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Imports of fertiliser phosphorus can be drastically reduced

A better understanding of the content and availability of phosphorus in waste products can help farmers reduce imports of phosphorus for crop fertilisation by two thirds.

[Translate to English:] Landbruget kan spare en del fosforgødning ved et bedre kendskab til restprodukters indhold af fosfor - til gavn for blandt andet miljøet. Foto: Janne Hansen

Phosphorus is an essential element for both plants and animals, but in the future there may be a shortage of this vital mineral because the rock phosphate that fertiliser phosphorus is mined from is a limited resource. Already there is worldwide demand for fertiliser phosphorus with prices rising as a result, and most of the known phosphorus resources are found in very few countries such as Morocco and China. There is therefore every reason why this resource should be conserved.

 

A new project that scientists from the Department of Agroecology at Aarhus University are leading aims to reduce Denmark's import of the precious phosphorus while avoiding the over- or under-supply of phosphorus to crops. The key to solving this problem is to learn about the plant availability of phosphorus in various waste products.

 

The project is a collaboration between Aarhus University, Knowledge Centre for Agriculture, Eurofins Agro, Danish Standards, Norconsult, Herning Water, Aarhus Water and HedeDanmark. It has a total budget of 14.6 million DKK of which 10 million was financed by the Green Development and Demonstration Programme (GUDP) of the Ministry of Food, Agriculture and Fisheries.

                                                            

The goal is to develop a method to determine the fertiliser value of the phosphorus in waste products such as sewage sludge, ash, struvite and biochar, and also in various fractions of animal manure.

 

- By declaring the phosphorus fertiliser value in waste products and animal manures, crops can receive precisely the amount of phosphorus they need. This means that instead of importing mineral phosphorus, we can utilise phosphorus from the animal manure sources we have in Denmark, explains associate professor Gitte Rubæk from the Department of Agroecology at Aarhus University.

 

Economic and environmental benefits

With a more efficient use of Danish sources of phosphorus, Danish farmers can reduce imports of phosphorus in commercial fertilisers to one third of the current level. Sales of waste products will increase and there will be a new market in the analyses of phosphorus fertiliser values. There will also be a market for alternative sources of fertiliser phosphorus to replace phosphorus from commercial fertiliser. Some of these alternative sources may in the long term also be used in organic farming.

 

There will also be a gain for the environment, since agricultural phosphorus surpluses can be reduced by 33 per cent.

 

The project partners will jointly analyse, describe, test and label phosphate fertiliser products and they will develop a decision-support tool that can guide the farmers in their selection of fertiliser phosphorus source.

 

Mapping of residues

The project will develop a model analysis package for determining the phosphorus fertiliser value of different waste products. The scientists will describe products that are adapted to specific fertilisation purposes and prepare labelling guidelines for the producers of these products. The project will also investigate the regulatory and market barriers to the use of waste products in conventional and organic crop production and focus on overcoming these.

 

- The idea is to ensure that residues can safely be used as a phosphorus fertiliser without risking yield losses due to phosphorus deficiency and that the products can be used in such a way that accumulation of phosphorus in agricultural soil is avoided. This will boost the value of the residues, says Gitte Rubæk.

 

An important element of the project is the investigation of the bioavailability of the phosphorus in waste products. The type and amount of fertiliser P is closely linked to the soil mechanisms of fixing and releasing phosphorus. This interaction determines how much phosphorus is actually available for crop uptake.

 

- Especially for complex composite residues there is a significant interaction between soil and residue which is not reflected in a traditional solubility analysis. This interaction can affect the release of phosphorus for up to several years after the fertiliser has been applied to the soil. The phosphorus fertiliser value therefore varies both from residue to residue, between soil types and over time, explains Gitte Rubæk.

 

For further information please contact: Associate professor Gitte Rubæk, Department of Agroecology, e-mail: gitte.rubaek@agrsci.dk, telephone: +45 8715 7686