Micro-climatic and crop responses to micro-sprinkler irrigation

The frequency and severity of droughts and heat stresses are becoming a threat to crop production and food security in arid and semi-arid regions worldwide. To ameliorate both stresses simultaneously, micro-sprinkler systems are being proposed and their performance is investigated here for gray jujube trees planted in an arid region. The experiments focused on the effects of different levels of micro-sprinkler irrigation amounts on air temperature, relative humidity, vapor pressure deficit, leaf-level physiological processes, yield, and quality of the fruit. The experiment was carried out over a two-year period in a jujube orchard consisting of three micro-sprinkler irrigation levels that spray water at 2 mm d-1 (T1), 4 mm d-1 (T2), 6 mm d-1 (T3) and the control at the flowering to fruit set stage. Within the canopy volume, the application of micro-sprinkler cooling system was shown to decrease air temperature by 1 to 3 ℃ and enhance air relative humidity by 11 - 17% when compared with the control. The associated decrease in air temperature and increases in air relative humidity reduced the vapor pressure deficit (VPD) from 3 kPa to 2 kPa. The measured VPD reduction across treatments explained much of the measured differences in physiological responses (net photosynthetic rate, transpiration rate, stomatal conductance and water use efficiency) at the leaf scale. The aforementioned physiological improvements increased the quantity and quality of the jujube fruit. The study adds to the growing literature that supports the use of micro-sprinklers as a cooling system to ameliorate the negative effects of droughts and heat under extreme heat stress conditions.