High-energy-moisture characteristic aggregate stability as a predictor for seal formation

Past attempts to use aggregate stability to predict soil susceptibility to seal formation indices (final infiltration rate and runoff) have yielded inconsistent results. We hypothesized that determining aggregate stability in a method in which a controlled wetting process was used to break aggregates will correlate well with seal formation indices, as the latter strongly depend on rate of aggregate wetting. We studied aggregate stability from soils varying in clay content, and exchangeable Na percentage (ESP), using the high-energy-moisture-characteristics (HEMC) method. Aggregate stability indices were correlated with previously published seal formation data for the same soils. Aggregates were placed in a funnel equipped with a fritted disk, and wetted either fast (100 mm h(-1)) or slow (2 mm h(-1)), using a peristaltic pump. Thereafter, the aggregates were subjected to a stepwise increase in matric potential up to 5.0 J kg(-1), to obtain a moisture retention curve, which served as the base for calculations of stability parameters. Aggregate stability correlated with clay content, but not with soil organic matter. Aggregate stability and sodicity correlated only in clay soils. Generally, poor correlation (R < 0.5) was obtained between aggregate stability and seal formation and runoff data, irrespective of soil ESP, when infiltration and runoff measurements were carried out on fast-wetted soils. Conversely, aggregate stability significantly correlated (R > 0.70) with seal formation and runoff data from slow wetted soils for samples having ESP of <6.6. Our results suggest that aggregate stability determined with the HEMC method could serve as a predictor for soil susceptibility for seal formation only under the aforementioned specific conditions.