Effects of irrigation intensity on preferential solute transport in a stony soil

Abstract

If irrigation intensity exceeds soil infiltration capacity, water may flow preferentially down cracks and large pores. In this situation, solute transport will involve only a fraction (ft) of the soil’s water and leaching rate may be affected. To assess whether irrigation intensity affects preferential solute flow, an experiment was performed at Lincoln using 12 steel-encased lysimeters with a Lismore Stony Silt Loam soil under two irrigation intensities, 5 and 20 mm h⁻¹. Burns’ equation was used to describe the measurements of non-reactive tracer concentration as a function of drainage. Under dry antecedent moisture conditions, bromide transport was not significantly different under the different irrigation rates, even though strong preferential leaching occurred, with (ft) of 0.23. For chloride, (ft) was 0.85 and 0.58, for 5 and 20 mm h⁻¹ respectively, sufficient evidence to confirm the effect of irrigation intensity (P < 0.05). By assuming (ft) to be 1.00 for the median rainfall at Lincoln, an exponential function was fitted to the data, suggesting a lower limit of 0.35 for (ft) under moist conditions. Implications for nutrient leaching are discussed.