be observed or measured without changing the composition of the soil. These properties include color, texture, structure, porosity, density, consistency, temperature, and air. The physical properties of soil affect various aspects of soil quality, such as water availability, nutrient retention, erosion potential, and plant growth.

• Soil color is determined by the organic matter content, mineral composition, and oxidation state of the soil. Soil color can indicate the fertility, drainage, and aeration status of the soil. For example, dark-colored soils usually have more organic matter and are more fertile than light-colored soils. Reddish or yellowish soils indicate the presence of iron oxides and good drainage. Grayish or bluish soils indicate poor drainage and low oxygen levels.
• Soil texture refers to the relative proportion of sand, silt, and clay particles in the soil. Sand particles are the largest (0.05-2 mm), silt particles are intermediate (0.002-0.05 mm), and clay particles are the smallest (<0.002 mm). Soil texture affects the water-holding capacity, drainage rate, aeration, nutrient availability, and susceptibility to erosion of the soil. For example, sandy soils have low water-holding capacity and high drainage rate, but also good aeration and low nutrient retention. Clay soils have high water-holding capacity and low drainage rate, but also poor aeration and high nutrient retention. Silt soils have intermediate properties between sand and clay. Loam soils are a mixture of sand, silt, and clay that have balanced properties for plant growth.
• Soil structure refers to the arrangement of soil particles into aggregates or peds that have distinct shapes and sizes. Soil structure is influenced by soil texture, organic matter content, biological activity, and physical processes. Soil structure affects the porosity, permeability, infiltration, shrink-swell potential, and erosion resistance of the soil. For example, granular or crumb structures have small and rounded aggregates that create many pores and allow good water infiltration and aeration. Platy structures have thin and flat aggregates that reduce pore space and impede water movement. Blocky structures have angular or subangular aggregates that create moderate pore space and water movement. Prismatic or columnar structures have vertical aggregates that facilitate drainage in subsoils.
• Soil porosity is the proportion of voids or spaces between soil particles that are filled with air or water. Soil porosity is determined by soil texture and structure. Soil porosity affects the water retention, drainage, aeration, root penetration, and microbial activity of the soil. For example, coarse-textured soils have large pores that drain quickly but retain little water. Fine-textured soils have small pores that drain slowly but retain more water. Well-structured soils have a range of pore sizes that allow both water storage and drainage.
• Soil density is the mass of soil per unit volume. There are two types of soil density: particle density and bulk density. Particle density is the mass of solid soil particles per unit volume and is usually constant for a given soil type (around 2.65 g/cm3). Bulk density is the mass of dry soil per unit volume (including pore space) and varies depending on soil texture and structure (ranging from 1 to 1.8 g/cm3). Bulk density affects the porosity and compaction of the soil. For example, high bulk density indicates low porosity and high compaction, which reduce water infiltration and root growth.
• Soil consistency is the ability of soil to stick together or resist deformation under different moisture conditions: air-dry, moist, or wet. Soil consistency is influenced by soil texture, organic matter content, and clay mineralogy. Soil consistency affects the tillage, erosion, compaction, and crusting of the soil. For example, air-dry consistency ranges from loose to hard depending on how easily the soil can be crushed by hand; moist consistency ranges from friable to plastic depending on how easily the soil can be molded by hand; wet consistency ranges from nonsticky to sticky depending on how much the soil adheres to other objects.
• Soil temperature is the average heat content of the soil at a given depth and time. Soil temperature is influenced by solar radiation, air temperature, moisture content, vegetation cover, and soil color. Soil temperature affects various biological, chemical, and physical processes in the soil such as seed germination, plant growth, microbial activity, organic matter decomposition, nutrient cycling, and water movement. For example, warm soils tend to have higher biological activity and nutrient availability than cold soils, but also higher evaporation and decomposition rates.
• Soil air is the mixture of gases that occupy the pore space in the soil. Soil air is mainly composed of nitrogen, oxygen, carbon dioxide, and water vapor, but may also contain other gases such as methane and radon. Soil air is influenced by soil texture, structure, moisture, temperature, and biological activity. Soil air affects the respiration, photosynthesis, nitrification, denitrification, and oxidation-reduction reactions in the soil. For example, well-aerated soils tend to have higher microbial activity and nitrification rates than poorly-aerated soils, but also lower carbon storage and denitrification rates.

