Topic 3.3_Soil Chemistry.pdf

Topic 3.3: Soil Chemistry References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Learning Outcomes 3.3.1 Describe the major components of a soil and how they vary to produce different types of soil 3.3.2 Discu...

Topic 3.3: Soil Chemistry References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Learning Outcomes 3.3.1 Describe the major components of a soil and how they vary to produce different types of soil 3.3.2 Discuss factors affecting soil formation 3.3.3 Use texture triangle to classify soil 3.3.4 Determine acidity and alkalinity of soil  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning What are the four most important natural constituents that permit life as we know it to exist on Earth? Many people if asked that question would reply, “air, water, and sunlight,” right away, but they might have to think harder and longer about their fourth answer. Most people give little attention to that fourth natural resource, but it is essential for their life on Earth, and it lies right below their feet.  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://core.ac.uk/download/pdf/215276225.pdf Soil is that critical resource. The soil mantle that covers most land surfaces is indispensable, but fragile, and threatened by erosion, pollution, or being covered over by the human- built environment. Soil provides nutrients that directly or indirectly support much of life on Earth.  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://agriculturegoods.com/the-complete-guide-on-crops-suitable-for-loamy-soil/ Soil is a dynamic natural body capable of supporting a vegetative cover. It contains chemical solutions, gases, organic refuse, flora, and fauna. The physical, chemical, and biological processes that take place among the components of a soil are integral parts of its dynamic character. Soil responds to climatic conditions (especially temperature and moisture), to the land surface configuration, to vegetative cover and composition, and to animal activity.  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Soil has been called “the skin of the Earth.” The condition and nature of a soil reflects both the ancient environments under which it formed, and today’s environmental conditions. A soil functions as an environmental system, adapting, reflecting, and responding to a great variety of natural and human- influenced processes.  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Soil is an exceptional example of the integration, interdependence, and overlap among Earth’s subsystems because the characteristics of a soil reflect the atmospheric, hydrologic, lithologic, and biotic conditions under which it developed. In fact, because soils integrate these major subsystems so well, they are sometimes considered a separate system called the pedosphere (from Greek: pedon, ground)  Soils and Soil Development References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://foodprint.org/blog/why-is-soil-important/ Soil is also home to numerous living organisms, forming the environments in which they live, both above and below the ground surface. The life-forms that live in or on a soil play significant roles in the development and characteristics of a soil, and through human population growth and expanding civilizations, potentially negative impacts on soils have increased dramatically. Soils and Soil Development References: https://international-soil-radiocarbon- database.github.io/SOC- Hub/climate%20and%20carbon%20stocks/ 2018/07/10/Ecosystem-Services/ The main ecosystem services provided by soils (Food and Agriculture Organization of the United Nations).  Major Soil Components References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning What soil characteristics support and influence variations in Earth’s vegetational environments? Soils contain four major components, and there are many processes that act on these components. The four major components of soil are inorganic materials, soil water, soil air, and organic matter.  Inorganic Materials References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://horticulture.tekura.school.nz/soils/soils-1/ht1031-soils-1-study-plan/soil/ Soils contain varying amounts of insoluble materials—rock fragments and minerals that will not readily dissolve in water. Soils also contain soluble minerals, which supply dissolved chemicals held in solution. Most minerals found in soils are combinations of the common elements of Earth’s surface rocks: silicon, aluminum, oxygen, and iron. Some of these constituents occur as solid chemical compounds, and others are found in the air and water that are also vital components of a soil. Soils sustain Earth’s land ecosystems by providing a great variety of necessary chemical elements and compounds to life-forms. Carbon, hydrogen, nitrogen, sodium, potassium, zinc, copper, iodine, and compounds of these elements are important in soils. References: https://slideplayer.com/slide/406 0749/ Petersen, et al. 2017. Physical Geography. Cengage Learning  Inorganic Materials References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://thegrowingseason.wordpress.com/2013/05/10/soils-management-the-old-jar-test/ The chemical constituents of a soil typically come from many sources—the breakdown (weathering) of underlying rocks, deposits of loose sediments, and minerals dissolved in water.  Inorganic Materials References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Organic activities help to disintegrate rocks, create new chemical compounds, and release gases into the soil. Plants need many chemical substances for growth, and having a knowledge of a soil’s mineral and chemical content is necessary for determining its potential productivity. Soil fertilization is the process of adding nutrients or other constituents in order to meet the soil conditions that certain plants require.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning The original source of soil water is precipitation. When precipitation falls on the land, the water that is not evaporated away is either absorbed into the ground or by vegetation, or it runs downslope. Soil water is both an ingredient and a catalyst for chemical reactions that sustain life and influence soil development.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Water also provides nutrients in a form that can be extracted by vegetation. As water moves through a soil it washes over and through various soil components, dissolving some of these materials and carrying them through the soil. Soil water is not pure, but is a solution that contains soluble nutrients.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Plants need air, water, and minerals to function, live, and grow, and they depend on soil for much of these necessities. A soil functions as an open system. Matter and energy flow into and out of a soil, and they are also held in storage. Understanding these flows—inputs and outputs, the components and processes involved, and how they vary from soil to soil—is a key to appreciating the complexities of this natural resource.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.vedantu.com/question-answer/differentiate-between-hygroscopic-water-and-class-11-biology- cbse-5f6545a4dc3f5e711e51f56e The water in a soil is found in several different circumstances. Soil water adheres to soil particles and soil clumps by surface tension (the property that causes small water droplets to form rounded beads instead of spreading out in a thin film). This soil water, called capillary water, serves as a stored water supply for plants. Capillary water can move in all directions through soil because it migrates from areas with more water to areas with less. Thus, during dry periods, when there is no gravitational water flowing through the soil, capillary water can move upward or horizontally to supply plant roots with moisture and dissolved nutrients.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.vedantu.com/question-answer/differentiate-between-hygroscopic-water-and-class-11-biology- cbse-5f6545a4dc3f5e711e51f56e Capillary water migrates upward and moves minerals from the subsoil toward the surface. If this capillary water evaporates away, the formerly dissolved minerals remain, generally as alkaline or saline deposits in the topsoil. High concentrations of certain mineral deposits, like these, can be detrimental to plants and animals existing in the soil. Lime (calcium carbonate) deposited by evaporating soil water can build up to produce a cementlike layer, called caliche, which like a clay hardpan prevents the downward percolation of water.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning gy2-Absorption_Of_Water.htm Soil water is also found as a very thin film, invisible to the naked eye, that is bound to the surfaces of soil particles by strong electrical forces. This is hygroscopic water, which does not move through the soil, and it also does not supply plants with the moisture that they need.