VARIATION OF STRUCTURAL STABILITY WITH WATER-CONTENT - INFLUENCE OF SELECTED SOIL PROPERTIES

The objective of this study was to investigate whether selected soil properties influence the sensitivity of two structural stability parameters, wet aggregate stability (WAS) and dispersible clay (DC), to the variations in water content (theta) at sampling. Soil samples for WAS and DC measurements were collected at monthly intervals during the 1989 and 1990 growing seasons from 10 different soils under croprotation experiments established in 1989. Wet aggregate stability decreased linearly with increasing theta, whereas DC increased linearly with increasing theta. The variations in theta explained 14 to 73% of the variability in WAS and 33 to 72% of that of DC. The sensitivity of stability to theta, characterized by the slope of stability-theta relation, ranged from -2.54 to -0.73 for WAS and from 0.10 to 0.67 for DC. Clay and organic matter (OM) contents and pH of the soils explained 80 and 83% of the variability in the sensitivity of WAS and DC, respectively. The sensitivity of WAS increased with increasing clay and OM contents and decreasing pH. The sensitivity of DC increased with increasing clay content and decreasing pH and OM content. The selected soil properties and theta explained 63% of the variability in WAS, whereas the former alone explained only 48% of the variability. A similar trend was observed for DC. The results demonstrate that WAS and DC were strongly influenced by theta and that this sensitivity depended on the selected soil properties.