Effect of LED supplemental lighting and root zone heating on growth and yield of soil ridged substrate-embedded sweet pepper in solar greenhouses in China

In order to deal with resource and environmental issues of soil cultivation and sunlight deficiency and to enhance root-zone temperature for crop cultivation during low winter temperature periods in solar greenhouses in China, a field study was conducted with soil-ridged substrate-embedded cultivation (SRSC) method under greenhouse conditions to investigate the effect of root-zone heating and LED supplemental lighting on the growth and yield of sweet pepper. Six treatments were designed in the study, including the control without heating and lighting (CK), root zone heating at 15℃ (T15), root zone heating at 18℃ (T18), sole LED supplemental lighting (L), root zone heating at 15℃ plus LED supplemental lighting (T15+L) and root zone heating at 18℃ plus LED supplemental lighting (T18+L). The results showed that compared with CK, heating increased the root zone temperature under SRSC and root zone temperature changed with change in temperature of the environment. Root zone temperature under T18 was high throughout the day. Heat flux under T15 and T18 fluctuated with root zone heating and changed more violently than under CK. The data showed a lag in the time of inward heat transfer and an advance in the time of outward heat transfer with increasing root zone temperature in lateral and vertical directions, and there was more diurnal heat transfer in the vertical root zone. T15 and T18 treatments significantly increased plant height, canopy height and diameter of sweet pepper, which were more obvious under T18 than T15 treatments. The growth parameters of sweet pepper further improved with simultaneous root zone heating and LED supplemental lighting. Fresh and dry shoot and root weights of sweet pepper increased significantly under T18 than under T15 treatment. Plant biomass under simultaneous root zone heating and LED supplemental lighting was higher than that under root zone heating or sole LED supplemental lighting, and that under T18+L treatment was highest. Compared with CK, T15, T18 and L treatments improved sweet pepper yield by 30.74%, 53.0% and 14.81%, respectively. Furthermore, sweet pepper yield under T15+L and T18+L were respectively 32.86% and 15.50% higher than that under T15 and T18 and also 51.29% and 53.87% higher than that under L treatment. In summary, root zone heating and LED supplemental lighting proved to be beneficial agronomical soil cultivation measures in solar greenhouse conditions in China with high vegetable productivity and remarkably synergistic effect on single plant yield of sweet pepper. The interaction of root zone heating and LED supplemental lighting was more obvious than that of the single effect of the treatments. Also the effect of root zone heating on the growth and yield of sweet pepper was more obvious than that of LED supplemental lighting. The results of the study provided an important guide in actual crop production under solar greenhouse conditions in China.