Nitrate leaching from a municipal sewage irrigated soil in New Zealand

Land application of municipal sewage effluent is becoming increasingly popular worldwide as a means of disposal, treatment, nutrient recycling, irrigation to meet plants' water requirements, and groundwater recharge. We investigated nitrate leaching from a volcanic soil (Typic Udivitrand) under Pinus radiata plantation near Rotorua, New Zealand, which had received, on average, 0, 29, and 88 mm per week tertiary-treated municipal sewage effluent for the previous 4 years. Four replicate undisturbed lysimeters (200 mm diameter x 200 mm depth) from surface soil were used to study the influence of three different rates of effluent application on N leaching from topsoil. Breakthrough curves were characterised by a rapid emergence of nitrate-N in the drainage samples, and indicated that soil nitrate was readily leached beyond the topsoil. Nitrate concentrations in the drainage water increased substantially with effluent application rate, almost reaching the World Health Organisation recommended limits (approx. 10 g m(-3)) in plots receiving effluent at the highest rate. Possible strategies for minimising nitrate leaching losses under effluent irrigation are discussed.