Hydrothermally treated Eucalyptus globulus bark: an innovative organic material for plant substrates

C. Chemetova, J. Gominho, A. Fabião, H. Ribeiro
Eucalyptus globulus is the major pulpwood species planted in temperate regions worldwide. Bark surplus from the pulp industry has a low production cost and is permanently and locally available. This renewable resource may have potential for future substrate outlook. The present work evaluates fresh E. globulus bark (FEB) and studies the optimal hydrothermal treatment conditions, using response surface methodology approach. Model tested simultaneously the effect of time (t: 20-60’) and temperature (T: 60-140°C) on bark properties, resulting in nine different hydrothermally treated barks (HTBs). FEB and HTBs were blended at 25 and 50% (v/v) (M25; M50) with peat and evaluated in a pot experiment with Chinese cabbage. FEB was phytotoxic (0% root index of cress seeds and hydrothermal treatment was an effective technique to remove phytotoxicity, with an average root index in HTBs of 86.4%). Treatment temperature affected bark biological stability. During 14 days incubation, the HTBs treated with high temperatures (≥140°C) led to a high nitrogen immobilization (26.5 mmol N L‑1 bark) compared to low temperature (≤60°C) treatments (7.6 mmol N L‑1 immobilization) and FEB (11.2 mmol N L‑1 immobilization). Bark treatments had no effect on physical properties of each blend percentage. However, increasing bark percentage in the blend led to a significant increase of air-filled porosity at a suction of 1 kPa (from 9.1% in peat to 24.2% and 48.8% in M25 and M50 blends), and a decrease of easily available water (32, 25.9 and 13.8%, for peat, M25 and M50 blends, respectively). Potting tests showed greater Chinese cabbage growth in M25 compared to M50, because of lower water availability and nitrogen immobilization in M50 blends. Model responses for bark treatment suggests the lowest bark N immobilization (5.1 mmol N L‑1) at 40°C which means potential for resource exploitation by mixing 25% HTB with peat-based substrates.
Chemetova, C., Gominho, J., Fabião, A. and Ribeiro, H. (2019). Hydrothermally treated Eucalyptus globulus bark: an innovative organic material for plant substrates. Acta Hortic. 1266, 207-214
DOI: 10.17660/ActaHortic.2019.1266.29
wood fiber, hydrothermal treatment, phytotoxicity, biological stability, physical properties

Acta Horticulturae