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Potential phosphorus losses from grassland soils irrigated with dairy factory wastewater

journal contribution
posted on 2024-06-21, 03:50 authored by Carolina Lizarralde, Rich McDowellRich McDowell, Leo Condron, Jeffrey Brown
Applying phosphorus (P)-rich wastewater to land can significantly enrich P in topsoil and consequently increase the risk of P losses in surface runoff and leaching. We collected 654 samples of wastewater-irrigated and non-irrigated soils at seven sites across New Zealand to assess the potential P mobility in irrigated soils. The risk of P loss to surface runoff was tested by water extractable P (WEP) whereas the risk of P loss by leaching was tested by calcium chloride extractable P (CaCl2-P). The risk of P losses could be predicted only in non-irrigated soils, via a published relationship using anion storage capacity (ASC) and Olsen P. Wastewater-irrigated soils had a greater pH, WEP and CaCl2-P concentration to 30 cm depth. However, in both irrigated and non-irrigated soils a change point or threshold in ASC was found that could be used to show an increased likelihood of enhanced P leaching (as CaCl2-P) to deeper layers. In addition, the WEP and CaCl2-P thresholds can be used to signal the need for management changes to decrease the risk of P losses to surface water and groundwater.


Funded by the New Zealand Ministry for Business, Innovation and Employment's Our Land and Water National Science Challenge (Toitū te Whenua, Toiora te Wai) as part of project Phosphorus Best Practice


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  • English

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Journal title

New Zealand Journal of Agricultural Research

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