Analysis Of Meteorological Elements And Simulation Of Tomato Transpiration In Chinese Solar Greenhouse During Winter In Northern

Crop production in Chinese solar greenhouse(CSG)in the cold region of northern China is usually performed under the environment of no ventilation,low light intensity,high humidity and low temperature.Thus,the crop transpiration is different from those in other kind of greenhouses and in ventilated CSGs.Tomato is the most common crop grown in greenhouses.The study analyzed the variation characteristics of meteorological elements in CSG,the optimal submodels of boundary layer aerodynamic resistance(ra)and stomatal mean resistance(rc)are selected,a tomato transpiration model based on the Penman-Monteith(P-M)equation,ra,rc,soil heat flux and other parameters for the particular environment are used to estimate the transpiration rate of a tomato(Lycopersicon esculentum Mill)scales and validated by experiments.The analysis results show that:(1)the max temperature inside is sunny day>hazy day>cloudy day,and the daily variation is first increases and then decreases in the vertical direction.The air temperature of1.5m before and after noon is higher than 1m,It's difference in the rest time is relativly small.The change of humidity inside is cloudy day>hazy day>sunny day,the daily change is decreases first and then increases.Around noon,the humidity in 1m is higher than 1.5m,and at night,it's in 1.5m is higher than 1m.Both the global and net radiation above the canopy inside is sunny day>hazy day>cloudy day.The variation is first increases and then decreases.The maximum value of net radiation in cloudy and hazy days occurs between 10:00 to 13:00and lower than 150 w/m2.The one is evenly distributed around 11:00 and the maximum value is about 200w/m2 to 300w/m2.At this time,the conversion rate of global radiation to net one needed for plant growth is largest,which can reach more than 90%.(2)The selection of sub-models and parameters in P-M equation is particularly important for the accuracy of simulating plant transpiration,two sub-model of ra is selected based on leaf temperature and physiological indexes of plants;two sun-model of rc is selected based on indoor total radiation,air temperature and P-M equation inversion model;Further sub-model analysis is performed and select the optimal sub-model to simulate ra values based on air temperature,plant leaf temperature,leaf characteristic length and leaf area index(LAI);to simulate rc values based on P-M equation inversion model.for one plant,the aerodynamic resistance change range is from 147s/m to 438s/m during clear days and from 211s/m to 365s/m in cloudy days;the average resistance of stomatal is from 69s/m to 1506s/m during clear days and from 132s/m to 1151s/m in cloudy days.the changes of soil heat flux has remarkable influence on the transpiration rate.(3)Based on this model,the study reveals the daily variations of transpiration rate,net radiation,and saturation vapor pressure difference as well as the quantitative relationship between transpiration rate and net radiation above one plant.The results show that,during experiment period from December 11,2017 to January 3,2018,with a maximum daily solar radiation of 367 W/m2,relative humidity near 100% at night and during cloudy day,air velocity closing to 0 m/s,The average transpiration rate of a tomato simulated by the P-M equation is 0.06 mm/h at sunny noon and 0.02 mm/h at cloudy noon,compares with the measured values,Mean Relative Error of simulated values about 10%.The results also show that the transpiration rate of a single tomato plant in CSG mainly depends on the diurnal variation and number of the net radiation above it,while the variation of indoor air saturation vapor pressure difference(VPD)have a minor effect on it;about 43.5% of the net radiation above plant is transformed into latent heat by transpiration and the plant stem flow per hour accounted for only about 11% of the variation of substrate water content in the cultivation bag.The transpiration rate simulation model can be used to estimate one tomato transpiration during winter in the cold region of northern China and also give indication for water management inside CSG.