The unreasonable nitrogen management in paddy fields has resulted in the waste of nitrogen resources and environmental pollution. To solve this problem, this study analyzed the fate of nitrogen and its optimal management in typical paddy fields in Southern China. Based on the observation data of experimental fields under conventional field management in Gaogang village, Xiaochang County, Hubei Province in 2017, the DNDC model was used to simulate and analyze crop nitrogen uptake, nitrogen leakage, ammonia volatilization, and denitrification. The results showed that :①The DNDC model could accurately simulate different nitrogen outputs from paddy fields, with the fitting degree (R ²) as high as 0.649 3~0.860 2, and the Nash efficiency coefficient (NSE) as high as 0.513 5~0.786 2, which indicated that this model could be used to analyze the dynamic and structural characteristics of nitrogen fate in paddy fields.②Gaseous nitrogen loss, rather than water loss, was the main way of nitrogen loss in paddy fields, accounting for 83.86%~86.69% of the total nitrogen loss, and the period during tillering fertilizer application and yellow maturity was stage an important period for significant gaseous loss.③According to the scenario simulation, the optimal nitrogen management was to control the nitrogen application rate at 100 kg/hm² and to return paddy straw to fields, which increased nitrogen uptake of paddy by 12.67% compared with the low nitrogen fertilization, and reduced the nitrogen gaseous losses by 17.64%~65.57% compared with the high nitrogen fertilization and nitrogen surface fertilization method. This study results can be extended to paddy areas in southern China to achieve sustainable development of high nitrogen utilization and low nitrogen pollution.

In order to summarize the main research contents in the field of soil water and salt transport research at home and abroad and explore its development prospects, based on the CNKI and WOS core databases, the literature on soil water and salt transport from 2000 to 2020 was collected, the VOSviewer visual analysis software was used and combined with the visual analysis functions in CNKI and WOS to visually analyze the number of articles published, co-occurrence of keywords and author cooperation of the literature on soil water and salt transport in the past 21 years at home and abroad. The results showed that: from 2000 to 2020, the amount of papers published in the field of soil water and salt transport had shown an overall upward trend. Major core journals with more papers published in this field included “AGRICULTURAL WATER MANAGEMENT” 、“ Journal of Irrigation and Drainage” and “ Water Saving Irrigation”etc. A large number of countries have published papers in this field, which are mainly foucsed on experimental research and numerical model simulation under the condition of drip irrigation, brackish water irrigation, freeze-thaw and other conditions. China’s high-impact publishing organizations in this field are also in the forefront of the world. Future research on soil water and salt transport will mainly focus on several aspects such as soil structure, planting and management methods, model prediction, coastal saline-alkali land, and salt adaptability of salt-tolerant vegetation. It can be concluded that: in recent years, the research on the law of soil water and salt transport will be an important theoretical basis for the treatment of soil salinization. The study and simulation prediction of the law of soil water and salt transport under different coupling conditions are of great significance to the management of soil salinization in China.

In order to improve the nitrogen removal efficiency of stormwater bioretention system, physical model tests of soil column (1 000 mm high, 200 mm diameter plexiglass column, outlet pipe raised upward to form different submerged heights) were carried out to study the nitrogen removal efficiency of stormwater bioretention system under different operating periods (6 d, 12 d, 18 d, 24 d, 30 d) and different submergence heights (0 mm, 250 mm, 500 mm). The results showed that within 30 days, the permeability of the system increased with the increase of operating time, the permeability coefficient increased from 0.44 mm/min to 0.98 mm/min, and the clay particles in the system filler (<0.002 mm) migrated downward and enriched in the middle of the packing (250 mm). The removal of NH₄ ⁺-N changed little with the increase of operating time and the average removal rate was 93.60%, and the removal rates of NO₃ ^--N and TN increased first and then stabilized with the increase of operating time and the maximum removal rates were 54.45% and 71.01%, respectively. The removal rate of COD decreased firstly and then stabilized with the increase of operating time, the range of change was 59.56%~73.85%. The submerged zone had little effect on the removal rate of NH₄ ⁺-N, while the removal rates of NO₃ ^--N, TN and COD increased in different degrees, and the submerged heights corresponding to the maximum removal rates of TN, NO₃ ^--N, and COD were 250 mm, 500 mm and 250 mm, respectively. The nitrogen removal rate was relatively stable during the 30 d operation, and not decreased with the increase of the operation time. Setting submerged zone improved the removal efficiency of NO₃ ^--N, TN and COD. Comprehensively considering pollutants removal, the optimum submerged height is recommended as 250 mm.

