Growth Promotion for Seedling of Vegetable Plants with Supplemental Lighting

Abstract

A supplemental lighting system was installed at a large-scale seedling greenhouse (12.5 m×45 m), which supplies high quality and large quantity of seedlings to farmers through out the year. A test experiment of supplemental lighting for seedlings in this house was performed during the rainy season and winter-early spring to prepare for planting, when sunshine is sometimes insufficient. A mercury-free high pressure sodium lamp of 400W with a red to far-red photon flux (R/FR PF) ratio of 1.1 was developed and manufactured for this experiment. The average PPFD was 100μmol m-2 s-1. The experimental plants were lettuce, broccoli, and cabbage. In both rainy and winter-early spring experiments, we found that supplemental lighting was effective for seedling growth. Significant supplemental lighting effects in the rainy season were found for broccoli. Top fresh weights of both a 2h lit area before sunrise and after sunset were 30-60% greater than those of the non-lit area. A drop test of lettuce demonstrated that the remaining ratio of soil of both a 2h lit area before sunrise and after sunset were about 87%, and those of the non-lit areas were about 78%. Thus, good growth in roots was found. A significant supplemental lighting effect in winter-early spring was found in the lettuce experiment. Top fresh weights of both a 3h lit area before sunrise and after sunset were 165-200% greater than those of the non-lit area. In winter-early spring experiments, a clear difference between a 3h lit area before sunrise and after sunset was not found.