Responses of cabbage (brassica oleracea var. capitata), swiss chard (beta vulgaris), and pepper (capsicum annuum) seedlings to growing media pre-enriched with vermicompost.

Abstract

Seedling production is mainly achieved by using growing media as substrates; most nurseries in South Africa use pine bark and vermiculite in their ‘in-house’ medium. For the growing medium to effectively anchor and yield healthy and sound seedlings to develop into a mature vegetable crop, it must have a balance of certain physical, chemical and nutritional properties. The study was conducted concurrently at two nurseries (Top Crop Nursery and Sunshine Seedlings®) differing in nursery management and growing media types to investigate physical, chemical, and nutritional properties of growing media to develop various growing media mixes. These media were tested for their suitability for vegetable seed propagation, by monitoring and recording seedling growth parameters from sowing to the saleable seedling stage. Top Crop Nursery used the wattle and pine bark, whereas Sunshine Seedlings® used their standard growing media (75% Coir, 13% Peat, 12% Vermiculite + 0.2% Osmocote®). The study then tested the responses of cabbage (Brassica oleracea var. capitata), Swiss chard (Beta vulgaris var. cicla), and pepper (Capsicum annuum) seedlings. When developing growing media mixes, the pre-enrichment of growing media with vermicompost at varying levels of 0-20% was practiced at both nurseries. Top Crop Nursery had 15 treatments, with three controls (treatment 1, 2, and 3), where treatment 1 was pure pine bark, treatment 2 was pure wattle bark, treatment 3 was 50% pine bark and 50% wattle bark. Treatments 4 to 7 were pure pine bark with vermicompost pre-enrichment ranging from 5 to 20%. Treatment 8 to 11 were pure wattle bark with compost pre-enrichment ranging from 5 to 20%, whilst treatment 12 to 15 were 50% wattle bark + 50% pine bark with the same pre-enrichment ranging from 5 to 20%. Sunshine Seedlings® had 6 treatments with two controls (treatment 1 and 6), where treatment 1 was Sunshine Seedlings® Seedling Mix with 0% vermicompost, and treatment 6 being the Sunshine Seedlings® Mix without Osmocote®, with 0% vermicompost.

From sowing, emergence was recorded daily, until all replications showed no further germination. Other parameters (root development, leaf number, seedling height, pest and diseases, general appearance of the seedlings) were recorded on a weekly basis throughout the seven weeks of each experiment. Measuring chlorophyll and seedling mass was carried out at the saleable seedling stage, at week 7. Seedlings were randomly sampled for seedling mass (wet mass taken in field, dry mass taken after laboratory oven drying). From both nursery sites, statistical analysis for days to emergence, leaf number and seedling height showed no significant differences. Seedling mass, chlorophyll content and nutrient uptake showed significant differences, with cabbage showing greater mass gains over the seedling growing period, up to 10.46 g per 20 seedling tops. Statistical analysis revealed differences in nutrient uptake by the three crops at both nurseries. Pepper showed higher nitrogen, potassium and boron uptake than Swiss Chard and cabbage, with the most significant nutrient uptake noticed in treatment 2 (Wattle bark = 0% vermicompost), treatment 3 (Pine bark + Wattle bark + 0% vermicompost), treatment 4, 5, 6, 7 (Pine bark + 5 to 20% vermicompost), treatment 9, 11 (Wattle bark + 10 to 20% vermicompost), treatment 14, and 15 (Pine + Wattle bark + 15 to 20% vermicompost). In most treatments, especially in treatment 5, 7 (Pine bark + 10 & 20% vermicompost), 8, 9 (Wattle bark + 5 to 10% vermicompost) and 15 (Pine + Wattle bark + 20% vermicompost), Swiss Chard had the highest uptake of phosphorus, iron, magnesium, aluminium, zinc, and manganese. Cabbage only showed a high uptake of calcium and sulphur, especially with treatment 2 (Wattle bark + 0% vermicompost), 10, 11 (Wattle bark + 15 & 20% vermicompost), 12, 13 (Pine + Wattle bark + 5 & 10% vermicompost), and 15 (Pine + Wattle bark + 20% vermicompost). The study demonstrated that wattle bark affects seedling growth more so positively than pine bark; however, the Sunshine Seedlings® mix produced much more desired growing media attributes for almost seedling growth parameters, more especially the root development. The addition of vermicompost had very little to no effect on plant growth; however, the effect of the slow-release fertilizer, Osmocote® made a noticeable impact. Conducting this study in two separate nurseries did not allow for precise comparisons, therefore, a similar study should be conducted at one site, to compare treatments under similar growing conditions.