The mechanism of soil slaking is the breaking of soil aggregates by entry of water which is accompanied by salt releasing process when the soil contains salt. The objective of this paper is to describe the impacts of soil drying and slaking on cations release to outer solution and shift of cations during desalinization under different ini-tial water contents (IWC). A slaking test on natural and air-dried soils was carried out for evaluating the effect of slaking in different IWC (60, 50, 40, 30, 20 and 10 % by weight). After 24 hours immersion in water, Na was pre-dominantly released in every case both of the natural and air-dried soils. At the water content of 30 % that is around optimum slaking water content, maximum Na was released and at the water content of minimum slaking rate the re-lease of Na was lowest. However, too dry condition (10 % water content) did not contribute to release Na more. On the other hand, we did not find any special relationship be-tween the IWC and release of other cations like Ca, Mg and K in outer solution. Most of the Ca2+ and Mg2+ stay in exchange site (60 to 80 %) in soil and little amounts of them came out in outer solution. Water-soluble cations in slaked and unslaked soils followed the order of Na» K> Mg> Ca whereas, the amount of exchangeable state cations followed Na+ > Mg2+ > Ca2+ > K+. As a whole, the proportion of Na released in outer solution of natural soil was greater than that of air-dried soils. The results in-dicate that the water content for optimum slaking and the slower slaking rate is more efficient for desalinizing of Na from the saline soil.
The use of methyl bromide, which had been widely used all over the world, was banned in 2005 in Japan, so that it is very important to develop new tech-niques for soil sterilization. Using hot water for soil ster-ilization has become popular in Japan as an alternative for methyl bromide. Many studies have been done on bac-terial survival in soil when hot water was applied. Few studies focused on measurement temperature at multiple locations in the field. Even it is necessary to keep soil tem-perature between the surface and 30 cm deep with 45 ◦C for 5 h although hydraulic conductivity for hot water var-ied place to place at a field. Therefore, we investigated temperature distribution before and after using hot water for soil sterilization in a greenhouse by measuring soil sur-face temperature using thermography. We also focused on effect of water movement by repacked soil at field with hot water application. We found that a temperature mea-surement was expressed the representative temperature at the field by the sterilization with hot water applied. How-ever, a place, where we dag a hole for putting the sensors, was showed higher temperature than other places because of large amount of hot water application due to higher hydraulic conductivity and to destroyed hard pan layer. Therefore, we have to take care of refilling a hole after putting the sensors. Otherwise, over estimates of temper-ature occur due to applying large amount of hot water at such a place.
This study investigated the convective velocity of ponding water in a vegetated paddy lysimeter. We im-proved the measurement method for convective velocity by reducing the heat to the constantan line of the sensor. Then, to clarify the causes of ponding water convection in the vegetated paddy lysimeter, we conducted a model exper-iment under conditions of inhibited evaporation and with similar water temperature profiles to those in the vegetated paddy lysimeter. In the vegetated paddy lysimeter, the con-vective velocity of ponding water increased from 0.1 to 0.6 mm s−1 between 7:00 and 17:00, an increase that was re-lated to air-water vapor pressure differences. In the model experiment, the convective velocity remained constant at approximately 0.6 mm s−1 and 0.2 mm s−1 during night and day, respectively. In addition, less heat was lost by air-water temperature differences during the day than at night. These results suggest that evaporative heat loss induces the convection of ponding water in a vegetated paddy lysime-ter.