In order to explore the effects of water-nitrogen coupling on the activities of antioxidant enzymes (SOD, POD, CAT), malondialdehyde (MDA) content, proline (Pro) content, yield, water use efficiency and nitrogen fertilizer partial productivity in sand-peened cucumber leaves to provide a basic theoretical basis for scientific water and nitrogen management of greenhouse sand culture cucumbers, in this experiment, the response characteristics of antioxidant enzymes and water and nitrogen utilization in cucumber leaves under water and nitrogen coupling were studied by setting two factors of nitrogen application rate and irrigation level and adopting the quadratic saturated D-optimal design. The results showed that: the activities of SOD and CAT and the contents of Pro in cucumber leaves showed a single peak curve during the whole growth period, while the activities of POD and MDA showed an increasing trend during the whole growth period. The higher antioxidant enzyme activities were obtained in treatment T4 of medium water nitrogen and T5 of medium water and high nitrogen. Low water and high nitrogen treatment T3 could obtain the highest Pro content in leaves in each period. High or low irrigation level and nitrogen application rate would lead to the accumulation of MDA content and reduce SOD activity. Under appropriate irrigation level, sufficient nitrogen supply could achieve higher POD activity and CAT activity in leaves. The activities of SOD and POD in leaves should be kept at a high level by increasing nitrogen application at the end of watermelon stage. The highest yield of T5 was 107.43 kg/hm², followed by T4. Cucumber yield showed a downward trend with the increase of irrigation level and nitrogen application rate, which was in line with the law of decreasing returns. Low water and high nitrogen treatment T3 could obtain the highest water use efficiency. The highest partial nitrogen productivity was obtained at the nitrogen application rate of 150 kg/hm². In conclusion, on the basis of T4 treatment (i.e., 80.20% irrigation level and 623 kg/hm² nitrogen application) as the optimal water and nitrogen operation plan, appropriately increasing nitrogen application after entering the final melon stage can improve the physiological metabolic capacity of leaves, achieve the goal of high yield and improve the water and nitrogen utilization capacity.

Rainfall runoff is the key factor causing nutrient loss from drylands, and it is of great significance to understand the characteristics of phosphorus loss in drainage for agricultural management and water environment protection. Based on the natural rainfall process, in-situ drainage experiments of farmland in Huaibei area were carried out, the rainfall-runoff mechanism, the effect of land use type on the phosphorus emission, and the dynamic characteristics of phosphorus output were analyzed. The results showed that the soil moisture content and rainfall intensity were the main factors affecting runoff. When the soil volume moisture content of the lime concrete black soil plough layer reached 39%, the excess-infiltration runoff frequently occurred with continuous heavy rainfall, and the runoff intensity increased with the increase of rainfall intensity. Runoff was the carrier and driver of phosphorus output from farmland. The concentration and form of phosphorus output were different among different land use types, i.e., vegetable, summer maize, spring peanut, green plot in descending order of concentration. The PP/TP value of farmland was 58.94% higher than that of green plot (44.61%). The concentration, form and pollution load of phosphorus in runoff drainage varied greatly in different periods, and the output concentration and pollution load increased with the increase of rainfall intensity. The TP varied from 0.52 to 1.14 mg/L, and the cumulative output was 26.61 kg/hm². Through correlation and regression analysis, the empirical functions between accumulated runoff depth and accumulated rainfall (R2=0.964 6) and phosphorus output load (R2=0.997 5) were established, respectively. The results can provide a theoretical basis for the study of rainfall-runoff mechanism, the estimation of farmland phosphorus output load and farmland phosphorus management in this area.

Under different rainfall and runoff conditions, soil erosion will occur in sloping farmland in the Loess Plateau, which affects the quality of sloping farmland and the uniformity of agricultural irrigation. This study aimed to explore the mechanism of rill erosion and sediment yield under different flow discharge patterns on the loess slope through using three slopes (4°, 8°, 12°) and four flow discharge types, including recessed type (5.0-2.5-7.5 L/min), peak type (2.5-7.5-5.0 L/min), uniform type (5.0-5.0-5.0 L/min) and increased type (2.5-5.0-7.5 L/min). These conditions were combined in an indoor water-scouring test to study the rill erosion and sediment yield process. The results showed that under the same slope, the flow discharge type with the largest soil erosion rate was the peak type, followed by the uniform type (except for the slope of 4°). The soil erosion rates of peak type, recessed type and increased type were 1.36 times, 0.91 times and 0.95 times of that of uniform type, respectively. The erosion rate was positively correlated with the slope (P<0.05); the erosion rate under the same flow type increased with the increase of the slope. The relationship between the erosion rate and the flow intensity parameters (shear stress, stream power, effective stream power) could be described by a power function (R ²=0.37~0.94). The erosion rate was positively correlated with the energy dissipation rate (power function relationship), and soil erosion rate of the peak type changed most significantly with the energy dissipation rate, followed by the increased type, the uniform type and the recessed type. The variation range of sediment carrying coefficient was 20.84 to 83.57, with an average of 52.21, and the corresponding non-deposition guarantee rate was 95 %. The results of this study are of great significance to clarify the mechanism of soil erosion and sediment yield on loess soil slopes in the Loess Plateau under different flow types scouring, and will provide theoretical support for the establishment of erosion prediction models and erosion control in this area.

