Water And Heat Dynamics And Simulation In Soil-Plant System In Greenhouse

Water resourse is shortage in northwest China, but the region has abundant light resource and is highly suited for developing solar greenhouse industry. Adjustment of agriculture structure and developing solar greenhouse industry have become more and more important for water saving and increasing farmers’ income in this region in recently years. The study on dynamics and simulation of water and heat transfer in soil-plant system in greenhouse is of great importance and can help to recognize water and heat transfer mechanism and provide basic information for improving crop water use.This paper mainly studied the dynamics of water and heat transfer under different irrigation method, evapotranspiration patten and control factors, evapotranspiration models, root distribution character and root water uptake using stem sap flow meters, automatic wheather station, net radiometer, infrared radiation pyrometer and air velocity meter in2008-2012. The main results were shown as follows:(1) The ratio of daytime sensible heat flux to net radiation of hot pepper under drip and furrow irrigation and tomato under furrow irrigation over the whole growth stage was52.4-62.5%. The ratio of daytime latent heat flux to net radiation was32.440.7%. And the ratio of daytime soil heat flux to net radiation was only3.5-7.9%. Compared to drip irrigation, except for initial stage, the daytime net radiation, latent heat flux and sensible heat flux was increased by5-44%,39-70%and26-33%, respectively. While the daytime soil heat flux was decreasd by7-15%. The ratio of daytime latent heat flux to net radiation increasd linearly, while the ratio of daytime sensible heat flux to net radiation decreased linearly, with the leaf area index. The relationship between the ratio of daytime soil heat flux to net radiation and leaf area index was minus exponent.(2) The total seasonal evapotranspiration (ETC) of hot pepper under furrow and drip irrigation was519.3-559.8mm and361.6-412.7mm, respectively. The total seasonal ETC of tomato under furrow irrigation was341.0-562.3mm. The dairy average ETC of hot pepper and tomato was increased as solar radiation, air temperature, vapour pressure deficit and leaf area index increased. The relationship between the accumulated ETC and accumulated temperature was quadratic parabola.(3) Compared to sufficient water supply treatement, the average daily stem sap flow decreased by22.1%and42.8%, respectively, for2/3sufficient water supply and1/2sufficient water supply. The average daily stem sap flow between typical nitrogen application rate treatement and2/3typical nitrogen application rate treatment was similar, and both were about30%higher than that of1/2typical nitrogen application rate treatment. The nighttime stem sap flow of tomato under different water and nitrogen treatments accounted for12.6-14.8%and11.8-21.2%, respectively, of daily total stem sap flow.(4) Heat transfer in the greenhouses was conducted through mixed convection during about71-88%of study periods, while the rest was pure free convection (no pure forced convection occurred). Under pure free convection, the Penman-Monteith (P-M) model substantially underestimated the evapotranspiration of hot pepper with heat transfer coefficient (h) calculated by the McAdams equation and the model with h calculated by the Stanghellini equation performed similar to the ones by McAdams equation. Under mixed convection, the P-M model can accurately estimate the evapotranspiration of hot pepper with h calculated by the Stanghellini equation. To sum up, the P-M model with h calculated by the Stanghellini equation can well estimate the evapotranspiration rates of hot peppers and tomatoes grown in the solar greenhouses over short-time interval in northwest China without distinguishing the convection types. Dual crop coefficient model can accurate estimate daily evapotranspiration of hot pepper and tomato grown in solar greenhouse under plastic mulch condition. The average root mean square error was0.54mmd-1,0.21mmd-1and0.54mm d-1, respectively, for hot pepper under furrow and drip irrigation and tomato under furrow irrigation. And the average mean absolute error was0.44mm d-1,0.17mm d-1and0.44mm d-1, respectively.(5) The root of tomato in greenhouse centralized in the depth between0-50cm, and radial space between0-18cm at furrow side and0-30cm at bed side. And the amount of the roots accounted for over72.3%of total roots. The horizontal and vertical distributions of root density of tomao were minus exponent. The soil water distribution of tomato can be better simulated by Hydrrus2D. The slope of simulated and measured soil water content was0.987and the determine coefficient was0.89. The difference between estimated and measured soil water content was higher in the bottom layer due to the less root.