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.vedantu.com/question-answer/differentiate-between-hygroscopic-water-and-class-11- biology-cbse-5f6545a4dc3f5e711e51f56e Water that percolates down through a soil, under the force of gravity, is called gravitational water. Gravitational water moves downward through voids between soil particles and toward the water table—the level below which all available spaces are filled with water. The quantity of gravitational water in a soil is related to several conditions, including the amount of precipitation, the time since it fell, evaporation rates, the space available for water storage, and how easily the water can move through the soil.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.columbia.edu/~vjd1/soils.htm Gravitational water performs several functions in a soil. As gravitational water percolates downward, it dissolves soluble minerals and carries them into deeper levels of the soil, perhaps to the zone where all open spaces are saturated. Depleting nutrients in the soil by the through flow of water is called leaching. In regions of heavy rainfall, leaching is common and can be intense, robbing a topsoil of all but the insoluble substances.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://digitallylearn.com/leaching-of-soil-upsc-geography-optional/ Gravitational water moving down through a soil also takes with it the finer particles (clay and silt) from the upper soil layers. This downward removal of soil components by water is called eluviation. As gravitational water percolates downward, it deposits the fine materials that were removed from the topsoil at a lower level in the soil. Deposition by water in the subsoil is called illuviation.  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.sciencedirect.com/topics/earth-and-planetary-sciences/caliche Gravitational water also mixes soil particles as it moves them downward. One result of eluviation is that the texture of a topsoil tends to become coarser as the fine particles are removed. Consequently, the topsoil’s ability to retain water is reduced. Illuviation may eventually cause the subsoil to become dense and compact, forming a clay hardpan. How does deposition by capillary water differ from deposition (illuviation) by gravitational water? Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning  Soil Water References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://theconstructor.org/geotechnical/permeability-stratified-soil-deposits/29630/ Leaching and eluviation both strongly influence the characteristic layered changes with depth, or stratification. Fine particles and substances dissolved from the upper soil are deposited in lower levels, which become dense and may be strongly colored by accumulated iron compounds.  Soil Air References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.quora.com/Is-air-present-in-the-soil Much of a soil—in some cases, approaching 50%—consists of spaces between soil particles and between clumps (aggregates of soil particles). Voids that are not filled with water contain air or certain gases. Compared to the composition of the lower atmosphere, the air in a soil is likely to have less oxygen, more carbon dioxide, and a fairly high relative humidity because of the presence of capillary and hygroscopic water.  Soil Air References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.agupdate.com/iowafarmertoday/news/crop/seedling-disease-risk-higher-with-saturated-soil- conditions/article_3f8befd8-5c70-11e9-9a4b-eb7b95b89c10.html For most microorganisms and plants that live in the ground, soil air supplies oxygen and carbon dioxide necessary for life processes. The problem with a water- saturated soil is not necessarily excess water but, if all pore spaces are filled with water, there is no air supply. The lack of air is why many plants find it difficult to survive in water-saturated soils.  Organic Matter References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.gardeningknowhow.com/composting/basics/compost-vs-humus-in-garden.htm Soil contains organic matter in addition to minerals, gases, and water. The decayed remains of plant and animal materials, partially transformed by bacterial action, are collectively called humus. Humus is an important catalyst in chemical reactions that help plants to extract soil nutrients. Humus also supplies nutrients and minerals to the soil. Soils that contain humus are quite workable and have a good capacity to retain water. Humus also provides an abundant food source for microscopic soil organisms.  Organic Matter References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://web.extension.illinois.edu/worms/live/ Most soils are actually environments that teem with life, ranging from microscopic bacteria and fungi, to earthworms, rodents, and other burrowers. Animals contribute to the soil development and enrichment by creating humus from plant litter. They also mix organic material deeper into the soil, and move inorganic fragments toward the surface. In addition, the functions of plants and their root systems are integral parts of the soil-forming system.  Organic Matter References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://knowyoursurface.wordpress.com/skin-of-the-earth-soil/ Soils vary at local, regional, and global scales. Particularly strong relationships exist between a soil and the vegetation and climate at its location. For example, soils in middle- latitude grasslands normally have a very high proportion of organic matter; those in deserts are thin, and rich in minerals left behind by evaporating water, like lime and salts; and tropical soils typically have a high content of iron and aluminum oxides.  Characteristics of Soil References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Knowing a soil’s water, mineral, and organic components and their proportions can help us determine its productivity and what the best use for that particular soil might be. Several soil properties that can be readily tested or examined are used to describe and differentiate soil types. The most important properties include: Color Texture Structure Acidity or Alkalinity Capacity to hold and transmit water and air.  Color References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Color is the most visible soil characteristic, but it might not be the most important attribute. Most people are aware of how soils vary in color from place to place. Soils vary in color from black to brown to red, yellow, gray, and near-white. A soil’s color is generally related to its physical and chemical characteristics. When describing soils in the field or samples in the laboratory, soil scientists use a book of standardized colors to clearly and precisely identify this coloration.  Color References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.vanbeeks.com/news-events/blog/evaluate-quality-soil/ Decomposed organic matter is black or brown, so soils with high humus contents tend to be dark. If the humus content of soil decreases because of either low organic activity or loss of organics through leaching, soil colors typically fade to light brown or gray. Soils rich in humus are usually very fertile. For this reason, dark brown or black soils are often referred to as rich. However, this is not always true because some black or dark brown soils have little or no humus, but are dark because of other soil-forming factors.  Color References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://qsstudy.com/geology/red-yellow-soil-indian-subcontinent Soils that are red or yellow typically indicate the presence of iron. Soil colors provide useful clues to the physical and chemical characteristics of soils and make the job of recognizing different soil types easier. But color alone does not answer all the important questions about a soil’s qualities or fertility.  Color References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.gypsoil.com/reasons-to-use/southeast/make-your-soils-more-productive/expands-roots-zone In moist climates, a light gray or white soil indicates that iron has been leached out, leaving oxides of silicon and aluminum; in dry climates, the same color typically indicates a high proportion of calcium or salts.  Characteristics of Soil References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Cengage Learning Color o Red or yellow (iron) o Black (decomposed) Texture o Soil texture: particle size o Clay (< 0.002 mm) o Silt (0.002 to 0.05 mm) o Sand (0.05 to 2.0 mm) o Rocks (> 2.0 mm)  Soil Texture References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Soil texture refers to the particle sizes (or distribution of sizes) that make up a soil. In clayey soils, the dominant size is clay particles, defined as having diameters of less than 0.002 millimeter (soil scientists universally use the metric system). In silty soils, the dominant silt particles are defined as being between 0.002 and 0.05 millimeter. Sandy soils have mostly sand-sized particles, with diameters between 0.05 and 2.0 millimeters. Rocks larger than 2.0 millimeters are regarded as pebbles, gravel, or rock fragments, and technically are not soil particles.  