Evaluation of physico-chemical properties of biochar-based mixtures for soilless growth media

Abstract

This study was done to evaluate the suitability of biochar-based mixtures for growth media. Biochars from agricultural wastes were produced by slow pyrolysis at 300 (B300) and 500 °C (B500). Organic substrates/biochars of sawdust (Sd), wheat straw (WS), rice hull (Rh), palm bunches (Plm) and sugarcane bagasse (SC), and inorganic substrates of vermiculite (V) and zeolite (Z) were used to prepare growth media. Based on the criteria of high water holding capacity (WHC), easily-available water (EAW), water buffering capacity (WBC), air-after-irrigation (AIR), low bulk density (BD), EC, pH, and water drop penetration time (WDPT), thirteen growth media were prepared with different volumetric ratios of individual substrates. Incorporation of biochars/inorganic components increased BD, pH, and EC of the mixtures compared to cocopeat-perlite. The EAW, WHC, and WBC were greater in the biochar-based mixtures than cocopeat-perlite. Physical properties of the biochar-based mixtures were within the optimum ranges for growth media (AIR > 10%v/v, WBC = 4‒10%v/v, WDPT < 50 s). All substrates except Rh-SCB300-Z, Plm-SCB300, and WSB500-Rh-V were not water-repellent (WDPT < 50 s) suggesting no hydrophobicity limitation for the use of these materials. The highest WHC was observed in Plm-WSB300-V, and WS-V and PlmB300-WS-V had WHC values similar to cocopeat-perlite. Overall, biochar-based mixtures such as PlmB300-WS-V and WSB500-Rh-V are suitable substitutes for cocopeat-perlite.