Chemistry for the Environment: Soil 2 PDF

UNIT IV. CHEMISTRY FOR THE ENVIRONMENT- SOIL Chemistry CONTENTS: Introduction. Soil Components Reaction Process in Soil Soil Acidity Soil salinity  Introducti on What is Soil?  Introducti on What is Soil? -soil is a com...

UNIT IV. CHEMISTRY FOR THE ENVIRONMENT- SOIL Chemistry CONTENTS: Introduction. Soil Components Reaction Process in Soil Soil Acidity Soil salinity  Introducti on What is Soil?  Introducti on What is Soil? -soil is a complex mixture of inorganic and organic solids, air, water, solutes, microoganism, plants and other types of biota that influence each other.  Introducti on What is Soil? -soil is a complex mixture of inorganic and organic solids, air, water, solutes, microoganism, plants and other types of biota that influence each other. -soil is formed through a complex process that involves the weathering of rocks and other materials, and the accumulation of organic matter, living organism, water, and air.  Units in Soil Chemistry  Soil Components  Soil Components A. Essential Elements.  Soil Components A. Essential Elements. B. Inorganic Components.  Soil Components A. Essential Elements. B. Inorganic Components. C. Organic Components.  Soil Components -The elements in rock minerals at Earth’s surface are the starting materials for soils and contain the essential elements from which soil and life evolved. Figure 1. Percent mass composition of elements is soil. (Source: DG Strawn, 2019)  A. Essesntial Elements -Referred to as essential nutrients, are the elements from which plants, animals, and humans evolved. Essential nutrients, in range of limit, are required for an organism to complete its life cycle. -Most essential elements are present as ions in the soil solution, and flow into the plant as it absorbs water.  A. Essesntial Elements Figure 2. Periodic table of elements, not including lanthanides and actinide, showing nutrients and common contaminants. (Source: DG Strawn, 2019)  A. Essesntial Elements Table 2. Ions of major interest in soil chemistry and their common species. B. Inorganic Components B. Inorganic Components C. Organic Components  Reaction Processes in Soil A. Sorption/ Desorption B. Precipitatio/Disollution C. Immobilization/Mineralization D. Complexation/Dissociation E. Gas Dissolution/Voltalization F. Oxidatio/Reduction  Reaction Processes in Soil The reactivity of soils greatly influences the composition of the soil solution. Main sources of ions to soil solution are mineral weathering, organic matter decay, rain, irrigation waters, fertilization, and release of ions adsorbed by clays and organic matter in Figure 3. Chemical reactions in soil soils. (Source: DG Strawn et al. 2019) A. Sorption/ Desorption -the association and release of a chemical from a particle (minerals, SOM, or a biological cell surface). A. Sorption/ Desorption -the association and release of a chemical from a particle (minerals, SOM, or a biological cell surface). B. Precipitation/Dissolution -the change in a chemical from solution to the solid state, where a new solid is formed from solution constituents. A. Sorption/ Desorption -the association and release of a chemical from a particle (minerals, SOM, or a biological cell surface). B. Precipitation/Dissolution -the change in a chemical from solution to the solid state, where a new solid is formed from solution constituents. C. Immobilization/Mineralization -are generally biologically mediated.  Immobilization - the uptake of chemical into the cellular structure of an organism. Mineralization - implies degradation, release, or conversion of a chemical to a form that is no longer a biomolecule.  Immobilization - the uptake of chemical into the cellular structure of an organism. Mineralization - implies degradation, release, or conversion of a chemical to a form that is no longer a biomolecule. D. Complexation/Dissociation - the interactions of two or more chemicals or aqueous ions. Protonation and deprotonation (gain and loss of H+ ions) are specific types of complexation and dissociation.  Immobilization - the uptake of chemical into the cellular structure of an organism. Mineralization - implies degradation, release, or conversion of a chemical to a form that is no longer a biomolecule. D. Complexation/Dissociation - the interactions of two or more chemicals or aqueous ions. Protonation and deprotonation (gain and loss of H+ ions) are specific types of complexation and dissociation. E. Gas Dissolution/Volatilization -the reactions occurring between the soil atmosphere and the soil solution – specifically, transfer of gaseous chemicals into the aqueous phase, and the reverse. F. Oxidatio/Reduction -the gain and loss of electrons of an element cause in change of oxidation state. F. Oxidatio/Reduction -the gain and loss of electrons of an element cause in change of oxidation state. 1. Electron donors in nature. -In soils, carbon compounds in roots, microbes, dead plant matter, and SOM are the major electron donors. The half‐ reaction for the oxidation of theoretical soil organic matter is F. Oxidatio/Reduction -the gain and loss of electrons of an element cause in change of oxidation state. 1. Electron donors in nature. -In soils, carbon compounds in roots, microbes, dead plant matter, and SOM are the major electron donors. The half‐ reaction for the oxidation of theoretical soil organic matter is F. Oxidatio/Reduction -the gain and loss of electrons of an element cause in change of oxidation state. 1. Electron donors in nature. -In soils, carbon compounds in roots, microbes, dead plant matter, and SOM are the major electron donors. The half‐ reaction for the oxidation of theoretical soil organic matter is  2. Electron acceptor in nature -In soils, O2 diffuses through pores to plant roots and soil microbes, where it can be utilized as a terminal electron acceptor (TEA). Soils and waters that have available O2 are called oxic while soils that have no available O2 are called anoxic. -The general order of preference for TEAs based on energy produced is: Figure 4. Correlation of soil redox potential with change in TEA, water, O2, metabolism and redox status category (Source: DG Strawn et al. 2019)  The most common secondary electron acceptors in soils include iron,manganese oxides, sulfate, and oxidized forms of nitrogen.  