Aiming at the traditional modified material of fly ash， new modified materials of nano clay and nano silica， the laser particle size analysis， scanning electron microscope analysis， industrial CT scanning analysis and BET specific surface area analysis experiments of modified loess were carried out， and the effects of modified materials on the structure， pore and specific surface area of loess was discussed. The results show that： with the content of three kinds of modified materials from 1%， 3% to 7%， the filling material between loess particles increases obviously， and the overhead pores decrease gradually； the reduction rates of porosity of three kinds of modified loess with the content of 7% are 10.99%， 15.10% and 30.84%， respectively， and the increase rates of specific surface area of loess are 15.02%， 46.15% and 68.22%， respectively. According to the number and area distribution of pores， it can be concluded that this is because the modified materials transform the large and medium pores in the loess into small pores with larger specific surface area. The surface and edge of loess particles added with nano-clay are more rough and porous， and the filling effect of nano-clay on the mesopores which occupy the majority of the loess area is stronger. The results laid a foundation for the subsequent study on the adsorption and migration of pollutants in the modified loess and provided a theoretical basis for the development of the modified loess foundation treatment technology.

Accurate estimation of water and nitrogen status is crucial for crop growth modeling and yield estimation. Data assimilation enables the integration of observations and models for more accurate simulations. However， the traditional data assimilation systems mostly focused on leaf area index (LAI) and soil moisture (SM)， and there are few studies on water and nitrogen coupled data assimilation. In this study， ensemble Kalman filter (EnKF) was used to construct a data assimilation system for winter wheat growth based on SWAP-WOFOST model. By introducing the observation of leaf nitrogen accumulation (LNA)， key state variables such as SM， LAI， LNA and crop yield were updated at the same time. The results showed that only LAI and SM could well update the soil water profile and LAI， but the simulation for LNA and yield was poor. By introducing LNA， the simulation accuracy of LAI， LNA and crop yield was effectively improved. Simultaneous state-parameter estimation (SSPE) was superior to updating-state-only (USO)， especially in estimating soil moisture. It was difficult to accurately estimate crop yield when water or nitrogen state simulation was poor， and the coupled data assimilation of water and nitrogen state turned to be the best result. What’s more， the data assimilation system demonstrated good robustness under various observation errors and frequencies. This study provides an insight into the relationship between winter wheat growth and water and nitrogen status， and is helpful for crop growth simulation and yield estimation in practical application.

It is important to study the applicability and appropriate mineralization degree of brackish water used for irrigating sunflower in arid and semiarid regions. Taking freshwater irrigation as control (KX1)， another four irrigation treatments were designed， which irrigate with freshwater in the seedling stage and brackish water of different mineralization degree in the budding and grain-filling stages， i.e.， 2.5 g/L(KX2)， 3.0 g/L(KX3)， 3.5 g/L(KX4)and 4.0 g/L(KX5). Yield and quality indexes of sunflower were measured to analyze their responses to mineralization degree of irrigation water. With the increase of mineralization degree， protein and oleic acid contents of the sunflower seed tend to increase， linoleate and fat contents tend to decrease， while palmitic acid， and stearic acid contents increase first and then decrease， vitamin E contents increase first， then decrease and then increase again. There exist strong correlations among part quality indexes， such as protein content with oleic acid content， fat content with fatty acid components (except linolenic acid) and vitamin E， fatty acid component with another fatty acid component except palmitic acid. The relationships of fat vs. oleic acid contents and linoleate vs. protein contents show sigmoid shape， while those of fat vs. linoleate contents show inverse sigmoid shape. Meanwhile， oleic acid content is linearly and negatively correlated with linoleate content， while the relationships of fat vs. vitamin E and oleic acid vs. protein contents are linearly and positively correlated. Based on integrated assessment results of sunflower seed quality， the irrigation treatments are ranked in the order of KX5>KX4>KX2>KX3>KX1， which tend to increase with mineralization degree of irrigation water. While the sunflower yields are ranked in the order of KX3>KX1>KX2>KX4>KX5， which tend to decrease with mineralization degree of irrigation water except KX3. Considering both yield and quality， the irrigation treatment with mineralization degree of 3.5 g/L is appropriate for irrigation of sunflower in the study region， which results in higher sunflower seed quality and yield.

