ABSTRACT
In the brief introduction of sodic soils in Chapter 1, sodium permeability hazard was noted as the primary problem under sodic conditions, which is assessed in soils by exchangeable sodium percent (ESP) and sodium adsorption ratio (SAR) criteria (for discussion of ESP and SAR, see Chapter 1, Section 1.1.2, “Classifying Salt-Affected Soils”; and Chapter 4, “Salinity Soil Tests and Interpretation”). In sodic soils, excess Na on the CEC sites and in Na carbonates precipitated in the soil causes soil degradation, resulting in reduced water permeability (inltration, percolation, and drainage), decreased gas exchange or permeability (low oxygen, reduced oxygen ¢ux into the soil prole, or aeration), and a less favorable rooting media due to soil structural breakdown (Rengasamy and Olsson, 1991; Naidu et al., 1995; Levy, 2000). Thus, this Na-induced salinity stress is often called an “Na permeability hazard” or “Na hazard.”
