Chemistry of Soil. Layer composition factors etc
- 2. Chemistry of soil Soil chemistry involves the chemical reactions and processes between these components and particularly focuses on investigating the fate of contaminants and nutrients within soils. Knowledge of soil chemistry allows scientists to monitor, control and predict the effects of pollutants in the environment. Chemical knowledge combined with understandings from the Earth sciences, physics and biology are needed to understand, prevent and remediate environmental issues with soils.
- 4. 1. Soil Layer Composition
- 5. 1. Soil Layer Composition -The study of soil is called pedology or, more simply, soil science. -To humans and most terrestrial organisms, soil is the most important part of the geosphere. -Though only a tissue-thin layer compared to the earth’s total diameter, soil is the medium that produces most of the food required by most living things. -Good soil and a climate conducive to its productivity is the most valuable asset a society can have.
- 6. Soil is a mixture of inorganic and organic solids, air and water
- 7. Soil consists of these major components
- 8. The amount of each of the four major components of soil depends on the quantity of vegetation, soil compaction, and water present in the soil. A good, healthy soil has sufficient air, water, minerals, and organic material to promote and sustain plant life.
- 9. The organic material of soil, called humus, is made up of microorganisms (dead and alive), and dead animals and plants in varying stages of decay. Humus improves soil structure, providing plants with water and minerals.
- 10. -The inorganic material of soil is composed of rock, slowly broken down into smaller. particles that vary in size. Soil particles that are 0.1 to 2 mm in diameter are sand. Soil particles between 0.002 and 0.1 mm are called silt, and even smaller particles, less than 0.002 mm in diameter, are called clay. Some soils have no dominant particle size, containing a mixture of sand, silt, and humus; these soils are called loams.
- 11. 2. Soil Forming Factors -The fundamental factors that affect soil genesis can be categorized into five elements: climate, organisms, relief, parent material, and time. -* The relief, climate, and organisms dictate the local soil environment and act together to cause weathering and mixing of the soil parent material over time
- 12. - As soil is formed it often has distinct layers, which are formally described as “horizons.” Upper horizons (labeled as the A and O horizons) are richer in organic material and so are important in plant growth, while deeper layers (such as the B and C horizons) retain more of the original features of the bedrock below.
- 13. *Climate The role of climate in soil development includes aspects of temperature and precipitation.
- 14. *Soils in very cold areas with permafrost conditions tend to be shallow and weakly developed due to the short growing season. Organic rich surface horizons are common in low-lying areas due to limited decomposition.
- 15. • In warm, tropical soils, soils tend to be thicker, with extensive leaching and mineral alteration. In such climates, organic matter decomposition and chemical weathering occur at an accelerated rate.
- 16. Animals, plants, and microorganisms all have important roles in soil development processes, in providing a supply of organic matter, and/or in nutrient cycling. Worms, nematodes, termites, ants, gophers, moles, etc. all cause considerable mixing of soil and help to blend soil, aerate and lighten the soil by creating pores (which help store water and air). Plant life provides organic matter to soil and helps to recycle nutrients with uptake by roots in the subsurface
- 17. The type of plant life that occurs in a given area, such as types of trees or grasses, depends on the climate, along with parent material and soil type. With the annual dropping of leaves and needles, trees tend to add organic matter to soil surfaces, helping to create a thin, organic-rich A or O horizon over time. Grasses, on the other hand, have a considerable root and surface masses that add to the soil each fall for annuals and short-lived perennials. For this reason, grassland soils have much thicker A horizons with higher organic matter contents, and are more agriculturally productive than forest soils.
- 18. Relief (Topography and Drainage) The local landscape can have a surprisingly strong effect on the soils that form on site. The local topography (relief) can have important microclimatic effects as well as affecting rates of soil erosion. In comparison to flat regions, areas with steep slopes overall have more soil erosion, more runoff of rainwater, and less water infiltration, all of which lead to more limited soil development in very hilly or mountainous areas. In the northern hemisphere, south-facing slopes are exposed to more direct sunlight angles and are thus warmer and drier than north-facing slopes. The cooler, moister north-facing slopes have a more dynamic plant community due to less evapotranspiration and, consequently, experience less erosion because of plant rooting of soil and have thicker soil development.
