In order to improve the pertinence and effectiveness of various construction projects in the construction of high-standard farmland, in this study, the project of high-standard farmland construction in Zhoutang Town of Suixian County, East Henan Plain, was selected as the research object, and the obstacle degree model was combined with the analytic hierarchy process to construct the evaluation model of high-standard farmland construction, and to explore the limiting factors and construction contents of farmland construction. The results showed that the comprehensive evaluation score of the high-standard farmland construction project area in Zhoutang Town was 0.732 8, the farmland construction level was average, and met the construction conditions of the high-standard farmland construction constituency. Through the analysis of obstacle degree model, it was found that the obstacle degree values of 8 indexes in the study area, including the machine-well electrical rate, farmland irrigation guarantee rate, soil organic matter content, machine-tilled road accessibility, farmland irrigation facility integrity, the proportion of farmland efficient water-saving area, farmland intelligent management, and the green rate of the field main road, were greater than their average values, which were the main obstacle factors for the construction of high-standard farmland in the project area, and needed to be solved. The research shows that the combination of obstacle degree model and analytic hierarchy process can accurately identify the main obstacle factors in the farmland construction in the study area, and can provide guidance for the determination of the priority construction content in the project area to improve the pertinence and effectiveness of the construction project.

The change of rice area and the groundwater development and utilization activities in Sanjiang Plain have a serious impact on the local groundwater dynamics. In order to clarify the characteristics of groundwater recharge and drainage and the existing problems in the Sanjiang Plain, a dynamic water cycle model was built based on the land use under the changing scenarios from 2000 to 2014. With other parameters and assumptions unchanged, a year by year static water cycle model and a prediction hydrological model were established to simulate the hydrological process under various land use scenarios and planned rice planting scale, to compared the groundwater flux under various scenarios, and to explore the rice planting scale under the balance of groundwater recharge and drainage. The results showed that based on the analysis of the status quo model of dynamic water cycle, the groundwater overdraft in Sanjiang Plain was serious, and the annual groundwater storage variable was -313 million m³; Comparing various static land use models under the current water resource allocation pattern, under the rice planting scale in 2005, the annual average groundwater storage variable was -0.25 billion m³, realizing the balance of groundwater recharge and discharge; The prediction model was established under the new pattern of water resources allocation, and the rice area in each sub basin was enlarged on a year-on-year basis. It was determined that when the rice planting scale was 3.041 million hm², the annual average groundwater storage variable was -0.84 billion m³, and the Sanjiang Plain has achieved the balance of groundwater recharge and discharge.

How to improve the utilization rate of brackish water and save freshwater resources is one of the key issues in the development of the rice industry in the Yellow River Delta saline-alkali land. In this study, multiple rice varieties were used to compare yield-related traits and yield changes through brackish water irrigation with different salinity contents at developmental stages. The results showed that irrigation with brackish water of 3 g/L and 5 g/L salinity in the whole growth period obviously both reduced rice yield. Irrigation with 3 g/L of brackish water mainly affected grain number per spike and 1 000-grain weight, while the effects of 5 g/L brackish water irrigation on rice yield were multifaceted. Irrigation with 3 g/L of brackish water reduced yields by about 10% throughout the growth period, while 5 g/L of brackish water irrigation reduced yields by more than 40%. Irrigation with 3 g/L of brackish water in the transplanting regreening stage reduced the seedling-survival rate, but it could improve the salt tolerance of rice to a certain extent and reduced the impact of salt stress on rice yield. Compared with other periods, only irrigation with 5 g/L brackish water at tillering stage had a relatively small impact on rice yield. Irrigation with brackish water during booting and filling stage seriously affected rice filling. Therefore, in the case of shortage of fresh water resources, it could be considered to use 3 g/L brackish water for irrigation in the transplanting regreening stage and the tillering period, but the number of seedlings should be appropriately increased to mitigate the yield loss caused by the reduction of seedling rate. In the tillering period, high salinity brackish water could be appropriately used for irrigation, but it should not exceed 5 g/L. The salinity of brackish water in booting and filling stage should be strictly controlled below 3 g/L. The utilization of brackish water resources in the Yellow River Delta could fully save fresh water resources, with good economic and ecological benefits.

