Abstract
The objectives of this study were to estimate 1) the net photosynthetic rate of sweetpotato plants canopy (Pcn) using Monsi and Saeki's mathematical model, and 2) the increase in dry weight of plants in closed-type transplant production system. The Pcn 2, 6, 9, 12, 13 and 14 d after planting were estimated to be 2, 8, 10, 17, 18 and 17 μmol m-2 s-1, respectively. Measured and estimated values of increase in dry weight per plant for 15 d were 337 and 357 mg, respectively. The maximum light utilization efficiency (Pcn divided by photosynthetic photon flux (PPF) on the tray surface) 2, 6, 9, 12, 13 or 14 d after planting was found at the PPFs of 10, 191, 260, 321, 323 or 360 μamol m-2 s-1, respectively. Hence, the electric energy consumption for lighting was reduced by 35% when PPFs were set at 50, 200 and 300pmol m-2 s-1 O-4, 5-8 and 9-14 d after planting, respectively, as compared with a constant PPF of 300μmol m-2 s-1, under the present experimental conditions. These results indicate that the mathematical model for estimating growth of sweetpotato plants can be applied to the energy conservative control of the environment (e.g., PPF) in the closed-type transplant production system.
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