soil science for bsc forestry / bsc agriculture/bsc environmental science, Lecture notes of Ecology and Environment

Download soil science for bsc forestry / bsc agriculture/bsc environmental science and more Lecture notes Ecology and Environment in PDF only on Docsity! Topic 1: Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil is the pedosphere, which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth's atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil. Pedology is the study of soils in their natural environment.[1] It is one of two main branches of soil science, the other being edaphology. Pedology deals with pedogenesis, soil morphology, and soil classification, while edaphology studies the way soils influence plants, fungi, and other living things. Edaphology is concerned with the influence of soils on living things, particularly plants. Edaphology includes the study of how soil influences humankind's use of land for plant growth [3] as well as man's overall use of the land.[4] General subfields within edaphology are agricultural soil science (known by the term agrology in some regions) and environmental soil science. Agricultural soil science Agricultural soil science is the application of soil chemistry, physics, and biology dealing with the production of crops. In terms of soil chemistry, it places particular emphasis on plant nutrients of importance to farming and horticulture, especially with regard to soil fertility and fertilizer components. Physical edaphology is strongly associated with crop irrigation and drainage. Soil husbandry is a strong tradition within agricultural soil science. Beyond preventing soil erosion and degradation in cropland, soil husbandry seeks to sustain the agricultural soil resource though the use of soil conditioners and cover crops. Environmental soil science Environmental soil science studies our interaction with the pedosphere on beyond crop production. Fundamental and applied aspects of the field address vadose zone functions, septic drain field site assessment and function, land treatment of wastewater, stormwater, erosion control, soil contamination with metals and pesticides, remediation of contaminated soils, restoration of wetlands, soil degradation, and environmental nutrient management. It also studies soil in the context of land-use planning, global warming, and acid rain. Regolith (/ˈrɛɡəlɪθ/θ/)[1] is a layer of loose, heterogeneous superficial deposits covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth Geological definition: „ Soil is an accumulation of loose material from mechanical and chemical weathering of rocks (also relocated) and containing a large admixture of various organic substances on the Earth's surface.“ 1 Pedological definition: „Soil is a natural body, which evolved from surface weathering of the Earth crust and organic residues. Its structure and composition are the result of climate and life. Functions of soil Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services.[19] Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms.[ Composition A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas.[32] The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other. Topic 2: Origin and development of soil from weathering: Soil is derived from rocks through a number of sequential or spontaneous steps. Soil forming rocks are of three types: 1. Primary rocks, formed due to solidification of molten magma and referred to as igneous rocks, eg granite , basalt 2. sedimentary rocks, the mechanical and chemical break down and redistribution of primary rocks give rise to sedimentary rocks, eg Sandstone, shale and limestone 3. Metamorphic rocks, formed due to influence of heat and /or pressure on the above type of rocks, slate, marble and gneiss. The predominant soil forming minerals are alimino- silicate minerals (feldspar, micas) which yield fine grained minerals matter, and silicates (or quartz) which persists in the soil as sand gravel. Soil formation occurs in two phases: 1, weathering of rocks and 2.Conversion of raw material into new body through the action of biosphere. Weathering is the breaking down of rocks, soil, and minerals as well as wood and artificial materials through contact with the Earth's atmosphere, water, and biological organisms. Physical weathering, also called mechanical weathering or disaggregation, is the class of processes that causes the disintegration of rocks without chemical change. The primary process in physical weathering is abrasion (the process by which clasts and other particles are reduced in size). However, chemical and physical weathering often goes hand in hand. Physical weathering 2 Topic 4: Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological and anthropogenic processes working on soil parent material Factors How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil. They are: parent material, climate, topography (relief), organisms, and time. When reordered to climate, relief, organisms, parent material, and time, they form the acronym CROPT. Parent material The mineral material from which a soil forms is called parent material. Rock, whether its origin is igneous, sedimentary, or metamorphic, is the source of all soil mineral materials and the origin of all plant nutrients with the exceptions of nitrogen, hydrogen and carbon. As the parent material is chemically and physically weathered, transported, deposited and precipitated, it is transformed into a soil. Typical soil parent mineral materials are:[78]  Quartz: SiO2  Calcite: CaCO3  Feldspar: KAlSi3O8  Mica (biotite): K(Mg,Fe)3AlSi3O10(OH)2 Climate The principal climatic variables influencing soil formation are effective precipitation (i.e., precipitation minus evapotranspiration) and temperature, both of which affect the rates of chemical, physical, and biological processes. Temperature and moisture both influence the organic matter content of soil through their effects on the balance between primary production and decomposition: the colder or drier the climate the lesser atmospheric carbon is fixed as organic matter while the lesser organic matter is decomposed. The direct influences of climate include:[108]  A shallow accumulation of lime in low rainfall areas as caliche  Formation of acid soils in humid areas 5  Erosion of soils on steep hillsides  Deposition of eroded materials downstream  Very intense chemical weathering, leaching, and erosion in warm and humid regions where soil does not freeze Topography The topography, or relief, is characterized by the inclination (slope), elevation, and orientation of the terrain. Topography determines the rate of precipitation or runoff and rate of formation or erosion of the surface soil profile. The topographical setting may either hasten or retard the work of climatic forces. Steep slopes encourage rapid soil loss by erosion and allow less rainfall to enter the soil before running off and hence, little mineral deposition in lower profiles. In semiarid regions, the lower effective rainfall on steeper slopes also results in less complete vegetative cover, so there is less plant contribution to soil formation. For all of these reasons, steep slopes prevent the formation of soil from getting very far ahead of soil destruction. Therefore, soils on steep terrain tend to have rather shallow, poorly developed profiles in comparison to soils on nearby, more level Organisms Soil is the most abundant ecosystem on Earth, but the vast majority of organisms in soil are microbes, a great many of which have not been described.[116][117] There may be a population limit of around one billion cells per gram of soil, but estimates of the number of species vary widely from 50,000 per gram to over a million per gram of soil. [116][118] The total number of organisms and species can vary widely according to soil type, location, and depth.[117][118] Plants, animals, fungi, bacteria and humans affect soil formation (see soil biomantle and stonelayer). Soil animals, including soil macrofauna and soil mesofauna, mix soils as they form burrows and pores, allowing moisture and gases to move about, a process called bioturbation.[119] In the same way, plant roots penetrate soil horizons and open channels upon decomposition.[120] Plants with deep taproots can penetrate many metres through the different soil layers to bring up nutrients from deeper in the profile.[121] Plants have fine roots that excrete organic compounds (sugars, organic acids, mucigel), slough off cells (in particular at their tip) and are easily decomposed, adding organic matter to soil, a process called rhizodeposition.[122] Micro-organisms, including fungi and bacteria, affect chemical exchanges between roots and soil and act as a reserve of nutrients in a soil biological hotspot called rhizosphere.[123] The growth of roots through the soil stimulates microbial populations, stimulating in turn the activity of their predators (notably amoeba), thereby increasing the mineralization rate, and in last turn root 6 growth, a positive feedback called the soil microbial loop.[124] Out of root influence, in the bulk soil, most bacteria are in a quiescent stage, forming microaggregates, i.e. mucilaginous colonies to which clay particles are glued, offering them a protection against desiccation and predation by soil microfauna (bacteriophagous protozoa and nematodes).[125] Microaggregates (20-250 µm) are ingested by soil mesofauna and macrofauna, and bacterial bodies are partly or totally digested in their guts.[126] Time Time is a factor in the interactions of all the above.[76] While a mixture of sand, silt and clay constitute the texture of a soil and the aggregation of those components produces peds, the development of a distinct B horizon marks the development of a soil or pedogenesis.[156] With time, soils will evolve features that depend on the interplay of the prior listed soil-forming factors.[76] It takes decades[157] to several thousand years for a soil to develop a profile, [158] although the notion of soil development has been criticized, soil being in a constant state-of- change under the influence of fluctuating soil-forming factors. That time period depends strongly on climate, parent material, relief, and biotic activity. For example, recently deposited material from a flood exhibits no soil development as there has not been enough time for the material to form a structure that further defines soil.[162] The original soil surface is buried, and the formation process must begin anew for this deposit. Over time the soil will develop a profile that depends on the intensities of biota and climate. While a soil can achieve relative stability of its properties for extended periods,[158] the soil life cycle ultimately ends in soil conditions that leave it vulnerable to erosion.[163] Despite the inevitability of soil retrogression and degradation, most soil cycles are long.[158] Soil-forming factors continue to affect soils during their existence, even on "stable" landscapes that are long-enduring, some for millions of years.