Salinity and sodicity influences on infiltration during surge flow irrigation

The interactive influences of water quality and surge-flow irrigation (inte rmittent application of water) on infiltration into a bare loam soil, packe d into a long metal flume, were measured with a laboratory recirculating in filtrometer devised for the experiments. Cumulative infiltration and final infiltration rates were measured over three irrigation episodes using synth etic waters of different qualities. Four water-quality combinations of low and high salinity levels (i.e., electrical conductivity, EC = 1.5 and 7.5 d S/m) and low and high degree of sodicity [i.e., sodium adsorption ratio in the range of 5-10 and 25-35 mmol(1/2)l(-1/2)] were tested. Results showed t hat surge-flow cumulative infiltration of low saline waters - especially du ring the first irrigation episode - was lower than the corresponding contin uous-flow cumulative infiltration. Conversely, it was higher for high salin e and high saline-sodic waters. Effects of the water-quality treatments on final infiltration rate were similar to and in agreement with the effects o n cumulative infiltration. However. the range of the final infiltration rat es among surge-flow treatments was larger than with the continuous-flow tre atments. Overall, infiltration was higher with surge-flow application of hi gh saline and high saline-sodic waters than with the continuous-flow treatm ent. The observed contrasting results for the surge effect with the low sal ine., high saline, and high saline-sodic water-quality treatments were attr ibuted to soil consolidation. formation of a depositional seal layer. and t he different levels of irrigation water salinity and sodicity. It was concl uded that the "surge effect" phenomena (reduction in soil infiltration caus ed by surge flow) under brackish (saline, sodic, and saline-sodic) water ap plication was not pronounced and had adverse effects, in comparison to the low saline-sodic water application. Consequently, from theory, practical ap plication of surge-flow irrigation under these circumstances', from viewpoi nts of infiltration reduction and irrigation efficiency improvements, is qu estionable.