Krystyna Malińska: Poultry manure – nutrient recycling and beyond

Poultry manure as a source of nutrients
The composition of poultry manure depends on a number of factors, including a breeding type and a breeding system, seasonality, but generally poultry manure is high in water (68-73%) and contains nitrogen (3-5%), phosphorous (0.9-3.5%) and potassium (1.5-3%) (after Kacprzak et al., 2022) making it a valuable natural fertilizer or a feedstock for production of various bio-based fertilizing products and soil improvers. Typical and quite common practices for managing poultry manure in Poland include direct soil application through land spreading of unprocessed poultry manure as well as applying different fertilizing products such as poultry manure derived composts, dried poultry manure in a form pellets, granules, etc.

Facing challenges and limitations
Although poultry manure is rich in nutrients such as nitrogen, phosphorous and potassium – making it a valuable natural fertilizer - it also contains various microcontaminants such as pharmaceuticals, heavy metals and also microorganisms which are potential threats to the environment, specifically to agricultural soils.  Handling, transporting and managing of poultry manure – especially from small and medium sized farms located in non-rural areas – poses many difficulties. Mostly, this is linked to high contents of moisture and organic matter, thus high susceptibility to decomposition contributing to e.g. gaseous emissions of ammonia, nitrous oxide, methane. Land spreading is no longer a sufficient method for management of unprocessed poultry manure to assure nutrient recycling and environmental safety. Composting of poultry manure still faces technological challenges due to high content of nitrogen, and thus, potential loss of nutrients through gaseous emissions (mostly ammonia) and leaching. Therefore, the excessive quantities of poultry manure need to be properly handled and managed to avoid air, water and soil contamination. 

From poultry manure to a versatile material with interesting properties
Poultry manure can be also managed with the use of pyrolysis to obtain biochar. Pyrolysis is a well-known thermal conversion of various types of biomass into biochar – a solid, carbon rich material with interesting chemical and physical properties such as chemical composition, specific surface area, porosity and presence of various surface functional groups. With pyrolysis parameters (e.g. pyrolysis temperature and heating time) and also different chemical and physical modifications biochars from poultry manure can be tailored to address specific applications.

Poultry manure derived biochars – depending on their properties – demonstrate high potentials to be used in various in-soil applications but also in many other areas. Primarily, biochars from poultry manure are used as soil improvers or components in developing bio-based fertilizing products to reduce the use of non-renewable fossil based mineral fertilizers. What is more, these biochars can be used as partial or complete peat substitutes in horticultural growing media. They can also function as sorbents to remove various contaminants from water and wastewater or prevent excessive gaseous emissions e.g. ammonia emissions during composting. For over two decades now, the properties and novel applications of different types of biochars have been excessively studied and new applications have been explored. One of these new applications is the use of biochar for developing bio-based and biodegradable plastics.

Biochars are considered potential renewable and sustainable fillers for developing bio-based and biodegradable plastics for agricultural use (so called “agribioplastics”). Bio-based and biodegradable plastics are alternatives to the conventional fossil-derived plastics which usually do not biodegrade, and thus are considered a serious source of microplastic pollution in agricultural soils. The idea is to incorporate biochar into the composite or blend and reduce the use of biodegradable polymers/blends in single-use “agribioplastics” such as those used in growing ornamental and edible plants (e.g. clips, supports, ties or mulching films). After harvesting these biochar-filled “agribioplastic” accessories mixed with plant residues can be managed through industrial composting. This assures efficient end-of-life management of plant residues and prevents from microplastic contamination.

Future outlook
With all the research work and field testing performed so far (e.g. Nutri2Cycle, H2020, 2018-2023), there is no doubt that poultry manure is a valuable source of nutrients and a feedstock for various products such as bio-based fertilizers or soil enhancers. With the current dynamics in poultry production in Poland it is anticipated that the quantities of poultry manure will be on the increase. Therefore, new solutions for sustainable and circular nutrient management will be needed to work towards the goals set by the European Commission in the Farm to Fork Strategy, primarily to decrease nutrient losses by at least 50% and to reduce fertilizer use by at least 20% by 2030. Poultry manure derived biochar – a versatile material with interesting properties and applications – is considered a promising sustainable and circular solution to address the most pressing environmental issues and contribute to decrease in nutrient losses, mitigation of gaseous emissions and reduction of non renewable resources (being an alternative to peat or a filler in “agribioplastics”). Although, in Poland scaling production of biochars from different types of feedstock still remains a challenge, there is a lot of research work currently being done to overcome technological issues. In addition to that, currently launched initiatives such as these within the AGRI-BIOCIRCULAR-HUB project (HORIZON-WIDERA-ACCESS: Excellence Hubs, 2025-2028) with various organizations from Ukraine, Latvia, Poland, Belgium and Spain are to enhance development and adoption of smart and circular technologies and innovations towards sustainable agriculture.

References
Dróżdż et al. 2020: https://doi.org/10.1016/j.jenvman.2020.110327 
Kacprzak et al. 2022: https://doi.org/10.1080/10643389.2022.2096983 
Malińska et al. 2024: https://doi.org/10.3390/ma17246208
Projects: Nutri2Cycle (H2020, 2018-2023), AGRI-BIOCIRCULAR-HUB (HE, 2025-2028)