[158] Materials are deposited on top[164] or are blown or washed from the surface. With additions, removals and alterations, soils are always subject to new conditions. Whether these are slow or rapid changes depends on climate, topography and biological activity. Topic 5: Soil profile A soil horizon makes up a distinct layer of soil. The horizon runs roughly parallel to the soil surface and has different properties and characteristics than the adjacent layers above and below. The soil profile is a vertical section of the soil that depicts all of its horizons. A soil horizon is a layer parallel to the soil surface, whose physical, chemical and biological characteristics differ from the layers above and beneath. Horizons are defined in many cases by obvious physical features, mainly colour and texture. These may be described both in absolute terms (particle size distribution for texture, for instance) and in terms relative to the surrounding material, i.e. ‘coarser’ or ‘sandier’ than the horizons above and below. Many soils have an organic surface layer, which is denominated with a capital letter (different letters, depending from the system). The mineral soil usually starts with an A horizon. If a well- 7 Sand is least active, having the least specific surface area, followed by silt; clay is the most active. Sand's greatest benefit to soil is that it resists compaction and increases soil porosity, although this property stands only for pure sand, not for sand mixed with smaller minerals which fill the voids among sand grains.[177] Silt is mineralogically like sand but with its higher specific surface area it is more chemically and physically active than sand. But it is the clay content of soil, with its very high specific surface area and generally large number of negative charges that gives a soil its high retention capacity for water and nutrients.[175] Clay soils also resist wind and water erosion better than silty and sandy soils, as the particles bond tightly to each other,[178] and that with a strong mitigation effect of organic matter.[179] Structure The clumping of the soil textural components of sand, silt and clay causes aggregates to form and the further association of those aggregates into larger units creates soil structures called peds (a contraction of the word pedolith). The adhesion of the soil textural components by organic substances, iron oxides, carbonates, clays, and silica, the breakage of those aggregates from expansion-contraction caused by freezing-thawing and wetting-drying cycles,[185] and the build- up of aggregates by soil animals, microbial colonies and root tips[186] shape soil into distinct geometric forms. The peds evolve into units which have various shapes, sizes and degrees of development.[187] A soil clod, however, is not a ped but rather a mass of soil that results from mechanical disturbance of the soil such as cultivation. Soil structure affects aeration, water movement, and conduction of heat, plant root growth and resistance to erosion.[188] Water, in turn, has a strong effect on soil structure, directly via the dissolution and precipitation of minerals, the mechanical destruction of aggregates (slaking)[189] and indirectly by promoting plant, animal and microbial growth. Density Particle density It is defined as the mass per unit volume of soil solids (in contrast to the volume of the soil, which would also include space between the particles). Soil particle density is typically 2.60 to 2.75 grams per cm3 and is usually unchanging for a given soil.[8] Soil particle density is lower for soils with high organic matter content,[205] and is higher for soils with high iron-oxides content. [206] 10 Soil bulk density is equal to the dry mass of the soil divided by the volume of the soil; i.e., it includes air space and organic materials of the soil volume. Thereby soil bulk density is always less than soil particle density and is a good indicator of soil compaction.[207] A high bulk density is indicative of either soil compaction or a mixture of soil textural classes in which small particles fill the voids among coarser particles.[212] Hence the positive correlation between the fractal dimension of soil, considered as a porous medium, and its bulk density,[213] that explains the poor hydraulic conductivity of silty clay loam in the absence of a faunal structure.[2 Porosity Pore space is that part of the bulk volume of soil that is not occupied by either mineral or organic matter but is open space occupied by either gases or water. In a productive, medium-textured soil the total pore space is typically about 50% of the soil volume.. Soil texture determines total volume of the smallest pores;[217] clay soils have smaller pores, but more total pore space than sands,[218] despite of a much lower permeability.[219] Soil structure has a strong influence on the larger pores that affect soil aeration, water infiltration and drainage.[220] Tillage has the short-term benefit of temporarily increasing the number of pores of largest size, but these can be rapidly degraded by the destruction of soil aggregation.[221] The pore size distribution affects the ability of plants and other organisms to access water and oxygen; large, continuous pores allow rapid transmission of air, water and dissolved nutrients through soil, and small pores store water between rainfall or irrigation events.[222] Pore size variation also compartmentalizes the soil pore space such that many microbial and faunal organisms are not in direct competition with one another, which may explain not only the large number of species present, but the fact that functionally redundant organisms (organisms with the same ecological niche) can co-exist within the same soil.[223] Consistency Consistency is the ability of soil to stick to itself or to other objects (cohesion and adhesion, respectively) and its ability to resist deformation and rupture. It is of approximate use in predicting cultivation problems Temperature Soil temperature depends on the ratio of the energy absorbed to that lost.[228] Soil has a temperature range between -20 to 60 °C with a mean annual temperature from -10 to 26 °C according to biomes.[229] Soil temperature regulates seed germination,[230] breaking of seed dormancy,[231][232] plant and root growth[233] and the availability of nutrients.[234] Soil temperature has important seasonal, monthly and daily variations, fluctuations in soil temperature being much lower with increasing soil 11 depth.[235] Heavy mulching (a type of soil cover) can slow the warming of soil in summer, and, at the same time, reduce fluctuations in surface temperature.[236] There are various factors that affect soil temperature, such as water content,[244] soil color,[245] and relief (slope, orientation, and elevation),[246] and soil cover (shading and insulation), in addition to air temperature.[247] The color of the ground cover and its insulating properties have a strong influence on soil temperature.[248] Whiter soil tends to have a higher albedo than blacker soil cover, which encourages whiter soils to have lower soil temperatures.[2 Colour In general, color is determined by the organic matter content, drainage conditions, and degree of oxidation. Soil color, while easily discerned, has little use in predicting soil characteristics.[269] It is of use in distinguishing boundaries of horizons within a soil profile,[270] determining the origin of a soil's parent material,[271] as an indication of wetness and waterlogged conditions,[272] and as a qualitative means of measuring organic,[273] iron oxide[274] and clay contents of soils. Soil color is primarily influenced by soil mineralogy. Many soil colours are due to various iron minerals.[274] The development and distribution of colour in a soil profile result from chemical and biological weathering, especially redox reactions.[272] As the primary minerals in soil parent material weather, the elements combine into new and colourful compounds. Iron forms secondary minerals of a yellow or red colour,[278] organic matter decomposes into black and brown humic compounds,[279] and manganese[280] and sulfur[281] can form black mineral deposits. These pigments can produce various colour patterns within a soil. Aerobic conditions produce uniform or gradual colour changes, while reducing environments (anaerobic) result in rapid colour flow with complex, mottled patterns and points of colour concentration.[282] Water Water affects soil formation, structure, stability and erosion but is of primary concern with respect to plant growth.[288] Water is essential to plants for four reasons: 1. It constitutes 80%-95% of the plant's protoplasm. 2. It is essential for photosynthesis. 3. It is the solvent in which nutrients are carried to, into and throughout the plant. 4. It provides the turgidity by which the plant keeps itself in proper position.[289] In addition, water alters the soil profile by dissolving and re-depositing minerals, often at lower levels,[290] and possibly leaving the soil sterile in the case of extreme rainfall and drainage. In a loam soil, solids constitute half the volume, gas one-quarter of the volume, and water one-quarter of the volume[32] of which only half will be available to most plants, with a strong variation according to matric potential.[291] 12  Root respiration and decomposition of organic matter by microorganisms releases CO2which increases the carbonic acid (H2CO3) concentration and subsequent leaching.  Plant growth: Plants take up nutrients in the form of ions (e.g. NO−3, NH+4, Ca2+, H2PO−4), and they often take up more cations than anions. However plants must maintain a neutral charge in their roots. In order to compensate for the extra positive charge, they will release H+ ions from the root. Some plants also exude organic acids into the soil to acidify the zone around their roots to help solubilize metal nutrients that are insoluble at neutral pH, such as iron (Fe).  Fertilizer use: Ammonium (NH+4) fertilizers react in the soil by the process of nitrificationto form nitrate (NO−3), and in the process release H+ions.  Acid rain : The burning of fossil fuels releases oxides of sulfur and nitrogen into the atmosphere. These react with water in the atmosphere to form sulfuric and nitric acid in rain.  