Irrigation with effluent water: Effects of rainfall energy on soil infiltration

Seal formation at soil surfaces is significantly affected by raindrop kinetic energy (KE). We hypothesized that the deterioration in seal permeability of soils irrigated with effluents, relative to that of soils irrigated with fresh water (FW), is affected by raindrop KE. The effects of four droplet KE levels (3.6, 8.0, 12.4, and 15.9 kJ m(-3)) on the infiltration parameters of four Israeli smectitic soils that had been irrigated with FW or effluents, were studied with a drip-type rain simulator. At the Lowest KE (3.6 kJ m(-3)), final infiltration rate (IR) values for the FW-irrigated samples were in the range of 9 to 14 mm h(-1) and were significantly higher than the corresponding values for the effluent-irrigated samples, suggesting that seals mere not fully developed at this low KE and that the irrigation water type played a major role in determining soil permeability. At high KE (15.9 kJ m(-3)), the differences between the final IRs of FW-irrigated and effluent-irrigated samples of a given soil were small (<1.1 mm h(-1)), suggesting that at high KE, the effect of drop impact overshadowed the effects of water quality on the final IR. Rate of seal formation was faster in the effluent-irrigated samples than in the FW-irrigated ones, regardless of rain KE. The sensitivity of all four soils to the use of effluents was the greatest at a rain KE of 8 kJ m(-3). At both lower and higher rain KE levels, the effect of effluents on the final IR, relative to that of FW, was less severe.