The chemical properties of soil are aspects of soil that relate to the presence, availability, and reactions of nutrients, minerals, organic matter, and microorganisms. These properties affect the soil fertility, plant growth, microbial activity, and environmental quality. Some of the chemical properties of soil are:

• Soil pH: Soil pH is the measure of the hydrogen ion concentration in the aqueous solution of soil, which determines the acidity or alkalinity of the soil. Soil pH ranges from 3.5 to 9.5, with 7 being neutral. Soil pH affects the availability of nutrients, the activity of microorganisms, and the toxicity of some elements in the soil. Usually, soils with high acidity contain higher amounts of aluminum and manganese, and soils with high alkalinity have higher concentrations of sodium carbonate. Most plants prefer a slightly acidic to neutral soil pH for optimal growth.
• Cation exchange capacity (CEC): Cation exchange capacity is the maximum amount of total cations that a soil sample can hold at a given pH. Cations are positively charged ions such as calcium, magnesium, potassium, sodium, hydrogen, and aluminum that are attached to the negatively charged surfaces of soil particles or soil organic matter. CEC is an indicator of soil fertility, nutrient retention, and the ability of soil to protect groundwater from cation contamination. Soils with high CEC can hold more nutrients and buffer against pH changes better than soils with low CEC.
• Electrical conductivity (EC): Electrical conductivity is the measure of the ability of soil to conduct an electric current. EC is influenced by the amount and type of dissolved salts in the soil solution. EC is an indicator of soil salinity, which is the accumulation of soluble salts in the soil. High salinity can reduce plant growth, impair soil structure, and affect microbial activity. Salinity can be caused by natural factors such as weathering of rocks or sea spray, or by human activities such as irrigation or fertilization.
• Organic matter: Organic matter is the non-mineral component of soil that consists of living organisms (such as plants, animals, and microorganisms) and their dead or decomposing residues. Organic matter influences many chemical properties of soil, such as nutrient availability, CEC, pH buffering, water holding capacity, and aggregation. Organic matter also serves as a source of energy and carbon for soil microorganisms that drive various biogeochemical cycles.
• Nutrients: Nutrients are essential elements or compounds that are required for plant growth and development. Nutrients can be classified into macronutrients and micronutrients based on their relative abundance in plant tissues. Macronutrients include nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S), while micronutrients include iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl), and nickel (Ni). Nutrients can be supplied by organic matter decomposition, mineral weathering, atmospheric deposition, or fertilization. Nutrients can also be lost from the soil by leaching, runoff, erosion, volatilization, or crop removal.
• Trace metals: Trace metals are metals that occur in very low concentrations in the soil (<100 mg/kg). Some trace metals are essential micronutrients for plants and microorganisms (such as Fe, Mn, Zn, Cu), while others are non-essential or toxic (such as cadmium (Cd), lead (Pb), mercury (Hg), arsenic (As)). Trace metals can originate from natural sources such as parent material or volcanic activity, or from anthropogenic sources such as mining, industrial waste, sewage sludge, or pesticides. Trace metals can affect plant growth, soil quality, and human health depending on their availability, mobility, and bioaccumulation in the food chain.

Soil is a complex mixture of minerals, organic matter, water, air, and living organisms that varies in composition and properties depending on different factors. One of the ways to classify soil is based on the size and proportion of mineral particles that make up the soil. These particles are sand, silt, and clay, and they determine the soil texture, which affects the soil`s physical and chemical characteristics. The four main types of soil based on texture are sandy soil, clay soil, silt soil, and loam soil.

• Sandy Soil

Sandy soil is a type of soil that contains a high proportion of sand particles (more than 50%) and a low proportion of clay particles (less than 10%). Sandy soil has a coarse texture that feels gritty to the touch. It has large pores that allow water and air to drain quickly through it, making it dry and warm. Sandy soil has low water retention capacity and low nutrient content, which makes it less fertile and less suitable for plant growth. However, sandy soil can be improved by adding organic matter or compost to increase its moisture and nutrient levels. Sandy soil is found in arid and semi-arid regions, coastal areas, and river deltas.

Some advantages of sandy soil are:

• It is easy to work with and cultivate.
• It warms up quickly in spring and allows early planting.
• It is well aerated and has good drainage.
• It is less prone to waterlogging and compaction.

Some disadvantages of sandy soil are:

• It dries out quickly and needs frequent watering.
• It has low fertility and needs regular fertilization.
• It is susceptible to erosion and leaching of nutrients.
• It has poor structure and stability.

Some plants that grow well in sandy soil are:

• Cacti and succulents
• Carrots, radishes, potatoes, and other root vegetables
• Lavender, rosemary, thyme, and other herbs
• Sunflowers, zinnias, marigolds, and other flowers
• Clay Soil

Clay soil is a type of soil that contains a high proportion of clay particles (more than 40%) and a low proportion of sand particles (less than 20%). Clay soil has a fine texture that feels smooth or sticky to the touch. It has small pores that hold water and air tightly within it, making it wet and cold. Clay soil has high water retention capacity and high nutrient content, which makes it fertile and suitable for plant growth. However, clay soil can be difficult to work with as it becomes hard and compact when dry and sticky and heavy when wet. Clay soil can be improved by adding organic matter or sand to increase its drainage and aeration. Clay soil is found in low-lying areas, floodplains, and deltas.

Some advantages of clay soil are:

• It holds water and nutrients well and needs less watering and fertilizing.
• It supports a diverse range of plants and crops.
• It has good structure and stability.
• It is resistant to erosion.