Soil Texture References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning The proportion of particle sizes determines a soil’s texture. For example, a soil composed of 50% silt- sized particles, 45% clay, and 5% sand would be identified as a silty clay. A triangular graph is used to discern different classes of soil texture based on the plot of percentages for each soil grade (as sand, silt, and clay are called) within each class. Point A within the silty clay class represents the example just given.  Soil Texture References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://martinsfarmcompost.com/gallery/3/11/Loam--Compost-mix A second soil sample (B) that is 20% silt, 30% clay, and 50% sand would be referred to as a sandy clay loam. Loam soils, which occupy the central areas of the triangular graph, are soils with a mix of the three grades (sizes) of soil particles without any size being greatly dominant. It is interesting to note that loam soils are generally best suited for supporting vegetation growth.  Soil Texture References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.toppr.com/ask/question/water- holding-capacity-of-sandy-soil-as-compared-to-clay-soil-is/ Soil texture helps determine a soil’s capacity to retain moisture and air that are necessary for plant growth. Soils with a higher proportion of larger particles tend to be well aerated and allow water to infiltrate (seep through) the soil quickly— sometimes so quickly that plants are unable to use the water. Clay soils present the opposite problem because they retard water movement, becoming waterlogged and deficient in air. Aeration of the soil is an important process in cultivation, and plowing a soil opens its structure and increases its air content.  Soil Structure References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.nzsoils.org.nz/Topic- Describing_Soils/Soil_Structure-Peds_and_the_Types_of_Structural_Units/ In most soils, particles clump into distinctive masses known as soil peds, which give a soil a distinctive structure. Soil structure influences a soil’s porosity — the amount of space that may contain fluids. Soil structure also influences permeability — the rate at which fluids such as water can pass through. Permeability is usually greatest in sandy soils, and porosity is usually greatest in clayey soils. Both of these factors control soil drainage as well as the available moisture in a soil. Soils with similar textures may have different structures, and vice versa.  Soil Structure References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Soil structure can be influenced by outside factors such as moisture regime and the nutrient cycles that plants use to interchange chemicals with the soil, keeping certain ones in the system while others are leached away. We have all seen the structural change in soils that occurs when soils are wet compared to when they are dry. Human activities also influence soil structure through cultivation, irrigation, and fertilization. Fertilizers, as well as lime or decayed organic debris, encourage clumping of soil particles and the maintenance of clumps. Excess sodium and magnesium have the opposite effect, causing clay soils to become a sticky muck when wet and like concrete when dry. The absence of smaller particles typically hinders the development of a well-defined soil structure.  Soil Structure References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Scientists classify soil structures according to their form: columns laminated plates prism crumbs angular blocks granules nutlike spheroids Soils with massive and fine structures tend to be less useful than aggregates of intermediate size and stability, which permit good drainage and aeration.  Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning An important aspect of soil chemistry is a soil’s departure from neutrality toward either acidity or alkalinity (baseness). Levels of acidity or alkalinity are measured on the pH scale of 0 to 14. A pH reading indicates the concentration of reactive hydrogen ions present. The pH scale is logarithmic, meaning that each change in a whole pH number represents a tenfold change. It is also an inverted scale—a lower pH means a greater amount of hydrogen ions present (higher acidity). Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning  Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Low pH values indicate an acid soil, and high pH indicates alkaline conditions. Alkalinity in a soil can be tested in the field with drops of a dilute acid. If the soil fizzes in the acid solution, alkalinity is typically high. Soil acidity or alkalinity helps determine the available nutrients that affect plant growth. Plants absorb nutrients that are dissolved in liquid.  Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.backyarddigs.com/gardening/how-to-make-soil-acidic/ However, soil water that lacks some degree of acidity has little ability to dissolve these nutrients. As a result, even though nutrients are in the soil, plants may not have access to them. Most complex plants will grow only in soils with levels between pH 4 and pH 10, although the optimum pH for vegetation growth varies with the plant species. Around the world, vegetation has evolved in and adapted to a variety of climates and soil environments, both of which can affect soil pH. Certain species tolerate alkaline soils, and others thrive under more acid conditions.  Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Leaching caused by high rainfall gradually replaces soil elements such as sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) with hydrogen. Falling rain picks up atmospheric carbon dioxide and becomes slightly acidic: H2O + CO2 = H2CO3 (carbonic acid), so desert soils tend to be alkaline and soils in humid regions tend to be acidic. The humus content in the soils of humid areas also contributes to higher soil acidity.  Acidity and Alkalinity References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://agriculture90.blogspot.com/2015/11/liming-right-solution-in-soil-wry-as-rainy-season.html To correct soil alkalinity, common in the arid regions, and to make the soil more productive, the soil can be flushed with irrigation water. Strongly acidic soils are also detrimental to plant growth. In acidic soils, soil moisture dissolves nutrients, but they may be leached away before plant roots can absorb them. Soil acidity can generally be corrected by adding lime to the soil. In addition to affecting plant growth, soil acidity or alkalinity also affects microorganisms in the soil. Microorganisms are highly sensitive to a soil’s pH, and each species has an  Development of Soil Horizons References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning https://etheses.whiterose.ac.uk/20696/1/Joshua_John_Blacker_PhD_Thesis_2018_University_of_Leeds.pdf Soil development begins when plants and animals colonize rocks or deposits of rock fragments, the parent material on which soil will form. Once organic processes begin among mineral particles or rock fragments, differences begin to develop from the surface down through the parent material.  Development of Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning Initially, vertical differences result from the surface accumulation of organic litter and the removal of fine particles and dissolved minerals from upper layers by percolating water that deposits these materials at a lower level. The vertical cross section of a soil from the surface down to the parent material is called a soil profile. Examining soil profiles and the vertical differences they contain is important to recognizing different soil types and how those soils developed. As climate, vegetation, animal life, and characteristics of the land surface affect soil formation over time, this vertical differentiation becomes more and more apparent.  Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://knowyoursurface.wordpress.com/skin -of-the-earth-soil/ Within their soil profiles, well-developed soils typically exhibit several distinct layers, called soil horizons, that are distinguished by their physical and chemical properties. Soils are classified largely on the differences in their horizons and in the processes responsible for those differences. Soil horizons are designated by a set of letters that refer to their composition, dominant process, and/or position in the soil profile.  Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning At the surface, but only in locations where there is a sufficient cover of decomposed vegetation litter, there will be an O horizon. This is a layer of organic debris and humus; the “O” designation refers to this horizon’s high organic content. Immediately below is the A horizon, commonly referred to as “topsoil.” In general, the A horizon is dark because it contains decomposed organic matter.  Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning Beneath the A horizon, certain soils have a lighter-colored E horizon, named for the action of strong eluvial processes. Below this is a zone of accumulation, the B horizon, where much of the materials removed from the A and E horizons are deposited. Except in soils with a high organic content that has been mixed vertically, the B horizon generally has little humus.  Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning The C horizon is the weathered parent material from which the soil has developed—either fragments of the bedrock, or deposits of rock materials that were transported to the site by water, wind, glacial, or other surface process. The lowest layer, sometimes called the R horizon, is unchanged parent material, either bedrock or transported deposits of rock fragments.  Soil Horizons References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://thefactfactor.com/facts/pure_science /biology/soil-profile/1977/ Certain horizons in some soils may not be as well developed as others, and some horizons may be missing altogether. Because soils and the processes that form them vary widely and can be transitional between horizons, the horizon boundaries may be either sharp or gradual. Variations in color and texture within a horizon are also not unusual.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://mammothmemory.net/geography/geography-vocabulary/coastal-landscapes-2/chemical- weathering.html Because of the great variety among the components of soils and the processes that affected them, no two soils are identical in all of their characteristics. One important factor is rock weathering, which refers to the many natural processes that break down rocks into smaller fragments. Chemical reactions can cause rocks and minerals to decompose and physical processes also cause the breakup of rocks. Just as statues, monuments, and buildings become “weatherbeaten” over time, rocks exposed to the elements eventually break up and decompose.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://secretofsoil.wordpress.com/2016/03/20/soil-formation-2/ Hans Jenny, a distinguished soil scientist, observed that soil development was a function of Factors: climate, Cl, O, R, P, T organic matter, relief, parent material, and time Among these factors, parent material is distinctive because it is the raw material. The other factors influence the type of soil that forms from the parent material.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.fao.org/fishery/docs/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm Parent Material All soil contains weathered rock fragments. If these weathered rock particles have accumulated in place— through the physical and chemical breakdown of bedrock directly beneath the soil—we refer to the fragments as residual parent material.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.fao.org/fishery/docs/CDrom/FAO_Training/FAO_Training/General/x6706e/x6706e01.htm Parent Material If the rock fragments that form a soil have been carried to the site and deposited by streams, waves, winds, gravity, or glaciers, this mass of deposits is called transported parent material. The development and action of organic matter through the life cycles of organisms and the climatic conditions are primarily responsible for changing the fragmented rocks or other parent material into a soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.123rf.com/photo_39684107_landscape-with-sandstone-weathering-formation-in-the-timna- park-israel-.html Parent Material Parent material influences the characteristics of a soil in varying degrees. Some parent materials, such as a sandstone that contains extremely hard and resistant sand-sized fragments, are far less subject to weathering than others. Soils that develop from weathering- resistant rocks tend to have a high level of similarity to their parent materials.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.civilsdaily.com/2017/08/page/2/ Parent Material If the bedrock is easily weathered, the soils that develop tend to be more similar to soils in other regions that have a similar climate than to those of comparable parent materials, which formed in a different climate. On a global basis, climate and the associated plant communities produce greater variations in soil characteristics than do parent materials.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://learn.weatherstem.com/modules/learn/lessons/85/06.html Parent Material Soil differences that are related to variations in parent material are most visible on a local level. The longer a soil develops, the influence of parent material on its characteristics diminishes. Given the same soil-forming conditions, recently developed soils will show more similarity to its parent material, compared to a soil that has developed over a long time.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning Parent Material Many of the chemicals and nutrients in a soil reflect the composition of its parent material. For example, calcium-deficient parent materials will produce soils that are low in calcium, and its natural fauna and plant cover will be types that require little calcium. Likewise, a parent material with a high aluminum content will produce a soil that is rich in aluminum. In fact, the ore of aluminum is bauxite, found in tropical soils where it has been concentrated by intense leaching away of the other bases.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.soil-net.com/dev/page.cfm?pageid=secondary_intro_weathering&loginas=anon_secondary Parent Material The particle sizes that result from the breakdown of parent material are a prime determinant of a soil’s texture and structure. A rock material such as sandstone, which contains little clay and weathers into relatively coarse fragments, will produce a soil of coarse texture. Parent materials are also an important influence on the availability of air and water to a soil’s living population.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://cwppra.wordpress.com/2018/03/28/soil-biology/ Organic Activity Plants and animals affect soil development in many ways. The life processes of plants growing in a soil are as important as its microorganisms— the microscopic plants and animals that live in a soil. Generally, a dense vegetative cover protects a soil from being eroded away by running water or wind.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://permacultureapprentice.com/building-soil/ Organic Activity Forests form a protective canopy and produce surface litter, which keeps rain from beating directly on the soil and increases the proportion of rainwater entering the soil rather than running off its surface. Variations in vegetation species and density of cover can also affect the evapotranspiration rates. A sparse vegetative cover will allow greater evaporation of soil moisture and dense vegetation tends to maintain soil moisture  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://permacultureapprentice.com/building-soil/ Organic Activity The characteristics of a plant community affect the nutrient cycles that are involved in soil development. As plants die and decompose, or leaves fall to the ground, nutrients are returned to the soil. Soils, however, can become impoverished if soluble nutrients that are not used by plants are lost through leaching. The roots of plants help to break up the soil structure, making it more porous, and roots also absorb water and nutrients from the soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://wwpl.librarycalendar.com/events/watch-wonder-deserts-and-rainforests-0 Organic Activity Leaves, bark, branches, flowers, and root networks contribute to the organic composition of soil, through litter and through the remains of dead plants. The organic content of soil depends on its associated plant life. For example, a grass-covered prairie supplies much more organic matter than the thin vegetative cover of desert regions.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://wwpl.librarycalendar.com/events/watch-wonder-deserts-and-rainforests-0 Organic Activity There is some question, however, as to whether forests or grasslands (with their thick root networks and annual life cycle) furnish the soil with greater organic content. Many of the world’s grassland regions, like the North American prairies, provide some of the world’s most fertile soils for cultivation in part because of the high amount of organic matter that a grass cover generates.