Salinity and sodicity influences on infiltration during surge flow irrigation

The interactive influences of water quality and surge-flow irrigation (intermittent application of water) on infiltration into a bare loam soil, packed into a long metal flume, were measured with a laboratory recirculating infiltrometer devised for the experiments. Cumulative infiltration and final infiltration rates were measured over three irrigation episodes using synthetic waters of different qualities. Four water-quality combinations of low and high salinity levels (i.e., electrical conductivity, EC=1.5 and 7.5 dS/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 that surge-flow cumulative infiltration of low saline waters - especially during the first irrigation episode - was lower than the corresponding continuous-flow cumulative infiltration. Conversely, it was higher for high saline and high saline-sodic waters. Effects of the water-quality treatments on final infiltration rate were similar to and in agreement with the effects on cumulative infiltration. However, the range of the final infiltration rates among surge-flow treatments was larger than with the continuous-flow treatments. Overall, infiltration was higher with surge-flow application of high saline and high saline-sodic waters than with the continuous-flow treatment. The observed contrasting results for the surge effect with the low saline, high saline, and high saline-sodic water-quality treatments were attributed to soil consolidation, formation of a depositional seal layer, and the different levels of irrigation water salinity and sodicity. It was concluded that the "surge effect" phenomena (reduction in soil infiltration caused by surge flow) under brackish (saline, sodic, and saline-sodic) water application was not pronounced and had adverse effects, in comparison to the low saline-sodic water application. Consequently, from theory, practical application of surge-flow irrigation under these circumstances, from viewpoints of infiltration reduction and irrigation efficiency improvements, is questionable.