The production planning of irrigation areas is very critical for grain production, and it is extremely important to extract the crop information of irrigation areas quickly and accurately for a reasonable production planning of irrigation areas. In this paper, R language was used as a tool and Zhanghe irrigation area in Hubei province was selected as the study area. Based on three different remote sensing data, the time series of crops in the study area were calculated and extracted, and five different classification algorithms were used to classify the main crops in the study area. The results showed that: ①Among the various methods, the classification effect of random forest method through using a combination of multiple vegetation index time series data was the best. Among the classification of various features, the classification effect of water was the best, and that of double cropping rice rotation area was the worst. ②R language could realize the process of remote sensing data downloading, preprocessing, analysis and visualization, avoid cross-platform data processing, simplify the process of remote sensing data processing, indicating that R language had applicability and superiority in remote sensing data processing.

With the rapid development of industrialization and urbanization, groundwater environmental problems are becoming more and more prominent. The study of groundwater hydrochemical characteristics and evolution law is helpful to effectively monitor and protect groundwater environment. Taking the groundwater of Weihai city as the research object, based on the monitoring data of groundwater quality in the past 15 years, this paper explored the hydrochemical characteristics and evolution law of groundwater in the research area by means of statistical analysis, Piper trigraph and dynamic graph, and further analyzed the causes of water quality change. The results showed that Ca²⁺, Mg²⁺, Cl^- and SO₄ ^2- were the dominant ions in surface water in the study area, and the main hydrochemical types were Ca·Mg-HCO₃, Ca·Mg-Cl and Ca·Mg-SO₄. However, HCO₃ ^- and Ca²⁺ were the main dominant ions in groundwater, and the hydrochemistry type was Mainly Ca·HCO₃, gradually evolving to Ca·HCO₃, Ca·SO₄ type. There were some differences between surface water and groundwater hydrochemistry type, because surface water was susceptible to human activities. The groundwater in Weihai was weakly alkaline, which was influenced by long-term hydrogeochemical processes in coastal areas. The weathering of carbonate rocks was the main factor controlling the chemical composition of the groundwater in Weihai city, and seawater intrusion and human activities were the important factors affecting the groundwater environment.

Spring parameters have an important effect on the performance of the irrigation flow stabilizer. In order to better study the flow regulation performance of the irrigation flow regulator, it is necessary to choose appropriate spring parameters for the irrigation flow regulator. In this paper, the mathematical model of the pressure difference between the inlet and outlet of the irrigation flow stabilizer was established through theoretical derivation. Based on the FLUENT software, the numerical models of the different displacement of the adjustment core of the irrigation flow stabilizer were calculated, and the unknown coefficient and function of the mathematical model of the inlet and outlet pressure difference were solved. The results showed that the mathematical model of the inlet and outlet pressure difference described the relationship between the displacement of the adjustment core and the outflow of the irrigation flow stabilizer, and the inlet and outlet differential pressure flow characteristic curves of the irrigation flow stabilizer with different spring parameters could be obtained by calculating the mathematical model of the inlet and outlet pressure difference. The influence of spring parameters on the flow regulation performance of the irrigation flow stabilizer was as follows: the greater the spring stiffness and its pre-compression amount, the higher the starting pressure difference and the larger the adjustment interval. The optimized spring parameters were stiffness of 5.0 N/mm and spring pre-compression length of 2.5 mm. The spring with the stiffness of 5.15 N/mm and pre-compression length of 2.5 mm was selected for test verification and the test results showed that the starting pressure difference was 0.127 MPa, the flow adjustment interval range was 0.127~0.384 MPa, and the flow rate was stable at about 640 L/h of the irrigation flow stabilizer. The flow calculated by the mathematical model was consistent with the regulation of the measured flow. The measured flow value was slightly larger than the calculated value of the mathematical model, and the deviation between the two was within 5.64%. The results of this study provide a method for selecting the spring of the irrigation stabilizer, which can improve the research and development efficiency of the irrigation stabilizer.

