In order to reveal the influence of irrigation at different time during the freeze-thaw period on transport of soil moisture and distribution of temperature， in this study， the unirrigated bare land labeled L0 and 7 plots irrigated at different times during the freezing and thawing period (labeled L1，L2，L3，L4，L5，L6 and L7，irrigated only once with the quota of 225 m³ per hm²) were set， and the soil profile temperature and soil moisture content of different plots during the freeze-thaw period were monitored. The results showed that irrigation at different time had a significant effect on the soil moisture content and temperature at the depth of 0 to 20 cm， and the initial irrigation in the unstable freezing stage had a significant cooling effect on the soil temperature during the freeze-thaw period； when the surface frozen layer was formed， the irrigation had a significant effect on improving the soil temperature. Earlier irrigation had a better effect on the water storage at the depth of 0 to 60 cm. Irrigation in the initial stage of unstable freezing increased the soil moisture content by 69.0% at the depth of 2 to 10 cm；irrigation in the stable freezing stage had an average effect on soil at the depth of 0 to 25 cm and the water content was increased by 44.5%；the irrigation during the thawing stage increased the average water content at the depth of 0 to 40 cm soil by 19.0%~34.0%. Irrigation in the stable freezing stage had a more positive effect on soil moisture and soil temperature.

The characteristics of soil water and salt migration are important factors affecting soil salinization and crop yield. In this paper，the typical experimental area of Yichang irrigation area in Hetao Irrigation District of Inner Mongolia was taken as the research object. Based on the field measurement data in the experimental area in 2013， the temporal and spatial distribution of water content， salt content and ion content in 0~150cm soil profile and the correlation between water and salt were analyzed. The results show that soil water and salt content were affected by multiple factors. The content of water and salt in shallow soil had great variability and obvious seasonal variation udder the effect of irrigation and evaporation. With the increase of soil depth， the variability of soil water and salt content changed from strong to weak， which was affected by depth to water table. Besides， soil salt content was inverse proportion to groundwater depth and soil moisture content， while directly proportional to ion content. In the soil salt composition，HCO₃ ^- ，Cl^- and SO₄ ^2– were the main anion and Na⁺ and K⁺ were the main cations. In addition， the salt content in the shallow soil changed frequently due to the influence of irrigation and meteorological factors during the crop growing period. However， during the freezing period， the salt tended to move upward. Therefore， it’s worth emphasizing that water drainage needs to be strengthened before soil freezing， which is particularly important for improving the effect of salt drainage and lowering the salt in top layer of soil in irrigated area.

Reference Evapotranspiration (ET ₀) is an important parameter for estimating crop water requirement， formulating irrigation system and improving water efficiency to achieve the goal of saving agricultural water saving. In order to solve the problem that the traditional Penman-Monteith (P-M) formula requires too many parameters and complex calculation，a gradient boosting decision trees (CatBoost) algorithm based on supported categorical features was proposed to estimate the daily reference evapotranspiration of greenhouse crops.The ET ₀ calculated by greenhouse modified Penman-Monteith formula was taken as the standard value，and the correlation between input parameters and ET ₀ was analyzed by Pearson's method，and different input feature vectors were combined as input. When the input parameter combination includes 3 parameters， namely average indoor temperature，average relative humidity and cumulative solar radiation，the performance of CatBoost model was the best with MAE = 0.220 mm/d and RMSE = 0.310 mm/d respectively.Furthermore， the estimation accuracy between six other machine learning models (XGBoost，AdaBoost， Random forest， decision tree，KNN，SVM) was presented. The results showed that CatBoost model had the estimation accuracy and stability，and could simulate the evapotranspiration of reference crops better.The evapotranspiration estimation model constructed in this paper provides a new approach to realize accurate management of water and fertilizer， development of irrigation control system.

