| Over the years,the grape industry has become an advantageous and characteristic industry for agricultural development in Ningxia,and it has also become one of the main channels for local farmers to increase their incomes and become rich.Affected by the northwest monsoon in winter,the problem of overwintering and cold protection of grapes has become a prominent problem restricting the development of grape industrialization in Ningxia.In order to solve this problem,local researchers have proposed the protective capsule,which achieved a better winter-proofing and late frost protection effect.However,there is still a problem in the practical application of this method that the humidity in the protective capsule is difficult to reasonably control during the period of moisture regain,which will not only lead to a reduction in the germination rate of the grapes,but even endanger the survival of the grapes.In response to this problem,this study proposes a method to control the surface moisture through the layered subsurface drip irrigation system,and then regulate the humidity in the protective capsule.Firstly,based on the theory of unsaturated soil hydrodynamics and the characteristics of soil water transport under layered subsurface drip irrigation,a soil water transport model of layered subsurface drip irrigation was constructed.At the same time,the theoretical analysis of the heat and moisture transfer process in the protective capsule was carried out.With the help of artificial climate chamber experiments,the functional relationship of temperature and humidity in the protection chamber with the change of soil surface moisture content and ambient temperature during the return period is determined,and the corresponding soil moisture content range when the relative humidity in the protective capsule is within the appropriate range is obtained.Finally,on the basis of the above,combined with the distribution characteristics of the grape root system,the suitable technical parameters of layered subsurface drip irrigation for the overwintering grapes at the eastern foot of Helan Mountain in Ningxia were put forward,and its effectiveness was verified by field experiments.The main conclusions are as follows:(1)The soil moisture transport model of layered subsurface drip irrigation was established,and the influence of the buried depth and the irrigation time on the distribution of soil moisture was clarified.Based on the theory of unsaturated soil hydrodynamics and the characteristics of soil water transport under layered subsurface drip irrigation,a soil water transport model of layered subsurface drip irrigation was established,and the accuracy of the model was verified through experiments.Using this model,the influence of the depth of the emitter and the length of irrigation time on the distribution of soil moisture was analyzed,and the results showed that:The amount of deep leakage increases with the increase of the depth of the emitter,and the inside of the wetted body which located in the optimal water content range increases with the increase of the buried depth of the two groups of emitters(shallow emitters and deep emitters).By reducing the difference in the irrigation time between the two emitters,the vertical distribution of the soil wetting body and soil moisture content can be made more uniform,and at the same time,the soil volume within the optimal moisture content range within the wetting body can be increased,thereby increasing soil moisture availability.(2)The law of the relative humidity in the protective capsule changes with weather and soil factors is revealed,and the range of the soil surface water content corresponding to the grapes in the protective capsule is determined when the grapes are at the appropriate humidity.Based on the principle of energy balance and heat transfer theories,the process of heat and moisture transfer in the protective capsule is analyzed,the key factors affecting the relative humidity in the protective capsule(soil surface moisture content and outside temperature)were determined.With the help of artificial climate chamber experiments,we explored the law of temperature and humidity in the protective capsule during the return period with the soil surface moisture content and external temperature:The relative humidity in the protective capsule increases with the increase of the surface moisture content until it reaches the water vapor saturation state,and when the surface moisture content is constant,as the ambient temperature increases,the relative humidity in the protective capsule decreases.On this basis,a functional relationship of relative humidity in the protective capsule with changes in soil surface moisture content and external temperature was established.It was determined that the suitable range of soil surface moisture content under the relative humidity conditions in the capsule should be controlled within 0.03 cm~3/cm~3-0.05 cm~3/cm~3.(3)The optimal irrigation technical parameters for winter irrigation of wine grapes in the eastern foothills of Helan Mountain in Ningxia have been preliminarily determined,and their effectiveness has been verified through field applications.Based on the obtained optimal soil surface water content range for wine grapes in Ningxia overwintering,and comprehensive consideration of the matching effect of roots and water,the optimal irrigation technology parameters for winter irrigation of wine grapes in the eastern foothills of Helan Mountain in Ningxia are theoretically selected as follows:The shallow emitter is 25 cm deep and the irrigation time is 5 h;the deep emitter is 45 cm deep and the irrigation time is 13 h.The field experiment results show that this technical parameter can effectively maintain the moisture of grape branches during the dormant period,and at the same time inhibit the growth of microbial pathogens,which proves that this preferred technical parameter for winter irrigation of wine grapes in Ningxia has good practicability and reliability. |
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