Variations in the characteristics and genesis of fluvial soils in the Kelantan Plain, Malaysia
The fluvial soils of the Kelantan plain, mainly cropped for rubber and paddy were studied along six transacts. Field examinations were made at fixed intervals and pedo-unit samples were collected for analysis. The transact data are presented as isopleth diagrams and analysed numerically. The variations in low chroma colours, red colours, structure, texture, segregation/concretions of Fe and Rn-oxides from the levees to the basin are systematic and predictable, being largely controlled by topography. Low chrome colours are useful for separating surface and ground water effects while red colours indicate the degree of aerobisa. m-oxides occur irregularly but they are always absent from the soil in depressions. Numerical analyses show that. 1. colour indices and structure discrMnate the soils while Mn-oxides do not, 2, lateral variations are continuous but there is a soil toposequence from the levees to the depressions, 3. the existing soil boundaries are usually valid as are most of the originally mapped soil series.Soil formation is sequential, following each sedimental accretion, The important soil characteristics are inherited, whether formed naturally or under paddy cultivation. The mineralogy and stratification are inherited; low chroma and red colours develop from the yellow brown sediments; soil coatings and mass transported materials are common; matrix anisotropism changes along the toposequenoe; Fe illuviation is weak but Mn illuviation is pronounced.Paddy cultivation promotes playing and the formation off strong brown mottles and microlaminations within the plough layer. Clay particles become disorientated and some are lost through suspension in the water. Although hydromorphism,:strongly influence the soils, natural biological activity causes some homogenisation. A redefinition of the series is proposed and the classification of the soils is discussed.