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Carbon and organic matter. Soil carbon is sometimes used as a synonym for organic matter, although the latter also includes nutrients and other chemical elements.Because carbon is the main building block of all organic molecules, the amount in a soil is strongly related to the total amount of all the organic matter: the living organisms plus fresh residues plus well-decomposed residues.
Dec 9, 2018 · Organic matter (OM) comprises a small percentage of most soils by volume, however, it plays a crucial role in soil health and ecosystem services because of its interaction with many other soil properties. Soil OM increases the soil’s water holding capacity, cation exchange capacity, fertility, microbial abundance and diversity, and soil ...
Nov 18, 2023 · The enormous influence of organic matter on so many of the soil’s properties—biological, chemical and physical—makes it of critical importance to healthy soils (Figure 2.3). Part of the explanation for this influence is the small particle size of the well-decomposed portion of organic matter, the humus.
- Introduction
- Soil Solution
- Soil Colloids
- Cation Exchange in Soils
- Anion Adsorption and Exchange
- Soil Ph
- Soil Salinity and Sodicity
- Oxidation-Reduction (Redox) Reactions
- Summary
- References
Soil chemistry is a branch of soil science that deals with the chemical composition, chemical reactions and chemical properties in soils. Abioticphases of the soil include solids (organic matter and inorganic minerals), liquids (soil water), and gases (soil air), while the biotic phase consists of living organisms. Soil, therefore, is a dynamic liv...
Soil water, including dissolved solutes, is referred to as the soil solution and is the lifeblood of soil. All chemical reactions, mineral precipitation/dissolution reactions, ion exchange reactions, redox reactions, and nutrient uptake by plants occur in, or are mediated by the soil solution. Without soil water, very few chemical or biological rea...
The soil colloidal fraction is defined as that fraction of the soil made up collectively of small (<0.002 mm) inorganic and organic particles (Brady and Weil, 2010). The high specific surface areaand the presence of electric charges on most particles are responsible for important soil characteristics such as swelling capacity, the ability of the so...
Negatively charged surfaces on soil colloids attract cations by electrostatic forces. Cations retained by soil colloids may be eventually released to the soil solution through exchange with other cations in the soil solution. The cations most commonly held by soil colloidal particles are Ca2+, Mg2+, K+, Na+, H+ and Al3+. Of these, Ca2+, Mg2+, K+, a...
Soils are able to retain anions in a similar fashion to retaining cations, particularly in the lower pH range when the surfaces of some colloids (e.g., oxy-hydroxides) have positive charges. Retention of anions through adsorption varies from one anion to another. Some anions are retained through non-specific adsorption mechanisms, while others are ...
Soil pH is a measure of the activity(cf. concentration) of hydrogen ions in the soil solution and describes the acidity or alkalinity in the soil. For our discussion herein we define activity as “effective” concentration, whereby activity is roughly equal to concentration in dilute solutions but generally deviating from concentration (typically bec...
Soil salinity levels are controlled by the concentration of total dissolved mineral salts present in the soil solution. Salts occur naturally in both soil and water and may, under certain conditions, accumulate in soil. The accumulation of soluble salts in the soil is known as salinization. Dissolved salts that contribute to soil salinity include t...
Oxidation-reduction reactions, or redox reactions, involve the transfer of electrons and the conversion of an element from one valence state to another. Understanding the behaviour of redox sensitive elements in soil is central to understanding the behaviour of Gleysolic and Organic soils, and gleyed soil subgroups that occur within all mineral soi...
Soil chemistry involves the study of the chemical composition, chemical properties and chemical reactions involving soil solids (organic matter and inorganic minerals), liquids (soil water), gases...Soil chemical properties are largely influenced by the type and quantity of inorganic minerals present in the soil and the organic matter (humus) content. Inorganic colloids mainly include phyllosi...The presence of surface charges in both inorganic minerals and humus particles is responsible for ion adsorption and exchange in soils. Most charges are permanent (not dependent on soil pH) and neg...Negative charges on soil particles can attract and adsorb cations, which can be released back to the soil solution through ion exchange. Cation exchange capacity, defined as the sum of total exchan...Acton D.F., and Gregorich L.J. 1995. The health of our soils: toward sustainable agriculture in Canada. Agriculture Agri-Food Canada, CDR Unit, Ottawa. Bowen H.J.M. 1979. Environmental chemistry of the elements. Academic Press, London, New York. Brady N.C. and Weil, R.R. 2010. The Nature and Properties of Soils 13th Ed. Pearson Education. Canada De...
The chemical structure of soil organic matter has been under debate for many decades and it was previously believed that the non-living component of soil organic matter was made of recognizable plant- or animal-derived biomolecules and humic substances, large by-products that resulted from both biological and chemical decay of organic inputs to soil (Schmidt et al., 2011; Lehmann and Kleber ...
- Myron S Anderson
- 1962
Organic matter buffers the soil from chemical, physical and biological changes. This means that lower organic matter soils (0% to 2%) may see changes within three to five years of changing management, while higher organic matter soils (4% to 7%) may take seven to 10 or more years to see a change.
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Active organic matter provides habitat and food for beneficial soil organisms that help build soil structure and porosity, provide nutrients to plants, and improve the water holding capacity of the soil. Several cases have demonstrated that it is possible to restore organic matter levels in the soil (Figure 8).
