Soil Chemistry Overview
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Questions and Answers

What are essential nutrients in soil primarily necessary for?

  • To complete an organism's life cycle (correct)
  • To facilitate rock weathering
  • To enhance soil's water retention abilities
  • To improve soil texture

What does the process of sorption involve in soil chemistry?

  • The binding of ions or molecules to soil particles (correct)
  • The release of gases from the soil
  • The dissolution of soil minerals in water
  • The accumulation of organic matter in the soil

Which of the following components is NOT considered part of soil?

  • Organic solids
  • Synthetic fertilizers (correct)
  • Air
  • Plant matter

Which reaction process in soil refers to the conversion of organic matter into plant-accessible nutrients?

<p>Mineralization (D)</p> Signup and view all the answers

How is the reactivity of soils important in soil chemistry?

<p>It influences the composition of the soil solution (B)</p> Signup and view all the answers

What is the outcome of the precipitation/dissolution process in soil?

<p>Formation or breakdown of soil minerals (B)</p> Signup and view all the answers

Which of the following is NOT a component of soil acidity?

<p>Alkaline minerals content (A)</p> Signup and view all the answers

What role do ions play in soil chemistry?

<p>They flow into plants and influence nutrient uptake (C)</p> Signup and view all the answers

What are the major electron donors found in soils?

<p>Carbon compounds in roots and dead plant matter (C)</p> Signup and view all the answers

What is the characteristic of soils referred to as 'oxic'?

<p>Soils with available O2 (B)</p> Signup and view all the answers

Which of the following is NOT a common secondary electron acceptor in soils?

<p>Oxygen (D)</p> Signup and view all the answers

What effect does soil acidification have on agriculture?

<p>Decreases availability of anionic nutrients (D)</p> Signup and view all the answers

What percentage of the earth’s soils are considered acidic?

<p>30% (D)</p> Signup and view all the answers

What can cause soil acidification?

<p>Addition of acids and natural fluxes (A)</p> Signup and view all the answers

Which of the following describes the term 'anoxic' in relation to soils?

<p>Soils with no available O2 (B)</p> Signup and view all the answers

What is the primary consequence of leaching in acidic soils?

<p>Decreased soil fertility (D)</p> Signup and view all the answers

What is the primary source of soluble salts in soil?

<p>Weathering of primary minerals (A)</p> Signup and view all the answers

Which parameter is used to determine the salinity of salt-affected soils?

<p>Sodium adsorption ratio (SAR) (A)</p> Signup and view all the answers

How is total dissolved solids (TDS) measured?

<p>By evaporating a known volume of water (B)</p> Signup and view all the answers

What does electrical conductivity (EC) indicate in soil solutions?

<p>Salinity levels (B)</p> Signup and view all the answers

What factor makes the measurement of total dissolved solids (TDS) variable?

<p>Varying hydrate states of salts (D)</p> Signup and view all the answers

Which method is used to express different values of electrical conductivity?

<p>Multiple EC types like ECw, ECe, ECp, and ECa (D)</p> Signup and view all the answers

Marion and Babcock (1976) developed equations relating which two variables?

<p>Electrical conductivity and ionic concentration (B)</p> Signup and view all the answers

Which of the following parameters does NOT characterize salt-affected soils?

<p>Nutrient deficiency levels (A)</p> Signup and view all the answers

What is the main role of precipitation/dissolution in soil chemistry?

<p>To change a chemical from solution to the solid state (A)</p> Signup and view all the answers

Which process involves the uptake of chemicals into the cellular structure of an organism?

<p>Immobilization (C)</p> Signup and view all the answers

Which of the following describes gas dissolution/volatilization?

<p>Transfer of gaseous chemicals into the aqueous phase (D)</p> Signup and view all the answers

What does the term complexation/dissociation refer to?

<p>Interactions of two or more chemicals or aqueous ions (B)</p> Signup and view all the answers

What is a characteristic of oxidation/reduction reactions in soil?

<p>Gain and loss of electrons causing a change in oxidation state (D)</p> Signup and view all the answers

Which process is primarily mediated by biological activity?

<p>Immobilization/mineralization (B)</p> Signup and view all the answers

Which of the following describes immobilization in the context of soil?

<p>Chemical uptake into the structure of living organisms (B)</p> Signup and view all the answers

What typically serves as a source of ions to the soil solution?

<p>Mineral weathering and organic matter decay (D)</p> Signup and view all the answers

What is one source of soil acidity?

<p>Acid rain (C)</p> Signup and view all the answers

Which type of soil acidity is primarily associated with hydrogen ions in the soil solution?

<p>Active acidity (C)</p> Signup and view all the answers

How is base saturation calculated?

<p>%BS = [(Ca2+ + Mg2+ + K+)/CEC] × 100 (B)</p> Signup and view all the answers

What is the main limitation when managing acidic soils through liming?

<p>Estimating the quantity of lime needed (C)</p> Signup and view all the answers

Which of the following is a method for measuring the activity of hydrogen ions in soil?