In order to explore the influence of irrigation and planting patterns on the growth and development of cotton seedlings under non-film drip Irrigation in southern Xinjiang, this study used local membrane-covered cotton as the control CK, and set three irrigation quotas T1 (36 mm), T2 (45 mm) and T3 (54 mm). and two planting densities of I1 (330 000 plants·hm^-2) and I2 (240 000 plants·hm^-2). The results showed that the plant height, thick stem, leaf area, root weight, root diameter and photosynthesis efficiency of cotton under non-film drip Irrigation were all significantly higher than that of other plants, however, the root length and overall root surface area had been greatly reduced. In addition, the net photosynthesis rate also plummeted with the increase of the planting density. The principal component analysis showed that the average root diameter, stomata aeration capacity, transpiration rate and root surface area of cotton were highly responsive to irrigation and planting modes. Besides, through the relevant function values, it can be summarized that the most suitable planting conditions for cottons under non-film drip irrigation were the following parameters: irrigation quota of 54 mm and planting density of 240 000 plants·hm^-2, which can provide excellent conditions for the initial growth of cotton grown under non-film drip irrigation.

Agricultural irrigation water is greatly affected by meteorological factors such as rainfall and evaporation. In order to make the distribution of agricultural water rights more scientific and more reasonable, dynamic water rights should be used in the distribution. However, there is no unified calculation method for agricultural dynamic water rights at present. IN this paper, Lilou town in Yindan irrigation area was taken as the research object, based on the analysis of historical data of water supply, meteorology and planting structure in the research area, according to the current distribution model, the basic agricultural water right in the project area was calculated to be 15.19 million cubic meters. The calculation model of agricultural dynamic water rights based on rainfall or drought index was proposed, and the maximum agricultural water rights in the project area was calculated to be 17.08 million cubic meters. Combined with the current situation of agricultural water measurement in the study area, a mixed distribution model based on the combination of irrigation area and irrigation water demand was proposed, in which the agricultural water right was allocated to the village and the village level agricultural basic water right and dynamic water right were determined. The research results of this paper can provide reference for other regions to determine and allocate agricultural water rights.

Based on the integrated technology of water and fertilizer, the effects of different irrigation frequency on the yield and root distribution of cucumber in solar greenhouse was studied in order to provide the basis for formulating water management system of early spring cucumber production in Ningxia irrigation area. The results showed that the stem, leaf number and fruit development of cucumber showed a low-fast-low growth trend. Medium frequency irrigation treatment (TR2) could promote the simultaneous increase of plant height, leaf number and fruit number, as well as fruit expansion and single fruit weight. In the early spring cultivation of cucumber in solar greenhouse, the dry matter weight of cucumber root accounted for more than 85% of the total root amount in 0~20 cm soil layer. The effect of different irrigation frequency on root growth was different in different growth stages of cucumber. In the early stage of cucumber growth, with the increase of irrigation interval, the root biomass and 0~20 cm soil distribution proportion increased. However, in the late growth stage, the root biomass of low-frequency irrigation treatment (TR3) was significantly decreased and the root biomass of TR2 was the highest with the highest yield of 115 365 kg/hm². Therefore, for the early spring production of cucumber in solar greenhouse in Ningxia irrigation area, under the condition that the average daily temperature is about 22 ℃ and the single irrigation quota is 70.05 m³/hm², the optimal irrigation interval of cucumber fruit bearing period is 2~3 d, the yield and water use efficiency are the highest, up to 115 365 kg/hm², and the water use efficiency is 42.51 kg/m³.