In order to clarify the effect of reducing nitrogen application on Yield and water and nitrogen utilization efficiency of double-season rice under the combined application mode of Chinese milk vetch and straw returning, five treatments, including non-returning with no fertilizer (S0N0), non-returning with total nitrogen fertilizer (S0N3), Chinese milk vetch and straw returning with no fertilizer (S1N0), Chinese milk vetch and straw returning with reduced nitrogen fertilizer (S1N1) and Chinese milk vetch and straw returning with reduced nitrogen fertilizer (S1N2) were set in this study. Nitrogen content and accumulation in plants of double-season rice in different growth stages were determined, and water and nitrogen utilization efficiency, yield and yield components of double-season rice were analyzed. The results showed that compared with S0N0 treatment, nitrogen content and accumulation, water and fertilizer utilization efficiency and yield of S1N0 were improved without nitrogen application. S1N2 treatment had the highest nitrogen content and nitrogen uptake in two-season rice at heading stage and yellow maturity stage. At early rice stage, the yield of early rice was the highest under conventional nitrogen application S0N3 treatment, and the yield of early rice under nitrogen reduction treatment S1N1 and S1N2 decreased by 7.43% and 1.68% respectively, while that of late rice increased by 0.68% and 2.35% respectively, but there was no significant difference. Compared with conventional nitrogen application (S0N3), reducing nitrogen application (treatment S1N1, S1N2) could reduce irrigation water, drainage and field water consumption of double-season rice, significantly improving water use efficiency by 5.24% and 25.86% respectively in late rice period, and significantly improving nitrogen use efficiency by 6.23% and 13.74% respectively. Therefore, based on comprehensive consideration of water and fertilizer utilization efficiency and yield, it was appropriate to reduce the amount of nitrogen fertilizer for early and late rice by 15% and 10% respectively under the way of returning aster and straw to field.

The Sanggan River Basin is located in the construction area of the capital water conservation area and eco-environment supporting area. However in the past decades, Sanggan River Basin was suffering severe non-point source pollution and ecological degradation. Exploring the mechanisms of changes in soil water, salt and nitrogen distributions in different farmland systems is critical for mitigating regional ecological crisis. In this syudy, three typical farmland use patterns (apricot garden, rain-fed corn and irrigated corn) in Sanggan River Basin were taken as the research objects, the distribution laws of water, salt and nitrate in soil profiles of different farmland use patterns were studied through the field sampling and experimental analysis. The aim was to clarify the potential leaching risks of soil salt and nitrogen. The results showed that: ① The average values of soil water content and electrical conductivity of irrigated corn farmland were the highest in different farmland use types, while the moisture content of apricot orchard was the lowest, and the electrical conductivity was close to that of rain-fed corn. ② Na⁺ and SO₄ ^2- were the main components of soil salt ions, while K⁺, Mg²⁺ and Cl^- were relatively few. Na⁺, K⁺ and Mg²⁺ in irrigated corn were significantly higher than those in apricot garden. ③ The distribution laws of soil water and salt were obviously different with complex distributions, and this was mainly due to different farmland management patterns. The vertical distributions of soil electrical conductivity and salt ions in apricot orchards were olive-shaped, that of SO₄ ^2- and electrical conductivity in rain-fed corn was higher in the middle and upper part, but less in the bottom, and Na⁺ in the soil of irrigated corn was S-shaped. ④ The average cumulative content of NO₃ ^--N in irrigated corn was significantly higher than that in rain-fed corn and apricot garden, and the profile distribution was characterized by more from top to bottom and less in the middle. The average NO₃ ^--N in deep soil reached 14.6 mg/kg, which had potential nitrate leaching risk. ⑤ Mg²⁺ and SO₄ ^2- in different land use types were positively correlated with water content and electrical conductivity, respectively, indicating that they were important factors to control regional water and salt changes. To sum up, different farmland uses patterns have obvious differences on soil water, salt and nitrogen distribution characteristics, and the content of water, salt and nitrogen is obviously the highest in irrigated corn soil, so it is necessary to take reasonable water and fertilizer management measures to mitigate environmental pollution risks.

Accurate simulation of soil moisture (SM) is of great significance for precision irrigation of farmland, optimal scheduling of regional water resources and improving agricultural water utilization efficiency. In this study, daily meteorological and soil moisture data were used to explore the applicability of random forest (RF) and support vector machine (SVM) to simulate SM at different depths (4 cm, 10 cm and 20 cm). Four input combinations of solar radiation (R_s ), air temperature (T), precipitation (P), wind speed (U ₂), air humidity (RH) and soil temperature (ST) data were used to explore the impact of different input variables on SM simulation. The results showed that RF model had the highest accuracy in simulating SM at different depths under four input combinations, while SVM model had lower accuracy, with R ² ranging of 0.871~0.914 and 0.710~0.814, RMSE ranging of 0.050~0.069 cm³·cm^-3 and 0.080~0.098 cm³·cm^-3, and MAE ranging of 0.030~0.051 cm³·cm^-3 and 0.060~0.077 cm³·cm^-3, respectively. Considering model accuracy and data accessibility, RF model had high accuracy under R_s, T, P, ST and RH input, with R ² ranging of 0.884~0.914, RMSE ranging of 0.050~0.064 cm³·cm^-3, and MAE ranging of 0.030~0.043 cm³·cm^-3. Therefore, RF model is recommended to simulate SM in different soil depths under R_s, T, P, RH and ST input.