In order to study the optimal irrigation and fertilization mode for apple trees， this paper took 7-year-old apple trees as the research object， and different irrigation lower limits and nitrogen application amount were used as the control variables [three treatments of irrigation lower limit： 50% θc (W1)， 60% θc (W2)， 80% θc (W3)； three treatments of nitrogen application amount： 50 kg / hm² (F1)， 100 kg / hm² (F2)， 200 kg / hm² (F3)]. And the experiment was carried out to compare and analyze the fruit quality differences under different fertilization and irrigation modes. On this basis， the GC-ITOPSIS fruit evaluation model was established by MATLAB software， and then the best irrigation and fertilization mode was determined. The results showed that：①under W2F2 irrigation and fertilization mode， the flesh hardness， solid content， fruit shape index and single fruit weight were the highest； when the irrigation and fertilization mode was W3F1， the peel hardness and flesh fineness were the highest； the pericarp brittleness was the highest under W2F1 treatment； the acidity was the highest under W1F1 treatment.②Through the comprehensive evaluation of GC-ITOPSIS model， it was found that when the irrigation and fertilization mode was W2F2 treatment， the greater the comprehensive closeness degree， the best the fruit quality.③Through correlation analysis， the results of apple quality comprehensive ranking determined by GC-ITOPSIS model were basically consistent with most single quality ranking results， that is， the GC-ITOPSIS model could be used to evaluate the comprehensive quality of fruit. So it can be concluded that when the lower limit of irrigation is 60%θ_c and the amount of nitrogen application is 100 kg/hm²， the fruit quality is the best， namely the mode of medium water and medium fertilizer is the most reasonable.

The purpose of this study was to explore the effects of different fertilization methods (flood irrigation and soil covering) combined with urease-nitrification inhibitor [N-(n-Butyl) thiophosphoric triamide NBPT] and nitrification inhibitor (dicyandiamide DCD) on soil N₂O emission. In the indoor culture experiment， five treatments were set up， including no nitrogen application (CK)， flood irrigation application (S)， soil covering application (D)， flood irrigation application +NBPT-DCD combination (S+UI+NI)， and soil covering application +NBPT-DCD combination (D+UI+NI). The results showed that the application methods of anaerobically digested pig slurry significantly affected the N₂O emission from soil. The flood irrigation of anaerobically digested pig slurry obviously promoted the emission of soil N₂O， and its cumulative emission was higher than that of other treatments， reaching 2 420.39μg /m². The soil covering significantly reduced the peak value of N₂O emission and delayed the peak time. Compared with the flood irrigation treatments， the cumulative emission of N₂O decreased by 21.94% to 72.90%. Adding NBPT-DCD was beneficial to reduce soil N₂O emission， and the cumulative N₂O emission of D+UI+NI treatment was 5.96% to 33.80% lower than that of D treatment. The lowest apparent nitrification rate was only 40.65% in all fertilization treatments. Therefore， soil-covered fertilization can effectively reduce the N₂O emission from soil caused by flooding of anaerobically digested pig slurry， and the effect of N₂O emission reduction is better when combined with NBPT-DCD application.

Organosilicon fertilizer， as a new type of composite material to improve saline-alkali soil， has the characteristics of easy application， short cycle and large area promotion， and has a great application prospect. In this paper， the effects of organic silicon functional fertilizer and straw on the water transport and electrical conductivity of saline-alkali soil were studied through laboratory soil column tests. Four application amounts were set， respectively 0.5%， 1%， 1.5% and 2%. The results showed that with the increase of organic silicon functional fertilizer and straw application amount， the wetting front and cumulative infiltration amount of the wet front decreased continuously， among which straw had a great influence on the wetting front and cumulative infiltration amount of the wet front. Both the organic silicon functional fertilizer and straw could increase the soil moisture to a certain extent， and the addition of straw increased the soil moisture more obviously than that of organic silicon. Under the same application amount， the increase of the average water content in the 0~20 cm soil layer was -1.10%， 0.36%， 2.40% and 5.25%， respectively. The results of soil conductivity showed that at the depth of 0~10 cm， the conductivity decreased gradually with the increase of organic silicon functional fertilizer application and was lower than that of the control group. When the soil depth was below 10~15 cm， the conductivity gradually increased with the increase of silicone functional fertilizer application amount. The conductivity of treatment group at the depth below 15 cm was larger than that of the control group. Under the treatment of straw application， the electrical conductivity increased with the increase of straw application and was higher than that of the control group. Among them， with the same amount of addition， the average conductivity of the organic silicon functional fertilizer ratio straw in 0~10 cm soil layer decreased by 30%， 39%， 47%， 54% in turn. Thus， it can be seen that organosilicone functional fertilizer can effectively reduce the soil salinity， improve the desalination rate of saline and alkaline soil， and contribute to the improvement of the quality of saline and alkaline soil， which provides a theoretical basis for the application of organosilicone functional fertilizer in the treatment of saline and alkaline soil.

