| Summary: | Investigation has been made into the properties of Red Soils in West Java, Indonesia, selected from two different parent materials. Profiles P. Tb and P. Rb are derived from dacitic tuff and P. Js from pumice volcanic ash, both of which are acid in character. Profiles L. Km, L. Dr and L. Pk are derived from andesitic to basaltic volcanic ash, intermediate to basic in character. For comparison, soils from each group of parent materials were selected to be representative of areas of different climate, ranging from two annual dry months, to no dry month in the year. This study area is reviewed in chapter one. Chapter two discusses the factors and processes of soil formation in the tropics relevant to the soils studied. Chapter three discusses some characteristics of Latosolic and Podzolic soils, criteria for distinguishing them and their position in the Indonesian National Classification system (INCS). Soil clay fractions were extracted by several different selective dissolution methods: Na2CO3 (cold), 0.5 M NaOH (2.5 min boil), IM potassium pyrophosphate and dithionite-citrate-bicarbonate. Extraction enhanced the intensity of X-ray diffraction peaks and clarified identification of some minerals that were difficult to distinguish in the untreated clay. The effect was much more pronounced in the Latosolic than inthe Podzolic soils, mainly as a result of the different characteristics of the weathering products of these two groups of soil. Chapter four discusses some previous work that has been carried out in connection with selective dissolution analysis and includes some important new thoughts about microcrystalline minerals. Chapter five describes the methods that have been used in this study. They include particle size analysis, soil reaction (pHH20 and pHKCI), cation exchange properties, total nitrogen and carbon, selective dissolution analysis of clays by several different treatments, X-ray and thermal analyses and micromorphological observations. The principal results of this study are as follows: (i) The physical characteristics of the soils are mostly determined by the parent materials. Micromorphological examination substantiates this by showing the difference in the properties of the clay in these two groups of soils: Latosolic soils contain clay with the properties of flocculated paste; in Podzolic soils the clay is similar in nature to a deflocculated paste(ii) Climate in the study area exerts considerable control over weathering and leaching and determines the chemical properties of the soils. t. iii) In the study area climate and parent material seem to play the most important role in determining the properties of the soils studied. Civ) Microcrystalline and poorly ordered material in the clay fraction are more abundant in Latosolic than in Podzolic soils. Kaolinite is the most abundant clay mineral in profiles P. Tb, P. Rb, L. Km; its degree of crystallinity is greater in Podzolic soils. Other common minerals are (meta) halloysite in profiles P. Dr and P. Js and smectite in profile P. Js. Minor amounts of 2: I and interstratified minerals occur in most soils. Proposals for the improvement of soil classification are suggested: (i) The soils should be classified on the basis of the parent material. (ii) Since CEC is one of the best parameters to illustrate the stage of weathering of these soils it should be used to differentiate perhaps at the group level. Thus, the position of this factor is one level below the position of parent material. (iii) Soil chemical characteristics relate well to the climatic variation in the area. It is suggested that these characteristics should be considered at a lower level than CEC. This lower level should have a close relationship with soil fertility and so, with agricultural practice. The results of this study suggest that further detailed investigation on "Red Soils" in Indonesia, should be carried out on the same lines as here. The aim should be to establish one "Indonesian National Classification System" that is relevant to the conditions, economics and purposes of the country
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