Oxidative weathering : Oxidation of some primary minerals, especially sulfides and those containing Fe2+, generate acidity. This process is often accelerated by human activity: o Mine spoil : Severely acidic conditions can form in soils near some mine spoils due to the oxidation of pyrite. o Acid sulfate soils formed naturally in waterlogged coastal and estuarine environments can become highly acidic when drained or excavated. Sources of alkalinity Total soil alkalinity increases with:[11][12]  Weathering of silicate, aluminosilicate and carbonate minerals containing Na+, Ca2+, Mg2+and K+;  Addition of silicate, aluminosilicate and carbonate minerals to soils; this may happen by deposition of material eroded elsewhere by wind or water, or by mixing of the soil with less weathered material (such as the addition of limestone to acid soils);  Addition of water containing dissolved bicarbonates (as occurs when irrigating with high- bicarbonate waters). The accumulation of alkalinity in a soil (as carbonates and bicarbonates of Na, K, Ca and Mg) occurs when there is insufficient water flowing through the soils to leach soluble salts. This may be due to arid conditions, or poor internal soil drainage; in these situations most of the water that enters the soil is transpired (taken up by plants) or evaporates, rather than flowing through the soil.[11] The soil pH usually increases when the total alkalinity increases, but the balance of the added cations also has a marked effect on the soil pH. For example, increasing the amount of sodium in 15 an alkaline soil tends to induce dissolution of calcium carbonate, which increases the pH. Calcareous soils may vary in pH from 7.0 to 9.5, depending on the degree to which Ca2+or Na+ dominate the soluble cations.[11] Effect of soil pH on plant growth Acid soils Plants grown in acid soils can experience a variety of stresses including aluminium (Al), hydrogen (H), and/or manganese (Mn) toxicity, as well as nutrient deficiencies of calcium (Ca) and magnesium (Mg).[13] Aluminium toxicity is the most widespread problem in acid soils. Aluminium is present in all soils, but dissolved Al3+ is toxic to plants; Al3+ is most soluble at low pH; above pH 5.0, there is little Al in soluble form in most soils.[14][15] Aluminium is not a plant nutrient, and as such, is not actively taken up by the plants, but enters plant roots passively through osmosis. Aluminium inhibits root growth; lateral roots and root tips become thickened and roots lack fine branching; root tips may turn brown. In the root, the initial effect of Al3+ is the inhibition of the expansion of the cells of the rhizodermis, leading to their rupture; thereafter it is known to interfere with many physiological processes including the uptake and transport of calcium and other essential nutrients, cell division, cell wall formation, and enzyme activity. Proton (H+ ion) stress can also limit plant growth. The proton pump, H+-ATPase, of the plasmalemma of root cells works to maintain the near-neutral pH of their cytoplasm. A high proton activity (pH within the range 3.0–4.0 for most plant species) in the external growth medium overcomes the capacity of the cell to maintain the cytoplasmic pH and growth shuts down.[17] In soils with a high content of manganese-containing minerals, Mn toxicity can become a problem at pH 5.6 and lower. Manganese, like aluminium, becomes increasingly soluble as pH drops, and Mn toxicity symptoms can be seen at pH levels below 5.6. Manganese is an essential plant nutrient, so plants transport Mn into leaves. Classic symptoms of Mn toxicity are crinkling or cupping of leaves. Nutrient availability in relation to soil pH As discussed above, aluminium toxicity has direct effects on plant growth; however, by limiting root growth, it also reduces the availability of plant nutrients. Because roots are damaged, nutrient uptake is reduced, and deficiencies of the macronutrients (nitrogen, phosphorus, potassium, calcium and magnesium) are frequently encountered in very strongly acidic to ultra- acidic soils (pH<5.0).[19] 16 Molybdenum availability is increased at higher pH; this is because the molybdate ion is more strongly adsorbed by clay particles at lower pH.[20] Zinc, iron, copper and manganese show decreased availability at higher pH (increased sorbtion at higher pH).[20] The effect of pH on phosphorus availability varies considerably, depending on soil conditions and the crop in question. The prevailing view in the 1940s and 1950s was that P availability was maximized near neutrality (soil pH 6.5–7.5), and decreased at higher and lower pH. [21][22] Interactions of phosphorus with pH in the moderately to slightly acidic range (pH 5.5–6.5) are, however, far more complex than is suggested by this view. Laboratory tests, glasshouse trials and field trials have indicated that increases in pH within this range may increase, decrease, or have no effect on P availability to plants.[22][23] Water availability in relation to soil pH Strongly alkaline soils are sodic and dispersive, with slow infiltration, low hydraulic conductivity and poor available water capacity.[24] Plant growth is severely restricted because aeration is poor when the soil is wet; in dry conditions, plant-available water is rapidly depleted and the soils become hard and cloddy (high soil strength).[25] Many strongly acidic soils, on the other hand, have strong aggregation, good internal drainage, and good water-holding characteristics. However, for many plant species, aluminium toxicity severely limits root growth, and moisture stress can occur even when the soil is relatively moist. [14] Soil Acidification correction by lime Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil additive made from pulverized limestone or chalk. The primary active component is calcium carbonate. Additional chemicals vary depending on the mineral source and may include calcium oxide, magnesium oxide and magnesium carbonate. Unlike the types of lime called quicklime (calcium oxide) and slaked lime (calcium hydroxide), powdered limestone does not require lime burning in a lime kiln; it only requires milling. The effects of agricultural lime on soil are:  it increases the pH of acidic soil (the lower the pH the more acidic the soil); in other words, soil acidity is reduced and alkalinity increased[1]  it provides a source of calcium and magnesium for plants  it permits improved water penetration for acidic soils  it improves the uptake of major plant nutrients (nitrogen, phosphorus, and potassium) of plants growing on acid soils.[2] 17 The addition of a small amount of lime, Ca(OH)2, will displace hydrogen ions from the soil colloids, causing the fixation of calcium to colloids and the evolution of CO2 and water, with little permanent change in soil pH. The above are examples of the buffering of soil pH. The general principal is that an increase in a particular cation in the soil water solution will cause that cation to be fixed to colloids (buffered) and a decrease in solution of that cation will cause it to be withdrawn from the colloid and moved into solution (buffered). The degree of buffering is often related to the CEC of the soil; the greater the CEC, the greater the buffering capacity of the soil. Importance of soil buffering capacity It is important for two primary reasons. First, buffering tends to ensure some stability in the soil pH, preventing drastic fluctuations that might be detrimental to plants, soil microorganisms, and aquatic ecosystems. For example, well –buffered soils resist the acidifying effect of acid soil, preventing the acidification of both the soil and the drainage water. Second, buffering influence the amount of amendments, such as lime or sulfur, required to bring about desired change in soil pH Topic: Biological Properties of soil: The soil is home to a large proportion of the world's biodiversity. The links between soil organisms and soil functions are observed to be incredibly complex. We know that soil organisms break down organic matter, making nutrients available for uptake by plants and other organisms. The nutrients stored in the bodies of soil organisms prevent nutrient loss by leaching. The soil biota includes:  Megafauna: size range - 20 mm upward, e.g. moles, rabbits, and rodents.  Macrofauna: size range - 2 to 20 mm, e.g. woodlice, earthworms, beetles, centipedes, slugs, snails, ants, and harvestmen.  Mesofauna : size range - 100 micrometres to 2 mm, e.g. tardigrades, mites and springtails.  Microfauna and Microflora: size range - 1 to 100 micrometres, e.g. yeasts, bacteria (commonly actinobacteria), fungi, protozoa, roundworms, and rotifers.  Soil organisms numbers are influenced by the amount and quality of food available.  Physical factors( temperature and moisture  Chemical factors( soil pH, nutrient and chemicals present) 20  Biological properties(prey- predators, competition among organisms) Role of organisms: o Decomposition o Detoxification of chemicals o Inorganic transformation o Nitrogen fixation Chapter: Soil organic matter and soil fertility: Topic: soil organic matter – amount and distribution and its function Soil organic matter to encompass all the organic components of a soil: 1. Living biomass (intact animal and plant tissues and microorganisms); 2.dead roots and other recognizable plant residues or litter; and 3.a large amorphous and colloidal mixture of complex organic substances no longer identifiable as tissues. Only third category of organic matter is properly referred to as soil humus. The total organic matter in a soil contain several pools, namely active pool, slow pool and passive pools Active organic matter The active pool of soil organic matter consists of labile (easily decomposed) materials with half – lives of only a few days to a few years. Organic matter in active pool has a relatively high C/N ratio and includes such organic matter fractions as the living biomass, tiny pieces of detritus, most of the polysaccharides, and other non-humic substances. This active pool provides most of the readily accessible food for the soil organisms and most of the readily mineralizable nitrogen. It is responsible for most of the beneficial effects on the soil structural stability that lead to enhances infiltration of water, resistance to erosion, and ease of tillage 21 The active pool can be readily increased by the addition of fresh plant and animal residues. This pool rarely comprises more than 10 to 20% of the total organic matter. Passive pool of organic matter The passive pool of soil organic matter consists of very stable materials remaining in the soil for hundreds or even thousands of years. This pool includes most of the humus physically protected in clay- humus complexes, most of the humin, and much of the humic acid. The passive pool is most closely associated with the colloidal properties of soil humus, and it is responsible for most of the cation-and water holding capacities contributed to the soil by organic matter. It accounts for 60 to 90% of the organic matter in the most soils, and its quantity is increased or diminished only slowly. Slow pool Intermediate in properties between the active pool and passive pools is the slow pool of organic matter. This pool probably includes the finest fractions of particulate matter that are high in lignin and other slowly decomposable and chemically resistant components. The half- life these materials are typically measured in decade. This pool is important source of mineralizable nitrogen, other plant nutrients, and it provides much of the underlying food source for the steady metabolism of the k- selected soil microbes. Topic: Humus, its formation and characteristics Humus, definition: As the decomposition of organic matter proceeds, microbes slowly break down the complex components in simple compounds. In this process some of the lignin is broken down into its phenolic subunits. The soil microbes then metabolize the resulting simpler compounds using some of the carbon not lost as carbon dioxide in respiration. Along with most of the nitrogen, sulfur and oxygen from these compounds, the microorganisms synthesize new cellular components and bimolecules. Some of the original lignin is not completely broken down, but only modified to complex residual molecules that retain many of the characteristics of the lignin. The microbes polymerize some of the simpler new compounds with each other and with the complex residual products into long, complex chains that resist further decomposition. High molecular compounds interact with nitrogen- containing amino compounds, giving rise to significant components of resistant humus. The presence of colloidal clays stimulates the complex polymerization. These ill- defined, complex, resistant, polymeric compounds are called humic substances. The tern non- 22  These microaggregates are like the building blocks for improving soil structure. Improved soil structure increases water infiltration and increases water holding capacity of the soil  Bacteria perform important functions in the soil, decomposing organic residues from enzymes released into the soil.  