Microclimate and Plant Transpiration of Tomato (Solanum lycopersicum L.) in a Sunken Solar Greenhouse in North China

The solar greenhouse is a common protected structure for crop production when ambient temperatures are low. In the North China Plain (NCP) winter temperatures are very low and an improved solar greenhouse with a lowered soil surface (0.5-1.5 m deep), referred to as a sunken solar greenhouse (SSG), is used. A four-season experiment was conducted in a commercial SSG with tomato crops to characterize internal microclimate, sap flow (SF) and crop coefficients. Results show that temperature inside the SSG could be more than 20 degrees C higher than outside in winter, which favors tomato growth and resulted in acceptable yields. Daily total SF was related to solar radiation, vapor pressure deficit (VPD) and temperature, in that order, both in winter and summer. The decoupling coefficient (which is the ratio of radiative to aerodynamic influences on evapotranspiration) in daytime was 0.76 in winter and 0.84 in summer, indicating strong decoupling (i.e., predominance of radiative influences) of the internal environment where wind speed was low. Basal crop coefficients at the mid stage of crop growth averaged 1.15-1.43 in winter and 0.91-0.92 in spring and summer. Thus, in the SSG, for similar climatic conditions sap flow in winter was higher than that in summer, which should be considered in irrigation scheduling.

Automated summary

The solar greenhouse is a common protected structure for crop production when ambient temperatures are low. In the North China Plain, a sunken solar greenhouse (SSG) is used in winter to take advantage of higher temperatures. A four-season experiment with tomato crops in a commercial SSG found that the temperature inside the SSG could be more than 20 degrees C higher than outside in winter, leading to favorable tomato growth and yields. The sap flow of the crops was influenced by solar radiation, vapor pressure deficit, and temperature, with decoupling coefficient indicating strong radiative influences in the SSG. Crop coefficients varied throughout the seasons, with higher sap flow in winter compared to summer, suggesting the need for irrigation scheduling considerations.