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United States Department of Agriculture

Agricultural Research Service

Research Project: Developing Sustainable Cropping Systems to Improve Water Productivity and Protect Water and Soil Quality in Irrigated Agriculture

Location: Water Management Research

Title: Soil salination indicators

Authors
item Lin, Z -
item Banuelos, Gary

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 15, 2014
Publication Date: N/A

Interpretive Summary: Soil salinity is one of the important soil properties that significantly affects agricultural production and environmental quality. A salinity indicator is a sign or symptom that suggests the soil is experiencing the impacts of salinity. Conventional chemical indicators of soil salinity include: electrical conductivity (EC), total dissolved solids (TDS), and sodium adsorption ratio (SAR), while salt crystals and stains in surface soils are physical evidence of soil salinity. Indicator plants species have been commonly used in combination with physical and chemical indicators to determine soil salinity. The variation of environmental conditions may influence the behaviors of bioindicators. Therefore, it is important to determine the plant salt tolerance under similar environmental conditions when the tolerance range of plant species is used as an indication of soil salinity. This chapter discusses measurements of soil salinity, potential impacts of soil salinity on plant growth, and available soil salinity indicators, along with agricultural salinity management.

Technical Abstract: Salts are naturally present in soils, and many salt elements are essential nutrients for plants. The most common soluble salts in soil include major cations of sodium (Na+), magnesium (Mg2+), calcium (Ca2+), potassium (K+), and anions of chloride (Cl-), sulfate (SO42-), bicarbonate (HCO3-) and carbonate (CO32-). Soils are considered saline when soluble salt ions are elevated to high levels in soil. In the laboratory, soil salinity is usually assessed by determining either the total soluble salts (TSS) by evaporation of a soil water extract or the electrical conductivity (EC) from the soil saturation extract. Soil sodicity is more often expressed by the sodium absorption ratio (SAR). SAR can be calculated from concentrations of K+, Na+, Ca2+ and Mg2+ in soil solution or water extracts. Based on soil EC measurements, crops can be classified into one of the following categories: salt sensitive (1.0-1.8 dS/m), moderately sensitive (1.5-2.8 dS/m), moderately tolerant (4.0-6.3 dS/m) and tolerant (6.8-10 dS/m). Plant species with distinctive responses to salts at the whole plant, tissue, or cellular level can be selected as effective bioindicators of soil salinity. This chapter discusses how the relationship between EC and SAR will serve as an important baseline, with modifications such as soil texture, clay type, leaching fraction, and rainfall, for a better site-specific understanding of how plants will be affected by salts, and in particular, sodium.

Last Modified: 9/22/2014
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