Physico-chemical characteristics, genesis and classification of soils from forest ecosystems in Kerala
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Date
1989
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Department of Soil Science and Agricultural Chemistry,College of Horticulture, Vellanikkara
Abstract
A study was conducted to evaluate the morphological, physical and chemical characteristic of soil representing different forest ecosystem. In Kerala. Six soil profiles representing predominent vegetation types of Kerala, were selected for the study. The study areas were representative of the tropical evergreen, semi evergreen, moist deciduous, grasslands, hill top evergreen and dry deciduous types of forests. Profiles were excavated in these areas and detailed morphological studies of the soils were carried out. Soil samples representing the different horizons were collected for laboratory characterisation. The interrelationships of various physico-chemical characteristics and the distribution of iron and phosphorus fractions in soils were studied with a view to relate these characteristics to the genesis of the soils. Based on the available data attempts have also been made to classify the soils under soil taxonomy.
The surface soils from all the profiles were rich in organic matter and had darker colours, ranging from greyish brown to brown. Increasing redness in the subsurface horizon though noticed in all the soils, was a conspicuous feature observed in the soils from the dry deciduous forests.Weak granular structure in the surface followed by sub- angular blocky structure in the subsurface layers was a feature common to all the soils. Coarse fragments, mostly in the form of secondary latorite gravel constituted a major portion of the soils under investigation.Wide variations in texture was observed between the soils from various ecosystems. Increase in clay content with depth was another feature observed in all the soils. Silt \ was the lowest, among the various size fractions. Positive and significant correlation was obtained between moisture at 0.3 and 15 bar with clay# while available water and clay showed a positive but nonsignificant correlation.The maximum water holding capacity and volume expansion were found to be closely related to the nature and content of clay and organic matter. The soils under dry deciduous forests registered the highest volume expansion and maximum water holding capacity.
All the soils under investigation were found to be acidic in reaction. Organic carbon# nitrogen and C/H ratios were high in the surface horizons with decreasing profile trends in soils from most of the locations. Silica constituted the predominant constituent in all tho soils followed by Iron oxide content was less than Al2O3 and showed a positive correlation with clay. The total reserves of MgO, CaO, K2O and P2O5 expected of humid tropical soils.
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