Energy partitioning and microclimate of solar greenhouse under drip and furrow irrigation systems

The microclimate under the drip and furrow irrigation systems inside a solar greenhouse located in the arid regions of northwestern China was evaluated during the two consecutive tomato growth cycles. Influence of soil hydrothermal conditions and the energy partitioning process were also analyzed. The results showed that when adopting the same water management measures, the irrigation amount, evapotranspiration (ETC) and soil water content within the planned wet layer of the drip irrigation were significantly lower than those of the furrow irrigation, but the soil temperature showed an opposite trend. The average air temperature (T) and vapor pressure deficit (VPD) for the drip irrigation were significantly higher than furrow irrigation during the whole experimental periods, but relative humidity (RH) was relatively lower. However, there was no significant difference of the daily average total solar radiation and other radiation components between drip and furrow irrigation systems. Actually, the distinct microclimate of each irrigation system was generated by the specific energy partitioning ratio of the underlying surface, mainly due to the application of different irrigation amount. Higher leaf area index (LAI), irrigation amount, soil water content and lower VPD under furrow irrigation reduced the daily average sensible heat flux by 14.5% and 20.0%, and reduced the solar radiation heating factor by 11.8% and 27.9%, respectively, for summer and winter cycle. While daily average latent heat flux increased by 20.0% and 11.1%, and the evaporation coefficient increased by 14.3% and 6.0%, respectively, for summer and winter cycle. This paper showed that for the low-cost and low-technology solar greenhouse without an active environmental control system, the reasonable water and vent opening management can be used to create a suitable environment for sustaining crop growth, by regulating the partitioning and exchange of solar energy inside the greenhouse.