de Jager, Megan und Giani, Luise und Röhrdanz, Michael
(2019)
Influence of hydrochar from hydrothermal carbonisation (HTC) on plant growth aspects and soil improvement.
In: Jahrestagung der DBG/BGS Erd-Reich und Boden-Landschaften, 24. – 27. August 2019,, Bern, Schweiz.
Kurzfassung
Hydrochar (HC), produced by hydrothermal carbonization (HTC), offers technical advantages compared to biochar (BC) produced by pyrolysis and is suitable for soil amelioration, carbon (C) sequestration, and enhanced plant growth. However, this suitability is dependent on the feedstock, HTC process conditions, application rate, and environmental and soil conditions. BC grain size has shown to influence, inter alia, nutrient retention, microbial colonization, and aggregate formation, however, such research for HC’s is lacking. This study conducted pot trials to investigate the influence of HC grain size (coarse (6.3-2 mm), medium (2-0.63 mm) and fine (<0.63 mm)), produced from biogas digestate, for soil improvement in three soils: loamy Chernozem, sandy Podzol, and clayey Gleysol, at a 5% HC application rate. All soils, including two controls (with and without plants) were analyzed for germination and bio-mass success, pH, and plant-available nutrients, namely phosphate (PO4), potassium (K) and mineral nitrogen (Nmin) content using standard laboratory methods. Results showed no germination inhibition using Chinese cabbage seeds at a 5% HC application rate, while its influence on biomass production was mostly insignificant. Soil pH showed a compensatory shift toward the pH of the HC, based on the initial pH of the soils and the HC. This effect was most pronounced in the fine-grained HC treatments. The HC served as a short-term source of nutrients, namely PO4, K (both nutrients showing the greatest effect in the fine-grained HC treatments) and ammonium (NH4+) due to the relatively more easily mineralized fraction of the HC, which allowed for the quick release of these nutrients. However, the duration of this contribution is dependent on the presence of this particular fraction in the soil. A relationship between HC and nitrate (NO3-) content was indeterminable due to the variable results between controls and HC grain size over the course of the study. In conclusion, the 5% HC application rate was insufficient to induce substantial changes to those soil properties affecting plant growth, nor to sustain a longer-term supply of nutrients.
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