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://eschooltoday.com/learn/soil-formation-factors/ Organic Activity Plants and animals affect soil development in many ways. The life processes of plants growing in a soil are as important as its microorganisms— the microscopic plants and animals that live in a soil. Generally, a dense vegetative cover protects a soil from being eroded away by running water or wind.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://temperategrasslandbiomeproject.weebly.com/north-americas-prairie.html Organic Activity Forests form a protective canopy and produce surface litter, which keeps rain from as to whether forests or grasslands (with their thick root networks and annual life cycle) furnish the soil with greater organic content. Many of the world’s grassland regions, like the North American prairies, provide some of the world’s most fertile soils for cultivation in part because of the high amount of organic matter that a grass cover generates.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://socratic.org/questions/what-type-of-organisms-break-down-rock-to-make-soil Organic Activity In terms of their contribution to soil formation, bacteria are perhaps the most important microorganisms that live in soils. Bacteria break down organic matter, humus, and the debris of living things into organic and inorganic components, allowing the formation of new organic compounds that promote plant growth.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://gardenculturemagazine.com/closeup-microscopic-world-plants/ Organic Activity It has been suggested that the number of bacteria, fungi, and other microscopic plants and animals living in a soil may be 1 billion per gram (a fifth of a teaspoon) of soil. The activities and remains of these microorganisms, minute though they are individually, add considerably to the organic content of a soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://plantmateorganics.com/2018/07/26/organic-matter-om-and-the-soil/ Organic Activity Earthworms, nematodes, ants, termites, wood lice, centipedes, burrowing rodents, snails, and slugs also stir up the soil, mixing mineral components from lower levels with organic components from the upper portion. Earthworms contribute greatly to soil development because they take soil in, pass it through their digestive tracts, and excrete it in casts. The process not only helps mix the soil but also changes the texture, structure, and chemical qualities of the soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.researchgate.net/figure/Climate-vegetation-and-soil-formation-in-East-European-Plain- modified-from-Walter_fig1_268884975 Climate On a world regional scale, climate is a major factor in soil formation. Of course, if the climate is the same in a region where the soils vary, other factors must be responsible for the local variation.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://international-soil-radiocarbon-database.github.io/SOC- Hub/climate%20and%20carbon%20stocks/2018/07/10/Ecosystem-Services/ Climate Soil differences that are apparent at a local level tend to reflect the influence of factors such as parent materials, land surface configurations, vegetation types, and time.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://thebritishgeographer.weebly.com/the-climate-of-tropical-regions.html Climate Temperature directly affects soil microorganism activity, which in turn affects the decomposition rates of organic matter. In hot equatorial regions, intense activities by soil microorganisms preclude thick accumulations of organic debris or humus.  Factors Affecting Soil Formation References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Climate Figure 12.16 shows that the amounts of organic matter and humus in a soil increase toward the middle latitudes and away from polar regions and the tropics. In the mesothermal and microthermal climates (C and D), microorganism activity is slow enough to allow decaying organic matter and humus to accumulate in rich layers.  Factors Affecting Soil Formation References: Brown, et al. 2018. Chemistry for Engineering students. Cengage Learning Petersen, et al. 2017. Physical Geography. Cengage Learning Climate Moving poleward into colder regions, retarded microorganism activity and limited plant growth tends to result in thin accumulations of organic matter.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.grida.no/resources/3613 Climate Chemical activity increases and decreases directly with temperature, given equal availability of moisture. As a result, parent materials of soils in hot, humid equatorial regions are altered to a far greater degree by chemical means than are parent materials in colder zones.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning Climate Temperature affects soil indirectly through its influence on vegetation associations that are adapted to certain climatic regimes. Soils generally reflect the character of plant cover because of nutrient cycles that tend to keep both vegetation and soil in chemical equilibrium.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning Climate The combined effects of vegetative cover and the climatic regime tend to produce soil profiles and characteristics that tend to share certain characteristics among different regions that have similar climates and vegetation associations.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://cropwatch.unl.edu/heavy-rains-how-likely-n-leaching-unl-cropwatch-may-31-2013 Climate Moisture conditions affect the development and character of soils more directly than any other climatic factor. Without precipitation, and the soil water it provides, terrestrial plant life would be impossible. Ample precipitation supports plant growth that can greatly increase the organic content and thereby the fertility of a soil. However, extremely high rainfall will cause leaching of nutrients, and a relatively infertile soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://forestrypedia.com/vegetation-influence-on-precipitation/ Climate Gravitational and capillary water have pronounced effects on soil development, structure, texture, and color. Precipitation is the original source of soil water (disregarding the minor contribution of dew), and the amount of precipitation received affects leaching, eluviation, and illuviation and thereby rates of soil formation and horizon development.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.researchgate.net/figure/Changes-in-the-water-budget-after-forest-conversion-into-fruit- plantation-The-origin-and_fig3_280519593 Climate The evaporation rate is a very important factor as well. Salt and gypsum deposits from the upward migration of capillary water are more extensive in hot, dry regions—such as the southwestern United States where evaporation rates are high—than in colder, dry regions.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://earthsurface.readthedocs.io/en/latest/hillslope.html Land Surface Configuration The slope of the land, its relief, and its aspect (the direction it faces) all influence soil development. Steep slopes are generally better drained than gentler ones, and they are also subject to rapid runoff of surface water.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://earthsurface.readthedocs.io/en/latest/hillslope.html Land Surface Configuration As a consequence, there is less infiltration of water on steeper slopes, which inhibits soil development, sometimes to the extent that there will be no soil. In addition, rapid runoff on steep slopes can erode surfaces as fast or faster than soil can develop on them.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://sciencesamhita.com/soil-and-its-formation/ Land Surface Configuration On gentler slopes, where there is less runoff and higher infiltration, more water is available for soil development and to support vegetation growth, so erosion is not as intense. In fact, erosion rates in areas of gently rolling hills may be just enough to offset the development of soils. Well-developed soils typically form on land that is flat or has a gentle slope.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://en.wikipedia.org/wiki/Coastal_sage_scrub Land Surface Configuration Slope aspect has a direct effect on microclimates in areas outside of the equatorial tropics. North-facing slopes in the middle and high latitudes of the Northern Hemisphere have microclimates that are cooler and wetter than those on south-facing exposures, which receive the sun’s rays at a steeper angle and are therefore warmer and drier. Local variations in soil depth, texture, and profile development result directly from microclimate differences.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.cdema.org/virtuallibrary/index.php/charim-hbook/data-management-book/3-base-data- collection/3-6-soil-maps Land Surface Configuration Topography, through its effects on vegetation, indirectly influences soil development. Steep slopes prevent the formation of a soil that would support abundant vegetation, and a modest plant cover yields less organic debris for the soil.