Study On The Patterns And Modeling Of Water Consumption And Soil Water And Heat Transfer Of Greenhouse Multi-cropping Vegetablesin Cold Regions

Greenhouses are able to provide an appropriate environment for crop growth by fully regulating and utilizing light,heat,water and soil resources.In the context of severe water shortage,water-saving irrigation technology,mainly the drip irrigation,becomes more and more popular in greenhouse vegetable production,highlighting its superiority and significance.This thesis takes tomatoes and beans as the research objects,since they are widely cultivated in greenhouses in cold regions of North China and favored by the people.Water consumption and water and heat transfer experiments were carried out for the multi-cropping vegetables under different water treatments at the greenhouse of State-level Irrigation Experimental Station in the Heilongjiang Hydraulic Science and Technology Experimental Research Center from 2014 to 2015.Through the two-year systematic field experiments,as well as analyses based on a large number of informative greenhouse experimental data,water consumption,final yield,water use efficiency and root-zone soil water and heat dynamics were investigated,and evapotranspiration estimation,soil water and heat simulations were conducted.Main research achievements are as follows:(1)Under the condition of drip irrigation,water consumption was closely related to irrigation for multi-cropping vegetables.Water consumption of tomatoes displayed an “M-shaped” variation over the whole growth period,while beans revealed an inverted “V-shaped” variation.Spring tomatoes achieved its maximum water consumption in the middle and end of May,i.e.the midterm of tomato fruit setting;the water consumption rate of tomatoes throughout the entire growing period was larger for the early stage while smaller for the latter stage.The water consumption rate of beans over the whole growth period showed an increasing trend followed by a decline.It was a fast rise however a slow decrease.For greenhouse autumn beans,the water consumption modulus became the highest during seedling stage and the lowest during fruiting stage,whereas the water consumption rate was the largest during flowering period and smallest during harvesting period.Water consumption of beans at different growing stages was mainly dependent on the irrigation amount.Water consumption of vegetables was well linearly correlated to greenhouse accumulated air temperature,accumulated soil surface temperature,together with the accumulated 10 cm soil temperature.These correlations could be applied to estimate the vegetable water consumption over the whole growth period.There was a binomial relationship between the accumulated waterconsumption during vegetable growth period and the accumulated soil surface temperature,by means of which the vegetable water consumption at different growing stages could be estimated.(2)An evapotranspiration model was established for the cold-region greenhouse multicropping vegetables based on the crop coefficient approach.Its availability and reliability indicated that the crop coefficient method could be adopted to estimate evapotranspiration for the cold-region greenhouse spring tomatoes and autumn beans under drip irrigation.Crop evapotranspiration was mainly influenced by the meteorological factors.Based on the modified Penman-Monteith equation,the reference crop evapotranspiration ET0 was calculated for the cold-region greenhouse spring tomatoes and autumn beans during their growing period,and the variation pattern of ET0 was analyzed.ET0 displayed an irregular trend over the growth,i.e.ET0 of spring tomatoes generally showed an increase-decrease-increase trend,while ET0 of autumn beans presented a gradual decline.Sensitivity analyses were conducted for ET0 to the regular greenhouse meteorological factors i.e.air temperature,relative humidity,and sunshine duration.An approximate linear relationship was detected between variations in the climate factors and relative change in ET0.Sensitivity of ET0 to air temperature was affected by the base temperature.The lower the base temperature at any given month,the larger impact of air temperature variation would be on ET0.Similarly,the base value impacted the sensitivity of ET0 to relative humidity,however they were negatively correlated.The higher the base relative humidity,the larger the negative influence of varied relative humidity on ET0.Sensitivity analysis of ET0 to sunshine duration reflected that ET0 was most sensitive to changes in solar radiation.Irrespective of the magnitude of base sunshine hours,ET0 was quite sensitive to variations in the sunshine duration.(3)Air temperature,soil surface temperature and root-zone soil temperature inside the greenhouse revealed a similar variation as the outside air temperature.Soil temperature was positively correlated to air temperature,displaying a diurnal sinusoidal variation.Soil surface temperature was fluctuating dramatically,while root-zone soil temperature was changing moderately,with a hysteresis effect.Averages of the four temperatures differed significantly,and the soil surface temperature was the highest.In spring during seedling period,plastic film mulching surface and root-zone soil temperatures for vegetables were increased by 1.45 ? and1.42 ? in average respectively,comparing to those for bare soils,implying that plastic mulch posed a notably warming effect.Soil water depletion was controlled by temperature.The larger the soil temperature was,the faster soil moisture recessed,and vice versa.With temperature change at the same gradient,the changing rate of soil potential was larger during the temperature-rise period than that at the cooling stage.The change in soil potential slowed down when temperature decreased.The lower the temperature was,the more unstable the temperature variation after irrigation would become.(4)According to the features of soil moisture variation under drip irrigation,based on the dynamical equation of soil water movement and the soil heat transport equation,a mathematicalmodel of soil water and heat transfer was established under drip irrigation for cold-region greenhouses.The Hydrus-1D software was used for the modelling.One-year experimental data was for model calibration,while another year of data was for validation.In both spring and autumn,good agreements were observed between the simulations and measurements for soil water suction and soil temperature inside the greenhouse at cold regions.Simulation errors for the temperature were less than those for the moisture.Hydrus-1D was able to well reproduce the soil water and heat variations and distributions for the cold-region greenhouse vegetables under drip irrigation.Due to easy accessibility of the meteorological data,soil properties and irrigation information,soil wetness and thermal conditions needed for greenhouse vegetables could be appropriately monitored and timely adjusted with the help of numerical modelling.(5)Different irrigation schemes exerted significant influences on the yields and water use efficiencies of tomatoes and beans.T4 irrigation treatment was the optimal treatment for tomatoes,and T5 was the best for beans.The two optimal treatments could achieve a unity of guaranteed production and highly efficient water utilization.