Soil Chemistry PDF

## WHAT IS SOIL CHEMISTRY - Chemistry is a branch of science that involves the study of the composition, structure and properties of matter. - Often known as the central science, it is a creative discipline chiefly concerned with atomic and molecular structure and its change, for instance through c...

## WHAT IS SOIL CHEMISTRY - Chemistry is a branch of science that involves the study of the composition, structure and properties of matter. - Often known as the central science, it is a creative discipline chiefly concerned with atomic and molecular structure and its change, for instance through chemical reactions. - Soil Chemistry is the branch of soil science that deals with the chemical composition, chemical properties, and chemical reactions of soils. - Soil chemistry has traditionally focused on the chemical reactions in soils that affect plant growth and plant nutrition. ## Environmental Soil Chemistry - A knowledge of environmental soil chemistry is paramount to predicting the fate of contaminants, as well as the processes by which they are initially released into the soil. - Once a chemical is exposed to the soil environment myriad chemical reactions can occur that may increase or decrease contaminant toxicity. - These reactions include adsorption/desorption, precipitation, polymerization, dissolution, complexation and oxidation/reduction. - These reactions are often disregarded by scientists and engineers involved with environmental remediation. - Understanding these processes enable us to better predict the fate and toxicity of contaminants and provide the knowledge to develop scientifically correct, and cost-effective remediation strategies. ### Adsorption - Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. - This process creates a film of the adsorbate on the surface of the adsorbent. - This process differs from absorption, in which a fluid (the adsorbate) is dissolved by or permeates a liquid or solid (the absorbent), respectively. - Adsorption is a surface phenomenon, while absorption involves the whole volume of the material. - The term sorption encompasses both processes, while desorption is the reverse of it. ### Desorption - Desorption is a phenomenon whereby a substance is released from or through a surface. - The process is the opposite of sorption (that is, either adsorption or absorption). - This occurs in a system being in the state of sorption equilibrium between bulk phase (fluid, i.e. gas or liquid solution) and an adsorbing surface (solid or boundary separating two fluids). - When the concentration (or pressure) of substance in the bulk phase is lowered, some of the sorbed substance changes to the bulk state. ### Precipitation - Precipitation is the creation of a solid from a solution. - When the reaction occurs in a liquid solution, the solid formed is called the 'precipitate'. - The chemical that causes the solid to form is called the 'precipitant' ### Polymerization - Polymerization is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. ### Dissolution - In chemistry, the process of dissolving a solute into a solvent to make a solution. ### Complexation - Complexation is the association between two or more molecules to form a nonbonded entity with a well-defined stoichiometry. ### Oxidation/Reduction - Oxidation reduction or Redox is a type of chemical reaction in which the oxidation states of atoms are changed. - Redox reactions are characterized by the transfer of electrons between chemical species, most often with one species (the reducing agent) undergoing oxidation (losing electrons) while another species (the oxidizing agent) undergoes reduction (gains electrons). - Oxidation is the loss of electrons or an increase in the oxidation state of an atom by another atom, an ion, or a molecule. - Reduction is the gain of electrons or a decrease in the oxidation state of an atom by another atom, an ion, or a molecule. ## PHYSICAL PROPERTIES OF SOIL ### Soil Texture - The particles that make up soil are categorized into three groups by size – sand, silt, and clay. - Sand particles are the largest and clay particles the smallest. - Most soils are a combination of the three. - The relative percentages of sand, silt, and clay are what give soil its texture. - A clay loam texture soil, for example, has nearly equal parts of sand, slit, and clay. - These textural separates result from the weathering process. ### Soil Structure - The arrangement of soil particles into small clumps, called peds or aggregates. - Soil particles (sand, silt, clay and even organic matter) bind together to form peds. - Depending on the composition and on the conditions in which the peds formed (getting wet and drying out, or freezing and thawing, foot traffic, farming, etc.), the ped has a specific shape. - They could be granular (like gardening soil), blocky, columnar, platy, massive (like modeling clay) or single-grained (like beach sand). - Structure correlates to the pore space in the soil which influences root growth and air and water movement. ## EROSION & SOIL ### Erosion - The geological process in which earthen materials are worn away and transported by natural forces such as wind or water. - A similar process, weathering, breaks down or dissolves rock, but does not involve movement. - The opposite of deposition, the geological process in which earthen materials are deposited, or built up, on a landform. - Most erosion is performed by liquid water, wind, or ice (usually in the form of a glacier). - If the wind is dusty, or water or glacial ice is muddy, erosion is taking place. - The brown color indicates that bits of rock and soil are suspended in the fluid (air or water) and being transported from one place to another. - This transported material is called sediment. #### Types of Erosion - **Splash Erosion:** Describes the impact of a falling raindrop, which can scatter tiny soil particles as far as 6 meters (2 feet). - **Sheet Erosion:** Describes erosion caused by runoff. - **Rill Erosion:** Describes erosion that takes place as runoff develops into discrete streams (rills). - **Gully Erosion:** The stage in which soil particles are transported through large channels. - Gullies carry water for brief periods of time during rainfall or snowmelt but appear as small valleys or crevasses during dry seasons. - **Valley Erosion:** The process in which rushing streams and rivers wear away their banks, creating larger and larger valleys. - **Physical Erosion:** Describes the process of rocks changing their physical properties without changing their basic chemical composition. - Physical erosion often causes rocks to get smaller or smoother. - Rocks eroded through physical erosion often form clastic sediments. - Clastic sediments are composed of fragments of older rocks that have been transported from their place of origin. - Landslides and other forms of mass wasting are associated with physical weathering. - These processes cause rocks to dislodge from hillsides and crumble as they tumble down a slope. ## SOIL COLOR - Influenced primarily by soil mineralogy - telling us what is in a specific soil. - Soils high in iron are deep orange-brown to yellowish-brown. - Those soils that are high in organic matter are dark brown or black. - Color can also tell us how a soil “behaves” - a soil that drains well is brightly colored and one that is often wet and soggy will have a mottled pattern of grays, reds, and yellows. ## EROSION BY WATER - Liquid water is the major agent of erosion on Earth. - Rain, rivers, floods, lakes, and the ocean carry away bits of soil and sand and slowly wash away the sediment. - Rainfall produces four types of soil erosion: splash erosion, sheet erosion, rill erosion, and gully erosion. ## OTHER FORCES OF EROSION - **Thermal erosion:** Describes the erosion of permafrost along a river or coastline. - Warm temperatures can cause ice-rich permafrost to break off coastlines in huge chunks, often carrying valuable topsoil and vegetation with them. - These eroded "floating islands" can disintegrate into the ocean, or even crash into another piece of land-helping spread new life to different landscapes. - **Mass wasting:** Describes the downward movement of rocks, soil, and vegetation. - Mass wasting incidents include landslides, rockslides, and avalanches. - Mass wasting can erode and transport millions of tons of earth, reshaping hills and mountains and, often, devastating communities in its path. ## FACTORS IMPACTING EROSION - **Climate:** Perhaps the most influential force impacting the effect of erosion on a landscape. - Includes precipitation and wind. - Climate also includes seasonal variability, which influences the likelihood of weathered sediments being transported during a weather event such as a snowmelt, breeze, or hurricane. - **Topography:** The shape of surface features of an area, can contribute to how erosion impacts that area. - The earthen floodplains of river valleys are much more prone to erosion than rocky flood channels, which may take centuries to erode. - Soft rock like chalk will erode more quickly than hard rocks like granite. - **Vegetation:** Can slow the impact of erosion. - Plant roots adhere to soil and rock particles, preventing their transport during rainfall or wind events. - Trees, shrubs, and other plants can even limit the impact of mass wasting events such as landslides and other natural hazards such as hurricanes. - Deserts, which generally lack thick vegetation, are often the most eroded landscapes on the planet. - **Tectonic activity:** Shapes the landscape itself, and thus influences the way erosion impacts an area. - Tectonic uplift, for example, causes one part of the landscape to rise higher than others. ## EROSION AND PEOPLE ### Deposition, Soils, and Sediments - Eroded sediments have profoundly influenced the development of civilizations around the world. - Agricultural development is often reliant on the nutrient-rich soils created by the accumulation of eroded earth. - When the velocity of wind or water slows, eroded sediment is deposited in a new location. - The sediment builds up in a process called sedimentation and creates fertile land. - River deltas are made almost entirely of sediment that has eroded from the banks and bed of a river. - The rich delta soils of the San Joaquin and Sacramento rivers in northern California, for example, have created one of the most agriculturally productive areas in the world. - Loess is an agriculturally rich sediment made almost entirely of wind-blown, eroded sediment. - The Yellow River in central China gets its name from the yellow loess blown into and suspended in its water. - The fertile lands around the Yellow River have been among China’s most productive for thousands of years. ### Erosion Control - Erosion is a natural process, but human activity can make it happen more quickly. - Human activity altering the vegetation of an area is perhaps the biggest human factor contributing to erosion. - Trees and plants hold soil in place. - When people cut down forests or plow up grasses for agriculture and development, the soil is more vulnerable to washing or blowing away. - Landslides become more common. - Water rushes over exposed soil rather than soaking into it, causing flooding. - Global warming, the current period of climate change, is speeding erosion. - The change in climate has been linked to more frequent and severe storms. - Storm surges following hurricanes and typhoons can erode kilometers of coastline and coastal habitat. - These coastal areas are home to residences, businesses, and economically