Inorganic and organic soil components

Soil is a multi-phase system consisting of solids, liquids, and gases. In a typical soil, solids, liquids and gases compose about 50%, 20-30% and 20-30% respectively of the total soil volume (Brady and Weil, 1999). The solid phase can be broken down into two components inorganic and organic matter, with organic matter ranging from 1 to 5% of the soil. 

The soil solution will contain numerous inorganic and organic compounds derived from the solid components making up the soil. Common compounds include oxides, particularly those of silicon, aluminum, iron, and titanium in low concentrations. These compounds move down the soil profile sometimes contributing to formations such as the spodic horizon, which can contain aluminum and iron oxides along with highly decomposed carbon. 

Simple cations are those that exist only in one oxidation state in soil and are mostly associated with water, although they may also be chelated and form other associations with inorganic and organic components. 

IR spectroscopy, unlike ultraviolet-visible (UV-Vis) spectroscopy, can be used to directly measure both inorganic and organic components in soil, although it is more commonly used to identify organic compounds. It is carried out in two different wavelength ranges, the NIR, which is from 0.8 to 2.5 pm (800-2500 nm), and the MIR, which is from 2.5 to 25 pm (4000-400 cm ). ... 

Making a direct measurement of soil organic matter requires that the soil have a relatively large amount of organic matter. It also requires that the soil sample have low water content as water absorbs strongly in the MIR. In spite of these limitations, IR spectroscopy can be used to identify both inorganic and organic components and molecules present in soil and can yield valuable data about the chemistry of soil. 

In general, soil is an unconsolidated combination of inorganic and organic materials. The inorganic components of soil are principally the products of rocks and minerals that have been gradually broken down by weather, chemical action, and other natural processes. Soil particles, also known as soil separates, are divided into three main size groups sand, silt, and clay minerals [14]. 

The aim of this chapter is to provide the current state of knowledge on the factors that affect the mobility of trace elements in soil environments. Special attention is given to the influence of inorganic and organic ligands, including nutrients and root exudates, on the sorption—desorption processes of trace elements in cationic and anionic forms on/from soil components and soils. 

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