Tea plants consume more water and need more fertilizer. Engineering water shortage and seasonal water shortage in drought-prone tea areas lead to low utilization rate of traditional fertilizer. With the popularization of agricultural water-saving technology, the integration system of water and fertilizer dominated by drip irrigation and micro-sprinkling irrigation has been gradually applied to tea gardens, the screening of water-soluble fertilizer for tea trees and the research on supporting fertilization strategies have become the focus of technical personnel. Therefore, by analyzing the present situation of tea tree water-soluble fertilizer products and patent application, it was found that the water-soluble fertilizer of tea tree was mainly foliar fertilizer, and less water-soluble fertilizer was used for irrigation and fertilization. At the same time, based on the application of bulk element water-soluble fertilizer, trace element water-soluble fertilizer and functional water-soluble fertilizer in tea garden, the effects of water-soluble fertilizer application on the yield, quality and water-fertilizer utilization rate of tea trees in existing literatures were summarized. On the basis of summarizing the existing researches, the research and development direction, application trend and screening standard of water-soluble fertilizer for tea plant were put forward from two perspectives of leaf spraying and micro-irrigation, in order to provide reference for the research and application of water-fertilizer integration technology in tea garden.

In order to explore the effect of potato subsurface irrigation depth on the distribution of soil water and nitrogen and the optimal utilization efficiency mode in arid areas, the field experiment was conducted with three factors and three levels of orthogonal experiment, including three values of buried depth (5, 10, 15 cm), three values of irrigation amount (1 050, 1 500, 1 950 m³/hm²) and three values of nitrogen fertilizer application rate (120, 180, 240 kg/hm²). The results showed that the increase of dry matter accumulation of potato under each treatment was the largest in the seedling stage and tuber formation stage. The T6 treatment (infiltration irrigation pipe buried depth of 15 cm, irrigation amount of 1 950 m³/hm², nitrogen application rate of 120 kg/hm³) had the largest amount of dry matter accumulation and chlorophyll relative content in potato leaves at three growth stages, which were significantly different from the total accumulation amount of other treatments (P<0.05); with the increase of the buried depth of the infiltration irrigation pipe, the soil moisture content gradually moved downward, and the soil moisture content of the same soil layer was higher. The commercial potato percentage of T6 treatment was 69.23%, which was significantly different from that of other treatments (P<0.05); the highest yield of T9 treatment was 28.60 t/hm², which was not significantly different from T6 treatment (P>0.05); but the highest WUE and N partial productivity of T6 were 10.91 kg/m³ and 237.08 kg/kg, respectively, which were significantly different from those of other treatments (P<0.05). In summary, in the arid region of Ningxia, the combination of buried depth of 15 cm, irrigation quota of 1 950 m³/hm² and nitrogen application rate of 120 kg/hm³ can improve potato yield and water and nitrogen use efficiency, and realize high potato production..

The problem of nitrogen leaching due to unreasonable water and nitrogen application in agricultural production in northern China was addressed. The experiment for summer maize was carried out at the Irrigation Experiment Centre of Shandong Province. The objective of this study was to analyze the distribution and leaching characteristics of nitrogen and its transport and transformation patterns. Two irrigation levels and two nitrogen application levels were applied in the experiment. Two irrigation level were I1 (67.5 mm) and I2 (121.5 mm). Two nitrogen levels were N1(150 kg/hm²) and N2 (200 kg/hm²). A blank control treatment (CK) was set up and each group had three replicates. The results showed that the I2 treatment promoted the downward migration of nitrogen at the surface layer (0~20 cm) and increased the accumulation of nitrogen at the middle layer (20~60 cm). And nitrate leaching was obviously affected by irrigation. I2 treatment increased cumulative nitrate leakage. Nitrogen leakage increased by 8.44% under N2 treatment compared to N1 treatment, and inorganic nitrogen accounted for around 14.07%~20.75% of the total nitrogen. Nitrate was the major component, accounting for 83.11%~87.14% of the inorganic nitrogen. The nitrogen content in the top soil layer in the I1 treatment was 75.88%~77.53% higher than that in the I2 treatment. While the nitrogen content in the middle layer was 44.38%~44.92% lower than that in the I2 treatment. Nitrogen can remain in the top layer for a long time without irrigation at the nodulation stage, which was not conducive to crop uptake and utilization. Above all, the I2N1 treatment can not only increase nitrogen transport and accumulation in the middle layer (20~60 cm), but also reduce the nitrogen leakage. This regime can meet the needs of agricultural production and reduce leachate pollution on groundwater quality.