- 19. Relief (Topography and Drainage) Soil drainage affects organic matter accumulation and preservation, and local vegetation types. Well- drained soils, generally on hills or side slopes, are more brownish or reddish due to conversion of ferrous iron (Fe2+) to minerals with ferric (Fe3+) iron. More poorly drained soils, in lowland, alluvial plains or upland depressions, tend more be more greyish, greenish-grey (gleyed), or dark colored, due to iron reduction (to Fe2+) and accumulation and preservation of organic matter in areas tending towards anoxic. Areas with poor drainage also tend to be lowlands into which soil material may wash and accumulate from surrounding uplands, often resulting in overthickened A or O horizons. In contrast, steeply sloping areas in highlands may experience erosion and have thinner surface horizo
- 20. Parent Material The parent material of a soil is the material from which the soil has developed, whether it be river sands, shoreline deposits, glacial deposits, or various types of bedrock. In youthful soils, the parent material has a clear connection to the soil type and has significant influence.
- 21. Parent Material Over time, as weathering processes deepen, mix, and alter the soil, the parent material becomes less recognizable as chemical, physical, and biological processes take their effect. The type of parent material may also affect the rapidity of soil development.).
- 22. Parent Material Parent materials that are highly weatherable (such as volcanic ash) will transform more quickly into highly developed soils, whereas parent materials that are quartz-rich, for example, will take longer to develop. Parent materials also provide nutrients to plants and can affect soil internal drainage (e.g. clay is more impermeable than sand and impedes drainage
- 23. Time In general, soil profiles tend to become thicker (deeper), more developed, and more altered over time. However, the rate of change is greater for soils in youthful stages of development. The degree of soil alteration and deepening slows with time and at some point, after tens or hundreds of thousands of years, may approach an equilibrium condition where erosion and deepening (removals and additions) become balanced.
- 24. Young soils (< 10,000 years old) are strongly influenced by parent material and typically develop horizons and character rapidly. Moderate age soils (roughly 10,000 to 500,000 years old) are slowing in profile development and deepening, and may begin to approach equilibrium conditions. Old soils (>500,000 years old) have generally reached their limit as far as soil horizonation and physical structure, but may continue to alter chemically or mineralogically. Time
- 25. . Soil development is not always continual. Geologic events can rapidly bury soils (landslides, glacier advance, lake transgression), can cause removal or truncation of soils (rivers, shorelines) or can cause soil renewal with additions of slowly deposited sediment that add to the soil (wind or floodplain deposits). Biological mixing can sometimes cause soil regression, a reversal or bump in the road for the normal path of increasing development over time. Time
- 26. 3. Soil Properties All soils contain mineral particles, organic matter, water and air. The combinations of these determine the soil’s properties 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 texture can influence whether soils are free draining, whether they hold water and how easy it is for plant roots to grow.
- 27. • Sand particles are quite big. The pore spaces between the particles in sandy soils are also quite large. This allows water to drain quickly and air to enter the soil. Sandy soils tend not to get waterlogged in winter but can be subject to drought during summer.
- 28. Silt particles are too small for us to see with our eyes. Silt soils have much smaller pore spaces but a lot more of them.
- 29. Clay particles are smaller than 0.002 mm in diameter. Clay soils are poorly drained and hold on to the water in their pore spaces for much longer. However, they can become very hard if they dry out
- 30. Soil structure Soil structure is 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.
- 31. Soil structure . Bulk density reflects the soil’s ability to function for structural support, water and solute movement, and soil aeration. Bulk density is an indicator of soil compaction. It is calculated as the dry weight of soil divided by its volume. This volume includes the volume of soil particles and the volume of pores among soil particles. Bulk density is typically expressed in g/cm3. Soil porosity refers to the pores within the soil. Porosity influences the movement of air and water. Porosity, the percent by volume of a soil sample not occupied by solids, is directly related to bulk density and particle density. If particle density remains constant, as bulk density increases porosity decreases.
- 32. Soil structure Particle density is a measure of the mass of soil solids per given volume (g/cm3); however, pore space is not included as it is with bulk density. Particle density is similar to the specific gravity of a solid and is not impacted by land use. Particle density is approximated as 2.65 g/cm3, although this number may vary considerably if the soil sample has a high concentration of organic matter, which would lower particle density, or high-density minerals such as magnetite, garnet, hornblende, etc.
- 33. Soil chemistry Clays and organic matter in the soil carry negative charges. Water in the soil dissolves nutrients and other chemicals. Nutrients like potassium and ammonium have positive charges. They are attracted to the negatively charged organic and mineral matter, and this prevents them from being lost through leaching as water moves through the soil. Nitrate has a negative charge so it is not protected from leaching in most soils.
