Centrifugation method for rapid measurement of total soil water-soluble salt

Abstract

The gravimetric method is the most precise and intuitive technique for measuring the total soil water-soluble salt (TS). However, its application in intensive testing tasks is limited by the time-consuming suction filtration process. Therefore, this study aimed to improve the efficiency of the traditional gravimetric method by replacing the suction filtration process with the centrifugation technique. Soil samples of five salinity gradients were prepared and used for completely randomized and orthogonal design experiments, to obtain optimal parameters by assessing the degree of influence of four key parameters (centrifugation speed, centrifugation time, centrifugation cycle, and uptake volume of soil solution extracts) on the measured results. The accuracy and reliability of the proposed method were then validated through spike recovery and comparative experiments. The results demonstrated that the proposed centrifugation method enhanced the testing efficiency by more than 100%. For soils with TS $\le$ 8 g/kg, the optimal parameters were 4000 r/min for 8 min in a single cycle, with an uptake volume of 20 mL of soil solution extracts. For soils with TS $>$ 8 g/kg, the best choice for optimal centrifugation parameters was 4000 r/min for 6 min in two cycles, with an uptake volume of 20 mL of soil solution extracts. Applying these parameters to the other three soil types, the spike recovery rates ranged from 98.9% to 105.3%, and the relative standard deviations ranged from 0.4% to 4.6%, meeting the laboratory quality control standards. This newly proposed method can provide an effective alternative solution for measuring TS during the reclamation of saline-alkali soils.