In order to clarify the effects of irrigation on grain filling characteristics, soil respiration rate and yield of summer maize, five irrigation systems ( W0, W1, W2, W3, W4 ) were set in winter wheat season under the field environment of Heilonggang Basin, and no water treatment was applied in summer maize season. The grain filling characteristics, yield, soil respiration rate and its influencing factors of summer maize were analyzed. The results showed that the soil water consumption of summer maize and the total water consumption in the whole growth period increased with the increase of irrigation times of winter wheat. The fitting effect of grain weight and time of summer maize by Logistic model was good. The filling duration of summer maize was prolonged with the increase of irrigation times. Compared with W1, W2, W3 and W4, W0 treatment reached the maximum filling rate in advance and the duration was the shortest. The maximum filling rate ( V_m ) and average filling rate ( V_a ) of W2 treatment were 1.17 g/d and 0.57 g/d, respectively. The soil respiration rate of summer maize was positively correlated with soil volumetric water content and soil temperature. The correlation between soil respiration rate and soil volumetric water content of different treatments was significant. The correlation between soil respiration rate and soil temperature of W0 and W1 treatments was significant. The average soil respiration rate and total emission of summer maize during the whole growth period were the lowest in W2 treatment, which were 5.78 μmol / (m²·s ) and 2 260.75 g/m², respectively. The previous irrigation system had no significant indigenous effect on the agronomic traits, yield and yield components of summer maize, but the yield of summer maize increased with the increase of irrigation times in winter wheat season. In summary, W2 treatment can effectively reduce greenhouse gas emissions while ensuring yield and water saving, so as to achieve the purpose of saving water and reducing emissions without reducing production, which is the best irrigation system.

In order to study the influence of biochar and water regulation measures on available nutrients in polluted soil so as to provide a basis for using water regulation measures to promote the restoring effect of biochar on polluted soil, in this paper, heavy metal polluted soil with biochar was set as research object, the effects of biochar and water regulation on cation exchange capacity (CEC), available phosphorus (AP), available potassium (AK) and alkali-hydro nitrogen (AN) of soil with biochar were studied. The experimental results showed that : ① water regulation of low levels could increase the contents of CEC, AP, AK and AN. ②when the content of soil water increased to high levels, soil CEC, AP, AK and AN would decrease. Especially at 100% field capacity, soil CEC, AP, AK and AN were 30.2%, 12.7%, 31.3% and 21.5%, separately, lower than those of control, and the differences were significant (P<0.05).③Soil pH had irregular change with the changes of field capacity, and the differences were not significant compared with control (P>0.05). The results indicate that appropriate increase of soil water content can increase soil available nutrients, while overdose increase may decrease soil available nutrients.