- 34. Soil chemistry Soils can be acid, alkaline or neutral. Soil pH influences nutrient absorption and plant growth. Some plants, like kumara and potatoes, grow best in a more acidic soil (pH of 5.0–6.0). Carrots and lettuces prefer soils with a neutral pH of 7.0. Soils can become more acidic over time as minerals are leached away. Lime is often added to soil to make it less acidic.
- 35. Soil color If you thought that all soils are brown, think again. Soil colors range from black to red to white. Sometimes it can even be blue! Soil color mostly comes from organic matter and iron. Topsoil is often dark because of organic matter. An even, single color indicates the soil is well drained. In contrast, rusty spots and grey patches (sometimes even a light blue in color) indicate poor drainage.
- 36. 4. Soil Pollution Soil pollution refers to the contamination of soil with anomalous concentrations of toxic substances. It is a serious environmental concern since it harbors many health hazards. For example, exposure to soil containing high concentrations of benzene increases the risk of contracting leukemia. It is important to understand that all soils contain compounds that are harmful/toxic to human beings and other living organisms. However, the concentration of such substances in unpolluted soil is low enough that they do not pose any threat to the surrounding ecosystem. When the concentration of one or more such toxic substances is high enough to cause damage to living organisms, the soil is said to be contaminated.
- 37. 4. Soil Pollution • Agriculture (excessive/improper use of pesticides) The root cause of soil pollution is often one of the following: • Excessive industrial activity • Poor management or inefficient disposal of waste
- 38. 5. Soil Pollutants Some of the most hazardous soil pollutants are xenobiotics – substances that are not naturally found in nature and are synthesized by human beings. The term ‘xenobiotic’ has Greek roots – ‘Xenos’ (foreigner), and ‘Bios’ (life). Several xenobiotics are known to be carcinogens. An illustration detailing major soil pollutants is provided below.
- 39. 5. Soil Pollutants Heavy Metals The presence of heavy metals (such as lead and mercury, in abnormally high concentrations) in soils can cause it to become highly toxic to human beings. Some metals that can be classified as soil pollutants
- 40. 5. Soil Pollutants Heavy Metals These metals can originate from several sources such as mining activities, agricultural activities, electronic waste (e-waste), and medical waste. Heavy Metals
- 41. 5. Soil Pollutants Polycyclic Aromatic Hydrocarbons Polycyclic aromatic hydrocarbons (often abbreviated to PAHs) are organic compounds that: 1. Contain only carbon and hydrogen atoms. 2. Contain more than one aromatic ring in their chemical structures. Common examples of PAHs include naphthalene, anthracene, and phenalene. Exposure to polycyclic aromatic hydrocarbons has been linked to several forms of cancer. These organic compounds can also cause cardiovascular diseases in humans. Soil pollution due to PAHs can be sourced to coke (coal) processing, vehicle emissions, cigarette smoke, and the extraction of shale oil.. Heavy Metals
- 42. 5. Soil Pollutants Industrial Waste The discharge of industrial waste into soils can result in soil pollution. Some common soil pollutants that can be sourced to industrial waste are listed below. • Chlorinated industrial solvents • Dioxins produced from the manufacture of pesticides and the incineration of waste. • Plasticizers/dispersants • Polychlorinated biphenyls (PCBs)
- 43. 5. Soil Pollutants Pesticides Pesticides are substances (or mixtures of substances) that are used to kill or inhibit the growth of pests. Common types of pesticides used in agriculture include: • Herbicides – used to kill/control weeds and other unwanted plants. • Insecticides – used to kill insects. • Fungicides – used to kill parasitic fungi or inhibit their growth. However, the unintentional diffusion of pesticides into the environment (commonly known as ‘pesticide drift’) poses a variety of environmental concerns such as water pollution and soil pollution. These chemicals pose several health risks to humans. Examples of health hazards related to pesticides include diseases of the central nervous system, immune system diseases, cancer, and birth defects.
- 44. 6. Measures to Avoid Soil Pollution • The contaminated soil can be excavated and transported to a remote disposal site. • Thermal remediation of contaminated soil, which involves heating up the soil in order to vaporize the volatile toxic pollutants. • Soil decontamination via surfactant leaching.
- 45. Chemistry of Soil Group 3 Herminiano Jericko G Mira Ronald Benito Denice Sarawad Jezreel Vicente Jingoy Lucucan Renz De los Trinos Ryan