Some disadvantages of clay soil are:

• It is hard to work with and cultivate.
• It warms up slowly in spring and delays planting.
• It is poorly aerated and has poor drainage.
• It is prone to waterlogging and compaction.

Some plants that grow well in clay soil are:

• Trees like willow, birch, maple, ash, elm, oak
• Shrubs like azalea, rhododendron, hydrangea
• Perennials like hosta, aster, iris
• Vegetables like cabbage, broccoli
• Silt Soil

Silt soil is a type of soil that contains a moderate proportion of silt particles (40-80%) along with sand (0-50%) and clay (0-27%). Silt particles are smaller than sand but larger than clay. Silt soil has a smooth texture that feels silky or floury to the touch. It has medium-sized pores that retain water and air moderately well within it. Silt soil has moderate water retention capacity and moderate nutrient content. Silt soil can be fertile if it has enough organic matter in it. However, silt soil can also be easily eroded by wind or water if it lacks organic matter or vegetation cover. Silt soil can be improved by adding organic matter or mulch to increase its fertility and stability. Silt soil is found near water bodies, such as rivers, lakes, and ponds.

Some advantages of silt soil are:

• It is easy to work with and cultivate.
• It has good drainage and aeration.
• It has moderate fertility and supports a variety of plants.
• It has a smooth and soft texture.

Some disadvantages of silt soil are:

• It is susceptible to erosion and leaching of nutrients.
• It can become compacted and lose its structure.
• It can dry out quickly and need frequent watering.
• It can become waterlogged and cold in wet conditions.

Some plants that grow well in silt soil are:

• Grasses like wheat, barley, oats, rye
• Vegetables like lettuce, spinach, celery
• Flowers like poppy, lily, cosmos
• Fruits like apple, pear, plum
• Loam Soil

Loam soil is a type of soil that contains a balanced proportion of sand (25-50%), silt (25-50%), and clay (7-27%). Loam soil has a crumbly texture that feels soft and friable to the touch. It has a mixture of pore sizes that allow water and air to move freely through it. Loam soil has high water retention capacity and high nutrient content. Loam soil is considered the ideal soil for gardening as it is fertile, easy to work with, and suitable for most plants. Loam soil can be maintained by adding organic matter or compost regularly to replenish its nutrients and structure. Loam soil is found in various regions depending on the parent material and climate.

Some advantages of loam soil are:

• It holds water and nutrients well and needs less watering and fertilizing.
• It drains excess water and prevents waterlogging.
• It aerates the roots and prevents compaction.
• It supports a wide range of plants and crops.

Some disadvantages of loam soil are:

• It can be expensive or difficult to obtain or create.
• It can lose its structure or fertility if not managed properly.
• It can vary in composition and quality depending on the source.
• It can be affected by pests or diseases if not monitored.

Some plants that grow well in loam soil are:

• Trees like cherry, peach, walnut
• Shrubs like rose, lilac, hibiscus
• Perennials like daisy, peony, geranium
• Vegetables like tomato, cucumber, carrot

Soil is not only a medium for plant growth but also a vital component of the global ecosystem. Soil performs various functions that are important for different agricultural, environmental, nature protection, landscape architecture and urban applications. Some of the major functions of soil are:

• Food and other biomass production: Soil provides an anchor for plant roots and a water holding tank for needed moisture. Soil also supplies nutrients and oxygen to plants and regulates the temperature of the root zone. Soil supports the production of food and other biomass such as wood, fiber, and fuel.
• Environmental interaction: Soil regulates water supplies by absorbing, storing, and releasing water. Soil also filters, buffers, and transforms materials between the atmosphere, the plant cover, and the water table. Soil can capture contaminants and reduce pollution. Soil can also store carbon as soil organic matter and mitigate climate change by reducing greenhouse gas emissions.
• Biological habitat and gene pool: Soil is a habitat for a large variety of organisms, from microorganisms to insects to animals. Soil hosts a rich biodiversity and a gene pool that is essential for life on Earth. Soil also participates in biogeochemical cycles and decomposes organic matter into simpler forms that can be reused by other living beings.
• Source of raw materials: Soil provides raw materials for human use and impacts human health directly. The composition of human food reflects the nature of the soil in which it was grown. Soil also provides materials such as clay, sand, gravel, and minerals for various purposes such as ceramic production, construction, mining, and manufacturing.
• Physical and cultural heritage: Soil preserves the physical and cultural heritage of human civilization. Soil contains archaeological artifacts, fossils, and historical records that reveal the past of humanity. Soil also reflects the cultural values, beliefs, and practices of different societies that have shaped the land use and management of soil resources.
• Platform for man-made structures: Soil acts as a base for building homes, roads, bridges, dams, and other structures. Soil provides stability, support, and drainage for these structures. Soil also influences the design, construction, and maintenance of these structures.

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