Evaluation of Peat-Free, Compost-Based Growing Media for Organic Open-Field Tomato Production

The primary objective of this study was to evaluate experimentally formulated peat-free and peat-reduced growing media prepared from composts obtained from commercial composting facilities and intended for use in organic farming. The study aimed to assess these locally sourced, sustainable seedling substrates by examining their effects on seed germination, subsequent plant development, yield, and fruit quality parameters. During the 2023 and 2024 growing seasons, a standard peat substrate served as the control, while a pine-wood-chip-based material was used in treatment T9. Experimental seedling substrates were formulated using composts sourced from four facilities and mixed in different proportions. The formulations comprised either 100% green compost or 80% green compost combined with 10% pine wood chips and 10% peat. All treatments were amended with cattle manure at 1.5% (w/w). Seedlings were grown under controlled conditions for six weeks, and seedling emergence was recorded. Following transplantation into the open field, plant height and SPAD values were measured throughout the growing season. At harvest, the number of fruits, mean fruit weight, and yield per plant were recorded. Fruit samples were also analysed by high-performance liquid chromatography to determine their carotenoid, tocopherol, and vitamin C contents. Comparison of the four source-matched treatment pairs showed that adding 10% peat and 10% pine wood chips to an 80% compost base was associated with different responses depending on the treatment pair. These paired comparisons are descriptive because the effects of the altered components cannot be separated. Overall, the incorporation of green compost had variable effects on growing-medium performance. Several green-compost-based media were competitive with the peat control and may therefore represent promising alternatives for organic tomato seedling production. In particular, treatment T8 significantly increased yield per plant, while treatment T3 combined stable germination performance with an increased fruit vitamin C concentration. The results demonstrate substantial treatment-specific variation among the tested growing media. Because the compost source and formulation were not independently crossed in a complete factorial design, their separate contributions could not be determined.