Split Versus Single Applications of Solid and Liquid Vermicompost: Impacts on Growth, Chlorophyll Content and Soil Characteristics of Tea (Camellia sinensis L.) Seedlings

Limited information is available on how vermicompost form, form-specific dose, and application schedule jointly affect tea seedling development. This 135-day humid outdoor nursery study evaluated solid and liquid vermicompost applied at two doses as either single or three split applications to 270 individually potted Camellia sinensis seedlings assigned to eight factorial treatments and an untreated control. Repeated measurements of seedling height, root collar diameter, and leaf chlorophyll content were analyzed using linear mixed-effects models fitted by restricted maximum likelihood (REML); the control was retained only in supplementary one-way ANOVAs. Soil pH, electrical conductivity (EC), and temperature were analyzed by two-way ANOVA. Vermicompost form, measurement time, and their interaction significantly affected seedling height and root collar diameter. Application schedule significantly affected root collar diameter (F = 7.35, p = 0.007) and chlorophyll content (F = 19.74, p < 0.001), but not seedling height, whereas dose within form showed no significant main effect on any of these traits. The form × application schedule × time interaction was significant for seedling height, whereas dose within form × application schedule × time was significant for root collar diameter and chlorophyll content. Treatment differences generally emerged from day 30 onward. The 30 g solid vermicompost treatment applied in three equal doses produced the highest final seedling height (24.80 cm) and root collar diameter (14.00 mm) and the highest chlorophyll content recorded during the experiment (914.98 µmol m−2 on day 75). Treatment, measurement time, and their interaction significantly affected soil pH, EC, and temperature; pH remained within 4.90–5.76, and EC values did not indicate salinity stress. Selected split applications of solid vermicompost therefore showed potential to improve tea seedling growth, but significant higher-order interactions demonstrated that responses depended on vermicompost form, dose within form, application schedule, trait, and measurement time.