Transmission And Simulation Of Water And Heat In Soil-Plant System Under Drip Irrigation In Solar Greenhouse

For the problems of water resource waste,low yield and quality caused by unscientific irrigation in Solar Greenhouse in North China,the purpose of this paper was to optimize the drip irrigation system and improve the water use efficiency,ecological environment and realize water control,as well as fruit yield and quality.The variation of water and heat flux,the effects of irrigation on crop physiology,ecology and yield and quality,characteristics of multi-scale evapotranspiration,evapotranspiration model of greenhouse tomato were discussed.This study was to provide theoretical support and technical reserves for the development of greenhouse water saving and high quality industrial system.An experiment was conducted to investigate the water and heat transfer mechanisms and simulation of evapotranspiration for drip–irrigated tomato,which was planted in a solar greenhouse in the North China,under different water conditions at different growth stages in 2015 and 2016 at Xinxiang Comprehensive Experimental Station,Chinese Academy of Agricultural Sciences.Irrigation amount was determined based on accumulated pan evaporation(E_p)of 20 cm pan evaporation,and three treatments were designed with full(0.9 E_p),medium(0.7 E_p)and deficit(0.5 E_p)irrigation.The results were as follow:(1)The variations of environmental characteristics,water and heat fluxes and their responses to environmental factors were analyzed systematically at different growth stages.The solar radiation,temperature and humidity,and vapor pressure deficit inside the solar greenhouse were in good agreement with outside.It is feasible using ventilation flux to build the relationship of air speed between inside and outside.Net radiation(R_n)and latent heat flux(?ET)were the lowest in the seedling stage,while highest in the full fruiting stage.The?ET/R_n were the highest in the full fruiting stage,while lowest in the seedling stage.However,the H/R_n and G/R_n showed the opposite law.The hourly and daily latent heat fluxes were affected by net radiation,vapor pressure deficit,air speed,air tempareture,relative humidity,surface soil temparrture,and surface soil moisture.(2)The variations of evapotranspiration at different spatial scales and their controlling factors were quantitatively studied.The crop coefficients at different stages of greenhouse tomato were obtained.The leaf transpiration(T_r),crop transpiration(T_p)and farmland evapotranspiration(ET)in different water treatments was 0.9E_p>0.7E_p>0.5E_p.The effects of net radiation on leaf,plant and farmland scale were significant.The influence of wind speed should be considered in estimating T_p and ET.Besides,adding variable leaf temperature could significantly improve the estimation accuracy of T_p and ET under water stress conditions.The LAI and VPD were the key parameters to realize ET scale conversion in conversion of ET below farmland scale.The soil evaporation accounts for 25%of total ET over the whole growing period,and the relationship between soil evaporation and LAI can be expressed by an e exponent function,as well as surface soil moisture.The crop coefficient of 0.9E_p was 0.45,0.89,1.06and 0.93 in the initial,development,middle,and late stage,respectively,and 0.45,0.89,0.87 and 0.41for 0.5E_p.(3)The applicable conditions and shortcomings of the Penman-Monteith(PM)model,Shuttleworth-Wallace(SW)model and dual crop coefficient method(DK)were discussed to estimate tomato ET of solar greenhouse,and improved PM and SW model.The PM model integrated with bulk surface resistance established in this paper and aerodynamic resistance using mixed convection theory can estimate tomato ET accurately in solar greenhouse.The SW model preferred well in estimating ET when LAI was between 0.5 and 2.7,and the estimation accuracy of SW model in the seedling stage can be improved by introducing water deficit coefficient.The DK method was the best in estimating ET in solar greenhouse by comparing with the PM model and SW model,especially wetting soil and soil water stress conditions.Meteorological correlation method between inside and outside and energy balance method significantly underestimated crop transpiration from 12:00 to 16:00,and underestimated crop transpiration 1.7%and 6.3%over the whole growing period,respectively.(4)The soil water and heat dynamics of root zone were simulated by UZFLOW-2D software in combination with the actual water absorption characteristics of tomato roots system under drip irrigation in greenhouse.The root distribution of one and two dimensional accords with e exponential decay law,and the root length density function of two dimensional were obtained with determination coefficient of0.77.Using the UZFLOW-2D software can accurately simulate the change of soil water&heat,and its evaluation and application were analyzed.The UZFLOW-2D software can simulate soil water&heat from 0 to 70 cm between two crop rows and lines,and it can accurately reflect the dynamic changes of soil water after irrigation.Predicting the irrigation and water consumption of 0.9E_p?0.7E_p and 0.5E_p by using the UZFLOW-2D software were in good agreement with the measurements from weighing lysimeter in 2016.