Acid sulphate soil (ASS) is said to be problematic for agriculture and fish or shrimp aquaculture. We have collected 29 soil samples from 17 different shrimp aquaculture ponds in operation in Kalimantan of Indonesia. The ponds were constructed from 1991 to 1998. Element and X-ray diffraction analysis showed the presence of pyrite in the soil samples. Three types of soil pH measurements, Wet soil, Air dried soil and H_2O_2 processed, were carried out. The pH values varied widely and showed the potential of further acidification but in any case no sign of continuous linear decrease of pH with progress of time was observed. In these 17 ponds shrimp was cultured 70 times in total and 700kg of Black tiger shrimp was produced per pond per crop without any feeding in 2007. Older ponds showed larger average body weight of shrimp than newer ponds. In our study ponds shrimp has been cultured since 1991 and no case of shrimp mortality caused by soil acidification was observed. The proper pond management based on the usage of large tidal differences and river water flow might have contributed to this sustainable aquaculture production in potential ASS area.

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In the Japanese countryside, bamboo stands are spontaneously expanding and invading adjacent forests and farmlands due to poor management. In order to obtain basic information regarding the influences of this expansion on nutrient dynamics in forest ecosystems, this study monitored inorganic ion and Si concentrations as well as fluxes in incident precipitation, throughfall, and soil solution in an expanding bamboo stand, Phyllostachys pubescens (BB), in Kochi Prefecture in comparison to a planted Japanese cypress stand, Chamaecyparis obtusa (HN). The soil in BB was less acidic with higher contents of exchangeable bases-especially Ca-than in HN. The allocation of the incident precipitation into throughfall and stemflow, and the amount of percolating water did not differ much between HN and BB. The pH and EC levels, and K^+, Ca^<2+>, Cl^-, SO_4^<2->, H_2PO_4^-, and Si concentrations of throughfall and soil solution were much higher in BB than in HN-particularly from June to July, i.e. during and immediately after the leaf-fall season of the bamboo species. The differences were less obvious during winter. Nutrient fluxes in throughfall and soil solution gradually became larger in BB than in HN. These results can be attributed mainly to nutrient leaching from dead bamboo leaves that were still attached to the plants and subsequently fell to the ground.

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Serpentinitic soil has an exchangeable Ca/Mg ratio much lower than those shown by non-serpentinitic soils. The ratio of these cations is known to increase as serpentinitic soil is subject to natural weathering processes. We investigated the vertical trends in the exchangeable Ca/Mg ratio in four soil profiles developed on different topographic locations; a forested hill summit (Js-F1), a hill shoulder (Js-F2), a footslope (Js-F3) and a paddy field on an alluvial fan (Js-P) in the Sekinomiya serpentinitic terrain. These soils were classified as Epileptic Cambisols (Dystric), Haplic Cambisols (Dystric), Haplic Cambisols, and Gleyic Fluvisols (Eutric), according to the WRB soil classification, respectively. Chlorite and talc were dominant in the clay assemblages, and both transformation to vermiculite from chlorite and neoformation of smectite were not apparent in the clay assemblages of the hill soils, which indicated the secondary formation of clay minerals had not occurred to a significant extent. Additionally, illite, though it is not included originally in serpentinite, was evident in the clay assemblages of the soils in the alluvial fan (Js-P). This observation suggested that mineral contamination by felsic materials containing illite had occurred in the paddy field. In all of the profiles, the exchangeable Ca/Mg ratio at the surface horizon was higher than that of subsurface horizons. Weathering of Mg-silicates followed by leaching of Mg^<2+> in the development of the profiles, as well as Ca accumulation at surface horizon by nutrient cycling may have caused the vertical gradients. The exchangeable Ca/Mg ratio in the subsurface horizons increased as the elevation decreased from the hill summit to the alluvial fan. While the ratio in the Js-F1 and F2 profile was much less than 0.1, it was around 0.1 in the Js-F3 soil. The ratio in the Js-P profile had further increased to greater than 1.0, which can then be regarded as suitable for plant growth. As suggested by the soil type and clay mineralogy, the higher exchangeable Ca/Mg ratio in Js-P was not caused by strong weathering of the Mg-silicates but by contamination of non-serpentinitic minerals such as from fluvial deposits from up-stream. In summary, the hill soils had an extremely low exchangeable Ca/Mg ratio particularly at higher elevations due to both the direct inheritance of the elemental composition from serpentinite and the relatively weak degree of weathering there, whereas the paddy soils on the alluvial fan had a ratio higher than the threshold value unfavorable for most plant growth (i.e.<0.7), probably due to contamination by non-serpentinitic fine-grained materials. As an extremely low exchangeable Ca/Mg ratio has been determined as a qualifier for magnesic soils in the Australian soil classification system, such criteria could be applied to the classification of Dark-red Magnesian soils in the United Soil Classification System of Japan to better determine the agro-ecological functions of serpentinitic soils in Japan.

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Information related to environmental conditions such as soil characteristics is essential for the development of an effective lowland rice production strategy in the mountainous region of northern Laos. In this study, we investigate soils of lowland rice fields located at various topographical positions in an intermountain basin in order to evaluate the soil characteristics with special reference to mineralogical properties, charge characteristics, and P status of the soils. Five rice field sites were selected, including those located in the lower part of the basin (LP), upper part of the basin (UP), floodplain (FP), and fallow land at a hill slope (MF). The clay mineral composition was dominated by kaolin minerals and quartz in UP and MF and by kaolin minerals in LP. A higher proportion of illite and predominance of quartz was found in FP. All the soils showed point of zero salt effect (PZSE) values of less than 4.0, irrespective of horizon and site, which are 2.0-3.0 units lower than pH_w. The σ_p values ranged from 3.88 to 9.76 cmol_c kg^<-1> at the A horizon. The Feo/Fed and Alo/Ald ratios ranged mostly from 0.2 to 0.4 and 0.2 to 1.0, respectively. On the basis of these results, the soils in the study area were considered to be at a stage prior to a strongly weathered phase. The total P and Bray-P contents of the soils ranged from 139-503mg kg^<-1> and 1-63mg kg^<-1>, respectively. The Bray-P contents were in the order FP>UP>LP>MF. The total P contents and most of the inorganic P fractions extracted by sequential P analysis were highest at the A horizon in FR. The amount of inorganic P fractions in the surface soils of UP were higher than those of MF and LP. Therefore, it was suggested that eroded soil materials, including nutrients such as P from MF, were translocated to UP; however, they were prevented from reaching LP owing to its topographical position. The soils in FP seemed to be affected by the different soil materials transported by occasional flooding. These results indicated that it is necessary to establish lowland rice field management technologies by taking into account the difference in topography and its influence on soil fertility.

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