Design and experiment of root heating system for greenhouse potted crops

Objective  To design a root heating system suitable for dwarf crops, so as to solve the problem that potted crops in greenhouse without heating equipment in the Yangtze river delta region are vulnerable to low temperature and cold damage in winter.

Method  A nested double-layer cultivation pot was designed. The interlayer was filled with insulating fat foaming agent. Two silicone rubber heating plates of 80 W/m² and 15 cm ×12 cm were placed in the substrate of the cultivation pot. The heating plate was controlled by STM32 MCU, which output signals to the solid state relay for heating power control. Fuzzy PID control algorithm was used to control the temperature of the crop root area to the set value in real time.

Result  The relative error of root zone temperature control did not exceed 5%. Under the condition of continuous low temperature (average temperature below 5 ℃ for a week), when the root zone set temperature was 15, 20 and 25 ℃, the average daytime temperature of the aboveground parts with 30-35 cm height of crops increased by 1.4, 2.6 and 3.7 ℃ respectively compared with the control group, while their average night temperature increased by 2.1, 2.9 and 4.0 ℃ respectively. Compared with the common pot, the pots with root zone temperature of 15, 20, 25 ℃ saved electric energy by 24.2%, 25.3% and 23.8% respectively.

Conclusion  Under the condition of continuous low temperature, our system can not only effectively increase the temperature of crop root zone, but also can heat up the aboveground part of crop. Under certain conditions, our system can alleviate the effects of cold stress on winter crop growth.