The decomposers consume the easy-to-digest carbon compounds and simple sugars and tie up soluble nutrients like nitrogen in their cell membranes. Bacteria dominate in tilled soils but they are only 20-30 percent efficient at recycling carbon (C).  there are four bacteria types that convert atmospheric nitrogen (N2) into nitrogen for plants. There are three types of soil bacteria that fix nitrogen without a plant host and live freely in the soil and these include Azotobacter, Azospirillum and Clostridium.  The Rhizobium bacteria species associate with a plant host: legume (alfalfa, soybeans) or clover (red, sweet, white, crimson) to form nitrogen nodules to fix nitrogen for plant growth.  Nitrification is a process where nitrifying bacteria convert ammonia (NH4+) to nitrite (NO2-) and then to nitrate (NO3-).  Denitrifying bacteria allow nitrate (NO3-) to be converted to nitrous oxide (N2O) or dinitrogen (N2) (atmospheric nitrogen).  Pathogenic bacteria cause diseases in plants and a good example are bacteria blights. Healthy and diverse soil bacteria populations produce antibiotics that protect the plants from disease causing organisms and plant pathogens. Actinomycetes Actinomycetes are filamentous and often profusely branched, appearing somewhat like tiny fungi. Howerver their genetic makeup and cellular properties clearly place them in the bacterial domin—they do not have niclar membrane, are about the same diameter as other bacteria., and often break up in spores that closely resemble cocci bacterial cell. Decomposition activities. Generally aerobic heterotrophs, the actinomycetes live on decaying organic matter in the soil or on compounds supplied by plants certain species form parasitic or symbiotic relationship. They are undoubtedly are of great importance in the decomposition of soil organic matter and the liberation of its nutrients. They are capble of breaking even resistant compounds, such as cellulose, chitin, and phospholipids, into simpler forms. They often become dominant in the later stage of decay when the easily metabolized substrates have been used up. They are very important in the final stages of composting. 25 Actinomycetes develop best in moist, warm, well aerated soil. However, they tolerate low osmotic potential and are active in arid- region, salt affected soils, and including period of drought. Fungi Soil fungi comprise an extremely diverse group of organisms. Tens of thousands of species have been identified in soil, representing 170 genera. They are eukaryotes with a nuclear membrane and cell walls. As heterotrophs, they depend on living or dead organic materials for both their carbon and their energy. Fungi are aerobic organisms, although some can tolerate the rather low oxygen concentration. Activities in soil. As decomposers of organic matter in soil, fungi are the most versatile and persistent of any group. Cellulose, starch, and lignin, as well as the easily metabolizes proteins and sugars, succumb to their attack. Fungi play major roles in the process of humus formation and aggregate stabilization. They usually dominated the upper horizon of forested soils, as well as very acid or sandy soils. Fungi are quite efficient in using the organic materials they metabolize. Up to 50% of the substances they decompose may become fugal tissues, compared to about 20% for bacteria. In addition to the breakdown of organic matter and the formation of humus, numerous other fugal activities have significant impact on soil ecology. Certain species even trap nematodes. Soil fungi can synthesize a wide range of complex organic compounds in addition to those associated with soil humus. Certain fungi produce compounds that kills other fungi or bacteria that provide competitive edge over rival microorganisms in the soil. Unfortunately, a few fungi produce chemical: mycotoxin that are highly toxic to plants or animals. Mycorrhiza A mycorrhiza is the symbiotic association between a green plant and a fungus. The plant captures the energy coming from the sun by means of its chlorophyll and supplies it to the fungus, and the fungus supplies water and mineral nutrients taken from the soil to the plant. Mycorrhizas are located in the roots of the plant. Most plant species form mycorrhizal associations, though some families like Brassicaceae and Chenopodiaceae cannot. Mycorrhizas are commonly divided into ectomycorrhizas and endomycorrhizas. The two types are differentiated by the fact that the hyphae of ectomycorrhizal fungi do not penetrate individual cells within the root, while the hyphae of endomycorrhizal fungi penetrate the cell wall and invaginate the cell membrane. Ectomycorrhizas, or EcM, are typically formed between the roots of around 10% of plant families, mostly woody plants including the birch, dipterocarp, eucalyptus, oak, pine, and rose[10] families, orchids,[12] and fungi belonging to the Basidiomycota, Ascomycota, and Zygomycota. 26 Some EcM fungi, such as many Leccinum and Suillus, are symbiotic with only one particular genus of plant, while other fungi, such as the Amanita, are generalists that form mycorrhizas with many different plants.[13] An individual tree may have 15 or more different fungal EcM partners at one time.[14] Thousands of ectomycorrhizal fungal species exist, hosted in over 200 genera. Endomycorrhizas are variable and have been further classified as arbuscular, ericoid, arbutoid, monotropoid, and orchid mycorrhizas.[8] Arbuscular mycorrhizas, or AM (formerly known as vesicular-arbuscular mycorrhizas, or VAM), are mycorrhizas whose hyphae penetrate plant cells, producing structures that are either balloon-like (vesicles) or dichotomously branching invaginations (arbuscules) as a means of nutrient exchange. The fungal hyphae do not in fact penetrate the protoplast (i.e. the interior of the cell), but invaginate the cell membrane. The structure of the arbuscules greatly increases the contact surface area between the hypha and the cell cytoplasm to facilitate the transfer of nutrients between them. Role in soil: mycorrizae greatly enhance the ability of plants to take up phosphorus and other nutrients that are relatively immobile and present in low concentrations in the soil solution. Water uptake may also be improved my mycorrizae, making plants more resistant to drought and salinity stress. They also protect plants from certain soil-borne diseases and parasitic nematodes by producing antibiotics. Algae Most soil algae range in size from 2 to 20 um. Many algal species are motile and swim in soil pore water, some by means of flagella. Most grow best under moist to wet conditions, but are also very important in hot or cold desert environments. Sometimes the growth of algae may be so great that soil surface is covered with a green or orange algal mat. Some algae (as well as certain cyanobacteria) form lichen. These are important in colonizing bare rock and other low- organic matter environments. In unvegetated patches in deserts, algae commonly contribute to the formation of microbiotic crusts. In addition to producing a substantial amount of organic matter in some fertile soils, certain algae excrete polysaccharides that have very favorable effects on soil aggregates. Protozoa Protozoa are mobile single celled creature that capture and engulf their food. Soil protozoa include amoebas, ciliates, and flagellates. They swim about in the water- filled pores and water films in the soil can form resistant resting stages (cyst) when soils dry out or food became scarce. Sometimes as many as 40 to 50 different species may occur in a single sample of soil. Protozoa generally thrive best in moist, well drained soils and most numerous in surface horizons. They are generally active in the area immediately around the plant foots. Their main influence on organic matter decay and nutrient release is through their effects on bacterial populations. 27 Termites There are about 2000 species of termites, most of which use cellulose in the form of plant fibre as their primary food. Yet most termites cannot themselves digest cellulose. Instead, a termite depends on a mutaulistic relationship with protozoa and bacteria that live in its gut. These gut microorganisms secrete enzymes that degrade cellulose and allow termite to derive their energy from it. Most termite species eat decaying logs, grasses, or fallen tree leaves, but some attack sound wood in standing trees. These groups have become infamous because of their habit of invading the houses of people build of woods. Termites are social animals that live in very complex labyrinths of nests, passages, and chambers that they build below and above the soil surface. Termite mounds built from soil particles and feces cemented with saliva are characteristic features of many landscapes in different places. In building their mounds, termites transport soil from lower layers to the surface, thereby extensively mixing the soil and incorporating into it the plant residues they use as food. Scavenging a large area around each mound, these insects remove up to 4000kg/ha of leaf and woody material annually. They also annually move 300 to 1200 kg/ha of soil in their mound- building activities. Termites mound material often has a lower organic matter and nutrient content than the surrounding undisturbed topsoil. This is because termites build their mounds mainly with subsoil, which is typically lower in organic matter content than topsoil. However, where the sub soil is richer in mineral nutrients than the topsoil or is rich in clay compared to very sandy surface soil, the material from abandoned mounds may provide islands of relatively high plant protection, due to greater availability of phosphorus, potassium, calcium, and moisture. Topic: Plant Nutrient (Macro and micro nutrient and their role in plant growth) There are seventeen most important nutrients for plants. Plants must obtain the following mineral nutrients from their growing medium:-[2]  the macronutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sulfur (S), magnesium (Mg), carbon (C), oxygen(O), hydrogen (H)  the micronutrients (or trace minerals): iron (Fe), boron (B), chlorine (Cl), manganese (Mn), zinc (Zn), copper (Cu), molybdenum (Mo), nickel (Ni) 30 These elements stay beneath soil as salts, so plants consume these elements as ions. The macronutrients are consumed in larger quantities; hydrogen, oxygen, nitrogen and carbon contribute to over 95% of a plants' entire biomass on a dry matter weight basis. Micronutrients are present in plant tissue in quantities measured in parts per million, ranging from 0.1[3] to 200 ppm, or less than 0.02% dry weight.