Coal fly ash-based synthetic aggregates as potential alternative container substrates for ornamentals

This research was carried out to study the characteristics and the potential utilization of coal fly ash-based synthetic aggregates (CSA) with oil palm waste as an alternative container substrate for ornamental-plant production. CSA only, oil palm waste only, and two mixing ratios of CSA with oil palm waste at the ratio of 1:5 and 1:10 (V/V) were utilized under this study. Zeolite was utilized as a standard substrate to compare characteristics of other substrates. The physical and chemical properties of all substrates were characterized. Scanning electron microscopy (SEM) of coal fly ash and CSA were conducted in order to study the structural configuration of the CSA. Developed CSA gave an alkaline pH (9.82), high electrical conductivity (96.1 mS m⁻¹), high cation concentrations, high water-holding capacity, and low bulk density (0.56 g cm⁻³) compared to zeolite. Mixing of CSA with oil palm waste at the ratio of 1:10 gave enhanced physical and chemical properties such as bulk density (0.25 g cm⁻³), particle density (1.76 g cm⁻³), air space (20.6%), total pore space (85.8%), total water-holding capacity (652 mL L⁻¹), pH (6.18), and electrical conductivity (42.4 mS m⁻¹), which were in the established ideal substrate range. Moreover, SEM study revealed that CSA is a dual-composite material, which had well enmeshed coal-fly ash particles in the fibrous paper-waste matrix creating porous spaces within the aggregate. The growth of French marigold (Tagetes patula), which is a popular ornamental plant in Japan, was assessed using these newly developed substrates. The mixing ratio of CSA and oil palm wastes at 1:10 reported the best maximum growth and yield parameters of French marigold, with increase in shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, plant height, and number of flowers per plant by 51%, 93%, 54%, 150%, 19%, and 61%, respectively, compared to the zeolite. It is revealed that a mixture of CSA and oil palm waste at the ratio of 1:10 can be successfully utilized as an alternative container substrate for French marigold production.