During the drying process, dredged sludge undergoes the process of shrinkage that typically begins at the surface, followed by the formation of three dimensional networks of planar cracks that break the sludge into fragments (clods) of various sizes. This paper presents the description of the crack networks by the processes of image analysis for describing the sludge response to change in moisture content with the morphological features of the cracks and clods during the drying process. From analysis, all crack features increased with a decrease in sludge moisture content; the clod features, except the number of clods, decreased with a decrease in sludge moisture ; while the crack elongation remain fairly constant with a decreasing sludge moisture content. At 8% d. b, the equilibrium moisture content, the crack area was 0.96 times as large as the clod area ; and the crack-clod ratio had a good logarithmic relationship with the sludge moisture content. The crack pattern was found to depend on the sludge drying rate and the moisture level within the sludge body.
We were defined a major change in land use and assessed consequent environmental impact in Songkhla lake basin, southern part of Thailand using remote sensing techniques for geographic information system applications. 35 percent of forest area in the basin was disappeared during 1982 to 1996, contributing to 22 and 76 percent increas in rubber and aquaculture areaes respectively. Consequently, the basin was deteriorated by soil erosion. It was estimated that the average rate of soil loss increased from 4.91 ha-1 y_, in 1982 to 7.21 ha-1 y_1 in 1996. The rate of soil loss was found higher in greater slope or rubber area. The destruction of forest cover disturbed hydrological function in the basin, caused soil erosion and increased sediment in Songkhla lake system.
In the field of Kuroboku soil with humus top layer (Komekamito) at the Metropolitan Tokyo Agricultural Experiment Station (Tachikawa City) we investigated, in connection with the continuous application of organic matter, the effects of rotary tilling over a period of 20 years on the physico-chemical properties of surface soil and on crop yields. The results showed that the total carbon and total nitrogen contents of soil increased with the application of organic matter, but the rate of increase was smaller in tilling plot. In the plot where chemical fertilizers were continuously used, we found no effect of tilling on T-C and T-N. Available soil moisture content tended to decrease gradually over 20 years especially, the gaseous phase ratio at pF 1.5 tended to increase gradually, however, we observed a trend, as the years passed, that there were decreasing differences among the plots. Mineral nutrient content of the soil hardly differed between tilled and untilled soil, but it increased greatly in the plots where organic matter has been used repeatedly. Similarly to T-N of soil, available P2 05 increased with the continuous use of organic matter, but the rate of increase was lower in the tilled than in the untilled plot. Rotary tilling had little effect on the yields of cabbage and radish, though they were slightly higher with the continuous use of organic matter and the practice of rotary tilling. Even when chemical fertilizer alone was used, yields were higher when tilling was employed. Rotary tilling did not decrease crop yields. However, we noticed the formation of furrow pan due to rotary tilling, a tendency that was especially strong when only chemical fertilizers were used. Therefore 20 years of crop cultivation had no impact on the yields of cabbage and radish, but soil management that does not allow the formation of furrow pan is necessary, and for that reason the application of organic matter is important.
Field capacity is a widely used concept for irrigation management, but its definition is still controversial. Field capacity has been recognized by soil physicists a process of free drainage and it can not be defined as an intrinsic properties of the soil. To investigate further the meaning of field capacity, soil water content to a depth of 1 m and matrix flow by Darcy’s law at 1-m depth were measured and calculated every 30 minute for 1997 and 1998 at a maize-Chinese cabbage cropping field. Matric potential profiles with depth of a soybean field were also measured at a heavy rain event in 1991. The field soil is a well-drained volcanic ash soil. As the matrix flow is influenced by soil water content profiles during rain event and rainfall distribution pattern, the rain events whose amounts at the final day of consecutive rainy days were more than 10 mm/d, and brought the maximum values of matrix flow exceeding 5 mm/d at 1-m depth on the day following the rainfall were applied for discussing field capacity. When soil water conditions on the second day after the rainfall were applied as a field capacity, the matrix flow was 4 mm/d, and the hydraulic conductivity and the hydraulic gradient at 1-m depth were approximately 1X10-5 cm/s and 0.5, respectively. The amount of water stored to a depth of 1 m was 620 mm and the matric potential in the subsoil ranged between -50 to —100 cm. The matrix flow of 4 mm/d was very small compared to 620 mm water stored to a depth of 1 m. Although free drainage was still lasting on the second day after heavy rain events, the day can be applied as the field capacity for well-drained volcanic ash soils.