| As an important production area of winter jujube(Ziziphus Jujuba Mill.)in China,Yellow River Delta has been plagued by the shortage of fresh water resources and soil salinization,which limits its sustainable development.Brackish water irrigation is a source available to supplement the shortage of freshwater resources.However,unreasonable irrigation strategies and the salt accumulation caused by long-term brackish irrigation can cause soil secondary salinization,resulting a reduction in yield and quality of winter jujube.Furthermore,the shallow groundwater table and highly mineralized,making it easy for salt in the groundwater to accumulate on the surface.This complex and fragile water and soil environment poses a challenge to the safe use of brackish water.At present,there is no systematic study on the response of soil moisture distribution and winter jujube salt tolerance regulation to brackish water irrigation,and there is no long term utilization model of brackish water irrigation in Yellow River Delta.To solve these problems,a field experiments was set up and a model simulation was established in this paper.5 irrigation salinity levels(1,2,3,4,and 5 g/L)were designed for brackish water irrigation with drip irrigation.The effects of different salinity brackish water on soil water and salt dynamics,growth,yield,quality,and physiology of winter jujube was analyzed.On this basis,the response relationship between soil salinity and crop yield under salt stress was thoroughly clarified,and the photosynthetic physiological regulation mechanism of winter jujube at different growth stages under salt stress was revealed.In addition,the impact of groundwater on soil water and salt was quantitatively analyzed,and a groundwater-soil water and salt transport model for drip irrigation of jujube trees in shallow groundwater table areas was constructed.Based on the model,the water and soil environmental effects of long-term brackish water use were simulated,achieve the goal of soil environmental safety and winter jujube yield and quality improvement.The results provide a theoretical basis and technical support for the sustainable development of winter jujube industry and the safe and efficient use of brackish water in the Yellow River Delta.The main results were as follows:(1)To study the interannual differences and cumulative effects of different irrigation water mineralization levels on soil water and salt and crops,a 3-year field experiment was set up from 2020 to 2022.The water and salt variations within and among years was illustrated,and the response characteristics of winter jujube growth and quality under brackish water irrigation was observed.The salt tolerance threshold of winter jujube was further calculated using the crop salt tolerance function,which is the average soil salt content(conductivity)in the 0～100 cm soil layer during the growth period when the yield drops to 50%.In addition,the comprehensive effect of brackish water with different mineralization on the quality of jujube was analyzed by principal component analysis.The results demonstrated that the soil water and salt content fluctuated with variation of rainfall,irrigation and evapotranspiration.In the year with abundance of water,soil salt of root layer was completely washed out;while in drought years,salt accumulated in the root zone.After continuous brackish water irrigation over the 3 different hydrological years,soil salt content in the root zone did not accumulate.New shoot length,hanging length and yield of jujube decreased with increasing mineralization,with significant differences starting to occur in the 4 g/L treatment,but the 4g/L treatment had the best overall fruit quality.And the salt tolerance threshold for winter jujube was 0.27%(1.03 d S/m).(2)In response to the current lack of understanding of the salt resistance regulation mechanism of winter jujube,the response rules of various parameters under different treatments at different growth stages was analyzed.Mainly including the relative chlorophyll content,photosynthetic gas parameters,light response curves,and fluorescence parameters of winter jujube leaves.The physiological parameters of salt tolerance at different fertility stages were identified using principal component analysis to obtain the mechanisms of salt resistance regulation at different fertility stages.At the same time,the correlation between physiological parameters and yield and quality was analyzed.The research results indicated that different irrigation mineralization levels have a significant impact on the above parameters.The transformation from photosynthetic physiological regulation to fluorescence regulation as the fertility stage of dates progressed and the mineralization of irrigation increased.At the same time,it was found that winter jujube can resist salt stress through physiological regulation and have a positive effect on quality,which can bring benefits to jujube fields irrigated with brackish water.(3)In response to the potential impact of shallow groundwater depth and high mineralization in the study area on soil water salinity,the spatial and temporal distribution patterns of groundwater and soil water salts were analyzed through fixed-point monitoring of regional soil and groundwater,and the mutual effects of groundwater salts and soil water salts in the study area were explored through regression and correlation analyses.It was found that,when the groundwater depth was less than 2.0 m,a "cyclic" relationship is basically formed between soil water and groundwater salt,and various factors are mutually constrained.When it was deeper than 2.0 m,only the groundwater depth had an effect on soil salinity.From this,it can be found that the impact of groundwater on soil water and salt was mainly affected by the groundwater depth.(4)In response to the issue of considering the impact of groundwater on soil water and salt transport for brackish water irrigation in the research area,on the basis of long-term measured data of soil water salinity distribution and regional groundwater under different brackish water irrigation treatments,the simulation area,initial conditions,boundary conditions,crop parameters,soil water-salt transport parameters,and groundwater water-salt transport parameters were modified locally,and the diving surface was used as a link between soil water and groundwater to establish a joint regional soil and groundwater water-salt transport model.The model simulation results showed that the simulation error of water and salt concentration was controlled within 5%,and the simulation error of groundwater level was controlled within 10%.The model has a strong applicability in the study area and can be used to simulate the water and salt transport law of regional soils and groundwater.(5)In view of the issue of the adverse effects of long-term continuous use of brackish water drip irrigation on soil salinization and jujube growth in the Yellow River Delta region.The effects of different treatments of jujube,water and soil were compared and analyzed by TOPSIS analysis through a 3-year trial field experiment to determine the effects of different irrigation scenarios.The years 2010-2019 were chosen as the simulation period,and the model was used to predict the water and soil environmental effects of brackish water irrigation under different scenarios for a 10-year continuous period,to determine the brackish water irrigation scheme that can be used in the study area in the long term through the objective of ensuring soil environmental safety and yield quality of jujube.The specific irrigation system is that 3 g/L of brackish water can be directly used for irrigation during the growth period of winter jujube.In addition,in consecutive wet years,4 g/L of brackish water can be considered for irrigation.The above research achievements can provide theoretical basis for the use of brackish water and a highly operable brackish water irrigation model for producers,which has strong practicality and promotion value.Research results have important practical significance for alleviating the contradiction of irrigation water resource shortage in the Yellow River Delta as a whole,and promoting the sustainable development of the local winter jujube industry. |
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