In order to explore the influence of mulching film residue on tomato growth, in the experiment, 8 residual film treatments (0 kg/hm², 200 kg/hm², 400 kg/hm², 600 kg/hm², 800 kg/hm², 1 200 kg/hm², 1 600 kg/hm², 2 000 kg/hm²) were set to analyze the changes of soil moisture content, tomato growth indicators, and fruit quality. The results showed that the increase in residual film amount could cause uneven distribution of soil moisture content. With the increase of residual film amount, the soil moisture content of soil layers below 30 cm decreased significantly. When the residual film amount was 2 000 kg/hm², the ratio of stem thickness at mature period decreased with the increase of residual film amount, the change trend of plant height remained stable, and the yield decreased by 18.59% compared with T1 treatment. The increase of residual film amount was helpful for the improvement of fruit quality. When the residual film amount was 600~800 kg/hm², the Vc content and soluble sugar content of tomato increased by 85.55% and 21.05%, respectively, and the organic acid content decreased by 28.6% compared with T1 treatment. In order to comprehensively evaluate the positive and negative effects of residual film, the principal component analysis method was used to comprehensively evaluate the growth and quality indicators. The results demonstrated that the comprehensive score of tomato growth and fruit quality decreased and then increased with the increase of residual film amount. When the residual film amount reached 1 200 kg/hm², the comprehensive score of tomato growth and quality index was the highest. A large amount of plastic film residue had a significant effect on tomato growth, but could improve fruit quality in a certain range. Therefore, controlling the residual film amount within a specific threshold could reduce the damage caused by residual film to facility tomato.

In order to explore the suitable fertilization and irrigation regime for melon under the condition of water and fertilizer integration, in this study, a greenhouse pot experiment was carried out with different irrigation threshold levels (W1:75%θ_fc,W2:65%θ_fc,W3:55%θ_fc ) and different topdressing levels (F1:1 050 kg/hm²,F2:735 kg/hm²), by setting conventional spraying compound fertilizer coupled with flooded irrigation as the control, the melon growth, yield, water and fertilizer use efficiency, and quality were studied. The results showed that the plant height and stem diameter significantly increased with the increase of fertilizer application. After the vine extension stage, the plant stem diameter under W2 was significantly higher than that under W1 and W3. The fertilization level had no significant effect on the flowering and fruit harvest time, but the high irrigation threshold could make the crop enter the maturity stage early and improve the market value at harvest period. The fruit morphology index increased with the increase of irrigation and fertilization amount.The highest yield was found in W1F1, which was 35.5% higher than that of W3F2 and not significantly different from that of W2F1. WUE gradually increased and PFP gradually decreased with the reducing of irrigation threshold. The maximum value of WUE was W3F1, which was 1.58 times that of CK, the maximum value of PFP was W1F1, which was 28.4% higher than that of the CK. Reducing the amount of fertilizer was beneficial to the accumulation of melon quality. The high irrigation amount significantly reduced the accumulation of reducing sugar and soluble solids, the accumulation of VC and soluble protein increased first and then decreased with the decrease of irrigation amount. The ranking result of the comprehensive quality evaluation was that W2F2 was the best and W2F1 was the second. For the planting of protected melon in Changshu area, W1F1 can be adopted when only market value is considered, and W2F1 is more appropriate when the yield, quality, water and fertilizer use efficiency are considered comprehensively.

In order to explore the effect of potassium humate on the adsorption and leaching characteristics of clay soil salinity, Cl^-, SO₄ ^2-, Na⁺, the laboratory soil column simulation test was carried out with five potassium humate supplemental levels (0,0.6, 1.2, 1.8, 2.4 g/kg, and treatment numbers were CK, T1, T2, T3, and T4, respectively). The effects of potassium humate addition amount on soil salinity, Cl^-, SO₄ ^2-, Na⁺ content and characteristics of adsorption and leaching after leaching with salt and fresh water were analyzed. The results show that: ①after leaching with salt water, the soil salt content, Cl^-, SO₄ ^2-, and Na⁺ content in all treatments increased, but decreased with the increase of potassium humate. ② compared with the CK, the soil salinity, Cl^-, SO₄ ^2-, and Na⁺ content increments in the four treatments of T1 to T4 were significantly reduced, and the largest decrease in soil Cl^-, SO₄ ^2-, and Na⁺ content increments was 72.42%, 89.52%, and 54.10%, respectively. ③after fresh water leaching, the soil salinity, Cl^-, SO₄ ^2-, and Na⁺ content of the four treatments of T1 to T4 were significantly lower than those of CK. ④ compared with the CK, the reduction of the soil salinity, Cl^-, SO₄ ^2-, and Na⁺ content was significantly increased, and the largest increase in soil Cl^-, SO₄ ^2-, and Na⁺ content reduction was 34.61%, 42.31%, and 55.04%, respectively. Potassium humate can inhibit the adsorption of salinity, Cl^-, SO₄ ^2-, and Na⁺ in clay saline soil, and enhance the leaching effect of fresh water on soil salinity, Cl^-, SO₄ ^2-, so as to achieve the purpose of reducing soil salinity, Cl^-, SO₄ ^2- and Na⁺ content. Considering comprehensively, 1.8g /kg can be used as the recommended dosage for the improvement of clayey saline soil with potassium humate in the Yellow River Delta.

