Temperature Effect on Aggregate Stability of Volcanic Ash Soils.

Hot water soil sterilization is one of the most promising Methyl Bromide alternatives. There are reports that soil physical properties were altered after hot water treatments. It may be associated with collapsing soil aggregates, which play an important role to characterize soil hydraulic processes for well-structured volcanic ash soils. It has however not been fully investigated whether the volume of hot water applied or the water temperature caused such alteration. This study thus aims to investigate experimentally the effect of temperature on aggregate stability of volcanic ash soils.

In this study, a standard wet sieving test was used to obtain the water-stable aggregate size distribution and the mean weight diameter (MWD) of soil samples collected from experimental fields of Tokyo University of Agriculture and Technology. The effect of temperature was investigated by conducting the test under different temperature.  During the sieving, a stack of sieves with different diameters was immersed into a water tank with different temperature and was moved up and down. The test was conducted at water tank temperature of 20, 30, 40, 50, 60, and 70 degree C. To investigate the effect of exposure time, 1:2.5 soil/water suspensions were heated for 1, 5 and 9 hours using constant temperature water bath at 20, 45, 70 and 95 degree C. After heating, soil solution had been filtrated to measure turbidity and electric conductivity (EC) of soil solution. Water-stable aggregate size distributions were then measured by the standard wet sieving at 20 degree C.

There was no significant difference in MWD with increasing water temperature. There was also no significant effect on MWD due to exposure time. Turbidity and EC increased significantly with water temperature. Summarizing the above, while soil aggregates were not fully collapsed by temperature effect, finer particles and connecter with finer particles in soils aggregates were leached by temperature effect.

Keywords: hot water soil sterilization, soil physical properties, andosol, water-stable aggregation