The objective of this study was to explore the suitable amount of irrigation and fertilization for increasing the yield of sunflower in salinized soil under flood irrigation in the middle and lower reaches of the Hetao Irrigation District. Three irrigation levels of 180,195 and 210 mm (denoted as W1，W2 and W3，respectively) and three fertilization levels of 450,525 and 600 kg/hm² (denoted as N1，N2 and N3，respectively) were set in the field experiment to study the effects of different water and fertilizer application measures on the plant height， leaf area index， yield， and irrigation water productivity of sunflowers in salinized soil. The results showed that： Irrigation and fertilization could significantly affect sunflower plant height and leaf area index. High water and high fertilizer (W3N3) treatment and middle water and middle fertilizer (W2N2) treatment were more conducive to promoting sunflower plant height growth， but the difference between them was not significant. High water and high fertilizer (W3N3) treatment could significantly promote the increase of leaf area index. Different water and fertilizer regulation measures had significant effects on sunflower yield and irrigation water productivity. In terms of increasing yield， the effects of high water and high fertilizer treatment (W3N3) and middle water and middle fertilizer treatment (W2N2) were significantly better than those of other treatments， with yield increases of 17.60% and 14.78% compared with the control， respectively. In terms of improving irrigation water productivity， the effects of middle water and middle fertilizer treatment (W2N2) and low water and low fertilizer treatment (W1N1) were significantly better than those of other treatments， increasing by 5.95% and 6.37% compared with the control，respectively，but the difference was not significant. Through comprehensive optimization using the membership function method，the optimal water and fertilizer management measures suitable for sunflowers in salinized soil in the middle and lower reaches of the Hetao Irrigation District were preliminarily obtained as follows：the irrigation amount of 195 mm (120 mm in spring irrigation and 75 mm in bud stage and the fertilizer application rate of 525 kg/hm² (basic fertilizer diammonium phosphate 225 kg/hm²， topdressing urea 300 kg/hm²).

In order to explore the effect of crop roots on soil desiccation cracking behavior in farmland， the natural desiccation cracking experiments of farmland soil under the effect of roots and without roots was carried out， and the development law of soil desiccation cracks under the effect of roots and without roots was discussed. Also the effects of crop roots on soil desiccation crack morphology and Minkowski density were analyzed. The results showed that compared with the soil without root influence， the degree of soil desiccation cracks near the root was lower， the width of the cracks， the length of a single crack and the area of aggregates were smaller， and the morphological characteristics of soil desiccation cracks far away from the root were similar to those of the soil without root influence. Crop roots significantly reduced the Minkowski density of desiccation cracks. Compared with the desiccation cracks in farmland without roots， the area density (m ₀)， length density (m ₁) and Euler number density (m ₂) of the six maize roots decreased by 31%， 19% and 20% on average when the roots were present. In conclusion， crop roots have obvious inhibition effect on soil desiccation cracking. The effects of roots on soil desiccation cracking are mainly reflected in two aspects of locally increasing soil tensile strength and restricting soil material movement.

In order to investigate the effects of autumn tillage treatment modes on the water， heat and salt transport patterns of seasonal freeze-thaw soils in the northern Xinjiang， this paper compared and analyzed the differences in the spatial and temporal patterns of soil temperature， moisture content and conductivity under five autumn tillage treatments， including tillage (FG)， no-tillage (MG)， monopoly furrow (LG)， tillage straw mulch (FJ) and tillage activated carbon mulch (FH). The results showed that different autumn tillage treatments changed the freezing and thawing process of soil. The order of the ability to maintain stable soil temperature during the freeze-thaw period was FJ > FH > LG > MG > FG. Around the freeze-thaw period， FJ， FH and LG treatments significantly increased the water content of the 0~60 cm soil layer in the tillage layer， while the soil conductivity also significantly decreased， which was shown in the order of the water storage capacity of FJ > FH > LG and the salt suppression capacity of FH > FJ > LG. The freezing process made the effects of each treatment on soil hydrothermal salt transport converge， and there was a significant or highly significant linear correlation among soil temperature， water content and conductivity； during the thawing period， soil temperature， water content and conductivity of FJ and FH treatments showed a significant or highly significant positive correlation with each other， while there was no significant linear relationship among FG， MG and LG treatments. The study results demonstrated the feasibility of regulating soil moisture during freeze-thaw period by autumn tillage treatment， which was of practical guidance for guiding agricultural production in the northern Xinjiang.

