In the TOPKO project, the hydrochar and biochar are mixed with fresh compost. The charcoals are co-composted with green compost over a period of several weeks to months and are then available for planting trials. The compost in the mixtures has the task of colonising the charcoal with fungi and bacteria, which in turn break down any plant-damaging substances. At the same time, the compost brings a certain structure to the substrate, which ensures better aeration and drainage. The hydrochar in the substrate lowers the pH value, absorbs water and nutrients and releases these to the plants as required. Nutrients are also released in the course of the mineralisation of the biochar; the biochar can therefore be seen as a kind of long-term fertiliser. The biochar also stores water and nutrients so that they are available to plants. In addition, the solid carbon particles give the substrate a certain stability for aeration and drainage like compost, but without being mineralised. However, the greatest advantage of biochar is its stability against microbial decomposition. This means that biochar serves as a long-term store of carbon in the substrate. If these charcoal-based substrates are later buried in the garden soil at the end user (e.g. gardens of private households), a long-term carbon sink is created. The amount of carbon stored can then be determined using an environmental balance sheet.

The co-composting trials are initially carried out on a small scale (1-2 m³). Large-scale composting trials will be carried out at the project partner Moorkultur Ramsloh Werner Koch GmbH & Co KG to test the practical feasibility.

Pictures: Biochar and compost are piled up with a wheel loader (left picture) at the project partner Moorkultur Ramsloh to form an approx. 50 m³ pile (centre picture) and then mixed with a turner (right picture). M. Röhrdanz

Picture: Eight different coal compost mixtures of between 700 and 2000 litres were mixed partly by hand and partly with a wheel loader and composted for around four months.