Water Diffusivity of Sandy Soil of Different Particle Sizes in Typical Sandy Cropland

A laboratory experiment was conducted in May 2006 to measure water diffusivity (D_thetas) of sandy soil of different particle sizes. The method of cobalt chloride test paper (CCTP) was made to observe moving position of wetting front. Results showed that the rate of wetting front advancement (RWFA) is in the order: 0.50-0.25 mm soil > 0.25-0.10 mm soil > undisturbed soil > the soil of less than 0.10 mm. The relationship between infiltration distance and the RWFA was expressed as a power function. With decrease in the sand particle sizes, D_thetas was decreased gradually. The D_thetas change was most obvious in the soil of 0.50-0.25 mm, the least obvious one was the soil of less than 0.10 mm. There existed significant correlation between D_thetas and soil water content which met an exponential curve and was in accordance with the empirical equation. As a new attempt, CCTP was reliable to measure the position of wetting front and decrease the subjective error of visual method.