The measurement of soil moisture is the basis of modern agriculture. In order to verify the feasibility and applicability of rapid determination of soil moisture by using soil spectral characteristics, spectrophotometer was used to obtain the three color values L, a, b of five kinds of soil under different water content. The change laws of soil color value at different soil moisture were analyzed and correlation and regression analysis were carried out to validate their relationship. The results showed that:①there was a certain correlation between soil color values L, a, b and its water content. With the increase of soil moisture, L value showed a downward trend, showing that soil color gradually deepened; a and b were all positive values, but there were no obvious law. ② The degree of correlation between soil values L, a, b and their moisture varied with soil texture. The values L and b of sandy loam, Shajiang black soil, and volcanic ash soil had high correlations with their moisture, while latosol and loam were a, b values. ③Effects of water content of sandy loam soil on its color L value were extremely significant, and the correlation coefficient between L value and water content was above 0.77. ④The ternary regression equation established based on the water content of sandy loam and its three color values had a certain generality for latosol, Shajiang black soil, volcanic ash soil and loam, and the correlation coefficient of R² was bigger than 0.81. The determination of soil water content by spectrophotometer is labor-saving and easy to operate, which is expected to provide an alternative path for the rapid determination of soil water content.

In order to explore the influence of different salt content on SWCC of undisturbed saline soil, the SWCC of non-saline, light saline and heavy saline soil was measured. The van Genuchten-Mualem model was used to fit the soil-water curve and parameters of non-saline, light saline and heavy saline soil and the influence of different salt content on cumulative equivalent pore size distribution and soil moisture constant was analyzed. The results showed that the soil water characteristic curve of undisturbed saline soil was mainly affected by salt content; The salt content under slight salination increased the soil water holding capacity, but the salt content of severely saline soil decreased the soil water holding capacity; With the increase of salt content in undisturbed saline soil, the parameter n value of van Genuchten-Mualem model first decreased and then increased, while the reciprocal α value of intake value decreased; The fitting accuracy of VG model for soil water-curve of 60 cm soil layer in YZ1 and YZ3 plots were higher than that in YZ2 plot. Compared with saline soil, the proportion of microporosity in 40 cm and 60 cm soil layers increased by 11.75% and 19.25% respectively, and the field water holding rate increased by 32.6% and 28.8% respectively. With the increase of soil depth, the proportion of microporosity in the total porosity of severely saline soil decreased by 28.08%, 40.61% and 21.64% respectively, and the field water holding rate decreased by 34.4%, 34.1% and 6.5% respectively. The research can provide some theoretical basis for the prevention and improvement of saline soil.

Seasonal freeze-thawing aggravates the complexity of soil evaporation, so accurate prediction of field soil evaporation during freeze-thaw period is of great significance for efficient utilization of water resources in arid and semi-arid areas. Based on the measured data of field soil evaporation and meteorological data affecting soil evaporation during the freeze-thaw period from 2017 to 2018, the principal component analysis method was used to reduce the dimension of meteorological data, seven main meteorological factors were selected as the input variables of the model, the PCA-PSO-GRNN soil evaporation prediction model was established by selecting the optimal smoothing factor by particle swarm optimization. The results showed that the simulated values of PCA-PSO-GRNN model were well fitted with measured values. The root-mean-square-error between simulated values and measured values was 0.011 4 mm/d, the R ² was 0.992 1, the mean-square-relative-error was 0.002 9, the mean-absolute-error was 0.007 0 mm/d. The prediction accuracy and generalization performance of the model were significantly better than those of BP model and standard GRNN model, which could be used for the field soil evaporation prediction in freeze-thaw period.

In order to provide an effective basis for further understanding of soil water resources under climate change in Huaihe River Basin, regulating soil water status and increasing crop yield, taking Bengbu station as an example, based on the soil moisture observation data and meteorological observation data of Wudaogou hydrological experimental station in recent 33 years, the variation characteristics of soil water content, temperature and precipitation in Huaihe River Basin under the background of global warming were analyzed by using m-k test method and univariate linear regression method, and the correlation between soil moisture content and climate factors was studied. The results showed that: in the past 33 years, the annual average temperature and precipitation in Huaihe River Basin increased significantly, and the abrupt change year of temperature was 1994; the soil water content of 10 cm depth soil layer showed an upward trend, while that of 30 cm depth, 50 cm depth and 100 cm depth showed a downward trend; 100 cm depth soil moisture content had a significant positive correlation with precipitation in autumn; There was a significant positive correlation between soil water content and precipitation in summer and autumn. So it can be concluded that the soil water content in Huaihe River Basin is greatly affected by seasons, and the soil water content in different seasons and depths has different correlation with temperature and precipitation; the surface soil water content is mainly affected by precipitation, and the surface soil water content increases with the increase of precipitation; the deep soil water content is greatly affected by the temperature, and the deep soil water content is affected by the temperature Less.