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://biocyclopedia.com/index/principles_of_horticulture/natural_soil_profiles.php Time Soils have a tendency to develop toward a state of equilibrium with their environment. A soil is sometimes called “mature” when it has reached such a condition of equilibrium. Young soils are still in the process of developing toward being in equilibrium with their environmental conditions.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning Time Mature soils have well- developed horizons that indicate the conditions under which they formed. Young or “immature” soils typically have poorly developed horizons or perhaps none at all.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.chegg.com/homework-help/soil-foundation-life-land-soil-complex-mixture-eroded-rock-m- chapter-10-problem-1sf-solution-9781305090446-exc Time Another effect of time is that, as soils develop, their influence of their parent material decreases and they increasingly reflect their climate and vegetative environments. On a global scale, climate typically has the greatest influence on soils, provided sufficient time has passed for the soils to become  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.semanticscholar.org/paper/Toward-a-more-holistic-perspective-of-soil-erosion%3A-Field- Breshears/a8b2ca98127231262522d68dd591455b9eb2c32f/figure/0 Time The importance of time in soil formation is especially clear in soils developed on transported parent materials. Depositional surfaces are in many cases quite recent in geologic terms and have not been exposed to weathering long enough for a mature soil to develop.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://landscape.soilweb.ca/retreating-glaciers/ Time Deposition occurs in a variety of settings: on river floodplains where the accumulating sediment is known as alluvium; downwind from dry areas where dust settles out of the atmosphere to form blankets of wind- deposited silts, called loess; and in volcanic regions showered by ash and covered by lava. Ten thousand years ago, glaciers withdrew from vast areas, leaving behind jumbled deposits of rocks, sand, silt, and clay.  Factors Affecting Soil Formation References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.nzsoils.org.nz/Topic-Basics_Of_Soils/Time/ Time Because of the great number and variability of materials and processes involved in the formation of soils, there is no fixed amount of time that it takes for a soil to become mature. The Natural Resources Conservation Service, however, estimates that it takes about 500 years to develop 1 inch of soil in the agricultural regions of the United States. Generally, though, it takes thousands of years for a soil to reach maturity.  Soil-Forming Regimes References: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.nzsoils.org.nz/Topic-Basics_Of_Soils/Time/ The characteristics that make major soil types distinctive and different from one another result from their soil-forming regimes, which vary mainly because of differences in climate and vegetation. At the broadest scale of generalization, climate differences produce three primary soil-forming regimes: laterization, podzolization, and calcification.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Laterization Laterization is a soil-forming regime that occurs in humid tropical and subtropical climates as a result of high temperatures and abundant precipitation. These climatic environments encourage rapid breakdown of rocks and decomposition of nearly all minerals. A soil of this type is known as laterite, and these soils are generally reddish in color from iron oxides; the term laterite means “brick-like.” In tropical areas laterite is quarried for building material.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Laterization Despite the dense vegetation that is typical of these climate regions, little humus is incorporated into the soil because the plant litter decomposes so rapidly. Laterites do not have an O horizon, and the A horizon loses fine soil particles as well as most minerals and bases except for iron and aluminum compounds, which are insoluble primarily because of the absence of organic acids. As a result, the topsoil is reddish, coarse textured, and tends to be porous. In contrast to the A horizon, the B horizon in a lateritic soil has a heavy concentration of illuviated materials.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Laterization In the tropical forests, soluble nutrients released by weathering are quickly absorbed by vegetation, which eventually returns them to the soil where they are reabsorbed by plants. This rapid cycling of nutrients prevents the total leaching away of bases, leaving the soil only moderately acidic. Removal of vegetation permits total leaching of bases, resulting in the formation of crusts of iron and aluminum compounds (laterites), as well as accelerated erosion of the A horizon. Laterization is a year-round process because of the small seasonal variations in temperature or soil moisture in the humid tropics. This continuous activity and strong weathering of parent material cause some tropical soils to develop to depths of as much as 8 meters (25 ft) or more.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Podzolization Podzolization occurs mainly in the high middle latitudes where the climate is moist with short, cool summers and long, severe winters. The coniferous forests of these climate regions are an integral part of the podzolization process.Where temperatures are low much of the year, microorganism activity is reduced enough that humus does accumulate; however, because of the small number of animals living in the soil, there is little mixing of humus below the surface. Leaching and eluviation by acidic solutions remove the soluble bases and aluminum and iron compounds from the A horizon.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.worldatlas.com/articles/what-is-podzol-in-soil-science.html Podzolization The remaining silica gives a distinctive ash-gray color to the E horizon (podzol is derived from a Russian word meaning “ashy”). The needles that coniferous trees drop are chemically acidic and contribute to the soil acidity. It is difficult to determine whether the soil is acidic because of the vegetative cover or whether the vegetative cover is adapted to the acidic soil.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.ecopedia.be/encyclopedie/podzols Podzolization Podzolization can take place outside the typical cold, moist climate regions if the parent material is highly acidic—for example, on the sandy areas common along the East Coast of the United States. The pine forests that grow in such acidic conditions return acids to the soil, promoting the process of podzolization.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Calcification A third distinctive soil-forming regime is called calcification. In contrast to both laterization and podzolization, which require humid climates, calcification occurs in regions where evapotranspiration significantly exceeds precipitation. Calcification is important in the climate regions where moisture penetration is shallow. The subsoil is typically too dry to support tree growth, and shallow-rooted grass or shrubs are the primary forms of vegetation. Calcification is enhanced as grasses use calcium, drawing it up from lower soil layers and returning it to the soil when the annual grasses die. Grasses and their dense root networks provide large amounts of organic matter, which is mixed deep into the soil by burrowing animals.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.worldatlas.com/articles/which-deserts-are-in-north-america.html Calcification Middle-latitude grassland soils are rich in bases and in humus and are the world’s most productive agricultural soils. The deserts of the American West generally have no humus, and the rise of capillary water can leave not only calcium carbonate but also sodium chloride (salt) at the surface.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Calcification In many areas of low precipitation, the air is often loaded with alkali dusts such as calcium carbonate (CaCO3). When calm conditions prevail or when it rains, the dust settles and accumulates in the soil. The rainfall produces an amount of soil water that is just sufficient to translocate these materials to the B horizon.  Soil-Forming Regimes Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Calcification Over hundreds to thousands of years, the CaCO3-enriched dust concentrates in the B horizon, forming hard layers of caliche. Much thicker accumulations called calcretes form by the upward (capillary) movement of dissolved calcium in groundwater when the water table is near the surface.  