Accurate prediction of soil evaporation during the freeze-thaw period is of great significance for efficient utilization of water resources in arid and semi-arid regions. In this paper， a prediction model (PSO-ELM) based on particle swarm optimization (PSO) of soil evaporation during the freeze-thaw period was proposed in order to improve the prediction accuracy of the traditional extreme learning machine (ELM) with the random input weights and thresholds. By taking the nine factors affecting soil evaporation during the freeze-thaw period from 2016 to 2017 as input items and the measured soil evaporation as output items， the ELM model， GA-ELM model and PSO-ELM model were established respectively to predict soil evaporation in the freeze-thaw period. The results showed that the model prediction accuracy could be improved by processing the input factors through the random function and the prediction accuracy of the PSO-ELM model was better than that of the single ELM model and the GA-ELM model. The determination coefficient (R²)， root mean square error (RMSE)， mean absolute relative error， and mean relative error were 0.993 6， 0.010 9 mm/d， 0.007 9 mm/d， and 4.91%， respectively. Therefore， the PSO-ELM model could be used to predict soil evaporation during the freeze-thaw period.

The paper aimed to explore the conversion coefficients of different evaporators and the temporal and spatial variation of water surface evaporation， so as to provide theoretical support for the rational development and utilization of water resources in Mu Us Sandy Land. By collecting the simultaneous observation data of E-601 and 20 cm caliber small evaporators from 7 meteorological stations in Mu Us Sandy Land， the conversion coefficient K of two kinds of water surface evaporators in Mu Us Sandy Land was studied by linear fitting method and the annual and interannual variation rules of water surface evaporation were analyzed. There was a good correlation between the monitoring data of E-601 and 20 cm caliber small evaporators in Mu Us Sandy Land， and the K value was between 0.561 6 and 0.664 9. The average of the whole region was 0.632 4， and the conversion coefficients of the two kinds of water surface evaporation increased month by month from May to September. The annual variation of water surface evaporation of each meteorological station was the same， with the maximum in June， and its maximum value had a lag of one month compared with the air temperature. The interannual water surface evaporation showed a fluctuating change， with a significant downward trend， and the average decline rate was 64.3 mm/10a， which showed an overall trend of increasing from southwest to northwest in spatial distribution. The K value of Mu Us Sandy Land varied obviously from month to month， showing the characteristics of small in spring and large in autumn. The water surface evaporation in Mu Us Sandy Land is decreasing under the background of climate warming， indicating that human activities， such as ecological engineering， have improved the ecological environment of Mu Us Sandy Land.

In order to explore a new green and sustainable mulching mode of winter wheat in the semi-arid rain-fed agricultural area of Northwest China， two mulching modes， including straw crushing mulching with micro-ridges furrowing sowing (SM1) and straw crushing mulching with wide-width furrow sowing with small ridges (SM2) ， were set up in the dry farming area of Longzhong， and the effects of straw mulching on winter wheat yield and soil moisture and heat were studied with open field drilling (CK) as control. The results showed that， compared with CK， mulching significantly increased soil moisture content by 4.3% during the whole growth period of winter wheat， and the increase of soil moisture under SM2 treatment was greater than that under SM1 treatment. Mulching treatment could decrease the total soil temperature of winter wheat by 5.4%， but it had a slight warming effect (0.9~1.2 ℃) from overwintering to greening stage. Both SM1 and SM2 treatments could significantly increase the spike number per unit area， grain number per spike and 1000-grain weight of winter wheat， and then increase the yield by 8.9% and 15.7% compared with CK， respectively. In conclusion， the straw crushing mulching with furrowing sowing treatment can significantly improve the winter wheat moisture content and temperature in the whole stages， the photosynthetic assimilation capacity of winter wheat and then increase the yield of winter wheat significantly. In addition， SM2 treatment was better than SM1 treatment in increasing yield and soil moisture. Therefore， SM2 is a more suitable green and sustainable cultivation mode for winter wheat production in semi-arid areas.

