2019 ASHS Annual Conference

The cylindrical paper pots used for vegetable seedling culture greatly facilitates mechanical transplanting. However, the root substrates inside paper pots dry out fast mainly due to air spaces between paper pots created by chinks between the pot’s exterior and the holding tray. Frequent watering is necessary that contributes to the loss of nutrients by leaching during seedling production. This study was carried out to investigate the appropriate concentration of nitrogen added as a pre-planting fertilizer for growing fruit-bearing vegetable seedlings in cylindrical paper pots. For the experiment, the paper pots were made with the root substrate containing perlite (1-3 mm) and peat moss (10-mesh, 10-20% by volume) and they were placed into the 40-cell trays. The concentrations of all essential elements except nitrogen was equal in all treatments and the N concentration was adjusted to 0, 150, 250, 500, and 750 mg·L^-1 during the substrate formulation. Then, grafted seedlings of cucumber, watermelon and tomato were transplanted and seeds of hot pepper were sown directly into the paper pots. The growth of cucumber, watermelon, and tomato plants were measured at 15, 18 and 21 days after transplanting, respectively, and that of pepper at 5 weeks after seed sowing. The concentrations of macro-elements, pH, and EC of root substrates were analyzed every week. The pH of root substrates gradually increased during the seedling culture indicating leaching of liming materials such as dolomite and calcium carbonate incorporated as pre-planting fertilizer, but the differences in pH among N treatments were not significant. The ECs in all treatments did not changed significantly until one week after the transplanting of seedling grafts and 3 weeks after seed sowing of pepper. The concentration of Ca remained similar over time during the entire experimental period, but the concentration of Mg and K decreased 3 weeks after the seed sowing for the pepper growing root substrate. The concentrations of Ca, Mg, and K showed gradually decreasing tendencies since one week after transplanting of seedling grafts of cucumbers, watermelons, and tomatoes. Based on the growth measurements of plant height, fresh and dry weights of above ground tissue, 250 mg∙L^-1 treatment in tomato and those of 500 mg∙L^-1 in cucumbers, watermelons, and peppers showed the highest growth among N treatments. The seedling growths in the treatments lower than 150 mg∙L^-1 or higher than 750 mg∙L^-1 in N concentrations decreased significantly. In summary, the appropriate N concentration in the root substrate of paper pot was 250-500 mg∙L^-1, and post-planting fertilization at 1 week after transplanting of seedling grafts of cucumber, watermelon and tomato and 3 weeks after seed sowing of hot pepper is required.