SOIL AIR AND TEMPERATURE
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This document discusses soil air and temperature, detailing the importance of soil aeration, gaseous exchanges, and soil temperature characteristics. Key topics include the composition of soil air, processes affecting soil aeration, and the thermal properties of soils. The document emphasizes how soil moisture, texture, and biological activity influence both soil air and temperature, which are crucial for plant growth.
SOIL AIR AND TEMPERATURE
- 1. Submitted To Dr. K. Tedia Professor Deptt. Of Soil Science Submitted By Rakesh Giri Goswami Ph.D. Previous DEPARTMENT OF SOIL SCIENCE AND AGRICULTURAL CHEMISTRY INDIRA GANDHI KRISHI VISHWAVIDYALAYA, RAIPUR (C.G)
- 2. Soil Air and Temperature 1. Soil Air Introduction Soil aeration process Gaseous Exchanges Characterizing Soil Air Factors Affecting Soil Air 2. Soil Temperature Thermal Concept Thermal Properties of Soils Mode of transmission of heat
- 3. INTRODUCTION: Soil air and water share the pore space of soils So texture, structure, porosity, etc affect aeration The air is a mixture of few gases, mainly N , oxygen , CO2 , water vapour and inert gases. It envelopes the earth and extend up to a considerable height from the surface of the earth called atmosphere. Air (O2) is needed in the soil for root respiration as well as the activity of microorganisms in soil. Therefore a major management objective is to maintain a high level of air in the soil through a ventilation process. An ideal soil consists of about 25% air, 25% water, 45% minerals, 5% organic matter and less than 0.5% soil biota, with soil structure housing all these components.
- 4. SOIL AERATION PROCESS • Soil Aeration is a process by which air in the soil is replaced by air from the atmosphere. Soil aeration takes place due to the composition of soil air with that of atmospheric air. • The composition of soil air at any time is the results of two sets of rate processes such as – (a) The rate of production of CO2 consumption of Oxygen. (b) The rate with which carbon dioxide is escaped from the soil and be replaced Oxygen. • The two most important gases in soil aeration are oxygen and carbon dioxide
- 5. SOIL AERATION IN THE FIELD • Poor soil aeration – O2 in the root zone is insufficient to support optimum growth of most plants and aerobic microorganisms (>80% pores filled with water) • Waterlogged -When all soil pores (~100%) are filled with water, soil is said to be water saturated • Anaerobic soil environment is when the oxygen supply is virtually exhausted – Plants that are adapted to life in water saturated soils are called hydrophytes.
- 6. GASEOUS EXCHANGE Soil aeration process is achieved by gaseous exchange • The more rapidly roots and microbes use up oxygen and release carbon dioxide, the greater is the need for exchange of gases between the soil and the atmosphere. • Exchange of gases between soil and atmosphere is achieved through two mechanisms: a) Mass flow – gas exchange is due to fluctuations in water content of soil that force air in and out. b) Diffusion – gas exchange is by partial pressure.
- 7. Cont… Mass flow : in case of mass flow the moving forces consist of a total gas pressure and it causes the bulk movement of gas mixture such as air from zone of higher P to a zone of lower P. Diffusion: due to differences of partial pressure of individual gases although total pressure may be same in both. Although diffusion is more important mechanism of soil aeration than mass flow , but in some circumstances mass flow can contribute significantly to soil aeration specially at shallow depth and in soil with large pores. Diffusion process can be describe by the fick’s law.
- 8. Cont.…. This is the second law of fick’s which is arises at non- steady state Occasion .this equation gives the concentration profile for non- steady state diffusion
- 9. • But in case of gaseous diffusion partial pressure P is used instead of C • Where D diffusion coefficient for gas • The rate of gas diffusion in the soil (Ds) is a function of the aeration porosity (fa), for nonlinear relation Buckingham proposed the following relationship. • D0 is coefficient of diffusion through bulk air ,k is the diffusion constant ,Ds rate of gaseous diffusion in soil. for linear relationship k is tortuosity coefficient DS=D0 kfa 2 DS=D0 kfa
- 10. Graham 'Law of Diffusion • Some time used in diffusion of soil air is graham's law of diffusion .The rate of diffusion of two gases are inversely proportional to the square root of their densities . pa pb Rate of diffusion of gases (r) Where indicates the density. Grahams law is used to separate the different component of gaseous mixture such as air with help of the principle of different rate of diffusion. This process of separation of gases is known as Atmolysis.
