Simulation And Ventilation Regulation Of The Cucumber Leaf Dew In Solar Greenhouse

Cucumber is one of the main cultivated crops in Chinese Solar greenhouse in winter.It has long dew duration at night.The study found that long-term growth in high humidity?relative humidity?85%?environment,which not only did the physical properties change,but also increased the probability of fungal diseases.Epidermal permeability increased and stomatal sensitivity decreased and root water absorption capacity decreased.The research showed that the dew of the leaves in the high humidity environment was the direct cause of fungal disease.Excessively high or low relative humid is unfavorable to the growth of cucumber in the solar greenhouse.Therefore,simulating and regulating the relative humidity of the air in greenhouse is particularly important for healthy growth of cucumber.According to the difference of dew duration and dew yield of cucumber leaves in solar greenhouse,a model was established to simulate dew duration and dew yield of cucumber leaves.Based on the simulation results,the effects of different ventilation methods on the dew condensation of cucumber leaves were analyzed.The main results were as follows:When the relative humidity was higher than 91.3%?R²=0.843?,the average daily dew duration error of cucumber leaves was 0.7h,accounting for 6%of the average dew duration.The error is less than two hours of simulated time which is relatively accurate.When the cucumber leaves at the top of the temperature dew point temperature are less than 1.02??R²=0.877?,the average daily dew duration error of cucumber leaves was 0.3h,accounting for1.8%of the average dew duration.The error is less than one hour of simulated time which is relatively accurate.Energy balance model fitting degree of leaf leaf temperature?R²=0.880?,the amount of dew fitting?R²=0.952?,simulated and measured results are basically the same,dew amount of top cucumber leaves simulation error is less than 0.002mm.Solar altitude maximum relative humidity forecast model?R²=0.931?,simulated and measured values consistent,the error is less than 1%.The vertical distribution of greenhouse cucumber leaf dew duration and condensation amount is not consistent.The upper canopy dew duration and condensation amount were greater than middle and ground canopy leaves,but the middle and ground canopy leaves had no significant difference.Further research found that dew duration and dew amount had no linear relationship.The results showed that it was meaningful to establish a model with top cucumber leaves.The dew duration and dew amount should be studied separately.According to different research purposes,choose an appropriate simulation model and dew point temperature difference model to study dew duration,and the energy balance model to study dew amount.When the ventilation time was delayed from 10:00 to 12:00 and 14:00,the dew amount of cucumber leaves decreased to the original 1/2 and 1/5.The dew duration of cucumber leaves decreased by 10 minutes and 2 hours respectively.When the external wind speed increased from 0¹ m·s^-1 to 1² m·s^-1 and 2³ m·s^-1,the dew duration and the dew amount of cucumber leaves did not decrease.When the air vent increased from 25%to 50%and 75%,the yield of dew decreased to the original 1/3 and 1/2.The results showed that delayed ventilation time in greenhouse can effectively reduce cucumber leaf dew in greenhouse.The wind velocity has little effect on the dew duration and dew amount of cucumber leaves at night.Increasing air window area can reduce the dew yield of cucumber leaves at night.Further studies found that daytime radiation affected the dew duration of cucumber leaves.The higher the total daily radiation,the shorter the dew duration at night.When the external radiation conditions permitted,the ventilation time delayed and the area of the vent increased.The dew duration and the dew amount of the cucumber leaves would reduce at night.Which would ensure the healthy growth of the cucumber leaves.