Regimes of Local Importance Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.usgs.gov/media/images/dry-wash-san-rafael-desert-white-surface-salts Salinization Two additional localized soil-forming regimes merit attention. Both characterize areas with poor drainage although they occur under very different climate conditions. The first, salinization, or the concentration of salts in the soil, is often detrimental to plant growth. Salinization occurs in stream valleys, interior basins, and other low-lying areas, particularly in arid regions with high groundwater tables.  Regimes of Local Importance Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Salinization The high groundwater levels can be the result of water from adjacent mountain ranges, stream flow originating in humid regions, or a wet–dry seasonal precipitation regime. Salinization can also be a consequence of intensive irrigation under arid conditions. Rapid evaporation leaves behind a high concentration of soluble salts and may destroy a soil’s agricultural productivity. An extreme example of salinization exists in certain areas of the Middle East, where thousands of years of irrigated agriculture in the desert have made the soils too saline to cultivate today.  Regimes of Local Importance Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.facebook.com/Dr.NaingNaingAye/photos/a.339476266694960/710131836296066 Gleization Another localized soil regime, gleization, occurs in poorly drained areas under cold, wet environmental conditions. Gley soils, as they are called, are typically associated with peat bogs where the soil has an accumulation of humus overlying a bluegray layer of thick, gummy, water- saturated clay. In poorly drained regions that were formerly glaciated, such as northern Russia, Ireland, Scotland, and Scandinavia, peat has long been harvested and used as a source of energy.  Regimes of Local Importance Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.facebook.com/Dr.NaingNaingAye/photos/a.339476266694960/710131836296066 Gleization Another localized soil regime, gleization, occurs in poorly drained areas under cold, wet environmental conditions. Gley soils, as they are called, are typically associated with peat bogs where the soil has an accumulation of humus overlying a bluegray layer of thick, gummy, water- saturated clay. In poorly drained regions that were formerly glaciated, such as northern Russia, Ireland, Scotland, and Scandinavia, peat has long been harvested and used as a source of energy.  Soil Classification Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning http://www.fao.org/soils-portal/data-hub/soil-classification/usda-soil-taxonomy/en/ Soils, like climates, can be classified by their characteristics and mapped by their spatial distributions. In the United States the Soil Survey Division of the Natural Resources Conservation Service (NRCS), a branch of the Department of Agriculture, is responsible for soil classification (termed soil taxonomy). As with any classification system, the methods and categories are continually being updated and refined.  Soil Classification Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.nrcs.usda.gov/Internet/FSE_MEDIA/nrcseprd1295217.jpg Soil classifications are published in soil surveys, books that outline and describe the kinds of soils in a region and include maps that show the distribution of soil types, usually at the county level. These documents, available for most parts of the United States, are useful references for factors such as soil fertility, irrigation, and drainage.  The NRCS Soil Classification System Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://serc.carleton.edu/kskl_educator/soil_classification/chap_5_explore.html The NRCS soil classification system is based on the development and composition of soil horizons. The largest division in the classification of soils is the soil order, of which 12 are recognized by the NRCS.  The NRCS Soil Classification System Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://www.researchgate.net/figure/A-soil-with-a-mollic-epipedon-which-is-a-thick-black-surface-horizon- that-has-high_fig44_318239569 To provide greater detail, soil orders can also be subdivided into suborders, great groups, subgroups, families, and series. More than 10,000 soil series have been recognized in the United States. When examining a soil for classification under the NRCS system, particular attention is paid to characteristic horizons and textures. Some of these horizons are below the surface (subsurface horizons); others, called epipedons, are surface layers that usually exhibit a dark shading associated with organic material (humus). Examples of some of the more common horizons, illustrating how names were chosen to represent actual soil properties, are  The NRCS Soil Classification System Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning https://serc.carleton.edu/kskl_educator/soil_classification/chap_5_explore.html The 12 soil orders are based on a variety of characteristics and processes that can be recognized by examining a soil and its profile. NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Sequence illustrates the links between climate and soils.  NRCS Soil Orders References: Petersen, et al. 2017. Physical Geography. Cengage Learning https://international-soil-radiocarbon-database.github.io/SOC- Hub/climate%20and%20carbon%20stocks/2018/07/10/Ecosystem-Services/ Soil types in the Northern Hemisphere according to WRB and USDA taxonomy, their distribution by latitude, and the accompanying influential soil forming processes.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Global soils based on the NRCS classification of soil orders are shown in the figure.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Entisols are soils that have undergone little or no soil development and lack horizons, because they have only recently begun to form. They are often associated with the continuing erosion of sloping land in mountainous regions or with the frequent deposition of alluvium by flooding, or in areas of windblown sand.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Inceptisols are young soils with weak horizon development. The processes of A horizon depletion (eluviation) and B horizon deposition (illuviation) are just beginning, usually because of a very cold climate, repeated floodrelated deposition, or a high rate of soil erosion. In the United States, Inceptisols are most common in Alaska, the lower Mississippi River floodplain, and the western Appalachians. Globally, Inceptisols are especially important along the lower portions of the great river systems of South Asia, such as the Ganges- Brahmaputra, the Irrawaddy, and the Mekong. In these areas, sediments associated with periodic flooding constantly enrich Inceptisols, and form the basis for agriculture that supports millions of people.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Histosols develop in poorly drained areas, such as swamps, meadows, or bogs, as a product of gleization. They are largely composed of decomposing plant material. The waterlogged soil conditions deprive bacteria of the oxygen necessary to decompose the organic matter. Although Histosols may be found in low areas with poor drainage at all latitudes, they are most common in tundra areas or in recently glaciated, high-latitude locations such as Scandinavia, Canada, Ireland, and Scotland. Histosols in the subpolar latitudes are commonly acidic and only suitable for special bog crops such as cranberries. Histosols are the primary source of peat, which is a fuel source in some regions and also is used in landscaping.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Andisols are soils that develop on volcanic parent materials, usually volcanic ash, the dust-sized particles emitted by volcanoes. Because many of these soils are replenished by eruptions, they are often fertile. Intensive agriculture atop Andisols supports dense populations in the Philippines, Indonesia, and the West Indies. In the United States, Andisols are most common on the slopes of and downwind from volcanoes in the Pacific Northwest and to a lesser extent in Hawaii and Alaska.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Gelisols are soils that experience frequent freezing and thawing of the ground, above permafrost, permanently frozen subsoil. When soil freezes, the ice that forms takes up 9% more space than the liquid water that it replaces. To accommodate the increased space taken up by ice, the soil and the particles in it are pushed upward and outward, away from forming ice cores. When the surface soil thaws, gravity pulls the waterlogged ground back downward. Repeated cycles of freezing and thawing mix and churn the upper soil in a process called cryoturbation— mixing (turbation) related to freezing (cryo). Only the upper part of the soil undergoes freeze–thaw cycles. Permafrost does not permit soil water to percolate downward, so Gelisol soils are typically water saturated when they are not frozen at the surface.