Abstract
Sweetpotato plants were grown for 15 d under stepwise photosynthetic photon flux (PPF) and two levels of constant PPF conditions. In stepwise PPF condition, the PPFs were set at 100, 200 and 300μmol m-2 s-10-4, 5-9 and 10-14 d after planting, respectively. PPFs of 200 and 300μmol m-2 s-1 were chosen as the constant PPF conditions. Under same integrated PPF (PPF×photoperiod×experimental period), dry weight per plant 14 d after planting was 1.1 times higher in stepwise PPF condition than in constant PPF condition. The increase in dry weight per electric energy consumption of lamps was 1.1 times higher in stepwise PPF condition than in constant PPF conditions. Therefore, stepwise PPF control is a useful method for reducing electric energy consumption and increasing electric energy utilization efficiency (chemical energy contained in plants/electric energy consumption of the system) of the closed-type transplant production system.
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