Alternative sources of phosphorus for certified farms



Overall cost: 
Grant sought: 


Why this project: 

Development of the organic food sector is held back by a shortage of organic grain that is needed in almost every corner of the sector - from bread, breakfast cereals and snack foods, through to organic animal industries such as dairy and poultry. This is because low levels of available soil phosphorus in Australia are limiting organic grain production. Organic growers cannot use superphosphate to supply phosphorus for their crops.

The question is how to lessen this problem for farmers and ensure adequate crop nutrition on organic farms (see also Background, below).

Project goals: 

One possible way to improve the situation is to use wastewater precipitation products. The project seeks to clarify whether and under which conditions particular sources of phosphorus derived from wastewater, such as struvite (magnesium ammonium phosphate) or calcium phosphate, can be allowed as inputs in certified organic farming systems in Australia.

Also, if allowed in other countries, which are those countries and under which conditions is the use of these compounds allowed. If not allowed at present, what possibilities are there to have this input accepted in the future?   This project will seek to answer key questions concerning the situation in Australia and internationally (see also Questions to be answered, below). 

Project outcome: 

Answers to these questions, together with a cost benefit assessment of using phosphorus inputs currently allowed in Australian certified organic farming systems in comparison with potential future alternatives, will be presented in a discussion paper. The paper will be published on OTARE's website (, and sent to stakeholders such as the Australian certifying bodies. The aim is to get the results of the project in the public domain and to farmers as soon as possible.

People involved: 

Johannes Biala, Centre for Recycling of Organic Waste and Nutrients (CROWN), Brisbane.

Dr Paul Kristiansen, Associate Professor of Agricultural Systems, School of Environmental and Rural Science, University of New England (UNE), Armidale.

Proposed start: 
February 2018
Proposed finish: 
June 2018


Although organic growers cannot use superphosphate to supply phosphorus for their crops, they can use other sources, such as rock or soft phosphate, or tailor-made compost with elevated phosphorus levels.

A possible alternative for organic farmers might be the use of wastewater precipitation products such as struvite and calcium phosphate. Struvite is a slow-release phosphorus and magnesium fertiliser. It is produced from the decant water of anaerobic digestion facilities processing wastewater from municipal, food processing or intensive animal industry sources, by using magnesium salts in proprietary reactors. Alternatively, calcium phosphate can be produced but will generally result in reduced phosphorus capture efficiency (25% - 30% of influent P). However, P contained in calcium phosphate might be more plant-available and require lower capital cost for processing than struvite. Wastewater precipitation products contain very low levels of contaminants, even those made from municipal wastewater. Hence, struvite or calcium phosphate obtained from wastewater streams can offer a long-term sustainable source of phosphorus for organic farms, and ensure their continued productivity and production.

Questions to be answered


  1. What is the position of the Australian organic certification bodies regarding struvite / calcium phosphate becoming allowed as organic farming inputs and as means of overcoming the phosphorus deficit?
  2. If certification bodies are not in favour of struvite / calcium phosphate made from municipal and/or agricultural wastewater becoming an allowed farming input, what are the reasons? In other words: if this input is not allowed at present, what are the requirements and product specifications for this to occur?


  1. Is the compound acceptable under certified organic farming systems in different countries, by different certification organisations?
  2. What are the product specifications and conditions of use in some countries that are major trading partners?
  3. What is the position of IFOAM and other key international governing bodies on the use of wastewater precipitation products as a long-term sustainable means of supply phosphorus to organic farms?