Utilization of Acacia cyanophylla-Based Compost as a Renewable Alternative for the Production of Tomato (Solanum lycopersicum L.) Seedlings

Peat-based substrates are the preferred growing media in conventional and organic nursery production. However, there is growing interest in environmental impacts associated with peat extraction. The current study aims to see whether peat can be totally replaced with Acacia cyanophylla-based compost when used as soil media for nursery production. Acacia cyanophylla-based compost (100%) and a peat-based growing media (0% compost) along with the mixtures of varying proportions of compost at 25, 50, and 75% with the peat-based growing media were tested for the production of tomato (Solanum lycopersicum L.) transplants. The experiment was established in a completely randomized design. Different physical and chemical properties such as organic matter, electrical conductivity, porosity, and water content at saturation were determined for each cultivation substrate. Seed germination and different germination parameters (first germination time, mean germination time, speed of germination, coefficient of uniformity of germination, germination index), survival and several plant growth variables including seedling height, root collar diameter, height/diameter ratio, number of leaves, leaf area, fresh and dry weight of seedlings, and the shoot/root dry weight ratio were recorded. Growth variables were measured on all surviving seedlings at the end of the growth period, when seedlings reached commercial transplant size. All tested substrates, except 25% compost, significantly increased germination rates compared to the control substrate (100% peat-based substrate). Substrate type had no influence on survival rate, but significantly influenced seedling growth. Lowest mean values of both height (11.6 ± 0.5 cm) and diameter growth (2.7 ± 0.07 mm) were observed within the control, although significant differences were only noted under 75% compost (13.9 ± 0.4 cm) for seedling height, and 75% compost (3 ± 0.07 mm) and 100% compost (3 ± 0.07 mm) for seedling diameter. Results show that compost-based substrate may be a suitable substrate for tomato seedling production, since all tested substrate treatments had comparable or better effects on any of the studied growth parameters when compared to the peat control substrate. Therefore, a substrate of Acacia cyanophylla wastes can be used to successfully grow tomato transplants.