Using mine water for ecological irrigation can realize the coordinated development of coal mining, mine water resources utilization and mine ecological restoration. However, there are several pollutants in mine water. Thus, irrigation suitability evaluation should be carried out before irrigation. Setting Mindong mine as study area, this paper analyzed water quality and then used the salinity hazard (S), alkali hazard (SAR), soluble sodium content (SSP), permeability index (PI), and heavy metal pollution index (HPI) to evaluate mine water resource. At last, limit condition method was used to determine irrigation suitability. The results show that the main cations of 17 groups of water samples in the study area are Na⁺, and the main anions are HCO₃ ^-. The mass concentration of Fe, Mn, Zn, As and Pb in direct water source and mine water is higher. The SAR (13.29 ~ 32.40) and SSP (91.13 ~ 97.26) of water samples from direct water source, goaf, working face, roadway and silo, and HPI (150.43 ~ 448.81) of mine water samples do not meet the requirements of ecological irrigation, while the S (0.76 ~ 32.4) and PI (53.33 ~ 136.36) of all water samples meet the requirements of ecological irrigation. According to the limit condition rule, the indirect water source can be directly used for ecological irrigation, while the direct water source and mine water cannot be directly used for ecological irrigation. This is because the water quality is affected by the leaching of strata minerals and coal mining activities.

Improving water efficiency is an important measure to alleviate water shortages in the Yellow River Basin.Considering the dual pressure of water resource shortage and water pollution in the Yellow River Basin，the undesired super-efficiency SBM model was used to measure the water efficiency of the nine provinces (regions) along the Yellow River，and the spatial Dubin model (SDM) was used to analyze its influencing factors. The results showed that from the time series， the WUE decreased first and then increased.In terms of spatial differences，the nine provinces (regions) along the Yellow River were generally characterized by low upstream and high downstream.Economic development level， water resource utilization structure， urbanization level and wastewater treatment level had significant direct effects on WUE.Policy preference， industrial structure， industrial pollution control level and scientific and technological input had significant indirect effects on WUE.Based on this， the following suggestions were put forward： establishing water-saving mechanism and developing water-saving technology， reasonably guiding the urbanization construction of the nine provinces (regions) along the Yellow River， establishing a cooperative development mechanism for the exploitation and protection of water resources in the Yellow River Basin.

In order to determine the effects of water-nitrogen coupling and planting density on the yield and seed vigor of seed maize under ridge mulching-furrow irrigation pattern， and to propose the optimal population construction mode of water-nitrogen coupling suitable for high-vigor seeds， an orthogonal experiment with three factors and three levels was conducted in Zhangye Water-saving Experimental Station of Gansu Academy of Agricultural Sciences from 2016 to 2017. The effects of different treatments on seed germination rate， vigor index and maize yield were studied. The results showed that the irrigation quota， nitrogen fertilizer application and planting density had significant influence on seed vigor， grain yield and water use efficiency in growth stages of maize. Among the factors of irrigation amount， compared with the low irrigation quota (W1) and high irrigation quota(W3) treatments， the yield of irrigation quota W2 (4 800 m³/hm²) was increased by 14%， 15%， respectively. The germination rate and seed vigor index had the best effect at the level of irrigation quota W2. The germination rate was enhanced by 2.22% and 0.27%， and the seed vigor index was enhanced by 8.62% and 41.52%， respectively， than that of low and high irrigation quota. Among the factors of nitrogen fertilizer application， compared with the low nitrogen fertilizer application (N1) and high nitrogen fertilizer application (N3) treatments， the yield of nitrogen fertilizer application N2 (2，400 kg/hm²) was increased by 0.50% and 5.30%， respectively. The germination rate was 3.61% and 2.88% higher than that of low and high nitrogen fertilizer application， and the seed vigor index was enhanced by 13.50% and 19.60%， respectively. Among the planting density factors， the yield of density D16 (125 000 plants/hm²) was 28.8% and 29.7% higher than that of the other two treatments， and the water use efficiency was enhanced by 1.49% to 8.67%. In conclusion， the yield and seed vigor of seed maize were optimal under W2N2D16 treatment. In this experiment， the optimal irrigation quotas was 4 800 m³/hm²， the optimal N application rate was 240 kg/hm² and the optimal planting density was 125 000 plants/hm².

In order to explore the reasonable irrigation system of subsurface infiltration irrigation of cabbage (Brassica oleracea L.) in the arid climate area of Ningxia， a single-factor randomized trial design was adopted on the field scale， and a light (65%~75% FC) and a severe (55%~65% FC) regulated deficit irrigation were carried out in the rosette stage， early heading stage， and maturity stage of the cabbage， with full irrigation (75%~85% FC) throughout the growth period as the control (denoted as T1， T2， T3， T4， T5， T6， T7 (CK))， a total of 7 treatments. Before planting， 400 kg of compound base fertilizer (N>25%， P₂O₅>6%， K₂O>9%， total nutrient>40%) were applied per square hectare. The effects of different regulated deficit irrigation treatments on the dry matter quality， the yield， the quality and the water use efficiency of cabbage were studied. The results showed： the economic yield， the weight of per cabbage， the longitudinal diameter of cabbage， the length of central column， the soluble sugar content and V_C content were not significant different compared with full irrigation in the light regulated deficit irrigation treatment (T3) in the early stage of cabbage heading. However， the economic coefficient was increased by 2.73% compared with full irrigation (CK)， the horizontal diameter and the leaf ratio of cabbage were reduced by 7.90% and 5.37% compared with full irrigation (CK)， and the compactness of cabbage was increased by 24.60% compared with full irrigation (CK). In addition， the irrigation volume was reduced by 28.95%， and the water use efficiency was increased by 31.43% compared with full irrigation (CK). In the middle and late stages of cabbage heading， there were no significant differences in the dry matter quality， the economic yield， the weight of per cabbage， the longitudinal diameter of cabbage， the length of central column and the leaf ratio of cabbage under light regulated deficit irrigation (T5) compared with full irrigation. But the economic coefficient and the compactness of cabbage were increased by 3.25% and 19.67% compared with full irrigation (CK). Compared with full irrigation (CK)， the soluble sugar content and V_C content were increased by 28.74% and 13.81%， the irrigation volume was reduced by 25.09%， and the water use efficiency was improved by 27.78%. Compared with full irrigation (CK)， the economic yield of T3 and T5 were decreased by 1.61% and 1.22% respectively. Therefore， both T3 and T5 treatments can effectively achieve the purpose of water saving and stable yield. However， T3 treatment is more conducive to improving the physical quality of cabbage by subsurface irrigation in the arid climate area of Ningxia， and T5 treatment is more conducive to improving the nutritional quality of cabbage by subsurface irrigation in the arid climate area of Ningxia.

Rational allocation of water resources plays an important role in agricultural irrigation.In order to construct water resource management models， hydrological models are required to provide optimal solutions to water resource allocation problems with multiple sources， multiple objectives and multiple uncertainties， and rainfall data is a vital input in hydrological simulation. Many scholars use rainfall data from GCMS， but its resolution is too low to be directly applied to hydrological models. Taking Hengjiang River Basin as an example， this paper adopts four machine learning methods to conduct statistical downscaling research on rainfall data in ERA5 reanalysis. Meanwhile， the TS score， correlation coefficient and mean absolute error are used to evaluate the data effect after downscaling. The results show that the support vector machine (SVM) is effective in two aspects of fine rain accuracy and rainfall accuracy. The downscaling rainfall data is input into the Xin'anjiang model for hydrological simulation and the result show that the effect of ERA5 original data in hydrological simulation is poor， and the overall water quantity is too large. Artificial neural network (ANN) method has a better effect in statistical downscaling， which can provide support for agricultural irrigation.

In this study，the 5-year-old wolfberry (Lycium barbarum cv. Ningqi1) plants was used as experimental material， and water stress treatment was carried out in vegetative growth， flowering， fruiting and autumn fruiting stages to analyze the differences of its appearance quality， medicinal quality and nutritional quality. Principal component analysis was used to establish a comprehensive evaluation model for its quality. The results showed that the quality of wolfberry was different in different periods under water stress. The 10 quality traits were integrated into 3 principal component factors，and the cumulative contribution rate was 82.356 0% in full fruit stage. The medicinal quality had a great influence on the fruit quality of Lycium barbarum.The cumulative contribution rate was 85.234 7% in autumn fruit stage. The nutrient quality had a great influence on the fruit quality of Lycium barbarum. The comprehensive evaluation results showed that moderate stress treatment in full fruit stage and autumn fruit stage could improve the comprehensive quality of fruit.

5TE sensors are more and more widely used in soil evaluation because of their ability to measure soil temperature，volumetric water content and volumetric conductivity simultaneously.In order to better apply 5TE to salinization and low temperature areas， the effects of water content， salinity and temperature on volume dielectric constant and volume conductivity of 5TE were investigated by indoor sand column orthogonal experiment.The experimental results show that ：①the dielectric constant of 5TE volume is affected not only by water content， but also by temperature and salt. In saturated sand， when the salt concentration is higher than 2.0 g/L，the increase of temperature and salt will lead to the increase of volume dielectric constant，and then the measured value of water content is larger. When the salt concentration is lower than 2.0 g/L，the temperature and the change of salt have little influence on the volume dielectric constant，and the water content can be measured more accurately at 5TE.②The volume conductivity of 5TE is proportional to water content and proportional to temperature and salinity.The influence of temperature can be eliminated by temperature compensation. In the environment where the water content is basically constant (such as saturated soil and groundwater)，the pore solution can be inversely calculated by measuring the volume conductivity of 5TE sensor based on the good linear relationship between the salt concentration of pore solution and the volume conductivity of 5TE sensor.

