Soil aggregates and salt ion distribution after freezing saline-water irrigation

Irrigation with saline water is increasingly popular for reclaiming saline-alkali soil and for increasing crop productivity in some countries and regions. The purpose of this study was to investigate the alteration of salt ions distribution within different soil aggregate fractions after irrigation with freezing saline water. The experimental site is located on the coastal plain in Haixing County, Hebei Province, China. In a field experiment after irrigation with freezing saline water for 6 years, soil samples (0-10, 10-20 and 20-30 cm depths) were collected from three treatments: freezing saline water irrigation with plastic film mulching (IM); freezing saline irrigation without plastic film mulching (IO); and no saline irrigation and no mulching (CK). The bulk soils were separated into five size classes (i.e., 5-8, 2-5, 1-2, 0.25-1 and <0.25 mm) by the dry-sieving method. Then, the salinity and ion (i.e., Ca2+, Mg2+, K+, Na+, HCO3-, SO42- and Cl-) concentrations within each aggregate size class were determined following the methods of Lao (1988). The total salt content was calculated as the sum of the cations and anions.