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

If irrigation intensity exceeds the soil infiltration capacity, water may flow preferentially down cracks and large pores. In this situation, solute transport will involve only a fraction (f_t) of the soil’s water and leaching rate may be affected. To test the hypothesis that irrigation intensity does not affect solute preferential 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. Burn’s Equation was used to describe the measurements of non-reactive tracer’s concentration as function of drainage. For chloride, f_t was 0.85 and 0.58, for 5 and 20 mm/h respectively (P < 0.05), sufficient evidence to reject the hypothesis. Further, by assuming f_t to be 1.00 for 0.5 mm/h (median rainfall at Lincoln), we found that an exponential function fitted the data and a lower limit for f_t was 0.35. Implications for nutrient leaching are discussed.