HYDRAULIC-PROPERTIES OF SURFACE SEALS IN GEORGIA SOILS

To predict infiltration in a sealing soil, the seal hydraulic conductivity as a function of time or cumulative rainfall must be known. Few studies have reported measured seal hydraulic conductivities in soils from the southeast USA. Seven Georgia soils packed in columns were subjected to simulated rainfall at an intensity of 50 mm h(-1). The sandy loam soils were easily disrupted by rainfall. The calculated seal hydraulic conductivities (K-c) dropped sharply in 10 min of rain and were less than 10% of the initial saturated hydraulic conductivity (K-c) after 45 min. The sandy loam sail with low aggregate stability and Fe content was especially prone to sealing in that K-c dropped to 4% of K-c after 10 min. The well-structured soil with a clay texture declined in K-c gradually with time, indicating a high resistance to rainfall energy. The sandiest soil show-ed intermediate resistance to raindrop impact, and K-c leveled off at a high value after 20 min due to the low clay content. The loamy soil with smectitic clay had the lowest K-c and showed little change in K-c with time. Relative seal hydraulic conductivity after 10 or 60 min of rain were good indices differentiating the relative resistance of these soils to surface sealing. A sail stability factor, used to characterize the decrease of K-c in an exponential decay equation, was significantly correlated with water-dispersible clay on a soil basis.