Investigation of Biochar Potential to Improve Plant Growth and Water Retention in a High-Quality Potting Mixture

Biochar from lignocellulose-rich (woody) agricultural wastes has previously been shown to improve water holding efficiency and plant growth when added to low-quality soils. However, the potential of biochar from cellulose-rich feedstocks, and biochar’s potential with already excellent quality soil, is limited. In particular, it is unclear to what extent cellulose-rich biochar amendment from food waste is effective to improve the quality of potting mixture (PM), promote plant growth, and reduce water demand. Therefore, biochar was produced from cabbage wastes at 360 °C by pyrolysis and characterized along with PM. The plant growth rate was tested for basil (Ocimum basilicum) and bermudagrass (Cynodon dactylon) in 0% (control) and 4% biochar for 50 days. Biochar addition of 4% to PM creates a more neutral pH. Biochar addition increased basil plant height by 20%, though not statistically significant. Biochar showed no notable difference in the number of leaves and germination rate. Grass height did not show considerable improvement. However, there was an absolute increase of 21% for the water holding capacity with a 4% biochar amendment. The results suggest that the application of food waste biochar has some potential to improve even high-quality soil, though the benefits, if realized, will be significantly more limited than those previously reported for poor quality soils.