Soil Science Notes SSAC 111 PDF

Notes SSAC 111 \ Soil : it can be defined as natural dynamic body develop as a result of different pedogenic process which takes place during and after weathering ofrocks and in which all forms of life are able to grow (macro and microorganism)...

Notes SSAC 111 \ Soil : it can be defined as natural dynamic body develop as a result of different pedogenic process which takes place during and after weathering ofrocks and in which all forms of life are able to grow (macro and microorganism) OR Jenny (1941)- soil is a naturally occurring body that has been envolved owing to combined influence of climate and organism, acting on paent material, as conditioned by relief over period of time. Jofee and Marbut- soil as natural body developed by natural forces acting on natural material. Buckman and Brady- soil is a dynamic natural body on the surface of earth in which plants grow, composed of mineral and organic material and living form. Hilgard (1892)- soil is more or less a loose and friable material in which plants, by means of their roots, finds a foothold for nourishment as well as for other conditions of growth. V.V. Dokuchaiev (1900)- soil is natural body composed of mineral and organic constituents, having a definite genesis and a distinct nature of its own. V.V. Dokuchaiev- father of soil science and founder of modern pedology J. W. Leather- Father of Indian Soil Science Different Approaches 1) Pedalogical approach (origin of soil Survey, classification). 2) Edaphological approach (utility of soil) 1. Pedalogical approach: In this approach soil has been consider as natural body. In pedological approach origin of soil (genesis), survey, classification of soil ,examination of soil in the field etc. 2. Edaphological approach: In this approach soil has been consider as medium for plant growth based on its fertility and productivity What is soil science and branches of soil science? Soil Science : The science dealing with soil as a natural resource on the surface of the earth, including Pedology (soil genesis, classification and mapping) and the physical, chemical and biological and fertility properties of soil and these properties in relation to their management for crop production. 2. Soil fertility: Nutrient supplying properties of soil 3. Soil chemistry: Chemical constituents, chemical properties and thechemical reactions 4. Soil physics: Involves the study of physical properties 5. Soil microbiology: deals with microorganisms, its population, classification, its role in transformations 6. Soil conservation: Dealing with protection of soil against physicalloss by erosion or against chemical deterioration i.e. excessive loss of nutrients either natural or artificial means. 7. Pedology: Dealing with the genesis, survey and classification Component of soil: Mineral matter- The size and composition of mineral matter in soils are variable tonature of parent rock. Dominant minerals are quartz and feldsphars. Rock fragments are broken by disintegration (physically throughweathering and soil is formed. Material are usually coarse and mineral are extremely variable in size smaller rock fragments are colloidal clay particles cannot be seen without help of electron microscope. In general, primary minerals viz, quartz, biotite, muscovite etc,dominated the coarser fractions of soil and secondary minerals viz. silicate clays and hydrous oxide clays Fe and Al are present in veryfiner fraction, clays in soil Organic matter Soil organic matter exists as partly decayed and partically synthesised plant and animal residues. Organic residues are broken down as a result of microbial activity in soil due to constant change it must be replenished to maintain soil productivity. Organic matter is a store house of nutrients in soil. Organic matter improves water holding capacity, aeration, status of soil, desirable surface soil structure, promotes a greater proportion oflarge pore sizes. Organic matter act as chelate. Chelate- any organic compound that can bound to a metal by more than one bond and form a ring or cyclic structure by that bonding which makes nutrient available. Organic matter is a major source of N, 50-60% P and 80% S. It also supplies different stress element like boron and molybdenum. Soil water Significant role in plant growth relationship water vis held within the soil pores with the varying degrees of forces depending on amount of water present. with the increasing amount of water in soil the forces ofretension of water by the soil will be low and vice-versa.so movement of retension of water is the soil in primarily influenced by the characteristics of soil, viz texture, structure, nature of inorganic and organic colloids, types and amount of exchangeable cations ,size and total amount of pore spaces. Soil water also presents along with dissolved salts and makes up the soil solution (water + dissolved salts )act as important medium for supplying different essential nutrients to growing plants through exchange phenomenons between soil solid surfaces snd soil solution. Soil air Under field conditions pore space is occupied by air and water. Themore the water, the less the air and vice-versa. During rainy season water replace air from soil pore spaces but as soon as water disappears by downward movement, surface evaporation and transpiration etc, air gradually replaces the water as it is lost from the pore space. Soil air contains various gases like CO2, small amount of O2 and N etc.  