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

Seal formation at soil surfaces is significantly affected by raindrop kinet ic energy (KE). We hypothesized that the deterioration in seal permeability of soils irrigated with effluents, relative to that of soils irrigated wit h 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 paramete rs of four Israeli smectitic soils that had been irrigated with FW or efflu ents, were studied with a drip-type rain simulator. At the Lowest KE (3.6 k J 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 th e 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 effl uent-irrigated samples of a given soil were small (<1.1 mm h(-1)), suggesti ng that at high KE, the effect of drop impact overshadowed the effects of w ater quality on the final IR. Rate of seal formation was faster in the effl uent-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 greates t 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 sever e.