Department of Primary Industries and Regional Development
The Transform Peel program focuses on 42 000 hectares (ha) due east of Mandurah called the Peel Food Zone, 75 kilometres (km) south of Perth in the shires of Murray and Serpentine Jarrahdale and includes an assessment of intensified and enclosed agriculture and a business park. The Peel Integrated Water Initiative was developed through Transform Peel to identify water sources and minimise the effect of these projects on water quality by reducing the nutrient loads discharged into the Peel–Harvey Estuarine System, which has been suffering from poor water quality for this reason.
The mineral sand miner MZI Resources Pty Ltd (MZI) is located within the Peel Food Zone and works to rehabilitate farmland they have mined that previously contributed to nutrient losses and water quality issues in the Peel–Harvey Estuary. Rehabilitation has potential to improve this landscape by reshaping the mined area and increasing the soil’s capacity for nutrients by mixing subsoil clay into the soil surface. Preliminary monitoring of run-off across the mine site and associated farmlands indicates a reduction of phosphorus (P) and nitrogen (N) of up to 87%. If the rehabilitation is sustained, when mining is complete the MZI mine site has the potential to reduce the P loss in Nambeelup Brook by up to 16%.
Using the clay from mining as a soil amendment on the predominantly sandy Nambeelup Catchment located outside the mine site could reduce P loss by over 68% (4.6t of P per year based on 2006–15 data). Glasshouse studies during this project supported this 68% reduction at a catchment scale, with a 75% reduction in P leaching and no decrease in pasture productivity.
Bentonite clay reduced P leaching from nearby intensive annual horticulture and improved agronomic soil properties. However, using the local MZI clay instead of bentonite as a soil amendment for horticulture is, potentially, a cheaper option. Notably, using MZI clay reduced P leaching, but not enough to reach the environmental target reduction of 50% to allow horticulture land use approval, and N leaching was extreme and not reduced by bentonite or MZI clay.
A soil testing program to improve fertiliser management in the Peel–Harvey Catchment has been carried out since 2009. Analysis of the results has shown most paddocks in the Peel–Harvey Catchment do not need P. Analysis of P fertiliser sales indicated that P use has declined in localities where soil testing and farmer training has been focused. Modelling showed that combining soil amendment and soil testing reduced P loss by 79% (5.3t of P based on 2006–15 data) in the Nambeelup Catchment.
The widespread use of clay for controlling P loss from pasture requires field assessment and demonstration at the farm scale. Switching the mine site’s land use to horticulture may reduce P loss normally occurring from these sands, but it would require substantial changes to the landform to reduce inundation and water retention, and minimise N loss downstream. Modifying the landscape would require testing to confirm its effectiveness, as well as changes to mining approval and rehabilitation requirements from several agencies.
Number of Pages
soil amendment, phosphorus, Peel-Harvey, soil testing, Transform Peel
Summers, R, Richards, P, Weaver, D & Rowe, D 2020, ‘Soil amendment and soil testing as nutrient reduction strategies for the Peel Integrated Water Initiative’, Resource management technical report 416, Department of Primary Industries and Regional Development, Perth.
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