HTC-biochar as a soil conditioner – first results from a field trial with sugar beet

Addition of biochar derived from hydrothermal carbonization (HTC-biochar) to agricultural land may compensate for the growing humus-carbon deficit, caused by the increasing removal of crop residues, simultaneously offering the potential to sequester carbon. The objective of this study was a preliminary evaluation of HTC-biochar as a soil conditioner. A field trial was conducted on Luvisol near Göttingen, where two HTC-biochars (C:N 16, 38) were incorporated in spring 2010 at a rate of 10 t ha–1 (dry matter). Immediately afterwards, sugar beet was grown with four nitrogen (N) fertilization rates (0–150 kg N ha–1). The investigated soil chemical and physical properties were not affected by HTC-biochar addition. Three months after application, 12% of the carbon supplied to soil as HTC-biochar were already released as CO2. Compared to the non-amended control, adjusted sugar yield was reduced when HTC-biochar characterized by a wide C:N ratio was combined with zero N fertilizer application. The results suggest that HTC-biochar affected the N availability probably due to microbial immobilization processes.