Number of Sweetpotato Propagules Produced and Electric Energy Consumption in a Closed Transplant Production System as Affected by Cell Volume of a Tray

Abstract

Reduction in electric energy consumption is important for minimizing resources used for sweetpotato propagule production in a closed transplant production system. The objective of this study was to test whether or not an increase in cell volume of a tray can reduce electric energy consumption for sweetpotato (Ipomoea batatas (L.) Lam.) vegetative propagation in a closed transplant production system. Single node cuttings each with one unfolded leaf were used as propagules and grown for 18 days at cell volumes of 20, 40, 60 or 80 mL with the same planting density of 643 m^-2 in all treatments (number of cells per tray was 98) . The number of harvestable propagules per stock plant did not differ significantly among cell volumes 6 and 10 days after planting, but increased with increasing cell volume 14 and 18 days after planting. The electric energy consumption per propagule for cell volumes of 20, 40, 60 and 80 mL was 0.54, 0.42, 0.34 and 0.26 MJ, respectively, corresponding to electricity costs of 2.2-2.4, 1.7-1.8, 1.4-1.5 and 1.0-1.1 Japanese Yen, respectively, 18 days after planting. Thus, increasing the cell volume of a tray is a useful method for reducing electric energy consumption per propagule for sweetpotato vegetative propagation in a closed transplant production system.