Experiments on the control of salinity and sodicity in surface-irrigated fields in the upper yellow river valley (IV) tools for analyzing soil salinity and sodicity and related properties of the field soils

The electrical conductivity of the solution in a saturated soil, EC _SAT, which is determined by the dilution extraction (DE) method, is used in these experiments. The DE method is based on a regression equation of the electrical conductivity of the extract of the soil sample at 1:x soil-water ratio, EC_1;x, on x. The EC_SAT can also be measured automatically using time domain reflectometry (TDR) in the field, when the parameters of two models have to be identified for the soil concerned. The concentrations of exchangeable ions, such as Na⁺, in the solution in a saturated soil, such as [Na⁺]_SAT, are used as well. They are also determined by the DE method. The physical properties of the field soils of the Pingbu experimental field and the parameters of the two models identified for the typical soil in the field were presented. Example measurements of time changes in the depth profiles of volumetric soil water content and EC_SAT obtained in the field were also illustrated. Further, a comparison of the regression equations of EC_1;x on × and [Na₊]_1;x on × for several soil samples with different salinities was made. The results suggest that the difference in the concentration of an ion between the bulk solution and the electric double layer, or the diffusive force acting on the ion influences the power exponent in the regression equation for the ion.