Soil air influence the growth of the plants as well as the activity of different beneficial micro-organism present in soil.  Soil forming factors The variations are brought during soil profile formation bydifferent environmental factors are called as soil forming factors The evolution of true soil from regolith takes place by the combined actionof soil forming factors and processes. 1. The first step is accomplished by weathering (disintegration & decomposition) 2. The second step is associated with the action of Soil FormingFactors Dokuchaiev (1889) established that the soils develop as a result of the actionof soil forming factors S = f (P, Cl, O) Further, Jenny (1941) formulated the following equation S = f (Cl, O, R, P, T, …) Where, S- Any property of soilf- Function Cl –climate O – Organisms and vegetation (biosphere) R – Relief or topography P – Parent material T -Time JOFFE (1949) grouped into two –  Passive i) Parent material, ii) Relief, iii) Time  Active iv) Climate, v) Vegetation & organism Active Soil forming factors 1. Climate – a. Temperature b. Precipitation Soil forming under High rainfall and low temperature (Acidic soils)  High rainfall favors max leaching losses which is responsible forwashing of salts in downward direction ( max leaching losses)  Low temperature restricts upward movement of salts through evaporation (min. Upward movement of salts)  Under such conditions irrespective of parent material ( it maybealkaline , acidic or neutral) Soil forming under High temperature and low rainfall (Basic soils)  High temperature favors max. Upward movement of salt through evaporation (accumulation of salts in surface horizon)  Due to low rainfall downward movement of salts is restricted thus, under such conditions irrespective of parent material basic or alkaline soils are formed. Climatic conditions Ectodynomorphic soils When climatic conditions playing role in soil formation and effect of parent material has been subdivided by climatic conditions and soils are formed are called as ectodynamorphic soils e.g. basalt – high temperature convert into lateritic soil High rainfall laterization basalt lateritic lateritic soil Endodynamomorphic soils When parent material is playing dominant role and effect of climatic conditions has been marked and soil is formed is called asendodynamomorphic soils e.g. organic soils – peat soil, muck , mor soil 2. Organisms Human beings, vegetations, microorganisms. They bring briefvariation in soil profile. They do following actions – 1. Accumulation of organic matter 2. Profile manuring  3. Nutrient recycling 4. Structural stability Organisms include human beings, vegetation, microorganisms all these bring variation in soil profile based on 4 aspects as follow 1. Accumulation of organic matter , forestland but forest land contain organic horizon (o) 2. Profile manuring – it is churning of soil constituents from lower region or vice- versa 3. Nutrient recycling – well decomposed organic matter will serve as a good source of essential nutrients. availability of nutrients to plant is based on% organic matter present in the soil 4. Structure stability –it is based on % water stable aggregate present inthe soil structure Passive soil forming factors - 1) Parent material – it acts as a passive soil forming factor and serve as a source of mass. depending upon type of parent material , soil , temperature ,water holding capacity , cation exchange capacity (CEC) , nutrients , etc e.g if granite is parent material soil will have coarse texture , low CEC , low water holding capacity , low nutrients 2) Relief or topography (r) - it is nothing but slope of land and depending upon slop of land intensity of water movement varies it will have maximumintensity on slopy land and causes maximum leaching looses. soil erosion ,on flat land intensity of water flow in horizontal direction ids reduced thereby causing comparatively less soil erosion as compared to slopy land , thus , slopy land will have minimum depth of soil Properties of submerged or water logged soil are totally different than flat and sloppy lands  Soil forming Processes Fundamental Soil forming Processes 1. Humification: Humification is the process of transformation of raw organic matter into humus. It is extremely a complex process involving various organisms. First, simple compounds such as sugars and starches are attacked followed by proteins and cellulose and finally very resistant compounds, such as tannins, are decomposed and the dark colored substance, known as humus, is formed. 2. Eluviation (washing out): It is the mobilization and translocation of certain constituent’s viz. Clay, Fe2O3, Al2O3, SiO2, humus, CaCO3, othersalts etc. from one point of soil body to another. It is the process of removal of constituents in suspension or solution by the percolating water from the upper to lower layers. The horizon formed by the process of eluviation is termed as eluvial horizon (A2 or E horizon). 3. Illuviation (washing in): The process of deposition of soil materials (removed from the eluvial horizon) in the lower layer (or horizon of gains having the property of stabilizing translocated clay materials) is termed as Illuviation. The horizons formed by this process are termed as illuvial horizons (B-horizons, especially Bt). 4. Horizonation: It is the process of differentiation of soil in differenthorizons along the depth of the soil body.  