Korean Journal of Soil Science and FertilizerISSN:0367-6315(Print) 2288-2162(Online)한국토양비료학회

Electrical conductivity (EC) is a robust indicator of soil salinity. In South Korea, EC of 1:5 of soil:water extracts (EC_1:5) and soil saturated paste extracts (EC_e) are often used. The standard shaking time is 0.5 hr for EC_1:5 and standing time after soil saturation is 16 hrs for EC_e. In this study, we investigated the effects of equilibrium time (shaking and standing time for EC_1:5 and EC_e, respectively) to test if the standard time is enough for precise and accurate measurement of EC. Two soils (silt loam and sandy loam) with seven levels of EC were prepared by adding salt solutions (1, 2, 4, 8, 12, 16, and 24 dS m^-1) to the soils. The soils were used for experiments after 2-months aging. The EC_1:5 was measured after shaking soil-water mixture for 0.5, 1, 2, and 3 hrs, and EC_e was determined after standing the saturated soils for 4, 8, 16, 24, and 48 hrs. The results showed that 4 hrs of standing time for EC_e are sufficient for most saline soils regardless of soil texture. However, occasional occurrence of large variations in EC_e up to 25% indicates a necessity of longer (e.g., 24 hrs) standing time for some soils. Therefore, for long-term monitoring of EC_e, it may be necessary to determine site-specific standing time for EC_e. Unlike EC_e, the variations in EC_1:5 with shaking time was negligible. However, for soils treated with solution of high EC (24 dS m^-1), the variability increased up to 6% variations. Therefore, it may be necessary to increase shaking time to 1 hr to ensure a precise measurement of EC_1:5 particularly for high-saline soils.

For precise measurement of EC by achieving equilibrium of ions, shaking for 1 hr is required for EC_1:5 and standing for 24 hrs is appropriate for EC_e.