<p>pH probe or calorimetric analysis (D)</p> Signup and view all the answers

Which of these is NOT one of the four main exchangeable base cations?

<p>Iron (B)</p> Signup and view all the answers

What is measured by the Sodium Adsorption Ratio (SAR)?

<p>Proportion of sodium to calcium and magnesium (C)</p> Signup and view all the answers

What impact does soil salinity have on soils?

<p>Affects soil structure (D)</p> Signup and view all the answers

Flashcards

What is soil?

Soil is a complex mixture of inorganic and organic solids, air, water, dissolved substances, microorganisms, plants, and other living organisms that interact with each other.

How is soil formed?

The process of soil formation involves the breakdown of rocks and minerals, the accumulation of organic matter, and the activity of living organisms.

Essential nutrients

Elements essential for plant growth are called essential nutrients. These elements are absorbed by plants from the soil solution.

Inorganic components of soil

Major inorganic components of soil include minerals, which are naturally occurring solid compounds with a defined chemical composition.

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Organic components of soil

Organic components of soil are derived from living organisms and include decomposed plant and animal matter, humic substances, and microbial biomass.

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Sorption/Desorption in soil

Sorption/Desorption involves the attachment and release of substances to and from soil particles.

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Precipitation/Dissolution in soil

Precipitation/Dissolution refers to the formation of solid compounds from dissolved substances and the reverse process.

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Immobilization/Mineralization in soil

Immobilization/Mineralization involves the conversion of organic matter into inorganic forms and the opposite process.

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Sorption/Desorption

The process where chemicals bind to or detach from a solid particle, like minerals, soil organic matter (SOM), or biological cell surfaces.

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Precipitation/Dissolution

A chemical reaction where a substance in solution transforms into a solid, forming a new solid from dissolved components.

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Immobilization/Mineralization

The conversion of a chemical from a usable form for organisms into a less usable form, and vice versa. Involves biological processes.

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Complexation/Dissociation

Interactions between two or more chemicals or aqueous ions, including the gain and loss of H+ ions (protonation/deprotonation).

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Gas Dissolution/Volatilization

The transfer of gaseous chemicals between the soil atmosphere and soil solution, involving movement in and out of the liquid phase.

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Oxidation/Reduction

Chemical reactions involving the gain or loss of electrons by an element, leading to a change in its oxidation state.

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Mineral Weathering

The release of ions from minerals due to weathering, a process that involves the breakdown of rocks and minerals.

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Organic Matter Decay

The process of decomposing organic matter, releasing ions into the soil solution.

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What is oxidation in soil?

The loss of electrons by a chemical species. In soil, organic matter, roots, microbes, and dead plant material are major electron donors.

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What is reduction in soil?

The gain of electrons by a chemical species. In soil, oxygen, iron, manganese oxides, sulfate, and oxidized forms of nitrogen can serve as electron acceptors.

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What is the difference between oxic and anoxic soils?

In soils, it refers to the availability of oxygen. Oxic soils have available oxygen, while anoxic soils do not.

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What is a terminal electron acceptor (TEA) in soils?

A substance that gains electrons in a redox reaction. In soils, oxygen is the primary terminal electron acceptor followed by other elements like iron, manganese, and sulfur.

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What is soil pH?

A measure of the acidity or alkalinity of a soil solution. It is expressed on a scale from 0 to 14, with 7 being neutral. Soils below 7 are considered acidic.

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What is soil acidification?

The process of reducing pH (making it more acidic). It can be caused by natural factors such as the decomposition of organic matter or human activities such as the use of fertilizers.

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What are sources of soil acidity?

The various sources that contribute to acidification, naturally or through human activity.

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What are the forms of soil acidity?

These include active acidity, which is the concentration of hydrogen ions in the soil solution, and reserve or potential acidity, which refers to acidifying compounds like aluminum and iron.

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Active Acidity

The concentration of hydrogen ions (H+) in the soil solution, measured using a pH meter.

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Exchangeable Acidity

The amount of hydrogen (H+) and aluminum (Al3+) ions bound to soil particles, which can be exchanged for other cations.

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Liming Soil

The process of adding lime (calcium carbonate) to acidic soil to neutralize acidity and increase pH.

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Total Dissolved Solids (TDS)

The total amount of dissolved salts in the soil water, measured in parts per million (ppm) or milligrams per liter (mg/L).

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Electrical Conductivity (EC)

A measure of the ability of soil water to conduct electricity, which is directly related to the concentration of dissolved salts.

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Sodium Adsorption Ratio (SAR)

The ratio of sodium (Na+) to calcium (Ca2+) and magnesium (Mg2+) in the soil solution, influencing the movement of water and nutrients.

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Exchangeable Sodium Percentage (ESP)

The percentage of exchangeable cation positions on soil particles occupied by sodium (Na+).

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Soil Salinity

The presence of soluble salts in the soil water and salt solids in the soil, negatively impacting plant growth by reducing water availability.