Specific Soil Forming Processes The basic pedologic processes provide a framework for later operationof more specific processes a) Zonal soil forming process: the soil forming process that are occurring under prevailing condition of climate and biosphere (active soil forming factor). 1. Calcification: It is the process of precipitation and accumulation of calcium carbonate (CaCO3) takes place which leads to development of a calcic horizon and ultimately formation of calcareous soil is called calcification.The process occur in arid and semiarid climates. 2. Decalcification: It is the reverse of calcification that is the process of removal of CaCO3 or calcium ions from the soil by leaching. The process occur in humid conditions. 3. Laterization (Desilication): It is a process in which removal of silica and accumulation of Al & Fe oxides (sequioxides) takes place which leads to development of a are called laterite or latosols (Oxisols). 4. Podzolization (silication): It is a process in which removal of Al & Fe oxides (sequioxides) and accumulation of silica takes place which leads to development of podzolic soil. b) Intrazonal soil forming process: the soil forming process that are influenced by certain local condition such as relief or parent material (passive soil forming factor). 5. Salinization: It is the process of accumulation of salts, such as sulphates and chlorides of calcium, magnesium in soils in the form of a salty (salic) horizon. It is quite common in arid and semi-arid regions. 6. Alkalization- the process of accumulation of sodium ion on exchange complex of the clay, resulting in the accumulation of alkali soil. 7. Solodization or dealkalization: The process refers to the removal of Na+ from the exchange sites. This process involves dispersion of clay. Dispersion occurs when Na+ ions become hydrated. 8. Gleization: The Gleization is a process of soil formation resulting in the development of a glei (or gley horizon) in the lower part of the soilprofile above the parent material due to poor drainage conditions Suchsoils are called hydromorphic soils. 9. Pedoturbation: Another process that may be operative in soils is pedoturbation. It is the process of mixing of the soil. Mixing to a certain extent takes place in all soils. The most common types of pedoturbation are:  Faunal pedoturbation: It is the mixing of soil by animals  Floral pedoturbation : It is the mixing of soil by plants  Argillic pedoturbation: It is the mixing of soil by the churning process caused by swell shrink clays  Weathering of Rocks and Minerals Rocks and minerals are formed under a very high temperature and pressure, exposed to atmospheric conditions of low pressure and low temperature and they become unstable and weather. Rock ->Weathering ->Regolith ->Soil forming factors and processes ->True soil Two processes involved in the formation of soil are: 1. Formation of regolith by breaking down (weathering) of the bed rock. 2. The addition of organic matter through the decomposition of plant and animal tissues, and reorganization of these components by soil forming processes to form soil. Weathering: A process of disintegration and decomposition of rocks and minerals which are brought about by physical agents and chemical processes, leading to the formation of Regolith (unconsolidated residues of the weathering rock on the earth’s surface or above the solid rocks). (OR) The process by which the earth’s crust or lithosphere is broken down by the activities of the atmosphere, with the aid of the hydrosphere and biosphere (OR) The process of transformation of solid rocks into parent material or Regolith Parent material: It is the regolith or at least its upper portion. May be defined as the unconsolidated and more or less chemically weathered mineral materials from which soil are developed Two basic processes of Weathering: 1. Physical (or) mechanical - Disintegration 2. Chemical – Decomposition 3. Biological (Disint + Decomp) Depending up on the agents taking part in weathering processes, it is classified into three types. Different agents of weathering Physical/ Mechanical Chemical (decomposition) Biological (disint + (disintegration) decomp) 1. Nature of rock 1.Hydration 1.Man & animals 2.Change in temperature 2.Hydrolysis 2. higher plants &their roots 3.Action of H2O 3.Solution 3.Micro organisms 4.Carbonation - action of freezing 5.Oxidation - alter. Wet & drying 6.Reduction - action of glaciers 4.Action of wind 5.Atmospheric electric phenomenon Physical weathering: Breaking of rocks and minerals into smaller fragment due to physicalforces without any chemical change also called as disintegration of rocks. OR A mechanical process, causing disintegration of massive rocks into pieces under favorable climatic conditions through various agents. Factors affecting: 1. Nature of rock- Rock is aggregate of one or more than one mineral. Different material have different heat conductance, thus , this temperature differential causes variation in temperature between surface of rocks and inner side of rocks which develop temperature between outer surface of rocks & inner surface of rock which leads to peeling of thin layer from outersurface of rock, this phenomenon is called exfoliation. 2. Action of Temperature - During day time due to sun’s heat rocks get heated, which leads to expansion of rocks when temperature falls during night, decrease in temperature causes contraction of rock. Thus alternate expansion and contraction due to heating & cooling resp. Leads to development of cracks in rock. 3. Alternate wetting and Drying: Some natural substances increase considerably in volume on wetting and shrink on drying. (e.g.) smectite, montmorillonite  1. During dry summer/ dry weather – these clays shrink considerablyforming deep cracks or wide cracks. 