Lizarralde Piquet, CAMcDowell, RichardCondron, LBrown, J2022-03-152022-02-2020222021-11-290028-8233H9JA6 (isidoc)https://hdl.handle.net/10182/14723Soils irrigated with phosphorus (P)-rich wastewater can increase the risk of P losses from land to water. We investigated if wastewater-irrigated soils can leach P through the soil profile and enrich groundwater. Soils were sampled annually for 20 years to 7.5 cm depth and for one year to 2.2 and 15 m. A mass balance showed that topsoils >200 mg L¯¹ Olsen P (and <50% anion storage capacity, ASC) were no longer accumulating P and had very high concentrations of water and CaCl₂-extractable P (designed to indicate loss to runoff and leaching, respectively). Samples in five paddocks showed substantial P leaching to 2.2 m, while sampling to 15 m showed leaching to 4.5 m depth. Deeper layers, especially in the 15 m deep cores, had a coarse texture and low capacity to sorb P, which caused high P concentrations (1.9 mg L¯¹) at one groundwater site. Based on these data preventing soils from reaching the thresholds of 200 mg L¯¹ Olsen P and 50% ASC is necessary to prevent excessive P losses.19 pagesen© 2022 The Royal Society of New Zealand.dairygrasslandleachingsorptionsubsurface flowthresholdstrendJournal Article10.1080/00288233.2022.20370911175-87752022-03-10ANZSRC::300410 Crop and pasture waste water useANZSRC::300403 AgronomyANZSRC::410601 Land capability and soil productivityANZSRC::410603 Soil biologyANZSRC::370703 Groundwater hydrologyANZSRC::300399 Animal production not elsewhere classifiedANZSRC::3004 Crop and pasture productionANZSRC::3108 Plant biology