Growth of red leaf lettuce exposed to ultrasound in plant growth chamber

Abstract

Chemical-free vegetable is a kind of brand-name products in agriculture field. However, it is hard to control plant growth without plant growth regulators. In order to cultivate plants without them, physical stresses are attractive candidates for a plant growth control. Therefore, we proposed a plant growth control system by exposing ultrasound for plant factory with artificial light. In particular, we observed the growth of red leaf lettuces after roots of them exposed to ultrasound. To develop our concept, we fabricated the red leaf lettuce hydroponic cultivation device with ultrasound transducer in the plant growth chamber. The transducer was driven with 10-50 V_p-p at 28 kHz. We prepared saplings of red leaf lettuce cultivated for 2 weeks and cultivated them in the fabricated cultivation device for 2 weeks. Results show that root length and leaf numbers when exposed to ultrasound with 30 V_p-p were statistically longer and higher than those without ultrasound exposure. Meanwhile, root length and leaf numbers when exposed to ultrasound with 50 V_p-p were statistically shorter and lower. These results indicate that our plant hydroponic cultivation device achieves the growth control of plant using ultrasound. Such a technique may facilitate plant growth control without a plant growth regulator in a plant factory, beneficial for future agriculture applications.