Focus on Phosphorus: Agronomic strategies enhancing utilisation of insoluble phosphorus sources through amendments.

Project code: ELD03925

Project manager: Adam Hancock

Project duration: April 2025 - April 2026

 

 

About the project

This project aims to assess selected amendments or additives to monoammonium phosphate (MAP) to reduce the precipitation of soluble phosphorus (P) in calcareous, alkaline and high phosphorus buffering index (PBI) soils in South Australia (SA) Lower South East (LSE). 

Nutrient deficiencies are a key factor contributing to the disparity between actual yields and the predicted potential in the high rainfall zone. Surveys conducted by MFMG grower members highlight that improving the understanding of P cycling in these soils, along with the influence of CaCO3% on P investment decisions, could encourage broader adoption of soil testing and help narrow the yield gap.

This project will establish a trial site at Bool Lagoon comparing novel P treatment ideas and strategies.

The project will also fund further work on showcasing how variable rate P application can improve fertiliser management. The paddock hosting the trial site will be grid tested and analysed using OneSoil Pro (https://yield.onesoil.ai). Grid testing for the percentage of calcium carbonate (CaCO3%) is uncommon, this measure can assist in determining the spatial variability of calcareousness in paddocks. The use of this data layer to inform P applications will be explored.

The project funding includes an extension event organised by MFMG for growers in the Lower South East. The event will include other researchers with recent phosphorus research to present and conclude with Dr Melissa Fraser on practical decisions.

 

Project Objectives

• A replicated randomised trial site will be sown in 2025 and managed by SARDI, located south of Naracoorte, on a P responsive site where the Colwell P is below the critical range for wheat. The Colwell P range at Bool Lagoon is provided as 39-68 mg/kg. The site will be alkaline, have a high PBI, and contain more than 15 % CaCO3. This soil type will capture the treatment effect on calcareous soils.
• Site selection will be assisted by a 1 ha grid soil test being collected from the selected trial paddock to gauge the spatial variability of CaCO3%, DGT-P, PBI, Colwell P, and pH. These maps will assist with trial site location and will form part of the extension, showcasing precision agriculture for P management.
• Nineteen treatments will be evaluated
• A phosphorus response curve for the site using MAP
• MAP placement treatments, deep banded and broadcasted
• Fertiliser additives including sulphur bentonite and humic granules
• Compost treatments
• Liquid injection including APP versus liquid MAP.

 

Trial Results will be communicated to growers through:

• a half-day workshop in late August 2025 for Lower Limestone Coast growers
• an episode of The Prosperous Farmer podcast
• inclusion in the 2025 Annual MFMG Trial Results book

 

This project is funded by:

This project is supported by South Australian Grain Industry Trust and SA Drought Hub through the Australian Governments' Future Drought Fund. 

                        

 

This project is supported by:

SARDI

CSIRO

 

Project Resources: