Salinity Ion Concentration Limit And Optimization Of Irrigation System In Brackish Water In Lycium Barbarum Cultivation In Hetao Irrigation District

Due to the policy change in the Hetao Irrigation District of Inner Mongolia,water diversion from the Yellow River has decreased sharply.The contradiction between the supply and demand of agricultural water has become increasingly prominent.Brackish water irrigation has become an effective measure to alleviate the contradiction.Lycium barbarum can be both edible and medicinal,and it has high salt tolerance and economic value.In addition,the planting benefit of Lycium barbarum was affected by yield and fruit quality.The groundwater salinity types in the Hetao irrigation area varied,and the effects of different salt ions on the yield and quality of Lycium barbarum were different.Therefore,based on the yield and quality of Lycium barbarum,the optimal brackish water irrigation system in different water quality areas is very important for promoting the cultivation of Lycium barbarum and the safe utilization of brackish water.In this study,a combination of field experiment and model simulation was used to screen out the sensitive ion types which had a great influence on soil salinity and the growth of Lycium barbarum;The concentration limits of brackish water sensitive salt ions were proposed to ensure the planting benefits of Lycium barbarum.The effects of exogenous ions on soil salt ion distribution and salt stress of Lycium barbarum were analyzed,and the mechanism of brackish water salt ions on Lycium barbarum fruits was revealed;Based on the orthogonal experiment between sensitive salt concentration and irrigation quota,the optimal brackish water irrigation system for Lycium barbarum under different sensitive ion components was established.A deep neural network（PNN）with the preference mechanism was constructed,and the yield,appearance quality and nutritional quality of Lycium barbarum were simulated in small steps.Based on the simulation results,the optimal brackish water irrigation system under different salt ion components was proposed."Optimization of brackish water irrigation system under different salt ion components was proposed based on comprehensive consideration of yield and quality of Lycium barbarum,and prediction of fruit quality of Lycium barbarum based on deep learning model with preference mechanism"was the main innovation of this study.The research results have theoretical reference value for optimizing brackish water irrigation system with deep neural network and revealing brackish water influence mechanism from the ion level,and have positive practical significance for alleviating the contradiction between agricultural water supply and demand and safe utilization of brackish water in Hetao irrigation district.The main achievements of the thesis are as follows:1.Different kinds of anions and cations in brackish water have different effects on the distribution of salt ions in soil.Exogenous Na⁺and Mg²⁺increased the contents of K⁺,Mg²⁺and Cl^-in the root-soil of Lycium barbarum,and exogenous Ca²⁺increased the contents of Mg²⁺and Ca²⁺.Exogenous K⁺increased soil Ca²⁺and Cl^-contents,and decreased soil Mg²⁺contents.Exogenous HCO₃^-and SO₄^2-reduced the content of Cl^-and increased the content of HCO₃^-and SO₄^2-in soil.The concentration of sensitive salt in brackish water had different effects on the distribution of salt ions in soil.When the exogenous Na Cl was higher than 50mmol·L^-1,Na⁺accumulated in the main root zone of Lycium barbarum.Exogenous Ca Cl₂and Na₂SO₄were favourable for soil Na⁺leaching when lower than 40 mmol·L^-1and8 mmol·L^-1,respectively.Increasing concentrations of exogenous Na Cl and Ca Cl₂promoted the leaching and accumulation of soil Ca²⁺,while high and low concentrations of Ca Cl₂were beneficial to the leaching of soil Cl^-and HCO₃^-,respectively.2.The effects of brackish water salt ions on Lycium barbarum include direct effects during irrigation and indirect effects by changing soil salt distribution during non-irrigation.In terms of direct effects,exogenous Ca²⁺and HCO₃^-alleviated and intensified secondary stress of Lycium barbarum at the early growth stage,respectively,leading to the improvement and decrease of 100-grain dry quality.Exogenous Cl^-and SO₄^2-aggravated the osmotic stress in the early flowering period and decreased Lycium barbarum yield.The indirect effects were as follows:exogenous Na⁺increased the accumulation of Na+in soil,aggravated the osmotic stress at the early growth stage,and led to yield reduction.Exogenous Na⁺,HCO₃^-and SO₄^2-induced soil Ca²⁺leaching and reduced the protective effect of soil Ca²⁺against secondary stress at the early growth stage of Lycium barbarum,which resulted in the decrease of 100 grain dry quality.3.Increased concentrations of exogenous Na Cl,Na₂SO₄and Ca SO₄significantly inhibited the yield and dry mass accumulation of Lycium barbarum（P<0.05）;Two kinds of exogenous calcium salts（Ca Cl₂and Ca SO₄）promoted the accumulation of total sugars,betaine and amino acids in Lycium barbarum within certain limits,while Na Cl and Na₂SO₄continuously inhibited the accumulation of the three indexes.Exogenous Ca Cl₂,Ca SO₄,Na Cl and Na₂SO₄promoted the accumulation of flavonoids within a certain concentration,but significantly inhibited the accumulation beyond the limit.Carotenoids continued to decrease with the increase of exogenous Na Cl,Na₂SO₄and Ca SO₄.Based on the comprehensive score of yield and quality of Lycium barbarum and Gaussian regression,the limit of salt ion concentration of brackish water suitable.for irrigation of Lycium barbarum was obtained:The upper limit of exogenous Na⁺,Cl^-,SO₄^2-and HCO₃^-was 34.8,81.6,22.6and 21.4 mmol·L^-1,respectively,and the lower limit of Ca²⁺was 9.8mmol·L^-1.4.The orthogonal test results of sensitive salt concentration and irrigation water quota showed that irrigation water quota was the key factor affecting the yield,dry weight of 100grains and flavonoid content of dried Lycium barbarum.The yield and flavonoid content were the highest at 100 mm,and the dry quality of 100 grains was the highest at 70 mm.Exogenous Ca Cl₂was the key factor affecting the total amount of carotenoids,betaine and amino acids,and significantly promoted the accumulation of the three indexes.Na Cl had the greatest effect on total sugar and significantly inhibited the accumulation of total sugar.When the concentrations of Na⁺,Ca²⁺and Cl^-in brackish water were 34.8～38.8,15.3～15.6 and 50.9～55.9 mmol·L^-1,respectively,it was sui Table.for irrigation of Lycium barbarum.Under this water quality,the brackish water of 97～98 mm was irrigated around May 12,June 15,July 8 and August 9,and the planting efficiency of Lycium barbarum was high（C_i>0.7）.5.Based on the field experiment,a preference neural network model（PNN）was established,and the determination coefficient R²of yield and quality of PNN was 35%～52%higher than that of the traditional BP neural network.The simulation results of the PNN model showed that the model had good generalization,and the R²values of measured and predicted yields and quality of Lycium barbarum were higher than 0.75 under optimal irrigation system.Based on PNN simulation,it is found that the optimal irrigation quota changes in different amplitude with the increase of ion concentration:with the increase of SO₄^2-concentration,the optimal irrigation quota decreases by 4.37%;With the increase of Cl^-concentration,the optimal irrigation.