Effects of Adding Nitrogen to Vermicompost on Tomato Seedlings Under Greenhouse Conditions

Vermicompost, a byproduct of earthworm digestion of organic solid waste is receiving attention as a peat substitute in the production of plug seedling media. We aimed to test the effects of adding nitrogen to vermicompost on the morphological development of tomato seedlings. Nursery experiments on tomato seedlings were carried out in the greenhouse. Urea at 0.00 kg/m³, 0.25 kg/m³, 0.50 kg/m³, and 1.00 kg/m³ was added to vermicompost and to the vermicompost-vermiculite (at a volume ratio of 4:1) mixture. Results showed that (1) Nitrogen application at different rates to the vermicompost significantly increased the strong seedling index (SSI) at the middle (T1) and late (T2) seedling growth stages. Besides, nitrogen application significantly increased concentrations of available nitrogen (available-N) at the beginning of seedling cultivation (T0) and nitrate nitrogen (NO₃^?-N) at T2 in vermicompost. (2) Adding nitrogen to vermicompost significantly increased the number of root tips at T1 and T2 and the root volume at T2. And it significantly decreased the electrical conductivity (EC), total N (TN), available N, ammonium N (NH₄⁺-N), and NO₃^?-N at T1 and T2. (3) Adding nitrogen to the vermicompost-vermiculite mixture significantly increased the root/shoot ratio, and SSI at T1 and T2. And it significantly increased the pH and reduced the EC at T1 and the available-N, NH₄⁺-N, and NO₃^?-N at T2. In short, adding nitrogen (0.5～1.0 kg/m³ urea) to vermicompost improved the shoot and root morphological development of tomato seedlings, as well as the biomass accumulation and allocation. Adding nitrogen to the vermicompost-vermiculite mixture further promoted the development of tomato seedlings.