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Analytical Methods

Chemical Analyses: Solids: Sodium Absorption Ratio

Plants are detrimentally affected, both physically and chemically, by excess salts in some soils and by high levels of exchangeable sodium in others. Soils with an accumulation of exchangeable sodium are often characterized by poor tilth and low permeability making them unfavorable for plant growth. Plant growth is important for mine reclamation for several reasons: (i) it provides an erosion control measure for hillslope erosion and streambank erosion, (ii) it allows for revegetation of reclaimed areas, and (iii) it can possibly aid in metals uptake by phytoremediation. Sodium adsorption ratio (SAR), along with pH, characterize salt-affected soils. It is an easily measured property that gives information on the comparative concentrations of Na+, Ca2+, and Mg2+ in soil solutions. The equation used to calculate SAR is given as follows:

where [Na+], [Ca2+], and [Mg2+] are the concentrations in meq/L of sodium, calcium, and magnesium ions in the soil solution. Concentrations of sodium, calcium, and magnesium are determined by first extracting the ions from the soil into solution. The solution is then analyzed to determine concentrations of the selected ions. Na+, Ca2+, and Mg2+ concentrations are commonly determined using atomic absorption spectrometry (AA). For more info on AA, click here. The SAR of a soil extract takes into consideration that the adverse effect of sodium is moderated by the presence of calcium and magnesium ions. When the SAR rises above 12 to 15, serious physical soil problems arise and plants have difficulty absorbing water (Munshower, 1994)

 

Chemical Analysis | Physical Properties

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