MORPHOLOGICAL PROPERTIES OF SURFACE SEALS IN GEORGIA SOILS

The morphology of surface seals has not been extensively described for acid, sandy and loamy soils common in the U.S. Southeast. The objectives of this study were to: (i) evaluate evolution of seal morphological properties for seven soils in Georgia during the course of a rainfall event, and (ii) relate seal morphology and development to soil properties. Columns were packed with Ap horizons from seven soils in Georgia and subjected to simulated rainfall at 50 mm h-1 for intervals from 10 to 60 min. Seal morphological properties along with thickness and porosity were evaluated from thin sections. The most common feature of seals formed in all of the soils was a disruptional layer with 30 to 50% fewer pores >0.02-mm diam. than unaffected soil. In readily sealed soils with sandy loam textures, low Fe contents, and high amounts of water-dispersible clay, this layer formed within the first 10 min of rainfall, and thickness and porosity were constant at longer rainfall durations. In other soils, longer rainfall durations were required to form a disruptional layer. In addition to the disruptional layer, other morphological features observed in the seals included a thin layer of micromass concentration that occurred at the soil surface (skin seal). At intermediate rainfall durations in readily sealed soils, this layer was overlain by a layer of micromass-depleted grains, which was removed by erosion at longer rainfall durations. Grain size and initial development in microtopographic lows suggest that the micromass-depleted layer formed by transport and redisposition rather than in-place disjunction of micromass.