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Soil permeability

The movement of water through soil, influenced by the size and arrangement of soil particles.

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Soil infiltration

The rate at which water enters the soil, also affected by soil structure.

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Fossil salts

The main source of soluble salts in the soil, coming from the breakdown of rocks and minerals.

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Marion and Babcock equation

An equation relating the electrical conductivity of water (ECw) to the total soluble salt concentration (TSSin mmol L–1) and ionic concentration (C in mmol L–1) in water.

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Study Notes

Soil Chemistry

  • Soil is a complex mixture of inorganic and organic solids, air, water, solutes, microorganisms, plants, and other biota
  • Soil formation involves weathering of rocks and other materials
  • Soil accumulation of organic matter, living organisms, water, and air
  • Soil influences each other

Units in Soil Chemistry

  • Table 1 displays units in soil chemistry measurements (Hectare, Cubic Meter, Square meter per kilogram, Siemens per meter), and various conversions
  • Parameters include land area, volume, specific surface area, conductance/electric conductivity, amount of ion charge, concentration, cation capacity, total exchangeable acidity, sodium adsorption ratio, and total dissolved solids
  • Units and conversion factors are given for each parameter

Soil Components

  • Soil components include essential elements, inorganic components, and organic components

A. Essential Elements

  • Essential elements are nutrients vital for plant, animal, and human life cycles
  • Most essential elements exist as ions in soil solution and absorbed by plants during water uptake
  • Essential elements exist in a range of limit and are required in various forms

B. Inorganic Components

  • Inorganic components are the mineral elements in soil that are non-organic
  • Minerals in soil include primary minerals like Quartz, Feldspars, kaolinite, Muscovite, biotite, orthoclase, microcline, albite, amphiboles, tremolite, pyroxenes, enstatite, diopside, olivine, etc., secondary minerals like clay minerals, montmorillonite, vermiculite, chlorite, allophane, imogolite, goethite, hematite, maghemite, ferrihydrite, bohemite, gibbsite, pyrolusite, birnessite, dolomite, calcite, gypsum, jarosite, etc., with associated chemical formulas.

C. Organic Components

  • Organic components are those based on carbon

Reaction Processes in Soil

  • Soil reaction processes include sorption/desorption, precipitation/dissolution, immobilization/mineralization, complexation/dissociation, gas dissolution/volatilization, and oxidation/reduction

A. Sorption/Desorption

  • The absorption and release of chemicals from mineral, SOM, or biological cell surfaces

B. Precipitation/Dissolution

  • The chemical transformation from solution to the solid state; forming new solids from solution components

C. Immobilization/Mineralization

  • Biologically mediated reactions that convert chemicals to non-biomolecules

D. Complexation/Dissociation

  • Interactions between two or more chemicals/aqueous ions. Protonation and deprotonation (H+ gain and loss) are types of complexation & dissociation

E. Gas Dissolution/Volatilization

  • Exchange of gaseous chemicals between soil atmosphere and soil solution – gas transfer to/from aqueous phase

F. Oxidation/Reduction

  • Gain and loss of electrons in elements, changing their oxidation state

A. Soil Acidification

  • Soil acidification is detrimental to agriculture
  • Availability of anionic & cationic nutrients decreases
  • Occurs due to acid addition to soils (natural/human)

B. Source of Soil Acidity

  • Soil acidity sources include acid rain, agronomic practices, mine spoils, and sulfate soils
  • Primary components in atmospheric acid vapors are sulfur dioxide and nitric oxides.

C. Forms of Soil Acidity

  • Active acidity: Hydrogen ions in soil solution (measured using pH meter)
  • Exchangeable acidity: Associated with aluminum (Al) and hydrogen (H) on exchange sites

D. Measurements of Soil Acidity

  • pH meter or calorimetric analysis measure H+ activity in aqueous solutions
  • Base saturation measures the percentage of base cations (Ca2+, Mg2+, K+) within the soil’s total cation exchange capacity (CEC)

E. Managing Acidic Soils (Liming Soils)

  • Liming is a method of managing acidic soils
  • Improvement of soil health, increase crop & pasture productivity
  • Reduce cost of production
  • The challenge is estimating the quantity of lime needed to reach specific pH levels

Soil Salinity

  • Soil salinity includes soluble salts in soil water and salt solids
  • Salinity and sodicity affect soil structure, impacting permeability and infiltration

A. Source of Soluble Salts

  • Weathering of primary minerals & rocks
  • Residual fossil salts
  • Saline groundwater and seawater intrusion
  • Natural salt deposits

B. Characterization of Salinity in Soil and Water

  • Sodium adsorption ratio (SAR)
  • Exchangeable sodium percentage (ESP)
  • Total dissolved solids (TDS)
  • Electrical conductivity (EC)

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Description

This quiz covers the essential aspects of soil chemistry, including soil formation, components, and key parameters for measurement. Explore the units used in soil chemistry and their conversions as well as the role of essential elements necessary for life. Test your understanding of the complexities of this vital field.

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