Uncertainty involved in estimating water quality effects on soil permeability is an obstacle in appraising water quality for irrigation. This study examined salinity, sodicity and turbidity effects on hydraulic conductivity (HC) of three Torrifluvents ; Gila silt loam, Saneli clay loam and Glendale silty clay. HC was measured in laboratory columns containing initially dry aggregates (<2mm) at two bulk densities using ten saline solutions (electrical conductivity, EC of 0.4 to 4.8 dSm l, and sodium adsorption ratio, SAR of 0 to 20) with and without soil suspension. Hydraulic gradients, suspended solid concentrations of outflow, and aggregate size distributions were also measured. HC decreased at SAR less than 5 in all the tested soils, and the reduction followed an exponential form involving SAR/EC. Gila and Saneli soils developed surface seal, while Glendale silty clay that has shown swelling did not. The introduction of soil suspension into the saline solutions at a rate to form a depositional layer of less than 3 mm thick caused 4 to 7-fold reduction in HC of Gila and Saneli soils, but did not accentuate water quality effects on HC. The depositional layer did not reduce HC of Glendale soil. Increasing sodicity and/or reducing
salinity of saline solutions increased destruction of soil aggregates having a peak diameter of 0.18 mm, and HC was quantitatively related to the reduction in soil aggregates. Water intake into newly plowed and thoroughly disked soils may decrease at much lower SAR than commonly recognized, partly because of destruction of weak soil aggregates. The extent of reduction depends strongly on soil types. This results suggests that the soil permeabilty management requires the consideration of both soil properties and water quality.
It is known that soils of volcanic origin are generally well- aggregated. To describe their retention characteristics with the unimodal model of van Genuchten (1980), and subsequently predicting the hydraulic conductivity from it can lead to some errors. In this paper both the multi-porosity water retention model of Durner (1992) and the van Genuchten model are used to describe the retention characteristics of some samples of Daisen Kuroboku soil (Andosol). The two types of retention models are then combined separately with the conductivity model of Mualem (1976) to estimate the hydraulic conductivity of the samples. Estimated hydraulic conductivity using the two retention models differed by orders of magnitude. The disagreement between the estimated conductivities may be due to inadequate description of the retention data by the van Genuchten model.
The purpose of this study is to clarify the characteristics of desertification areas and to understand how desertification has progressed over the last 10-20 years in some model areas of diffrent types of desertification using Landsat data.
1) Desertification in eastern China was characterized by reactivation of fixed sand dunes at Naiman, surface erosion of the topsoil at Lanxi, and severe gully erosion resulting in badlands at Yuanmou.
2) Three indices were developed to extract desertified area using Landsat data. Vegetation Index for extracting non-vegetated area ; (TM4 —TM 3)/(TM4+TM 3) Structure Index for excluding man-made structure ; (TM5—TM 1)/(TM5 + TM 1) Soil Color Index for extracting specific soil area ; (TM 3 —TM 1)/(TM3 + TM 1) These equations were applied to three areas we studied. And yearly changes of desertified areas were obtained through superimposing those areas of different years.
3) No significant changes in areal extent of desertification were seen in any of the analyzed regions of Naiman, Lanxi, and Yuanmou. Land management around major settlements, roads, railway lines, etc., in all these regions was relatively meticulous and desert land was being reclaimed. However, in outlying regions new desert land was appearing, making it difficult to say that suitable land management was being practiced.
4) We evaluated the processes of desertification in Yuanmou Province, where gully erosion is prominent.
This study aims to relate phenomena of bare groud distribution with land condition in a fixed dune area in south western Niger. For that purpose, a geomorphological and pedological survey as well as that of the bare grounds were carried out. The results were as follows.
1) The study area was mainly divided into plateau and pediplain, where sand covers distributed with various depth. The soil types of each landform unit were characterized mainly by depth of sandy layers.
2) Four types of bare grounds were recognized in the study area ;(1)tiger bush type, (2) termite mound type, (3) wind erosion al type, and (4) slope-related type. The former two were considered as naturally -formed bare grounds, while the latter two as mainly human induced ones.
3) The rate of bare ground occupation increased considerably from 1975 to 1992, and their distribution was localized on the areas without sand cover (plateau) and with relatively thin sand cover (pediplain), and on the sloped areas with about 4% of gradient.
4) Depth of sandy layers, which may decide depth of effective layers for plant growth, was considered as one of important factors controlling phenomena of bare ground formation.
Soil surface management practices under conventional farming systems were studied in Mali and India with reference to human-induced soil degradation. The purposes of this study were : 1)to record and characterize the conventional farming practices ; 2) to find some requisites for sustainable farming systems under semi-arid environment; and, 3) to seek the possibility of horizontal (south-to-south) technology transfer. Upland fields in Thiongoni village, Mali, have been cultivated with a oxen-driven plow which was introduced from France during colonial era. By deep plowing (15-20 cm) in sandy textured soil, soil degradation process has accelerated in these decades through soil surface crusting, accumulation of sand fraction in plow layer and soil loss both by water and wind erosion. On the other hands, the conventional farming systems in some villages near Udaipur, Northwestern India, where agro-ecological condition is similar to Thiongoni village, have been sustained the upland fields for more then some hundred years without causing conspicuous soil degradation. The difference from the Thiongoni’s case is explained by the mode of surface management practices, e.g. shallow plowing, improvement of the quality of crop residues lor feeding by dense planting, utilization of a wide variety of cultivation tools, manure application, and soil band for erosion control. The above information provides great hint to improve the current soil-human relations in Thiongoni village.
In Kuwait, as a lot of crude oil flowed out on the desert area, soil was contaminated by crude oil. As the rate of infiltration was very slow, groundwater was not directly contaminated by crude oil. However when rain water infiltrated into the contaminated soil, groundwater could bring oil into the aquifer. Therefore, the concentration of hydrocarbon in groundwater increased. The tracer test using chemical compositions and isotopes in ground water is useful for determining the origin and recharge time. The tracer test injecting tracer solution into an aquifer is useful for determining parameters in the aquifer. Therefore tracer tests will be used for analyzing oil contamination of soil and groundwater in Kuwait.