important industries, such as fisheries. - The rise in temperature is also quickly melting glaciers. - The slower, more massive form of glacial erosion is being supplanted by the cumulative impact of rill, gully, and valley erosion. - In areas downstream from glacial snouts, rapidly melting glaciers are contributing to sea level rise. - The rising sea erodes beaches more quickly. - Erosion control is the process of reducing erosion by wind and water. - Farmers and engineers must regularly practice erosion control. ## CAUSES OF SOIL EROSION - Various agents, like wind, water, deforestation, overgrazing by cattle, etc., cause soil erosion. ### 1. Wind - When strong winds blow, the topsoil along with the organic matter is carried away by the wind. - This happens more often when the land is not covered with grass or plants. - Such conditions are very common in desert and semi-desert regions where strong winds blow very frequently. ### 2. Water - When it rains in the hilly areas, the soil gets washed away towards the plains. - The running water deposits the mineral-rich soil in the riverbed and over the years this deposition of soil can change the course of the river. - This can lead to floods which cause the destruction of life and property. - Water erosion leads to loss of agriculture potential. ### 3. Overgrazing - When cattle are allowed to graze on the same field repeatedly, all the available grass, including the roots are eaten by them. - This makes the topsoil vulnerable to wind and flowing water, leading to soil erosion. ### 4. Deforestation - Humans have taken land from the forest to cultivate in order to feed the ever-increasing population and to build houses, industries, etc. - Cutting down of trees on a large scale for these purposes is deforestation. - The roots of trees hold the soil together, thus preventing the soil from getting uprooted. - When large areas of the forest are cleared, the topsoil gets eroded by wind and flowing water. ## SOIL CONSERVATION - Prevention of soil erosion is also called conservation of soil. - The soil erosion can be prevented by the following ways: ### 1. Afforestation - Planting new trees and plants is afforestation. - We live because plants live. - If the plants die, all living things will also die. - Thus, whenever trees are cut down new trees should be planted. - Planting trees in hilly areas are most effective for conservation. ### 2. Crop Rotation - Between harvesting one crop and planting the next crop, the fields lie bare, there is a time period when the farmland does not have any crops. - During this period, the farmer either grows grass or grows other crops to prevent soil from erosion. - This helps the soil to regain the lost minerals. ### 3. Terrace Farming - In hilly areas, farming is done by cutting steps on the slopes of the hills. - This slows down the flow of water and soil removed from one step is deposited on the next step. - Thus, the soil is never completely lost. - This is terrace farming. ### 4. Building Dams - Dams are built to prevent floods, which not only damage the crops but also wash away the topsoil. ### 5. Shelterbelts - The cover of plants and trees around the field also breaks the speed of strong winds and protects the soil from being blown away. ### 6. Embankments - Bib strong structure called embankments along the banks of the river can protect fields from the floods. - These embankments prevent the fast overflowing rivers and rainwater from washing away a huge amount of rich fertile soil. ### 7. Van Mahotsav - It is an annual tree planting festival started by the Government of India. - The aim of this programme is to create awareness about the need for conservation of forest and soil. ## SOIL - The top layer of the earth's surface. - It is made up of dirt and rock. - Filled with air and life. - A variety of organisms, like insects, earthworm, live in soil. - For plants, soil serves as a storehouse of water and minerals needed for their growth. - It also provides shelter to many animals that live on or in the soil. - Without soil, there would be no grass, no crops, no trees, no food for us and other animals. ## SOIL EROSION - A process in which the top fertile layer of soil is lost. - Due to soil erosion, the soil becomes less fertile. - The top layer of soil is very light which is easily carried away by wind and water. - The removal of topsoil by the natural forces is known as soil erosion. ## Sometimes, engineers simply install structures to physically prevent soil from being transported. - Gabions are huge wireframes that hold boulders in place, for instance. - Gabions are often placed near cliffs. - These cliffs, often near the coast, have homes, businesses, and highways near them. - When erosion by water or wind threatens to tumble the boulders toward buildings and cars, gabions protect landowners and drivers by holding the rocks in place. ## Erosion control also includes physically changing the landscape. - Communities often invest in windbreaks and riparian buffers to protect valuable agricultural land. - Windbreaks, also called hedgerows or shelterbelts, are lines of trees and shrubs planted to protect cropland from wind erosion. - Riparian buffers describe plants such as trees, shrubs, grasses, and sedges that line the banks of a river. - Riparian buffers help contain the river in times of increased stream flow and flooding. ## Living shorelines are another form of erosion control in wetland areas. - Living shorelines are constructed by placing native plants, stone, sand, and even living organisms such as oysters along wetland coasts. - These plants help anchor the soil to the area, preventing erosion. - By securing the land, living shorelines establish a natural habitat. - They protect coastlines from powerful storm surges as well as erosion.