Crop water demand is an important basis for irrigation schedule. In order to accurately predict the water demand of winter wheat, Zhangfuhe irrigation area in Handan, Hebei Province was taken as an example, and the sentinel-1A radar image was used to retrieve the soil moisture in the irrigation area to correct the crop coefficient, combined with the reference evapotranspiration (ET₀) calculated from the weather forecast data in the next 15 days, to predict the demand for winter wheat in important irrigation periods of Zhangfu River irrigation area. The results showed that the soil water content retrieved by remote sensing was similar to the measured value, with an average relative error of 4.60%; the ET ₀ value of the study area from December 11 to December 25 was predicted to be 15.32 mm based on the meteorological forecast data; combined with the soil water content and the predicted ET ₀ data, the average water demand of winter wheat was calculated to be 12.64 mm, among which, the water demand of Ci county had the largest water demand of 14.23 mm and Guangping county had the smallest of 12.04 mm. The average water demand value calculated by MOD16A2 product was 10.65 mm, and the relative error was 18.69%. This method can provide a theoretical reference for the prediction and water management of the growth period of irrigation areas.

Soil moisture is one of the important parameters in the earth system simulation, which plays an important role in the study of climate change and drought. In this paper, the applicability of three sets of soil moisture data in Inner Mongolia, including the United States Global Land Data Assimilation System (GLDAS), the European Medium Range Weather Forecast Center's fifth generation reanalysis data (ERA5) and the Global High Resolution Land Data Assimilation System (FLDAS) released by NASA, are evaluated by using the ten-day data of crop growth and 0-10cm farmland soil moisture in Inner Mongolia from 2011 to 2013, in combination with the statistical indicators such as correlation coefficient, deviation, root mean square error and DISO. The purpose of this study is to select a large scale, long time series alternative data suitable for studying the spatial and temporal characteristics of soil moisture in Inner Mongolia. The results showed that the spatial distribution of the three sets of product data was basically consistent with that of the platform observation on an annual scale, and all of them could reflect the spatial distribution pattern of soil moisture in Inner Mongolia, which was wet in the east and dry in the west. The ERA5 had the highest correlation with the obseved data, but the error was large; Both ERA5 and GLDAS data sets could better capture and characterize the change characteristics of soil moisture with time on a monthly scale. The ERA5 data had a good correlation with the observed values in each month, while the GLDAS data had a smaller error; On the whole, the correlation coefficients between GLDAS, FLDAS, ERA5 and observation data were 0.93, 0.68, and 0.96 respectively, NAE was 0.031, 0.013, 0.022 respectively, and NRMSE was 0.032, 0.014, 0.023 respectively. The DISO distance between ERA5 and observation data was the smallest, 0.045, followed by GLDAS, and FLDAS data was the worst. The results of this study can provide a theoretical basis for the research and application of soil moisture in Inner Mongolia.

Biochar plays an important role in improving soil environment, promoting soil fertility, plant growth, water retention and evaporation inhibition. In order to explore the effects of biochar on the growth and development, and evapotranspiration water consumption of Amygdalus pedunculata Pall, a pot experiment was conducted to study the effects of corn stove biochar on the growth and evapotranspiration water consumption of Amygdalus pedunculata Pall with four treatments, including CK (no biochar addition), 2%, 4% and 6% of biochar supplementation. The results showed that biochar had significant effects on seedling growth, soil moisture and evapotranspiration. Compared with CK, 2% treatment was more conducive to the growth rate of plant height, basal diameter and leaf area of Amygdalus pedunculata Pall with the increase of 9.90%, 9.22% and 6.97%, respectively. The growth of Amygdalus pedunculata Pall wasinhibited by 4% treatment and 6% treatment, with the most obvious inhibition effect was 4% treatment. Soil water content increased with the increase of biochar, with an increase of 2.89%~59.98%. Biochar significantly improved soil water retention capacity and evapotranspiration water consumption of Amygdalus pedunculata Pall, which was significantly increased by 11.40% at 4% treatment. Therefore, appropriate amount of biochar can effectively improve soil water retention capacity and promote the seedling growth of Amygdalus pedunculata Pall. In higher fertility soil, it is recommended to add a low amount of biochar below 2% to introduce and plant Amygdalus pedunculata Pall.