Salinity Tolerance Indicators

Abstract

Soil salinity significantly affects agricultural production and environmental quality. A salinity indicator is that symptom which suggests the impacts of soil salinity. The visual characters serve as diagnostic criteria in identifying the salt-affected soils. The physical indicators of salt-affected soils include flocculation, dispersion of clays and surface salt crusts; and conventional chemical indicators of soil salinity include electrical conductivity (EC), pH, total dissolved solids (TDS), exchangeable sodium percentage (ESP), electrochemical stability index (ESI) and sodium adsorption ratio (SAR). Plant species that serve as indicator species can be commonly used in combination with physical and chemical indicators to determine soil salinity. The relationship between soil electrical conductivity and sodium adsorption ratio serves 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. Many plant species, found only grown in highly saline soil (true halophytes) or in tidal zone (mangroves), are the indicators of salinity. So is true with many microbes found in mud flats associated with high salinity in mangal formations. The variation of environmental conditions may influence the behaviours of bioindicators including plants and microbes. Halophyte plant species and halotolerant or halophilic bacteria also serve as viable indicators of salinity as they are adaptive to stress through different mechanisms. This chapter discusses various physical, chemical and biological indicators of soil salinity as well as sodicity, their measurements and impacts.