QUANTIFYING THE CHANGES IN CLAY STABILIZATION AFTER THE INTRODUCTION OF FORAGES

The objectives of this study were to (i) develop a semiempirical model to predict the changes in clay stabilization after the introduction of forages, (ii) assess the model using data from different soils, and (iii) determine the influence of soil properties on clay stabilization. Dispersible clay (DC) measurements were made at monthly intervals during the 1989, 1990, and 1991 growing seasons on seven soils under continuous conventionally tilled corn and forage treatments established in 1989. The influence of cropping treatment, time of sampling, water content (Θ) at sampling, and the interaction of these terms on DC was significant for each soil at P = 0.05. Using the variation in DC with Θ over time, a semi-empirical model was developed to predict the changes in the amount of clay stabilized by forages. The model parameters described (i) the rate at which clay stabilization occurred and (ii) the maximum potential amount of clay stabilized. The rate was characterized by half-life (t1/2) for the stabilization process. The R2 for the best fit of the model ranged from .48 to .84, and the fit was significant for each soil at P = 0.05. The projected t1/2 for clay stabilization ranged from 3.55 to 9.12 years. The maximum potential amount of clay stabilized ranged from 0.55 to 4.51%. The t1/2 decreased with increasing clay and organic matter contents and pH, whereas an opposite trend was observed for the maximum potential amount of clay stabilized. The model provided a framework for assessing the influence of changes in cropping practices and soil properties on clay stabilization