Soil Acidity  Soil Acidity A. Soil acidification.  Soil Acidity A. Soil acidification. B. Source of soil acidity.  Soil Acidity A. Soil acidification. B. Source of soil acidity. C. Forms of soil acidity.  Soil Acidity A. Soil acidification. B. Source of soil acidity. C. Forms of soil acidity. D. Measurements of soil accidity.  Soil Acidity A. Soil acidification. B. Source of soil acidity. C. Forms of soil acidity. D. Measurements of soil accidity. E. Managing Acidic Soils (Liming Soils).  Soil Acidity Approximately 30% of earth’s soils are acidic. Forest soils and wetland soils are often naturally acidic. Figure 5. The soil- pH scale (Source: DG Strawn et al. 2019)  A. Soil acidification Soil acidification can be detrimental for agriculture because it decreases the availability of anionic nutrients, causes cationic nutrients to be leached from the soil profile. Occurs when acids are added to soils. A continuum of reactions and include natural fluxes and human caused fluxes.  B. Source of soil acidity Soil acidity sources are acid rain, agronomic practices, and mine spoils and sulfate soils. Acid vapors, primarily sulfuric and nitric form in the atmosphere as a result of the emission of sulfur dioxide and nitric oxides. In most cases, the amount of soil acidification occurs naturally or results from agronomic practices higher than acid rain.  C. Forms of soil acidity There are two types of soil acidity: active and exchangeable: Active acidity: The hydrogen ions in the soil solution, which can be measured with a pH meter. Exchangeable acidity: Associated with aluminum (Al) and hydrogen (H) on exchange sites.  D. Measurements of soil acidity 1.The pH probe or calorimetric analysis are used to measure the H+ activity of aqueous solutions. 2.The concentration of base cations in soil solutions.The concentration of base cations in soil solutions is measured by base saturation, which is the percentage of the total cation exchange capacity (CEC) made up of base cations: Base saturation Formula: %BS = [(Ca2+ + Mg2+ + K+)/CEC] × 100  D. Measurements of soil 2.1 Exchangeableacidity base cations -cations that can be exchanged in a soil by a cation from an added salt solution. The four main exchangeable base cations are calcium , magnesium, potassium, and sodium. 2.2 Total exchangeable acidity -The amount of exchangeable H= and Al3+, measured in mmol(+)kg^-1 soil.  E. Managing acidic soil(Liming soil) Liming is an effective and economical way to manage acidic soil. Liming can improve soil health, increase crop and pasture productivity, and reduce the cost of production. A major challenge for managing acidic soils is to estimate the quantity of lime required to raise the soil pH to a certain level.  Soil Salinity  Soil Salinity A. Source of Soluble Salts  Soil Salinity A. Source of Soluble Salts B. Characterization of salinity in soil and water:  Soil Salinity A. Source of Soluble Salts B. Characterization of salinity in soil and water: 1. Sodium adsorption ratio (SAR) 2. Exchangeable sodium percentage (ESP) 3. Total dissolved solids 4. Electrical conductivity  Soil Salinity -Soil salinity includes soluble salts in soil water and salt solids in the soil. Soil salinity and sodicity can have a major effect on the structure of soils. Soil structure, is critical in affecting permeability and infiltration. A. Source of soil salinity Major source of soluble salts in soil are weathering of primary minerals and native rocks, residual fossil salts, saline ground water, seawater intrusion, brines from natural salts deposite, etc. The primary source of soluble salts is fossil salts. B. Characterization of salinity in soil and water Parameters determined to characterize salt-affected soils depend primarily on the concentrations of salts in the soil solution and the amount of exchangeable Na+ on the soil (sodicity). 1. Sodium adsorption ratio (SAR) 2. Exchangeable sodium percentage (ESP) 3. Total dissolved solids 4. Electrical conductivity 1. Sodium adsorption ratio (SAR) 1. Sodium adsorption ratio (SAR) 2. Exchangeable sodium percentage (ESP) 2. Exchangeable sodium percentage (ESP) 3. Total dissolve solids (TDS) Are determined by evaporating an unknown volume of water to dryness and the solid residue remaining are weighed. However, this measurement is variable since in a particular sample various salts exist in varying hydration states, depending on the amount of drying. 3. Total dissolve solids (TDS) Are determined by evaporating an unknown volume of water to dryness and the solid residue remaining are weighed. However, this measurement is variable since in a particular sample various salts exist in varying hydration states, depending on the amount of drying. The TDS can also be estimated by measuring an extremely important salinity index, EC, to determine the effects of salts on plant growth.  4. Electrical conductivity (EC) -EC is directly related to salinity of a solution. -A number of EC values can be expressed according to the method employed: ECe, ECp, ECw, and ECa. -The EC and temperature of the extract are measured using conductance meters/cells and thermometers and EC298 is calculated using below equation: Marion and Babcock (1976) - Developed a relationship between ECw (dS m–1) to total soluble salt concentration (TSSin mmol L–1) and ionic concentration (C in mmol L–1), where C is corrected for ion pairs. If there is no ion complexation, TSS = C. The equations of Marion and Babcock (1976) are: Marion and Babcock (1976) - Developed a relationship between ECw (dS m–1) to total soluble salt concentration (TSSin mmol L–1) and ionic concentration (C in mmol L–1), where C is corrected for ion pairs. If there is no ion complexation, TSS = C. The equations of Marion and Babcock (1976) are: Griffin and Jurinak (1973) - also developed an empirical relationship between ECw and ionic strength (I) at 298 K that corrects for ion pairs and complexes where ECw is in dS m–1 at 298 K. The relationships of soil salinity parameters to EC, SAR, and ESP. THANK YOU!!!  CHEMISTRY FOR THE ENVIRONMENT ; SOIL