Potting soils usually contain peat, which is formed from dead plant remains in bogs. However, peat extraction destroys the habitats of many plants and animals as well as a valuable carbon store. There are now alternative plant substrates such as coconut pulp and fibres. However, the raw materials have to be imported from India or Sri Lanka. In the TOPKO project, researchers at Oldenburg University of Applied Sciences and industrial partners now want to prove that regional raw materials are also suitable as a peat substitute for plant substrates.

Regional biochar-compost mixtures as a peat-free planting substrate

The project focuses on the production of various plant and hydro carbons from agricultural residues and waste materials. According to the researchers, green waste from landscape conservation and in particular from extensive peatland management such as paludiculture is used for this purpose. The aim of the project is to develop a market-ready, peat-free and regional garden substrate that can be used in agriculture, tree nurseries and private horticulture.

The production of hydrochar by means of hydrothermal carbonisation (HTC) focuses on liquid agricultural residues such as liquid manure or fermentation residues from biogas plants. Green cuttings are used for the biochar produced by pyrolysis. According to the researchers, hydrochar and biochar are then mixed with compost individually or together in different ratios to create new plant substrates.

Determining sustainability and market opportunities

Whether the novel coal-compost mixtures are suitable as peat-free potting soil will be tested as part of the project, initially under controlled conditions in the greenhouse and later in so-called container trials with typical trees and shrubs from the nursery. The researchers also want to use life cycle assessments to evaluate the sustainability of the carbon cycle and determine the acceptance and market opportunities of the new plant substrates as part of socio-economic analyses.

The ‘Peat-free, climate-friendly plant substrates from hydro and pyrolysis coal’ (TOPKO) project will run until 2027 and is being funded by the Federal Ministry of Food and Agriculture (BMEL) with around 633,000 euros.

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