[4] Most soil conditions across the world can provide plants adapted to that climate and soil with sufficient nutrition for a complete life cycle, without the addition of nutrients as fertilizer. However, if the soil is cropped it is necessary to artificially modify soil fertility through the addition of fertilizer to promote vigorous growth and increase or sustain yield. This is done because, even with adequate water and light, nutrient deficiency can limit growth and crop yield. At least 17 elements are known to be essential nutrients for plants. In relatively large amounts, the soil supplies nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur; these are often called the macronutrients. In relatively small amounts, the soil supplies iron, manganese, boron, molybdenum, copper, zinc, chlorine, and cobalt, the so-called micronutrients. Nutrients must be available not only in sufficient amounts but also in appropriate ratios. Macronutrients (derived from air and water) Carbon forms the backbone of most plant biomolecules, including proteins, starches and cellulose. Carbon is fixed through photosynthesis; this converts carbon dioxide from the air into carbohydrates which are used to store and transport energy within the plant. Hydrogen also is necessary for building sugars and building the plant. It is obtained almost entirely from water. Hydrogen ions are imperative for a proton gradient to help drive the electron transport chain in photosynthesis and for respiration. Oxygen is a component of many organic and inorganic molecules within the plant, and is acquired in many forms. These include: O2 and CO2 (mainly from the air via leaves) and H2O,NO−3, H2PO−4 and SO2−4 (mainly from the soil water via roots). Plants produce oxygen gas (O2) along with glucose during photosynthesis but then require O2 to undergo aerobic cellular respiration and break down this glucose to produce ATP. Macronutrients (primary) Nitrogen It is a major constituent of several of the most important plant substances. For example, nitrogen compounds comprise 40% to 50% of the dry matter of protoplasm, and it is a constituent of amino acids, the building blocks of proteins.[7] It is also an essential constituent of chlorophyll.[8] Deficiency Nitrogen deficiency most often results in stunted growth, slow growth, and chlorosis. Nitrogen deficient plants will also exhibit a purple appearance on the stems, petioles and underside of 31 leaves from an accumulation of anthocyanin pigments.[5] Most of the nitrogen taken up by plants is from the soil in the forms of NO−3, although in acid environments such as boreal forests where nitrification is less likely to occur, ammonium NH+4 is more likely to be the dominating source of nitrogen. Phosphorus Like nitrogen, phosphorus is involved with many vital plant processes. Within a plant, it is present mainly as a structural component of the nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), as well as a constituent of fatty phospholipids, that are important in membrane development and function. It is present in both organic and inorganic forms, both of which are readily translocated within the plant. All energy transfers in the cell are critically dependent on phosphorus. As with all living things, phosphorus is part of the Adenosine triphosphate (ATP), which is of immediate use in all processes that require energy with the cells. Phosphorus can also be used to modify the activity of various enzymes by phosphorylation, and is used for cell signaling. Functions Phosphorus is concentrated at the most actively growing points of a plant and stored within seeds in anticipation of their germination. Phosphorus is most commonly found in the soil in the form of polyprotic phosphoric acid (H3PO4), but is taken up most readily in the form of H2PO−4. Phosphorus is available to plants in limited quantities in most soils because it is released very slowly from insoluble phosphates and is rapidly fixed once again. Under most environmental conditions it is the element that limits growth because of this constriction and due to its high demand by plants and microorganisms. Plants can increase phosphorus uptake by a mutualism with mycorrhiza.[5] Deficiency A Phosphorus deficiency in plants is characterized by an intense green coloration or reddening in leaves due to lack of chlorophyll. If the plant is experiencing high phosphorus deficiencies the leaves may become denatured and show signs of death. Occasionally the leaves may appear purple from an accumulation of anthocyanin. Because phosphorus is a mobile nutrient, older leaves will show the first signs of deficiency. Potassium Unlike other major elements, potassium does not enter into the composition of any of the important plant constituents involved in metabolism,[7] but it does occur in all parts of plants in substantial amounts. Function 32 manufacture of lignin (cell walls) and involved in grain production. It is also hard to find in some soil conditions. Manganese is necessary for photosynthesis, including the building of chloroplasts. Manganese deficiency may result in coloration abnormalities, such as discolored spots on the foliage. Sodium is involved in the regeneration of phosphoenolpyruvate in CAM and C4 plants. Sodium can potentially replace potassium's regulation of stomatal opening and closing. Zinc is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of zinc deficiency is the stunted growth of leaves, commonly known as "little leaf" and is caused by the oxidative degradation of the growth hormone auxin. In higher plants, nickel is absorbed by plants in the form of Ni2+ ion. Nickel is essential for activation of urease, an enzyme involved with nitrogen metabolism that is required to process urea. Without nickel, toxic levels of urea accumulate, leading to the formation of necrotic lesions. In lower plants, nickel activates several enzymes involved in a variety of processes, and can substitute for zinc and iron as a cofactor in some enzymes. Chlorine, as compounded chloride, is necessary for osmosis and ionic balance; it also plays a role in photosynthesis. Cobalt has proven to be beneficial to at least some plants although it does not appear to be essential for most species.[28] It has, however, been shown to be essential for nitrogen fixation by the nitrogen-fixing bacteria associated with legumes and other plants. Aluminum is one of the few elements capable of making soil more acidic. This is achieved by aluminum taking hydroxide ions out of water, leaving hydrogen ions behind.[29] As a result, the soil is more acidic, which makes it unlivable for many plants. Another consequence of aluminum in soils is aluminum toxicity, which inhibits root growth.[30] Silicon is not considered an essential element for plant growth and development. It is always found in abundance in the environment and hence if needed it is available. It is found in the structures of plants and improves the health of plants.[31] In plants, silicon has been shown in experiments to strengthen cell walls, improve plant strength, health, and productivity.[32] There have been studies showing evidence of silicon improving drought and frost resistance, decreasing lodging potential and boosting the plant's natural pest and disease fighting systems. Vanadium may be required by some plants, but at very low concentrations. It may also be substituting for molybdenum. Selenium is probably not essential for flowering plants, but it can be beneficial; it can stimulate plant growth, improve tolerance of oxidative stress, and increase resistance to pathogens and herbivory. 35 Selenium is, however, an essential mineral element for animal (including human) nutrition and selenium deficiencies are known to occur when food or animal feed is grown on selenium- deficient soils. The use of inorganic selenium fertilizers can increase selenium concentrations in edible crops and animal diets thereby improving animal health. Topic: Fertilizer A fertilizer is any material of natural or synthetic origin (other than liming materials) that is applied to soils or to plant tissues to supply one or more plant nutrients essential to the growth of plants. Many sources of fertilizer exist, both natural and industrially produced.[1] Fertilizers enhance the growth of plants. This goal is met in two ways, the traditional one being additives that provide nutrients. The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration. Fertilizers are classified in several ways. They are classified according to whether they provide a single nutrient (e.g., K, P, or N), in which case they are classified as "straight fertilizers." "Multinutrient fertilizers" (or "complex fertilizers") provide two or more nutrients, for example N and P. Fertilizers are also sometimes classified as inorganic (the topic of most of this article) versus organic. Inorganic fertilizers exclude carbon-containing materials except ureas. Organic fertilizers are usually (recycled) plant- or animal-derived matter. Inorganic are sometimes called synthetic fertilizers since various chemical treatments are required for their manufacture.