Growth Control of Leaf Lettuce Using Pulsed Electric Field

Agriculture in Japan is approaching a crisis for two reasons: a declining self-sufficiency rate and a decreasing number of agriculture workers. To solve these problems, plant factories have been attracting attention recently. Plant factories are facilities that aid the steady production of high-quality vegetables year round by artificially controlling the cultivation environment, allowing growers to drastically decrease production time. Despite the many advantages of plant factories, a main impediment is the reduction of initial and running costs. This paper utilizes leaf lettuce (Early impulse), which is a typical item cultivated in plant factories, as a target to improve productive efficiency of plant factories due to its relatively high price. Various pulsed electric fields (PEFs) were applied to roots of the lettuce to increase lettuce growth rate. The experimental results show PEF intensity from 0.2 to 1.0 kV/cm is positive for growth stimulation. Conversely, those over 1.0 kV/cm resulted in growth inhibition. Furthermore, roots of the samples which exhibited increased leaf weight grew more robustly than those of decreased leaf weight. In addition, analysis results showed that there was no significant difference when liquid fertilizer was applied prior to or after application of PEF. The results suggest that PEF does not affect the composition change of liquid fertilizer but directly influences the growth of leaf lettuce.