Effective Vegetable Transplant Production Programs for Closed-Type Systems Under Different Lighting Regimes

Abstract

Since the high cost of electricity can limit the viability of artificial environment growing facilities, recent research has focused on the development of energy efficient lighting systems to reduce costs. In facilities designed for transplant production, however, reducing electricity usage per se is not enough to improve productivity. If plant growth can be increased and harvest stage reached more rapidly, both the fixed property cost per plant and the total production cost will decrease even if energy cost per plant remains constant. The present experiments test whether transplant production efficiency can be increased by shortening dark period length while maintaining a constant light period. Light treatments were initiated after cotyledon emergence in three crops (lettuce, cucumber and tomato). Light period was set at 10 hours in all regimes, while dark periods were set at 0, 2, 6, 8, or 14 hours. Lettuce plants grew faster with decreasing dark period length, requiring only 10 days to reach 1.2g in the 10:0 light/dark treatment, compared with 10, 13, and 17 days in 10:2, 10:8, 10:14 treatments, respectively. However, it should be noted that the 10:8 and 10:14 treatments received the approximately the same number of hours of light prior to harvesting. In contrast, shortening dark period length did not improve growth rates significantly in the tomato and cucumber plants, presumably because chlorosis occurred as a result of the shorter dark period. The facility efficiency can, therefore, be improved by shortening dark period and thereby promoting faster growth in some plants.