MODELING TEMPORAL CHANGES IN STRUCTURAL STABILITY OF A CLAY LOAM SOIL

Field measurements of short-term changes in structural stability often include an important temporal variability that tends to mas treatment effects. Adequate modeling of this temporal variability i needed to increase precision in treatment comparisons. Previous work has shown that this variability can be related to water content. However, the relationship between structural stability parameters and water content is complex, because different processes linked to water content (slaking, swelling, age hardening) may govern the response of structural stability to a change in water content. This study used a tim series analysis approach to describe the complex response of structural stability parameters to water content. Temporal changes in the we aggregate stability (WAS) and the dispersible clay fraction (DCF) o a clay loam soil under four different cropping histories were model using gravimetric water content (theta) as an independent variable. Th lowest predictability for WAS was observed for soil in bare plots an under continuous corn (Zea mays L.) production. The amount of variability in WAS explained by theta increased as the number of years o grasses increased (to a maximum of 3 yr in this study). Regression models indicated that the low predictability of WAS using theta observed for bare soils and soils under continuous corn production was improved by including values of the antecedent water content be sampling. The predictability of DCF using theta was generally higher tha the predictability of WAS, did not include past values of theta, and wa independent of cropping history.