[5] Single nutrient ("straight") fertilizers The main nitrogen-based straight fertilizer is ammonia or its solutions. Ammonium nitrate (NH4NO3) is also widely used. Urea is another popular source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate, respectively. A few percent of the nitrogen fertilizer market (4% in 2007)[6] has been met by calcium ammonium nitrate (Ca(NO3)2 · NH4NO3 · 10H2O). The main straight phosphate fertilizers are the superphosphates. "Single superphosphate" (SSP) consists of 14–18% P2O5, again in the form of Ca(H2PO4)2, but also phosphogypsum (CaSO4 · 2H2O). Triple superphosphate (TSP) typically consists of 44-48% of P2O5 and no gypsum. A mixture of single superphosphate and triple superphosphate is called double superphosphate. More than 90% of a typical superphosphate fertilizer is water-soluble. Multinutrient fertilizers These fertilizers are common. They consist of two or more nutrient components. Binary (NP, NK, PK) fertilizers Major two-component fertilizers provide both nitrogen and phosphorus to the plants. These are called NP fertilizers. The main NP fertilizers are monoammonium phosphate (MAP) and 36 diammonium phosphate (DAP). The active ingredient in MAP is NH4H2PO4. The active ingredient in DAP is (NH4)2HPO4. About 85% of MAP and DAP fertilizers are soluble in water. Manure It is organic matter, mostly derived from animal feces except in the case of green manure, which can be used as organic fertilizer in agriculture. Manures contribute to the fertility of the soil by adding organic matter and nutrients, such as nitrogen, that are utilised by bacteria, fungi and other organisms in the soil. Higher organisms then feed on the fungi and bacteria in a chain of life that comprises the soil food web. In the past, the term "manure" included inorganic fertilizers, but this usage is now very rare. There are three main classes of manures used in soil management: Animal manure Most animal manure consists of feces. Common forms of animal manure include farmyard manure (FYM) or farm slurry (liquid manure). FYM also contains plant material (often straw), which has been used as bedding for animals and has absorbed the feces and urine. Agricultural manure in liquid form, known as slurry, is produced by more intensive livestock rearing systems where concrete or slats are used, instead of straw bedding. Manure from different animals has different qualities and requires different application rates when used as fertilizer. For example horses, cattle, pigs, sheep, chickens, turkeys, rabbits, and guano from seabirds and bats all have different properties.[1] For instance, sheep manure is high in nitrogen and potash, while pig manure is relatively low in both. Horses mainly eat grass and a few weeds so horse manure can contain grass and weed seeds, as horses do not digest seeds the way that cattle do. Cattle manure is a good source of nitrogen as well as organic carbon.[2]Chicken litter, coming from a bird, is very concentrated in nitrogen and phosphate and is prized for both properties." Human manure Some people refer to human excreta as human manure, and the word "humanure" has also been used. Just like animal manure, it can be applied as a soil conditioner (reuse of excreta in agriculture). Sewage sludge is a material that contains human excreta, as it is generated after mixing excreta with water and treatment of the wastewater in a sewage treatment plant. Compost Compost is the decomposed remnants of organic materials. It is usually of plant origin, but often includes some animal dung or bedding. Green manure Green manures are crops grown for the express purpose of plowing them in, thus increasing fertility through the incorporation of nutrients and organic matter into the soil. Leguminous 37 Fungi as biofertilizer Mycorrizae: refer description of it in earlier page Topic Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric carbon dioxide[1] or other forms of carbon to mitigate or defer global warming. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels.[2] Carbon dioxide (CO2) is naturally captured from the atmosphere through biological, chemical, and physical processes.[3] Artificial processes have been devised to produce similar effects,[3] including large-scale, artificial capture and sequestration of industrially produced CO 2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks. Carbon sequestration is the process involved in carbon capture and the long-term storage of atmospheric carbon dioxide (CO2) and may refer specifically to:  "The process of removing carbon from the atmosphere and depositing it in a reservoir." [4] When carried out deliberately, this may also be referred to as carbon dioxide removal, which is a form of geoengineering.  Carbon capture and storage, where carbon dioxide is removed from flue gases (e.g., at power stations) before being stored in underground reservoirs.  Natural biogeochemical cycling of carbon between the atmosphere and reservoirs, such as by chemical weathering of rocks. Carbon dioxide may be captured as a pure by-product in processes related to petroleum refining or from flue gases from power generation.[5] CO2 sequestration includes the storage part of carbon capture and storage, which refers to large-scale, artificial capture and sequestration of industrially produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other carbon sinks. Carbon sequestration describes long-term storage of carbon dioxide or other forms of carbon to either mitigate or defer global warming and avoid dangerous climate change. It has been proposed as a way to slow the atmospheric and marine accumulation of greenhouse gases, which are released by burning fossil fuels.[2] Carbon dioxide is naturally captured from the atmosphere through biological, chemical or physical processes. Some artificial sequestration techniques exploit these natural processes,[3] while some use entirely artificial processes. Biological processes Biosequestration or carbon sequestration through biological processes affects the global carbon cycle. 40 1 Peat production Peat bogs act as a sink for carbon due to the accumulation of partially decayed biomass that would otherwise continue to decay completely. There is a variance on how much the peatlands act as a carbon sink or carbon source that can be linked to varying climates in different areas of the world and different times of the year.[6] By creating new bogs, or enhancing existing ones, the amount of carbon that is sequestered by bogs would increase.[7] 2 Forestry Reforestation is the replanting of trees on marginal crop and pasture lands to incorporate carbon from atmospheric CO2 into biomass.[8] For this process to succeed the carbon must not return to the atmosphere from mass burning or rotting when the trees die.[9] To this end, land allotted to the trees must not be converted to other uses and management of the frequency of disturbances might be necessary in order to avoid extreme events. Alternatively, the wood from them must itself be sequestered, e.g., via biochar, bio-energy with carbon storage (BECS), landfill or 'stored' by use in e.g. construction. Short of growth in perpetuity, however, reforestation with long-lived trees (>100 years) will sequester carbon for a more graduated release, minimizing impact during the expected carbon crisis of the 21st century. 3 Urban forestry Urban forestry increases the amount of carbon taken up in cities by adding new tree sites and the sequestration of carbon occurs over the lifetime of the tree.[10] It is generally practiced and maintained on smaller scales, like in cities. The results of urban forestry can have different results depending on the type of vegetation that is being used, so it can function as a sink but can also function as a source of emissions.[11] Along with sequestration by the plants which is difficult to measure but seems to have little effect on the overall amount of carbon dioxide that is uptaken, the vegetation can have indirect effects on carbon by reducing need for energy consumption.[11] 4 Wetland restoration Wetland soil is an important carbon sink; 14.5% of the world's soil carbon is found in wetlands, while only 6% of the world's land is composed of wetlands.[12] 5 Agriculture Compared to natural vegetation, cropland soils are depleted in soil organic carbon (SOC). When a soil is converted from natural land or semi natural land, such as forests, woodlands, grasslands, steppes and savannas, the SOC content in the soil reduces with about 30–40%.[13] This loss is due to the removal of plant material containing carbon, in terms of harvests. When the land use changes, the carbon in the soil will either increase or decrease, this change will continue until the soil reaches a new equilibrium. Deviations from this equilibrium can also be affected by variated climate .[14] The decreasing of SOC content can be counteracted by increasing the carbon input, this can be done with several strategies, e.g. leave harvest residues on the field, use manure as 41 fertiliser or include perennial crops in the rotation. Perennial crops have larger below ground biomass fraction, which increases the SOC content.[13] Globally, soils are estimated to contain approximately 1,500 gigatons of organic carbon to 1 m depth, more than the amount in vegetation and the atmosphere.[15][16] 6. Deep soil Soils hold four times the amount of carbon stored in the atmosphere.[18] About half of this is found deep within soils.[19] About 90% of this deep soil C is stabilized by mineral-organic associations. Topic: Role of forest in carbon sequestration The increase in greenhouse gases, particularly carbon dioxide, into the atmosphere is considered to be one of the main causes of global warming. Human activity is releasing vast amounts of carbon dioxide, principally through the burning of fossil fuels to power industry, transport, heating etc. Land-use changes such as the unsustainable exploitation and destruction of tropical forests are also having an impact. Trees and woodlands play an important role in the removal of carbon dioxide from the atmosphere. Through the biochemical process of photosynthesis carbon dioxide is taken in by trees and stored as carbon in the trunk, branches, leaves and roots. Carbon is also stored in the soil and indeed this is a major sink for carbon in the forest. Decay of the organic material eventually releases the CO2 back to the atmosphere, and providing the forests are sustainably managed, it is taken up by replacement trees, thereby maintaining a balance in the carbon budget. The release of CO2, however, can be delayed through the harvesting of trees as they mature if the wood is used for construction, furniture and other end uses that prolong its life. Sustainable forestry is positively contributing to the carbon sequestration and is an important management tool is combating climate change. International agreements to regulate carbon emissions such as the Kyoto Protocol recognise the importance of forests as carbon sinks. The area of forest this is taken into account when deriving national targets for allowable emissions. Topic: Measurement of soil carbon stock The carbon stock in a forest ecosystem can be broadly categorized into biotic (vegetative carbon) and pedologic (soil carbon) components. As trees grow, they sequester carbon in their tissues, and as the amount of tree biomass increases, the atmospheric carbon dioxide (CO2) is mitigated. Where is carbon stored? Carbon (C) is stored in five different pools: (1) aboveground biomass; (2) belowground biomass; (3) litter; (4) deadwood/woody debris; and (5) soil CONVERT TREE BIOMASS TO CARBON EQUIVALENT. 