CHARACTERIZING RATE OF WETTING - IMPACT ON STRUCTURAL DESTABILIZATION

Even though the rate at which water enters soil aggregates has an impa ct on structural stability limited information exists on characterizat ion of rate of wetting and the variables controlling it. The objective s of this study were to determine (i) if the first-order rate constant , k (defined wetting rate constant), can be used to characterize rate of wetting and (ii) if any relation exists between rate of wetting, in trinsic soil properties, and water stability. Soil aggregates, 2 to 4 mm in size, from six different soils under corn, the forage-phase of c orn forage rotation, and under permanent bluegrass were wetted to diff erent water contents, theta(t). Wetted aggregates were equilibrated fo r 2 weeks, and their water stability was determined by wet sieving. Wh en theta(t) was regressed nonlinearly against time (t) [using a first- order rate equation, theta(t) = theta(o) + Delta theta(m)(1 - e(-kt))] , 75 to 99% of the variability in theta(t) was accounted for by t. Dep ending on clay and organic matter contents, pH, and cropping treatment s, values of k ranged hom 0.097 to 0.198(-min). This implies that the impact of the variables controlling rate of wetting can be characteriz ed by values of k. Water stability decreased with increasing rate of w etting, suggesting that water stability following wetting depended on the extent of destabilization that occurred during wetting. The impact of rate of wetting on stability was more extensive on larger aggregat es than on smaller aggregates.