- 11. Characterizing Soil Air Soil air can be characterized by a) Content of oxygen and other gases in soil b) Air-filled soil porosity c) Oxidation-reduction potential
- 12. a). Content of oxygen and other gases in soil Gas % in atmosphere % in soil air O2 20.95 20.42 N2 78.08 78.08 Ar 0.934 0.934 CO2 0.035 0.56 Other 0.001 0.001 The main differences between soil air and atmospheric air are the concentrations of oxygen and carbon dioxide. Soil air always has lower oxygen levels. But has greater Carbon dioxide levels (8 to 300 times greater because CO2 is given off as a result of microbial and root respiration in the soil).
- 13. b). Air-filled soil porosity • Air field porosity may be defined as the volume fraction or percentage of soil masse occupied by air when water of a saturated soil is drained by normally 100 cm suction . • Recall, ideal soil composition for plant growth = 50:50, air and water. • Air filled porosity of less than 20% has been found to severely limit plant growth. • High soil moisture cause oxygen deficiency by blocking diffusion of O2 to replace that used by respiration in the soil.
- 14. c). Oxidation-reduction potential The oxidation states of chemical elements depend on the soil aeration. If soil is well aerated, oxides of elements dominate- FeOOH, NO3 - In poorly aerated soils, reduced forms of the elements are common. Oxygen plays very important role in oxidation-reduction of the other elements since it accepts electrons from many other elements. Other electron acceptors are N, Fe, Mn, and S
- 15. FACTORS AFFECTING SOIL AIR a) Drainage of water : - Amount of Macrospores Texture, Bulk density, Aggregate structure and stability, and Soil organic matter content. b) Rates of respiration in the soil : - O2 and CO2 depend on microbial activity Manure, crop residue, sewage sludge. c) Soil depth (subsoil vs. topsoil) : Subsoil usually wetter, higher bulk density, often less total and macrospore space, lower OM and slower respiration.
- 16. d) Changes in a Soil Condition: - Caused by: Tillage (short term introduces air; long term destroys macrospores). e) Seasonal Differences :(Moisture and Temperature) – humid temperate regions have wet and cold soils – More favorable temputre Stimulate aeration. f) Vegetation: – Remove water by transpiration (can affect depth to water table) – Affects soil temperature and therefore respiration rates (i.e. shading)
- 17. • Generally speaking, soil temperature affects many physical, chemical, and biological soil properties, and the plants growing in it. – It affects plant and microorganism growth – It affects many soil environmental processes such as soil drying by evaporation (therefore, water content) – It affects water movement and retention in soils – It affects soil formation 2. Soil Temperature
- 18. Thermal Concept Heat : The physical cause due to which the hotness and coldness is felt is termed as heat. • It can be also be transformed in to different from of energy. Solar radiation is the source of soil heat. • Unit in SI. Calories. Temperature : it is the measure of hotness of a body or tem.is a thermal condition of a body which determines whether the body will communicate the heat or receive heat from another body. Soil Temperature :The speed of vibration is directly proportional to temp. The intensity of heat or the ratio of energy absorbed by the soil is termed as soil temperature.
- 19. • Soil has a temperature range between -20 to 60 °C. • The differential form of Fourier's Law of thermal conduction shows that the local heat flux density, is equal to the product of thermal conductivity and the negative local temperature gradient, . The heat flux density is the amount of energy that flows through a unit area per unit time. where (including the SI units) is the local heat flux, J/m2/s is thermal conductivity, J/m/s/oC, where the del operator applied to the temperature • For many simple applications, Fourier's law is used in its one- dimensional form. In the x-direction,
- 20. Thermal Properties of Soils The thermal properties of soil are characterized in term of • Heat Capacity • Thermal Conductivity • Thermal diffusivity Applications – used to predict soil temperatures – used for measurement of soil moisture – used for remote sensing applications
- 21. Heat Capacity : The heat capacity of soil is defined as the ratio of heat supplied to a body to the corresponding rise in its tem. where C is the heat capacity,ΔQ is the quantity of heat ΔT is the increase in its temperature (oC) • Its S.I Units is J∙ gm−1∙ 0C−1 or cal∙ gm−1∙ 0C−1 Specific heat : • The heat capacity per unit mass of a body is called the specific heat (c). • Ability to store Amount of heat required to raise temperature of 1 g of substance by 1 degree C
- 22. • Its Units cal cm-3oC-1 • Soil: 0.2 cal/g Water: 1.0 cal/g • greater the heat capacity of a substance, the more heat it can gain (or lose) per unit rise (or fall) in temperature.