2. On subsequent wetting, it swells. 3. This alternate swelling and shrinking/ wetting or drying of clayenriched rocks make them loose and eventually breaks 4. Water - water has great capacity of transporting weathered material from one place to another place , it has also cutting \ grinding action which is based on quality of suspended material carried by running water and intensity of flow. 5. Freezing action of water - In cool regin water enter into cracks developed due to disintegration of rocks and get freezed which leads to increase in volume of water at least 1/10 times which exert tremendous pressure and widening of cracks takes place. 6. Glacier- In cool mountainous region when there is snow fall it gets accumulated and leads to formation of ice blocks. Such ice blocks moving under the influence of gravity called as glacier. Which has great destructive action on rocks in its path. 7. Wind - Especially in desert region wind which is blowing at a very high speed and carrying weathered material it, acts as a agent of physical weathering. Sometime due to sand storm in desert region a huge quality of sand particle carried out by wind at distant place and redeposited which maycause fertile land into infertile due to sand cover. 8. Electrical Phenomenon - helps in widening of cracks developed due to disintegration of rocks. Chemical Weathering In which rock is decompose due to different chemical reactions. Speed of chemical reaction increases due to dissolve CO2 andincrease in temperature. It is the most important process for soilformation. Chemical weathering takes place mainly at the surface of rocks and minerals with disappearance of certain minerals and the formation of secondary products (new materials). This is called chemical transformation. Factors affecting: 1. Solution : Rock is composed of different material. Some material is easysoluble in water ,this material is easily removed due to it’s solubility and rocks get decomposed. (e.g) halites, NaCl H2O + NaCl------ Na+ , Cl- + H2O Ions surrounded by water 2. Hydration: Chemical combination of water molecules with a particularsubstance or mineral leading to a change in structure. a) 2Fe2O3 + 3HOH ----- 2Fe2O3.3H2O (Hematite) (Red) (Limonite) (Yellow) b) Al2O3 + 3HOH ------ Al2O3.3H2O (Bauxite) (Hyd. aluminium Oxide) c) CaSO4 + 2H2O ------ CaSO4.2H2O (Anhydrite) (Gypsum) 3. Hydrolysis: Dissociation of water molecules into hydrogen(H+) and hydroxyl (OH-) ions.if H+ ions increases water will have acidic reaction which help in decomposition of rocks due to its acidity.minerals containing Al and Si are more susceptible for hydrolysis. KAlSi3O8+H2O -------- HAlSi3O+KOH (Orthoclase) (Acid silt clay) HAlSi3O8 + 8HOH ------ Al2O3.3H2O + 6H2SiO3 (Recombination) (Hyd. Alum. oxide) (Silicic acid)  In Al Silicates , hydroxides are formed. these can be easily removed through percolation , they may further react with other minerals which may lead to formation of clay. 5. Oxidation: The process of addition and combination of oxygen to minerals. The absorption is usually from O2 dissolved in soil water and that present in atmosphere. The oxidation is more active in the presence ofmoisture and results in hydrated oxides. (e.g) minerals containing Fe and Mg. 4FeO(Ferrous oxide) + O2 -> 2Fe2O3 (Ferric oxide) 4Fe3O4 (Magnetite) + O2 -> 6Fe2O3 (Hematite) 2Fe2O3 (Hematite) + 3H2O -> 2Fe2O3.3H2O (Limonite) 6. Reduction: The process of removal of oxygen and is the reverse of oxidation and is equally important in changing soil colour to grey, blue or green as ferric iron is converted to ferrous iron compounds. Under theconditions of excess water or water logged condition (less or no oxygen), reduction takes place. 2Fe2O3 (Hematite) - O2 -> 4FeO (Ferrous oxide) - reduced form In conclusion, during chemical weathering igneous and metamorphic rocks can be regarded as involving destruction of primary minerals and the production of secondary minerals. 6.Carbonation: The process of formation of carbonic acid due to dissolvation of CO2 into water is called carbonation. The material which is not easily soluble in water can be easily dissolved due to formation of carbonic acid specially rocks containing carbohydrate. CO2 + H2O--------- H2CO3 Carbonic acid CaCO3 + H2CO3 -------- Ca(HCO3)2 Not easily soluble in H2O Calcium bicarbonate (Easily soluble in water) Biological Weathering  The weathering in which disintegration anddecomposition of rocks take place due to biological agent (macro and microorganism + plants) 2. Man (Human being) –Cutting of rock for building construction dams, railway tracks, etc. Bring out disintegration of rocks at greater intensity. 3. Rats, Rabbits, termites, ants, earth worms provide passage for entry of water. 4.Higher plants –Roots of higher plants enter through cracks and exerttremendous pressure which leads to widening of cracks and crevice (disintegration).  Deep rooted plants provide passage for water entry due to growing of their roots deeper and deeper into soil.  Water loving plants like mosses, lichens, grass, ferns continuously keep rocks moist which bring further decomposition of rocks. 5. Microorganism –Microorganism bring decomposition of organic matter during decomposition strong acids are produced. These acids are mainly responsible for further decomposition.