Characterizing Salt-Affected Soils of Songnen Plain Using Saturated Paste and 1:5 Soil-to-Water Extraction Methods

In the Songnen Plain, Northeast China, chemical parameters of salt-affected soils were previously obtained from 1:5 soil-to-water (1:5) extracts so that there is no information available for soil salinity and sodicity from the saturated paste (SP) extracts. The work reported here characterized soil salinity and sodicity of SP extracts and compared salinity and sodicity measurements using SP and 1:5 extraction methods from 121 soil samples from various sites of salt-affected soil areas in the Songnen Plain. Electrical conductivity (EC), major cations (Na+, K+, Mg2+, Ca2+), sodium adsorption ratio (SAR), and pH were determined and analyzed using SP extracts and 1:5 extracts. The sodium ion was the predominant cation so that Na+ concentration was close to total cation concentration (TCC). The SAR in the 121 samples was remarkably high; 22 soils had a SAR1000 (mmolcL-1)1/2 with a maximum SAR value of 4042.57 (mmolcL-1)1/2 for SP extract. The SAR was highly correlated with EC (r20.86, P0.0001). The salt-affected soils are predominantly saline-sodic based on the classification of the USDA (1954). Through a regression analysis, total cation concentration was strongly related to EC with slopes of 10.3 and 9.8 without y intercept in SP and 1:5 extracts, respectively. Significant relationships (r20.81, P0.0001) existed between EC, Na+, and SAR in SP and 1:5 extracts. However, K+, Ca2+, and Mg2+ of SP extracts was not related to those of 1:5 extracts.