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?

Mineralization Signup and view all the answers

How is the reactivity of soils important in soil chemistry?

It influences the composition of the soil solution Signup and view all the answers

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

Formation or breakdown of soil minerals Signup and view all the answers

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

Alkaline minerals content Signup and view all the answers

What role do ions play in soil chemistry?

They flow into plants and influence nutrient uptake Signup and view all the answers

What are the major electron donors found in soils?

Carbon compounds in roots and dead plant matter Signup and view all the answers

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

Soils with available O2 Signup and view all the answers

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

Oxygen Signup and view all the answers

What effect does soil acidification have on agriculture?

Decreases availability of anionic nutrients Signup and view all the answers

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

30% Signup and view all the answers

What can cause soil acidification?

Addition of acids and natural fluxes Signup and view all the answers

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

Soils with no available O2 Signup and view all the answers

What is the primary consequence of leaching in acidic soils?

Decreased soil fertility Signup and view all the answers

What is the primary source of soluble salts in soil?

Weathering of primary minerals Signup and view all the answers

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

Sodium adsorption ratio (SAR) Signup and view all the answers

How is total dissolved solids (TDS) measured?

By evaporating a known volume of water Signup and view all the answers

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

Salinity levels Signup and view all the answers

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

Varying hydrate states of salts Signup and view all the answers

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

Multiple EC types like ECw, ECe, ECp, and ECa Signup and view all the answers

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

Electrical conductivity and ionic concentration Signup and view all the answers

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

Nutrient deficiency levels Signup and view all the answers

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

To change a chemical from solution to the solid state Signup and view all the answers

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

Immobilization Signup and view all the answers

Which of the following describes gas dissolution/volatilization?

Transfer of gaseous chemicals into the aqueous phase Signup and view all the answers

What does the term complexation/dissociation refer to?

Interactions of two or more chemicals or aqueous ions Signup and view all the answers

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

Gain and loss of electrons causing a change in oxidation state Signup and view all the answers

Which process is primarily mediated by biological activity?

Immobilization/mineralization Signup and view all the answers

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

Chemical uptake into the structure of living organisms Signup and view all the answers

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

Mineral weathering and organic matter decay Signup and view all the answers

What is one source of soil acidity?

Acid rain Signup and view all the answers

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

Active acidity Signup and view all the answers

How is base saturation calculated?

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

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

Estimating the quantity of lime needed Signup and view all the answers

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

pH probe or calorimetric analysis Signup and view all the answers

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

Iron Signup and view all the answers

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

Proportion of sodium to calcium and magnesium Signup and view all the answers

What impact does soil salinity have on soils?

Affects soil structure Signup and view all the answers

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.