Abstract

Meagre data exist in Kerala on the physical parameters of soils and their relation to eucalypt growth although published work indicates the influence of soil depth, texture, structure, stoniness, bulk density, permeability, aeration, infiltration andwater holding capacity on tree growth. The project whose results are described here aims at an in-depth elaboration of soil physical properties and their relation to height growth of Eucalyptus tereticornis and E. grandis at one site each; the respectivestudy areas were Kondazhi in Trichur and Muthanga in Kozhikkod Forest divisions, Kerala. Four plots (10X10 m for Kondazhi and 12.5X12.5 m for Muthanga) within a radius of 500 m were demarcated and soil sampled from 0-20, 20-40 and 40-60 cm depths in 3 pits in each plot. Top height and g.b.h. of 5-7 trees were also measured. Gravel, sand, silt, and clay contents are reported as percentages of the whole soil, and soil data are discussed for 0-20, 20-40, 40-60 and 0-60 cm depths. Among the properties, gravel content was the most variable and particle density the least variable; sand, silt and clay contents were highly variable, whereas water holding capacity, pore space and bulk density were intermediate. At Kondazhi significant correlations were found between tree height and gravel, sand, silt and clay contents, bulk density, pore space, and water holding capcity; however, at Muthanga correlations were found only with gravel and sand contents. Principal component analysis showed that a large part of thevariation in height (78-91) was explainable by the first two components. Multiple linear regression indicated that gravel, sand and water holding capacity were the most important physical properties influencing height growth at both sites