In order to explore the effects of alternate wetting and drying irrigation with slow-release fertilizer on nitrogen distribution and yield of rice， a plot experiment of rice planting with different water and fertilizer treatments was carried out in 2020. The dry matter weight， nitrogen content， yield and its components of aboveground parts of plants at yellow maturity were analyzed. The results showed that the total amount of dry matter was as follows： W2F2 > W2F1 > W1F1 > W1F2 (W1-flooding， W2-alternate wetting and drying irrigation， F1-conventional fertilizer and F2 slow-release fertilizer)， which were 18 310.4 kg/hm²，^{18 147.6 kg/hm2， 14 802.8 kg/hm2 and 13 832.2 kg/hm2 respectively， indicating that alternate wetting and drying irrigation could promote the dry matter accumulation of rice plants. The aboveground nitrogen accumulation of W2F2 was 112.7 kg/hm2， which was significantly higher than that of other treatments. The aboveground nitrogen uptake of W2F1， W1F2 and W1F1 were 93.2 kg/hm2， 82.9 kg/hm2 and 80.4 kg/hm2 respectively. The effect of irrigation mode on yield was significant (p<0.05)， but the effect of fertilization type on yield was not significant (p>0.05). The yield of W2F1 was higher than that of W1F1 by 367 kg/hm2， and the yield of W2F2 was higher than that of W1F2 by 249 kg/hm2. The rice yield under the same irrigation mode was very close.}

In order to improve the measurement accuracy in irrigation area， an open channel flow measurement method based on velocity area method is proposed by using the mathematical relationship between the horizontal rotation angle of transverse swing rod under the combined action of flow impact and torsion spring and the velocity of channel flow section. Through the physical experiment of the lateral swing rod open channel flow measuring device in the rectangular channel， and the simulation of the flow measuring process by using the VOF two-phase flow model and the standard k－ε turbulence model in the FLUENT computational fluid dynamics software， the flow measuring performance of the device and the hydraulic characteristics of the channel flow in the flow measuring process are comprehensively analyzed. The analysis of the physical experiment results shows that the flow measurement error of the flow measurement formula is less than 5%. After processing the numerical simulation results， it is found that the vertical velocity distribution in the cross section of rectangular channel increases first and then decreases with the increase of water depth， and the maximum velocity is below the water surface. The transverse velocity distribution is characterized by large in the middle and small on both sides， and the velocity at the side wall is 0， which is in line with the basic principle of hydraulics. The results show that the flow measurement accuracy of this method meets the requirements of water intake measurement and the transverse swing rod device has little disturbance to the flow field.

In order to compare the basic properties of different types of water retaining agents， taking polyacrylamide inorganic mineral type， polyacrylamide type， polyacrylic acid type and starch acrylic acid copolymer type as test materials， the water absorption capacity， water retention capacity and water absorption performance in different ionic solutions of different water retaining agents were studied through laboratory tests. The results showed that the water retaining agent gradually saturated after 90 min of water absorption in deionized water， and the water absorption ratio of starch acrylic acid copolymer was 777.43 g/g， which was the highest in all treatments. After 24 hours of sunlight， the water retention ratio was 68.41%， but the repeated drying and water absorption capacity was poor. After seven times of drying and water recovery， the water absorption ratio of starch acrylic acid copolymer decreased by 80.18%， this kind of substance was suitable for short-term drought resistant cultivation. After drying and rehydration， the water absorption ratio of polyacrylamide decreased by only 19.51%， and the water absorption performance was relatively stable， which was suitable for drought resistance of crops with long growth cycle. Ionic solution would reduce the water absorption performance of water retaining agents. The water absorption performance of each water retaining agent in different valence ions decreased， the change trend was not consistent， and basically tended to be saturated after 50 minutes of water absorption. This study clarified the basic properties of different types of water retaining agents， which is conducive to the development of dryland agricultural technology and improve the utilization rate of agricultural water resources.

