Effects Of Audio Control On The Growth Of Hydroponic Plants

With the continuous development of Bio+X science, multidisciplinary cross and integration among engineering, physics, and botany has been getting more and more attention by both engineering and academic community. Modern agriculture heavily relies on applications of fertilizers to promote plant growth and crop yield, but long-term fertilizer uses have brought severer environmental pollution. Reduction of chemical uses in crop production has been one of the major tasks for agricultural engineers. Recent studies have revealed that appropriate audible sound stimulation, a clean solution, has a great potential to improve plant growth and the quality of products. However, this new technology is still in the early stages of exploration. There was a lack of precise devices such as specialized research equipments and technical means to facilitate plant growth studies in the acoustic biology field. How plants sensing sound waves is still unknown. The mechanism of sound effects on plant growth haven’t reached consensus in scientific community because of insufficient theoretical support.This dissertation summarized and analysed the principle of generation and transmission of audible sound and the basic theory of acoustic detection technology. An audio frequency controllable experiment system was developed, a self-adaptive control method was put forward to reduce distortion characteristics of sound waves in facilities closed environment, and a measurement system was designed to detect vibration characteristics of plant under the stimulation of audible sound. Common audible sounds from Nature were analysed to obtain main frequency components, and based on the results, a series of basic tests and applied studies including sound effect on the growth, development, and nutrients absorption of hydroponic plant, and the integrated application of acoustic control technology and automatic control technology in production system were done. The major contents and results in this dissertation are as follows:1. An audio frequency controllable experiment system was created for experimental studies of audible sound effects on plant growth. The compressor and circulation fan of intelligent artificial climate box were separated from the plant cultivation chamber, and linked through ventilating duct with sound insulation. The internal noise was reduced by28dB. A control system was developed for audible sound generating. A solution was proposed for improving audible sound output based on closed-loop feed-forward control method. Results showed that pure tones, combination sound of pure tones, and normal music can be produced with high output accuracy.2. Different nature sound collected from environment of wild plants growth was analyzed. Results showed that:the acoustic frequency composition in most of nuture audible sound contained sound frequency of2.0kHz. The main frequency composition was from1.5kHz to2.0kHz in most of wild birds’chirm, from3.0kHz to4.0kHz in most of crickets and cicadas’ chirp, and from1.5kHz to2.0kHz in sound of trickling water and the sound of rain.3. Studies were carried out about the audible effect on the germination and growth of mung bean, the hydroponic Tomatoes’ early growth and absorption of N, P and other nutrients, etc. Experimental results indicated that the sound wave can reduce the germination period of mung bean and the mung bean under treatments of sound with intensity around90dB and frequency around2000Hz significantly increased in growth. Audible sound treatment can promote the growth of mung bean differently for distinct frequency and intensity. The volume of nutrient solution, total nitrogen, total phosphorus absorbed by tomato was exponentially increased versus growth time. Regression equation of the general formula can be represented as:y=y=aebx (a>0, b>0), where b can reflect the differences in abilities to absorb nutrients. The ability to absorb N or water of the audible sound treatment groups (N: b=0.0653; Water:b=0.0778) was better than the control groups (N:b=0.0591; Water: b=0.0765), but there was no difference between the ability to absorb P of the audible sound treatment groups (b=0.0649) and the control groups (b=0.0643), which indicated that audible sound with certain frequency can accelerate tomoto’s absorption of solution and N, but it have little effect on tomoto’s absorption of P. Audible sound with main frequency of2200Hz was a better one than audible sound with other main frequencies. 4. A technical proposal was made for Integration of plant acoustic control technology into an automated microalgae growth system for industrialized production. Test experiments were conducted to testify the automated microalgae growth system. The effect of the frequency of audible sound on biomass and algal oil production was examined. Results showed that audible sound with certain frequency can speed up the growth of microalgae and improve microalgae production. The mean biomass concentration of audible sound stimulation groups with main sound frequency of1100Hz,2200Hz, and3300Hz respectively increased by9.6%,35.5%, and10.7%than control groups. There was no distinct effect on increasing oil content in biomass of microalgae (PO) of after audible sound stimulation with main sound frequency of1100Hz,2200Hz, and3300Hz. However, the amount of oil production per unit volume of matured microalgae (PO) culture media increased through audible sound stimulation, and the maximum increase was about27.5%.