42  Planosols  Podzols  Podzoluvisols  Rankers  Regosols  Rendzinas  Solonchaks  Solonetz  Vertisols  Yermosols Topic: USDA soil taxonomy USDA soil taxonomy (ST) developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters (most commonly their properties) and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series. The classification was originally developed by Guy Donald Smith, former director of the U.S. Department of Agriculture's soil survey investigations. [1] Taxonomy is an arrangement in a systematic manner; the USDA soil taxonomy has six levels of classification. They are, from most general to specific: order, suborder, great group, subgroup, family and series. Soil properties that can be measured quantitatively are used in this classification system – they include: depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content and salt content. There are 12 soil orders (the top hierarchical level) in soil taxonomy. [2][3] The names of the orders end with the suffix -sol. The criteria for the different soil orders include properties that reflect major differences in the genesis of soils.[4] The orders are:  Alfisol – soils with aluminium and iron. They have horizons of clay accumulation, and form where there is enough moisture and warmth for at least three months of plant growth. They constitute 10% of soils worldwide.  Andisol – volcanic ash soils. They are young and very fertile. They cover 1% of the world's ice-free surface.  Aridisol – dry soils forming under desert conditions which have fewer than 90 consecutive days of moisture during the growing season and are nonleached. They include nearly 12% of soils on Earth. Soil formation is slow, and accumulated organic matter is scarce. They may have subsurface zones of caliche or duripan. Many aridisols 45 have well-developed Bt horizons showing clay movement from past periods of greater moisture.  Entisol – recently formed soils that lack well-developed horizons. Commonly found on unconsolidated river and beach sediments of sand and clay or volcanic ash, some have an A horizon on top of bedrock. They are 18% of soils worldwide.  Gelisol – permafrost soils with permafrost within two metres of the surface or gelic materials and permafrost within one metre. They constitute 9% of soils worldwide.  Histosol – organic soils, formerly called bog soils, are 1% of soils worldwide.  Inceptisol – young soils. They have subsurface horizon formation but show little eluviation and illuviation. They constitute 15% of soils worldwide.  Mollisol – soft, deep, dark fertile soil formed in grasslands and some hardwood forests with very thick A horizons. They are 7% of soils worldwide.  Oxisol – are heavily weathered, are rich in iron and aluminum oxides (sesquioxides) or kaolin but low in silica. They have only trace nutrients due to heavy tropical rainfall and high temperatures and low CEC of the remaining clays. They are 8% of soils worldwide.  Spodosol – acid soils with organic colloid layer complexed with iron and aluminium leached from a layer above. They are typical soils of coniferous and deciduous forests in cooler climates. They constitute 4% of soils worldwide.  Ultisol – acid soils in the humid tropics and subtropics, which are depleted in calcium, magnesium and potassium (important plant nutrients). They are highly weathered, but not as weathered as Oxisols. They make up 8% of the soil worldwide.  Vertisol – inverted soils. They are clay-rich and tend to swell when wet and shrink upon drying, often forming deep cracks into which surface layers can fall. They are difficult to farm or to construct roads and buildings due to their high expansion rate. They constitute 2% of soils worldwide. . Alfisol Andisol Aridisol Entisol Gelisol Histisol Inceptisol Mollisol 46 Oxisol Spodosol Utisol Vertisol The percentages listed above[5] are for land area free of ice. "Soils of Mountains", which constitute the balance (11.6%), have a mixture of those listed above, or are classified as "Rugged Mountains" which have no soil. The above soil orders in sequence of increasing degree of development are Entisols, Inceptisols, Aridisols, Mollisols, Alfisols, Spodosols, Ultisols, and Oxisols. Histosols and Vertisols may appear in any of the above at any time during their development. The soil suborders within an order are differentiated on the basis of soil properties and horizons which depend on soil moisture and temperature. Forty-seven suborders are recognized in the United States. The soil great group category is a subdivision of a suborder in which the kind and sequence of soil horizons distinguish one soil from another. About 185 great groups are recognized in the United States. Horizons marked by clay, iron, humus and hard pans and soil features such as the expansion-contraction of clays (that produce self-mixing provided by clay), temperature, and marked quantities of various salts are used as distinguishing features.[6] The great group categories are divided into three kinds of soil subgroups: typic, intergrade and extragrade. A typic subgroup represents the basic or 'typical' concept of the great group to which the described subgroup belongs. An intergrade subgroup describes the properties that suggest how it grades towards (is similar to) soils of other soil great groups, suborders or orders. These properties are not developed or expressed well enough to cause the soil to be included within the great group towards which they grade, but suggest similarities. Extragrade features are aberrant properties which prevent that soil from being included in another soil classification. About 1,000 soil subgroups are defined in the United States.[6] A soil family category is a group of soils within a subgroup and describes the physical and chemical properties which affect the response of soil to agricultural management and engineering applications. The principal characteristics used to differentiate soil families include texture, mineralogy, pH, permeability, structure, consistency, the locale's precipitation pattern, and soil temperature. For some soils the criteria also specify the percentage of silt, sand and coarse fragments such as gravel, cobbles and rocks. About 4,500 soil families are recognised in the United States.[7] A family may contain several soil series which describe the physical location using the name of a prominent physical feature such as a river or town near where the soil sample was taken. An 47 animals, and leaving fallow for 2-3 year periods. Barley, millet and potato are the main crops grown in this soil.  Cryumbrepts: Cryumbrepts are also the soils of high Himalayan and high hill regions generally found above 3,000m but, depending on the local climate altitude vary. Soils of this group have dark A horizons, high organic matter with wide C/N ratio low base saturation and contain no free carbonate. They are silty in texture. These soils are under snow for at least three months of the year. Vegetation ranges from monsoon grasses to Rhododendron and Betula in this type of soil. Ares under these soils are extensively used for seasonal grazing. Spodosols: Spondosols consists of spodic horizon (Bh,Bs). they are rare, but are important to pedologists as they indicate a stable but strongly leaching environment. Spondosols have strong reddish or black subsoil in which iron and organic have been deposited after initial leaching from the surface soil layers. They occur on stable landscapes at elevations above 3,000 meters where conifers dominate the forest. The best developed Spondosols in the country were sampled 1 km north of the old Tengboche monastery in the khumbu area. They were cryorthods (Annex 2, icimod.org). Agriculturally they are of very little importance. Spodosols have higher proportion of organic acids which accelerates weathering. This result in leaching of base cations. So Spodosols are not fertile soils. Mollisols: Soils with high organic matter content, usually under thick grass or forest, dark colour and high base saturation are classified under Mollisols. They develop on basic parent materials at higher elevations. They are formed on calcium rich parent materials and throughout rapid base recycling and/or low leaching, have maintained their high base saturation. Mollisols in humid regions generally have higher organic matter content and darker, thicker mollic epipedons than their lower-moisture-regime counterparts. Mollisols have been found sporadically in the Sal forest of upper terai and southern exposed grassland sites in western Nepal at higher elevations. Vegetation removal for cultivation results in the rapid oxidation of the organic matter in the surface of these soils and they are over time converted to Ustochrepts. Some groups under Mollisols are as follows:  Haplustolls: These are common in subtropical mixed forest of terai and inner valleys. They develop on alluvial materials and are distinguished by a soft and dark colored mollic Ah horizon with high base saturation and a well developed Bm horizon under an ustic moisture regime. Haplustolls develops under forest but not under grassland. These soils are generally fertile and have high productivity for few years but later yield of crop decreases as organic matter decreases.  Cryoborolls: These differ from Haplustolls mainly in their development on base rich parent materials under thick grassland of the high mountain in high Himalayan regions. They are found in cooler climate and an udic moisture regime. Alfisols: Alfisols are those soils with significant pedogenetic development, with obvious trans- located clay in the subsoil and a high base saturation percentage. Alfisols are characterized by a subsurface diagnostic horizon in which silicate clay has accumulated by illuviation (Brady & Well, The Nature and Properties of Soils, 13th edition, page no 106). Alfisols are common but do 50 not make up a large percentage of the soils. They represent the most mature landscape positions throughout the sloping lands of the mountain regions and also on older alluvium. The great groups of Alfisols found in Nepal are briefly described below:  Rhodustalf: They are the strong red soils common on ancient terraces, are among the oldest soils found in Western Nepal. They are also known to resource managers because of their tendency to crust on the surface after tillage. These soils have problems with phosphorous fixation and are occasionally subject to severe gullying. The extensive gullying found in Jajarkot on Bheri River in Mid Western Development Region shows the extent to which gullying and land degradation can proceed. Strong local relief, low infiltration rates, slow permeability of subsoil due to clay accumulation and occurrence of high intensity rainfall are dominant characteristics that results in the gullying of these soils.  