Land treatment is the preferred option for the disposal of wastewater in New Zealand. We applied secondary-treated municipal wastewater to 4 contrasting soils ( a Gley, Pumice, Recent, and Allophanic Soil) at the rate of 50 mm per week, for 4 years. Amounts of N and P in applied wastewater, leachates, and removed in herbage were measured every 1 - 4 weeks, and a range of soil chemical, biochemical and physical characteristics measured by destructive sampling after 2 and 4 years. After 4 years, leaching losses amounted to 290 - 307 kg N on the Gley and Recent Soils, representing approximately 22% of the N applied. Leaching losses from the Allophanic and Pumice Soils were 44 and 69 kg N/ha, respectively, representing < 5% of that applied. More than half of the N leached was in organic forms. Leaching losses of P were < 5 kg P/ha on the Pumice and Allophanic Soils (< 1% of that applied), 41 kg P/ha from the Recent Soil and 65 kg P/ha from the Gley Soil (8% and 13% of that applied, respectively). After 4 years, the total C and microbial C content in the A horizon of the irrigated Recent Soil were, respectively, 47% and 44% less than non-irrigated cores. All irrigated soils showed a rise in pH of up to 1 unit, and all had a marked increase in the exchangeable Na+ which reached 4 - 22% ESP. After 4 years, the saturated and near saturated hydraulic conductivity of the Gley Soil had declined from 567 and 40 mm/h to 56 and 3 mm/h, respectively. Allophanic and Pumice Soils are to be preferred over the Recent and Gley Soils for effective treatment of wastewater and to minimise the loss of nutrients to the wider environment.
Sparling, G. P., Barton, L., Duncan, L., Mcgill, A., Speir, T. W., Scipper, L. A., ... Van Schaik, A. (2006). Nutrient leaching and changes in soil characterisitcs of four contrasting soils irrigated with secondary-treated municipal wastewater for four years. Australian Journal of Soil Research, 44(2), 107-116. https://doi.org/10.1071/SR05084