Based on the long-term monitoring data of seawater intrusion in the past 50 years， the historical evolution of seawater intrusion in Daweijia area， a typical seawater intrusion area in Dalian， was analyzed. On the basis of the recent sampling and testing results， the suitability of current groundwater supply for drinking water and agricultural irrigation water was evaluated. Furthermore， the groundwater water quality situation and the main controlling factors affecting water quality in this area were analyzed and discriminated from two aspects of natural and human activities. According to the current situation of groundwater exploitation and utilization in this area， the corresponding countermeasures were put forward. This study results provide a scientific basis for the safety of water supply and rational utilization of groundwater in thisarea.

In order to explore the application effects of Hairuida super absorbent polymers in the cultivation of different crops in dry farming， such as water-saving，efficiency improvement，fertilizer reduction and plastic film replacement，production and efficiency increasing，this study took wheat，potato，corn and medicinal plants as the research objects，and carried out 49 field trials for two consecutive years (2018- 2019). The results showed that in winter wheat planting，the maximum yield increase of 22.69% could be achieved under the condition of saving 900 m3 and 1 800 m3 of irrigation water per hectare. In potato planting，the yield increased slightly under the condition of reducing fertilizer by 20% and 30%，and the maximum yield increased by 28.19%.In the planting of potato and corn in Northwest China，the yield was basically the same when the super absorbent polymers was applied without mulching film under suitable conditions. In the experiment of increasing yield and increasing efficiency of medicinal materials，the increase of yield could reach up to 46.64% with outstanding economic benefits. So it can be concluded that Hairuida super absorbent polymers has good application effect of saving water，preserving fertilizer， increasing yield and efficiency. In the cultivation of potato and maize under suitable conditions in northwest China，it is feasible to replace plastic film with super absorbent polymers which can fundamentally solve the problem of plastic film residue and the white pollution problem.

In modern agricultural production， fully automated equipment is often used to detect soil moisture and then irrigate the farmland. However， the existing system is difficult to accurately determine the humidity information of the entire farmland. When the soil moisture sensor fails， a control error will occur， resulting in the entire system breakdown. Therefore， through the combination with advanced technologies such as soil moisture sensor， Lora， Nb-iot wireless network transmission and microcontroller processing， a farmland moisture evaluation system based on improved K-means algorithm was designed in this paper. The system not only realizes the function of online evaluation of humidity information within one kilometer of farmland， but also can quickly locate faulty soil moisture sensors， send out alarm messages， and discard fault data. Finally， a large number of field experiments were performed on the humidity evaluation system. The results showed that the faulty sensor could be quickly located， and the relative error of the measured farmland humidity information was within 5%， which verified the feasibility of the humidity evaluation system.

In order to explore the effects of different ammoniated straw returning methods on water and salt transport and maize growth in saline alkali soil， a field maize experiment was conducted in Xiaodian District， Taiyuan City， Shanxi Province. Four straw returning methods were set in the experiment， including surface mulching of ammoniated straw1.2 kg/m²（F1）， ammoniated straw covered with 0.9 kg/m² on the surface of the soil and returned to the field 30cm below the soil at 0.3 kg/m² (F2)， ammoniated straw covered with 0.6 kg/m² at the surface of soil and returned to the field 30cm below the soil at 0.6 kg/m² (F3)， ammoniated straw mulched on the soil surface at a rate of 0.3 kg/m² and returned to the field 30 cm below the soil at 0.9 kg/m² (F4). At the same time， a control group without straw returning(CK) was set. The results showed that， compared with the control group， the different treatment groups all showed the effect of inhibiting salt accumulation and the difference was significant (P＜0.05)， among which the treatment group F2 showed the most significant effect of salt inhibition. The water retention effect of F1， F2， F3 and F4 treatment groups with double layer ammoniated straw returned to the field decreased successively， but with the growth and development of plants， the water retention effect of each treatment group became more and more significant.Straw returning could promote the growth and development of plants to a certain extent. The yields of F2 and F3 treatment groups were the highest and significantly different from those of control group (CK) (P＜0.05).Comprehensively considering the effects of water and salt retention and maize growth and development， F2 treatment is the most suitable.