Haplustalfs and Hapludalfs: The soils that do not meet the color criteria for Rhodic, soils are classified as Haplustalfs and Hapludalfs. Hapludalfs are found in the area just north of Godavari on the southern edge of ancient lake basin that once covered Kathmandu Valley. Ultisols: Only one Ultisol of any significance occurs in Nepal- the Rhodudult. Its properties are identical to those of the Rhodudalf, except that it has a low pH and a low base saturation. These soils are restricted to the old Tars in Central and Eastern Nepal, and they represent the oldest most weathered soils found in Nepal. The Jhikhu Khola just east of Kathmandu, is set between major terrace systems of Rhodudults. These soils are important to distinguish because soil acidification rapidly occurs through the use of chemical fertilizers. There is also considerable evidence that phosphorous management will be a serious problem as cropping intensity increases. Ultisols can be found in diverse climate from humid temperate to tropical climate. This soil is more weathered and acidic more than Alfisols but less than Spondosols. Aridisols:Aridisols occupy a larger area globally than any other soil order (more than 12%) except Entisols. Water deficiency is the major characteristic of these soils. The soil moisture level is sufficiently high to support plant growth for no longer than 90 consecutive days. The natural vegetation consists mainly of scattered desert shrubs and short bunchgrasses. Soil properties, especially in the surface horizons, may differ substantially between interspersed bare and vegetated areas (Brady & Well, 13th edition, 3.10 1st paragraphs). These are the soils that are dry for more than nine months of the year. They exhibit very little in the way of weathering and usually have free calcium carbonate and other salts at or near the surface. There is high accumulation of sodium salts. Aridisols are restricted to the rain shadow areas of the main Himalayan massive, where annual precipitation is less than 300 mm. The areas north to Jomsom in the Mustang district are dominated by Aridisols. With irrigation, in special microclimatic pockets, they can be productive: although the vast majority of Aridisols are covered with extensive grazing pastures at this time. Indigenous classification of soil and agricultural land (Nepal ‘own classification) There is a systematic criterion for distinguishing soils according to landform position, based on slope, elevation and drainage. Topsoil colour, texture and terrace type are the most dominant 51 criteria for local land classification and soil fertility management. Farmers also use broad climatic regimes to differentiate climatic conditions. These are based on elevation and aspect, which relate to temperature and which is in turn one of the most important factors influencing the choice of crops to be used in the rotation sequence, crop production and length of the growing.  Table: Broad classes of Nepal soil with their native vegetation- Broad soil classes Climatic regimes Altitude (metres) Mean annual air temp. (°C) Dominant forests Awal <1 200 20–25 Shorea robusta, Pinus roxburghii Kchard 1 200–1 600 15–20 Pinus roxburghii, mixed broad leaf forest Lekh 1 600–2 200 1–10 Oak (Quercus) mixed forest Soil colour Soil colour can be used as a key distinguishing criterion by farmers. Some of the colour differences relate to the age of the soil, the origin or parent material, and the carbon content. Farmers use major topsoil colours to differentiate soils. The colour categories noted by the farmers are a partial indication of organic matter content in the soil. At higher carbon content the soil colours are usually darker, the moisture content and cation-holding capacity are higher, and the structural stability of soil aggregates is greater. In addition, the very old soils in Nepal are deeply weathered and contain significant portions of Fe and Al. the former gives rise to the red soils which have a significant portion of kaolinite and distinct physical properties. Because of the long leaching processes, the red soils are generally low in phosphorous. The various types of soil colors found all over Nepal is given in table below. Local colour classification Munsell Soil Colour Chart Kalo (black) 10 YR 3/1–4/1 –dark greyish brown-very dark greyish brown Rato (red) 2.5 YR 4/6–5/6 – red Haluka rato mato (light red) 5 YR 5/6–6/6-yellowish red-reddish yellow Khairo mato (brown) 7.5 YR 4/2–5/2- brown-dark brown Phusro (grey) 10 YR 5/1–5/2- grey –greyish brown Kharani mato (light grey) 7.5 YR 7/10 YR 7/7- light grey 52 it is a map i.e. a geographical representation showing diversity of soil types and/or soil properties (soil pH, textures, organic matter, depths of horizons etc.) in the area of interest.[1] It is typically the end result of a soil survey inventory, i.e. soil survey. Soil maps are most commonly used for land evaluation, spatial planning, agricultural extension, environmental protection and similar projects.[2] Traditional soil maps typically show only general distribution of soils, accompanied by the soil survey report. Many new soil maps are derived using digital soil mapping techniques. Such maps are typically richer in context and show higher spatial detail than traditional soil maps. Soil maps produced using (geo)statistical techniques also include an estimate of the model uncertainty.  An example of a traditional soil map showing soil mapping units, described soil profiles and legend. In the digital era, soil maps come in various digital vector and raster formats and are used for various applications in geosciences and environmental sciences. In this context, soil maps are only visualizations of the soil resource inventories commonly stored in a Soil Information System (SIS), of which the major part is a Soil Geographical Database. A Soil Information System is basically a systematic collection of complete (values of the target soil variables available for the whole area of interest) and consistent gridded or vector soil property and/or class maps with an attached report, user manual and/or metadata. A SIS is in the most cases, a combination of polygon and point maps linked with attribute tables for profile observations, soil mapping units and soil classes. Different elements of an SIS can be manipulated and then visualized against the spatial reference (grids or polygons). For example, soil profiles can be used to make spatial prediction of different chemical and physical soil properties. In the case of pedometric mapping, both predictions and simulations (2D or 3D — geographic location plus soil depth) of values are visualized and used for GIS modeling. Topic: Land Capability Classification: Definition. Land capability classification is a system of grouping soils primarily on the basis of their capability to produce common cultivated crops and pasture plants without deteriorating over a long period of time. Classes. Land capability classification is subdivided into capability class and capability subclass nationally. Some states also use a capability unit. Categories: 55 Capability Class: Definition. Capability class is the broadest category in the land capability classification system. Class codes I (1), II (2), III (3), IV (4), V (5), VI (6), VII (7), and VIII (8) are used to represent both irrigated and non-irrigated land capability classes. Classes and definitions: Class I (1) soils have slight limitations that restrict their use. Class II (2) soils have moderate limitations that reduce the choice of plants or require moderate conservation practices. Class III (3) soils have severe limitations that reduce the choice of plants or require special conservation practices, or both. Class IV (4) soils have very severe limitations that restrict the choice of plants or require very careful management, or both. Class V (5) soils have little or no hazard of erosion but have other limitations, impractical to remove, that limit their use mainly to pasture, range, forestland, or wildlife food and cover. Class VI (6) soils have severe limitations that make them generally unsuited to cultivation and that limit their use mainly to pasture, range, forestland, or wildlife food and cover. Class VII (7) soils have very severe limitations that make them unsuited to cultivation and that restrict their use mainly to grazing, forestland, or wildlife. Class VIII (8) soils and miscellaneous areas have limitations that preclude their use for commercial plant production and limit their use to recreation, wildlife, or water supply or for esthetic purposes. Capability Subclass: Capability subclass is the second category in the land capability classification system. Class codes e, w, s, and c are used for land capability subclasses. Subclass e is made up of soils for which the susceptibility to erosion is the dominant problem or hazard affecting their use. Erosion susceptibility and past erosion damage are the major soil factors that affect soils in this subclass. Subclass w is made up of soils for which excess water is the dominant hazard or limitation affecting their use. Poor soil drainage, wetness, a high water table, and overflow are the factors that affect soils in this subclass. Subclass s is made up of soils that have soil limitations within the rooting zone, such as shallowness of the rooting zone, stones, low moisture-holding capacity, low fertility that is difficult to correct, and salinity or sodium content. Subclass c is made up of soils for which the climate (the temperature or lack of moisture) is the major hazard or limitation affecting their use. ……………………………………………………………………………………………………… Some terms pedon. [pĕd′ən] The smallest unit or volume of soil that contains all the soil horizons of a particular soil type. It usually has a surface area of approximately 1 sq m (10.76 sq ft) and extends from the ground surface down to bedrock. 56 The epipedon (Gr. epi, over, upon, and pedon, soil) is a horizon that forms at or near the surface and in which most of the rock structure has been destroyed. It is darkened by organic matter or shows evidence of eluviation, or both. In soil science, eluviation is the transport of soil material from upper layers of soil to lower levels by downward precipitation of water across soil horizons, and accumulation of this material (illuvial deposit) in lower levels is called illuviation A backwater is a part of a river in which there is little or no current. It can refer to a branch of a main river, which lies alongside it and then rejoins it, or to a body of water in a main river, backed up by the tide or by an obstruction such as a dam.[1] Manmade restrictions to natural stream flow or temporary natural obstructions such as ice jams, vegetation blockage, or flooding of a lower stream can create backwater.[2] Model questions from unit 6,7,8,9 1. What is soil classification? Discuss its principles and purposes.5 2. What is soil taxonomy? Write down the basic characteristics of USDA Classification Classes.10 3. What is USDA taxonomy? Explain the major soil orders found in Nepal.10 4. Why we need soil map? Write characteristics of Land Capability Classification Classes 5. What soil survey report? Why is it important?5 6. Differentiate between manure and fertilizer. Discusses the role of bio fertilizer in soil quality improvement.5 7. What is carbon sequestration? Discuss the role of forest on carbon sequestration.5 57