Seasonal variation in penetration resistance and shear strength of three rainforest soils from northeastern Queensland

Abstract

Large seasonal changes were noted in field measurements of penetration resistance and shear strength over the course of a sixteen-month study in three tropical soils supporting rainforest. Both penetration resistance and shear strength levels were seasonally higher in soils of basaltic origin than in those formed from alluvial or metamorphic parent materials. Both measures of soil strength clearly decreased with increasing gravimetric water content at all sites. Significantly increased penetration resistance with increasing bulk density was noted at all sites, although the variance accounted for by this variable was small. Shear strength was not significantly related to bulk density. Conversion of these soils to sugarcane culture has led to marked increases in surface-soil bulk density and strength, with the formation of a compacted zone close to the soil surface.