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Aridisols are soils of desert regions that develop primarily under conditions where precipitation is much less than half of potential evaporation. Consequently, most Aridisols reflect the calcification process. Where groundwater tables are high, evidence of salinization may also be present.Although Aridisols tend to have weak horizon development because of limited water movement in the soil, there is often a subsurface accumulation of calcium carbonate (calcic horizon), salt (salic horizon), or calcium sulfate (gypsic horizon). Soil humus is minimal because vegetation is sparse in deserts; therefore, Aridisols are often light in color. Aridisols are usually alkaline, but because few nutrients have been leached, they can support productive agriculture if irrigated to reduce the pH and salinity. Geographically, Aridisols are the most common soils on Earth because deserts cover such a large portion of the land surface.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Vertisols are typically found in regions of strong seasonality of precipitation such as the tropical wet and dry climates. In the United States, they are most common where the parent materials produce clay-rich soils. The combination of clayey soils in a wet and dry climate leads to the drying of the soil and consequent shrinkage that forms deep cracks during the dry season, followed by expansion of the soil during the wet season. The constant shrink–swell process disrupts horizon formation to the point that soil scientists often describe Vertisols as “self-plowing” soils. Vertical soil movement may damage highways, sidewalks, foundations, and basements that are built on shrink–swell soils. Vertisols are dark-colored, are high in bases, and contain considerable organic material derived from the grasslands or savanna vegetation with which they are normally associated. Although they harden when dry and become sticky and difficult to cultivate when swollen with moisture, Vertisols can be agriculturally productive.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Mollisols are most closely associated with grassland regions and are among the best soils for sustained agriculture. Because they are located in semiarid climates, Mollisols are not heavily leached, and they have a generous supply of bases, especially calcium. The characteristic horizon of a Mollisol is a thick, dark-colored surface layer rich in organic matter from the decay of abundant root material. Grasslands and associated Mollisols served as the grazing lands for countless herds of antelope, bison, and horses. Before the invention of the steel plow, the thick root material of grasses made this soil nearly uncultivable in the United States and thus led to the widespread public image of the Great Plains as a “Great American Desert.”  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Alfisols occur in a wide variety of climate settings. They are characterized by a subsurface clay horizon (argillic B horizon), a medium to high base supply, and a light- colored ochric epipedon. The five suborders of Alfisols reflect climate types and exemplify the hierarchical nature of the classification system: Aqualfs are seasonally wet and can be found in mesothermal areas such as Louisiana, Mississippi, and Florida; Boralfs are found in moist, microthermal climates such as Montana, Wyoming, and Minnesota; Udalfs are common in both microthermal and mesothermal climates that are moist enough to support agriculture without irrigation, such as Wisconsin, Ohio, and Tennessee; Ustalfs are found in mesothermal climates that are intermittently dry, such as Texas and New Mexico; and Xeralfs are found in California’s Mediterranean climate, which is characterized by wet winters and long, dry summers.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Spodosols are most closely associated with the podzolization soil-forming process. They are readily identified by their strong horizon development. There is often a white or light-gray E horizon (albic horizon) covered with a thin, black layer of partially decomposed humus and underlain by a colorful B horizon enriched in relocated iron and aluminum compounds (spodic horizon).Spodosols are generally low in bases and form in porous substrates such as glacial drift or beach sands. In New England and Michigan, Spodosols are also acidic. In these regions, as well as in similar regions in northern Russia, Scandinavia, and Poland, only a few types of agricultural plants, such as cucumbers and potatoes, can tolerate the microthermal climates and sandy, acidic soils. Consequently, the cuisine of these regions directly reflects the Spodosols that dominate the areas.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Ultisols, like Spodosols, are also low in bases because they develop in moist or wet regions. Ultisols are characterized by a subsurface clay horizon (argillic horizon) and are often yellow or red because of residual iron and aluminum oxides in the A horizon. In North America, the Ultisols are most closely associated with the southeastern United States. When first cleared of forests, these soils can be agriculturally productive for several decades. But a combination of high rainfall with the associated runoff and erosion from the fields decreases the natural fertility of the soils. Ultisols remain productive only with the continuous application of fertilizers. Today, forests cover many former cotton and tobacco fields of the southeastern United States because of a reduction in soil fertility and extensive soil erosion.  NRCS Soil Orders Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Oxisols have developed over long periods of time in tropical regions with high temperatures and heavy annual rainfall. They are almost entirely leached of soluble bases and are characterized by a thick development of iron and aluminum oxides. The soil consists mainly of minerals that resist weathering (for example, quartz, clays, hydrated oxides). Oxisols are most closely associated with the humid tropics, but they also extend into savanna and tropical thorn forest regions. In the United States, Oxisols are present only in Hawaii. Oxisols are dominated by laterization and retain their natural fertility only as long as the soils and forest cover maintain their delicate equilibrium. The bases in the tropical rainforests are stored mainly in the vegetation. When a tree dies, epiphytes and insects must recycle the bases rapidly before the heavy rainfall leaches them from the system.  Soil as a Critical Natural Resource Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning Regardless of their composition, origin, or state of development, Earth’s soils remain one of our most important and vulnerable resources. The word fertility, so often associated with soils, has a meaning that takes into consideration the usefulness of a soil to humans. Soils are fertile in respect to their effectiveness in producing specific vegetation types or associations. Some soils may be fertile for corn and others for potatoes. Other soils retain their fertility only as long as they remain in delicate equilibrium with their vegetative cover.  Soil as a Critical Natural Resource Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning It is clearly the responsibility of all of us who enjoy the agricultural products of farms, ranches, and orchards, as well as appreciate the natural beauty of Earth’s diverse biomes, to help protect our valuable soils. Soil erosion, soil depletion, and the mismanagement of land are problems that we should have great concern about in the world today.  Soil as a Critical Natural Resource Reference: Petersen, et al. 2017. Physical Geography. Cengage Learning We should also be aware that these problems have reasonable solutions. Conserving soils and maintaining soil fertility are critical challenges that are essential to maintaining natural environments, as well as supporting life on Earth today and for the future.  Solid Waste Management https://www.britannica.com/technology/solid-waste-management/Solid- waste-collection Solid-waste management, the collecting, treating, and disposing of solid material that is discarded because it has served its purpose or is no longer useful. Improper disposal of municipal solid waste can create unsanitary conditions, and these conditions in turn can lead to pollution of the environment and to outbreaks of vector-borne disease—that is, diseases spread by rodents and insects.  Solid Waste Management https://www.officialgazette.gov.ph/2001/01/26/republic-act-no-9003-s-2001/ REPUBLIC ACT NO. 9003 AN ACT PROVIDING FOR AN ECOLOGICAL SOLID WASTE MANAGEMENT PROGRAM, CREATING THE NECESSARY INSTITUTIONAL MECHANISMS AND INCENTIVES, DECLARING CERTAIN ACTS PROHIBITED AND PROVIDING PENALTIES, APPROPRIATING FUNDS THEREFORE, AND FOR OTHER PURPOSES