#23 Lærke: From bio-waste to fertiliser

How can we transition from mineral to biobased fertilisers?

Lærke Wester Larsen is a PhD student at the University of Copenhagen and part of the EU project LEX4BIO. Within LEX4BIO, scientists aim to optimise biobased fertilisers and to provide knowledge as basis for policies regarding the use of such fertilisers. Lærke looks at how well the biobased fertilisers work in the field, if there are environmental risks from using them and if they benefit the quality of the soil.

Department & Group: Department of Plant & Environmental Sciences, Soil fertility group

Supervisors: Lars Stoumann Jensen and Dorette Sophie Müller-Stöver

Dissertation title (as for now :)

Agronomic performance and environmental impact of novel biobased fertilizers

Topic – in brief

Mineral fertilisers either depend on finite resource, are energy intensive in their production –  or both. At the same time, society is confronted with detrimental effects and costs of having to deal with biological waste streams. Biobased fertilisers can close the loop between organic side-streams and agriculture as well as offer an alternative to mineral fertilisers.

Biobased materials that were formerly listed in waste regulations in the EU are now part of the Fertiliser regulation. Now it has to be assured that yields are not negatively impacted by using biobased fertilisers in the place of mineral fertilisers. And that they do not cause unwanted environmental pollution.

Main challenges compared to mineral fertilisers:

  • Biobased fertilisers may be less homogenous: as natural products they vary in composition
  • Biobased fertilisers may be less predictable: the availability of nutrients to crops depends on more factors

Lærke’s work

  • Impacts of biobased fertilisers on soil quality
  • Risk of ammonia volatilisation as environmental concern
  • Fertiliser replacement values of biobased fertilisers compared to mineral fertilisers; i.e. comparison of performance when it comes to yield


Soil quality (sometimes also referred to as soil fertility or soil health) describes the ability of a soil to ‘function’ and provide services such as provide nutrients to plants, filter water, buffer pollutants and sustain biodiversity. 

Lærke’s findings

  • Generally, it was found that biobased fertilisers improved soil quality indicators but to varying degrees.
  • Compost improved soil quality to the greatest extent but showed no fertilising effect.
  • The risk of ammonia volatilisation varies a lot with the different biobased fertilisers and is highest for digestates. It can be reduced by mixing the biobased fertiliser into the soil.
  • The biobased fertilisers generally performed well in the field experiments and for most of them they did not differ significantly from mineral fertiliser.

Additional thoughts:

  • Consumer and farmer acceptance could be an obstacle: Will people be okay with eating food that has been fertilised with processed animal bones or slaughter house waste?
  • Timing might be more important with biobased fertilisers than with mineral fertilisers as the availability of nutrients in biobased fertilisers is less ‘schedule-able’ than that in mineral fertilisers.

Lærke’s joys & struggles

Joys: Following her own curiosity & experiencing moments, when time is flying because findings or experiments are so interesting.

Struggles: balancing ambition and private life, accepting that experiments took longer than expected.

Lærke’s tip for PhDs (and anyone else): Keep track of your working hours to see how much you work. And then allow yourself to leave earlier or take days off when there is periods of less work-load. Seeing your extra-hours in numbers might make it easier for you to justify leaving early sometimes, in case you have a problems with it : )


Potential ammonia volatilization from 39 different novel biobased fertilizers on the European market – A laboratory study using 5 European soils

If you would like to connect with Lærke check out LinkedIn

Lærke’s funding: The Horizon 2020 project LEX4BIO.

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