Diurnal change in root zone temperature of soil ridge substrate-embedded cultivation method for sweet pepper in solar greenhouse

In order to deal with the production problems associated with low temperature stress in winter and early spring, continuous cropping obstacles, low yields and low utilization efficiencies of water and fertilizer in solar greenhouses in North China, a novel cultivation method named ‘soil ridge substrate-embedded cultivation’ (SRSC) was designed and its performance was investigated. An investigation on root zone temperature of sweet pepper seedlings in two types of SRSC patterns SRSC-P (polyethylene groove embedded in soil ridge) and SRSC-W (plastic film with wire mesh as support embedded in soil ridge), SR (soil ridge) and NPG (naked polyethylene groove) were conducted in early spring. The results showed that the dynamic changes of ridge root zone temperatures were significantly positively correlated with both inside and outside temperatures of greenhouse. Moreover, daily mean temperatures inside greenhouse and in ridge root zone were increased by 8.07 ℃ and 10.93 ℃, respectively, than temperature outside greenhouse. The effect of greenhouse was more remarkable at night, temperatures inside greenhouse and in ridge root zone enhanced by 9.9 ℃ and 14.81 ℃, respectively, compared with outside temperature. Based on the data analysis, the performance of root zone temperature in terms of preservation of SRSC-W was better than that of SR and SRSC-P at night. And average night temperature were increased by 1.34 ℃ and 0.52 ℃, respectively, compared with those of SR and SRSC-P. The highest root zone temperatures of SR, SRSC-P, NPG and SRSC-W were 28.06 ℃, 27.21 ℃, 29.93 ℃ and 26.05 ℃, respectively, at daytime. This suggested that SRSC-W had the best buffering capacity for high temperature while NPG had the worst buffering capacity. The performance of SRSC in terms of heat storage and preservation under cloudy conditions was worse than that under sunny conditions. Root zone temperature in ridge center of SR was higher than that in lateral ridge at both daytime and nighttime. On the contrary, SRSC-P and SRSC-W had higher lateral temperatures in the daytime and higher center temperature at night. Root zone temperature in north part of ridge was higher than that of south part, and temperature difference was the smallest between south and north under SRSC-W condition. In addition, the lag time for dynamic change in root zone temperature in ridge center was the longest under SRSC-W condition due to powerful temperature buffer capacity. In short, the effect of preservation temperature in root zone of SRSC-W was the best with strongest temperature buffer capacity during low temperature period among all treatments. SRSC-W had a broad prospect for application with low cost and most stable performance of heat storage and preservation.