Agricultural organic waste is increasing yearly. In Thailand, the palm oil industry generates high amounts of waste 13.71 million ton/year, mainly as boiler-ash and biogas-sludge. This study focused on the basic properties of boiler-ash and biogas-sludge from the palm oil industry after composting and their possible use as growing media for lettuce. Boiler-ash and biogas-sludge from the palm oil industry were pre-treated (composting) and after that evaluated as growing media in comparison with peatmoss under pot experiment conditions. Under the pre-treatment experiment, the results showed that the type of materials affected the pH, EC, OM, total N and the C:N ratio (P<0.05). The pre-treatment method was affected the pH and EC (P<0.05). The type of growing media and porous materials affected germination percentage, germination index, shoot length, and shoot fresh and dry weight (P<0.01). Interaction between the type of treated materials and porous materials affected germination percentage, germination index, shoot length, root length, and shoot fresh and dry weight (P<0.05). The best material was boiler-ash compost with perlite as the porous material which gave 92.6% germination, 23.05 germination index, 39.10 mm in shoot length, 28.67 mm in root length, 0.2 g shoot fw/plant, and 0.0397 g shoot dw/plant but these results were not statistically different from undisturbed boiler-ash with perlite as the porous material. Therefore, boiler-ash compost and boiler-ash left for 90 days were recommended to use as growing media.
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