In order to study the effects of silicon fertilizer on growth characters and yield of rice under brackish water irrigation， this paper took rice as the research object and selected the variety "Jinyuan 89". The experiment set three levels of salt content of irrigation water treatment W1，W2，W3 (salinity：3，4，5 g/L)，three different foliar silicon fertilizer application amount treatment F0，F1，F2 (silicon application amount：0、6、12 kg/hm²)，fresh water irrigation as the control treatment (CK). Statistical analysis was conducted by SPSS 26.0 to study the effects of silicon fertilizer application amount on rice growth characters under different irrigation conditions of different salinity at different growth stages. The results showed that irrigation water with different salinity degrees had different effects on the growth traits and yield of rice. 5 g/L brackish water had obvious inhibitory effect on the yield of rice，and the results of rice yield measurement were all affected after applying silicon fertilizer. Different silica application rates had different effects on rice yield. Applying silicon fertilizer could increase plant height， leaf area and yield increased by 4.96%~20.00%， 0.56%~18.45% and 6.15%~14.62% compared with that without applying silicon fertilizer. The rice yield was the highest when the salinity of irrigation water was 2.56g/L and the silicon fertilizer was 12 kg/hm². It can be concluded that applying silicon fertilizer under brackish water irrigation mode can alleviate salt stress to a certain extent， promote the growth and development of rice， and improve rice yield. Meanwhile，it can also save fresh water resources. The study results provided a reference for the development of water， fertilizer and salt regulation scheme.

Plants can absorb and use capillary water. Aiming at the shortage of water resources in the later stage of mine greening，a new idea of water-saving irrigation of mine greening vegetation with capillary water was put forward. In this paper， simulated column test was used to study the influence of the treatment of the bottom water storage layer， the upper soil layer and the contact surface between the water storage layer and the soil layer on the height and speed of capillary water rising. The results showed that∶ ①The water storage capacity of the bottom water storage layer was in the order of coarse sand > medium sand >mixed sand > fine sand. The rising rate of capillary water in the upper silty soil of different water storage layers was medium sand > coarse sand > mixed sand > fine sand； ② When the water storage layer was mixed sand， the rising rate of capillary water in different types of upper soil layer was silt sand > silt soil > silty clay. Residue (volume ratio 1∶1) > residue (volume ratio 1∶4) > residue (volume ratio 1∶2)； ③ The increasing rate of capillary water in the upper silt with different compactness was TM2 (compactness 70%) > TM1 (compactness 67%) > TM3 (compactness 74%)； ④ The increasing rate of capillary water in the upper silt with different initial water content was TS1 (compactness 4.5%~5.5%) > TS2 (compactness 9%~10%)； ⑤ After the contact interface treatment， the capillary water rising rate was higher than that without geotextiles. According to the test results，the following conclusions are drawn∶ ① Coarse， medium， fine and mixed sand as water storage layer can meet the rising height and rising speed of capillary water； ② The rising height and rising speed of capillary water in different soil types in the upper part can meet the needs of green vegetation； ③ The compaction degree and initial water content of the upper soil have little effect on the final rise height of capillary water； ④ Geotextiles on the sand interface can hinder the rise rate of capillary water， but do not affect the absorption of water by vegetation roots. According to the test results and combined with the actual situation of mine greening， the following application suggestions are put forward∶ ① Suitable mixing sand and slag should be selected for water storage layer； ② The planting layer of soil should follow the principle of local materials， and appropriate ratio with slag； ③ Geotextile should be selected with strong durability， good water permeability and anti-root puncture material.

In order to improve the physical and chemical properties of saline-alkali soil in western Jilin and increase crop yield， three materials including biochar， phosphogypsum and earthworm manure were selected to carry out orthogonal experiment in pot with different dosage combinations to study the improvement effect of different levels of mixing combinations on saline-alkali soil in western Jilin.The results showed that the pH value，exchangeable sodium-ion content and soil alkalization degree of saline-alkali soil were decreased by different dosage combinations compared with those without combined modifier (CK).The soil pH value of no.7 combination A3B1C3 decreased the most， reaching 26.48%.The soil exchangeable sodium and soil basicity of no.9 combination A3B3C2 decreased by 50.41% and 45.95%， respectively. The result of the analysis and calculation of comprehensive evaluation method showed that the optimum combination of the saline-alkali soil was 8% phosphogypsum， 6% corn stalk biomass carbon and 10% earthworm dung.