In order to explore the ability of Sentinel-2A remote sensing data to detect chlorophyll A, suspended matter and salt concentration in water, this experiment took Sentinel-2A remote sensing images as data sources, combined with laboratory test data of river and lake water samples in Songnen Plain, and introduced normalized vegetation index, suspended matter index and salt index as inversion factors. Using correlation analysis method and SPSS software, inversion models of chlorophyll-A, suspended matter and salt water quality parameters in the study area were established, and mapping of three water quality parameters in Songnen Plain was carried out. The results showed that the concentrations of chlorophyll A, suspended matter and salt were positively correlated with sentinel-2A image reflectance, and the correlation coefficients peaked at band 8, band 5 and band 9, reaching 0.688, 0.664 and 0.780, respectively. The band combination of normalized vegetation index, suspended matter index and salt index could effectively weaken the influence of noise in remote sensing image, and significantly improved the correlation with chlorophyll A, suspended matter index and salt, with the correlation coefficients reaching 0.862, 0.751 and 0.876, respectively. On this basis, the inversion model of chlorophyll a, suspended solids and salt concentration of Songnen plain water was established. And the following conclusions were drawn: the determination coefficient R2 of the three inversion models of water quality parameters established by unvariate quadratic modeling method was the highest, reaching 0.887, 0.765 and 0.848 respectively, which were higher than that of logarithm, reciprocal, exponential and power function inversion models. The results of water quality mapping showed that the concentrations of chlorophyll A, suspended matter and salt in Lianhuan Lake, Xiangyang Lake, Daqing Reservoir and the main stream and tributaries of Nenjiang River were low and the water quality was good.

In order to realize the prediction of reference crop evapotranspiration (ET ₀) under the absence of meteorological elements, based on the data of the daily maximum temperature (T _max), minimum temperature (T _min), 2 m high wind speed (u ₂), relative humidity (RH) and sunshine hours (n) from the Adcon-Ws wireless automatic weather station of Shanxi Fruit Tree Research Institute in 2020-2021, seven machine learning models, such as decision tree (CART), random forest (RF), gradient boosting decision tree (GBDT), extreme gradient boosting (XGBoost), support vector machine (SVR), BP neural network (BPNN) and deep learning (DL) were used for calculating ET ₀ under the absence of combination of 9 meteorological elements. The PM formula calculated value was used as the standard value and the predicted results were compared with that of empirical methods, such as Hargreaves-Samani, Irmak-Allen, Makkink and Priestley-Taylor. The results showed that deep learning and BP neural network could achieve higher simulation accuracy and better generalization ability in all meteorological element combinations. Other models had different rankings in simulation accuracy and generalization ability under different meteorological absence combinations, but the overall effect of support vector machine was better. The influence of different meteorological elements on the model simulation ET ₀ was different, and the order from large to small was n, T _max, T _min, RH, u ₂. Compared with the four empirical methods, the accuracy of the machine learning model was better for the same input combination.

In order to provide scientific support and theoretical guidance for scientific extension and planting structure adjustment of rice in pishihang irrigation district, the satisfaction of irrigation water during the growth period of ratooning rice were evaluated. Based on the meteorological data from 2000 to 2021, the effective rainfall in the growth period and the water requirement of crops were calculated, and the irrigation water requirement was obtained based on the principle of water balance. The irrigation water requirement was compared with the basic water quota of double cropping rice and single cropping medium rice respectively, and finally the irrigation satisfaction degree was obtained. The results showed that the effective rainfall during the growing period of ratooning rice from 2000 to 2021 was 306.0~600.1 mm, with an average of 494.7 mm. Crop water requirements ranged from 568.4 to 849.3 mm, with an average of 659.9 mm. According to the basic water quota of double cropping rice, the irrigation satisfaction of ratooning rice was 0.65~1.49, with an average of 1.10, which was suitable for the planting of ratooning rice. According to the analysis of mid-season rice in a single season, the satisfaction degree of irrigation was 0.42~0.89, with an average of 0.59, and the planting suitability of ratooning rice was poor. Most areas of the Pishihang Irrigation District are planted with single-crop medium rice. Therefore, from the perspective of irrigation water supply, there is a certain risk in the large-scale promotion of ratooning rice planting in the Pishihang Irrigation District.

In order to explore the blockage situation and causes of the micro-moistening pipe with reclaimed water as the water source, a 1 320 h blockage evaluation test was carried out on the micro-moistening pipe. Compared with tap water source, the blockage degree of micro water pipe was more serious when the reclaimed water was the water source. Under the condition of reclaimed water, after 312 h of test operation, the micro-moistening pipe began to be seriously blocked, and the discharge of the pipe showed a segmented downward trend of “slow decline-sharp decline-slow decline” as a whole. Under the condition of reclaimed water, the contents of biofilm components (Extracellular polymer, EPS) and the changes of microbial community in the microwetting tube wall were analyzed. The results showed that polysaccharides and proteins in EPS were the key factors leading to the blockage of micromoist tube. There was an s-shaped curve correlation between them and the degree of blockage, showing a change trend of “sensitively-weak sensitively-sensitive”, in which the polysaccharide content was higher and the correlation with the degree of blockage was closer. With the deepening of the blockage, proteobacteria that can secrete a large amount of EPS become the dominant bacteria, aggravating the blockage of the micro-moistening tube. This study can provide a theoretical basis for exploring the phenomenon and mechanism of microbial blockage in micromoist tubes.