Soil moisture distribution at a catchment scale is an important topic in hydrology. In this study, geostatistical semi-variograms were used to analyze the soil moisture profiles in a depth of 2 m sampled during dry and wet season over Siheshui catchment of Guangdong province. The results show that: at a catchment scale, soil moisture profile can be divided into 5 layers as top surface zone (0~20 cm), root zone (20~70 cm), matric potential zone (70~120 cm), groundwater affected zone (120~200 cm) and groundwater zone (>200 cm). Driven by rainfall and evaporation directly and also affected by interception of forest litter and water uptake of undergrowth roots, soil moisture in the top surface zone changes promptly seasonally and along depth. The roots of forest trees are mainly distributed in 20~70 cm soil depth. In this zone, soil moisture is replenished mostly by rainfall flow in gaps between roots and soil substrate, water consumption is mainly caused by root water absorption, soil matrix potential gradient plays a role of adjustment and distribution, and soil water changes greatly in season and between layers. There are few roots and little gap flow in 70~120 cm depth. Soil moisture in this depth is driven mainly by matric potential gradient and changes seasonally much less than that in upper zones and the change becomes less and less with the increase of depth. At 120 cm depth, the matrix potential gradient disappears, and soil moisture does not change between seasons or between soil layers, forming a zero flux layer. In the lower part of the slope, mountain depression and low-lying areas, the seasonal variation of groundwater level affects the soil moisture in the range of 120~200 cm. The effective vadose zone thickness is the depth from the ground to the zero flux surface of soil water, which is about 120 cm in Siheshui Basin. The soil water storage capacity of the basin is the seasonal difference of soil profile water content in this region, and the calculated result is 42 mm. The results can provide parameter support for hydrological simulation of watershed without data in south China hilly region.

Based on field experiments under natural conditions in the loess hilly and gully region, this paper used TDR to determine the water content of 15 different slopes on different radiation surfaces in the study area, calculated the evapotranspiration based on the water balance method, and revealed the change rule of evaporation in different radiation surfaces. The change law of evapotranspiration and the influence of slope aspect and slope on evapotranspiration was studied, a prediction model was constructed on this basis, and the prediction results were verified. The results showed that: ① The ET value in the loess hilly and gully region gradually increased after the wintering period, reached the first extreme value in early April; before entering the rainy season in June, it decreased slowly, and reached the minimum value before the rainy season; after entering the rainy season, it gradually increased and reached the maximum at the end of August; after the end of the rainy season, it showed a gradually decreasing trend; ② There was a certain correlation between the aspect and the ET value, and the ET value was close to the maximum value of the sunny slope in the southern region; There was also a certain correlation between the slope and the ET value. The larger the slope, the smaller the ET value, and vice versa; ③ The water balance method was used to predict the evapotranspiration in the study area. From the simulation results, it can be seen that the established model can well predict ET values of different radiation surfaces in the loess hilly and gully region under natural conditions. The research results are of great significance for agricultural production, irrigation system formulation, water resource shortage alleviation and realizing water resource management mode based on evapotranspiration in loess hilly and gully region.