- 23. cont…. If m1,m2 ,m3 and m4 are masses of mineral matter , organic matter, water and air in soil and c1,c2,c3 and c4 are their specific heat then the heat capacity- Cv = m1c1+m2c2+m3c3+m4c4 Where Cv is volumetric heat capacity “it is the amount of energy required to raise the temperature of a unit volume of soil by 1 degree (J m-3 K-1)” The volumetric heat capacity of soil solid is 0.53 cal cm-3 0C-1 or 2.219 J m-3 0C-1
- 24. Thermal conductivity • Thermal conductivity is the ability of the substance to transfer heat from molecule to molecule. For this reason it is sometimes called inolcular conductivity. It varies with porosity, moisture content and organic matter content of soil. It is expressed in Jm-1 s-1 K-1. • a measure of the soil's ability to conduct heat • The conductivity of soil increases with increase in water content till about 50 % of soil saturation. Where Qh is total quantity of heat, T1 - T2 is difference in temperature Kh is constant depending on nature of soil.
- 25. Cont… Affected by: Moisture • thermal conductivity of water is about two to three times greater than that of soil. • In saturated soils, pore spaces filled with water rather than air • Wet soils have higher conductivity than dry. Texture : • Thermal conductivity of air is about one hundred times less than that of soil . • Finer soils have more particle-to-particle contact and smaller pore spaces, therefore increased conductivity. • Conductivity increases as texture becomes increasingly fine. • Texture determines how quickly soil will heat (in spring) or cool (in fall).Sandy soils contain less water (lower porosity) and therefore heat more quickly than clay.
- 26. Thermal Diffusivity • It is the measure of the rate of which changes in temperature occur in the body • The rate of change of temperature with time is directly proportional to the thermal conductivity & inversely proportional to heat capacity. Thus, the ratio of Thermal conductivity to Volumetric heat capacity is Thermal Diffusivity. • It supports feasible use of crop rotations, crop residues, animal manures, off-farm organic waste, mineral grade rock additives and biological system of nutrient mobilization and plant protection.
- 27. • Heat transfer • Everything is made of molecules. • When molecules gain energy they move faster and create more heat. • (The faster the molecules move the hotter they are) Melting Evaporation CondensationFreezing liquidSolid Gas Molecules move very slowly! They are close together. Molecules move faster and are more spread apart. Molecules move very fast! They are very spread apart.
- 28. Mode of transmission of heat • Three distinct process by which heat transferred • Radiation – electromagnetic waves • Conduction – touching • Convection- through a fluid (liquid or gas) • All 3 work together to heat the troposphere but Convection causes most of the heating. • Heat transfer from a hotter object to a cooler object until both objects are the same temperature.
- 29. 1.Conduction • It is a process in which heat is transmitted from the hotter to the colder part of the body in contact with each other by internal molecular motion without any transference of material particle. • E.g. heat transmitted through solid • Air near earth’s surface is warmed
- 30. 2.Convection • It is the process in which heat is transmitted from one point to another by actual movement of the heated material particles from place of high temp. to another place of low temperature. • Liquid and gases heated by convection process
- 31. 3.Radiation • It is the process in which heat can transmitted from a hotter body to a colder body without intervention of any material medium. • The radiant heat travel in straight line • By Radiation energy is emitted in the form of electromagnetic wave from all body above 0ok. • The sun occurs as short wave radiation ranging 0.3 to 5.0 micron but 0.3 to 2.2 micron are most efficient for heat radiation. • Long wave radiation wave length range from 6.5 to 100 micron but 2.2 and 6.8 micron are inefficient • Cal/cm2 min