In order to explore the law of soil water and salt transport under the combination of irrigation and drainage, a soil column test was carried out indoors. The two factors and three levels of irrigation volume and drainage mode were used to complete the treatment. Three irrigation water quota values, 15 L, 25 L, 35 L (marked as W₁₅, W₂₅, W₃₅, respectively), and three kinds of drainage modes, drainage pipe d of 7 cm, drainage pipe d of 5 cm, no drainage pipe (marked as P₇, P₅, P₀, respectively) were set to study and analyze the dynamic changes of soil water and salt, and the HYDRUS-1D model was used to conduct numerical simulation analysis and verification of water and salt movement under irrigation and drainage.The results showed that with the same irrigation amount, the overall effect of soil moisture content and salt content changes was as follows: drainage pipe d of 7 cm > drainage pipe d of 5 cm > without drainage pipe, and the treatment with drainage pipe was significantly better than the treatment without drainage pipe (P<0.05). After three times of irrigation, the leaching effect of soil salt in the 0~20 cm soil layer was the most significant and the desalination rate reached the maximum of 83.69% under the treatment of irrigation quota of 35 L and drainage pipe d of 7 cm. Through the verification of the simulated values and measured values, it was found that with the change of irrigation water quantity, irrigation times, soil depth and drainage measures, the maximum value of the root mean square error RMSE of soil water and salt were 1.321 and 0.912 respectively, the minimum value of the biggest determination coefficient R ² were 0.813 and 0.842 respectively; the simulated and measured values of soil water and salt content had good fitting, and the model had certain reliability, which would provide help for the theoretical research of water and salt migration under the combined irrigation and drainage mode in arid areas.

In order to study the soil water movement rule under double point source drip irrigation system and to provide the theory guidance for drip system design, based on the unsaturated soil water dynamics theory and the character of soil water movement under drip irrigation from multiple point sources, the mathematic model was established and solved numerically by using the HYDRUS3D software. The comparison between the simulated and measured results shows that the difference between the simulated and measured soil moisture content in the humid area is small and basically consistent, and both follow the evolution rule of the convergence of point source infiltration and the humid area to form the humid body. The model was used to simulate the moisture distribution of soil wetting pattern under certain irrigation technology. The results showed that the wet front intersection time was 268 min when the dropper flow was 1.2 L/h and the dripper spacing was 30 cm. As the irrigation time increased, the soil moisture content of the intersection area increased, the maximum value was 0.32 cm³/cm³. The contour map of the soil in the humid area away from the emitters merged into a curve that moved downward over time, transitioning from a ridge to a horizontal shape. When the irrigation time was the same, the flow rate increased, the migration rate of the wetting front increased, the area of the wetting body section increased, the area of the soil wetting body section in the high water-bearing area at the drip head increased, and the soil moisture content at the same position in the wetting body increased. It can be concluded that the dropper flow and irrigation time have a certain influence on soil water infiltration, and the numerical simulation model of soil water infiltration can accurately reflect the soil water movement law under the condition of double-point source infiltration.

In order to explore the infiltration characteristics of the new insertion subsurface emitter to provide theoretical guidance for the optimization of the emitter structure and field application, in this experiment, under the condition of sandy loam, with water supply pressure (6, 8, 10, 12, 14, 16 m) as a variable, the indoor infiltration tests were conducted on a new insertion subsurface emitter with a buried depth of 20 cm. The relationship between the shape of the wet body, the migration of the wet front and the cumulative infiltration volume and the water supply pressure was analyzed. The results showed that the water supply pressure H of 14 m was the critical pressure of the erosion channel which generated inside the wet body; the water supply pressure significantly affected the shape of the wet body within the specified infiltration time; the wet body is approximately a spherical when H was not greater than 10m, while the wet body is irregular when H was greater than 10 m. The prediction models of water supply pressure, infiltration time and wet front migration distance were established. The prediction accuracy of the horizontal and vertical downward models was better than that of the vertical upward model. The cumulative infiltration volume was positively correlated with water supply pressure and infiltration time. A mathematical model describing the relationship between soil cumulative infiltration volume (I), infiltration time (t) and water supply pressure (H) was constructed. The average relative error (ARE) and root mean square error (RMSE) between the predicted values of the model and measured value were 5.90% and 0.045 3 L, respectively. When the insertion subsurface emitter is applied in the field, the water supply pressure should be lower than the critical pressure. The prediction model of the wet front migration distance and the cumulative infiltration volume under this test condition can be used to estimate the range of wet body, infiltration time and infiltration water volume, which can provide a reference for the establishment of field irrigation system for new insertion subsurface emitter.

Wind can cause sprinkler droplets drift, leading to the decrease of water use efficiency and coefficient of spray uniformity. This study used 2D-Video-Distrometer to observe the micro-physical features of sprinkler droplets under windy conditions. Oblateness, velocity, landing angle and drift distance of droplets with various particle sizes were measured and a droplet drift model was constructed. The results showed that wind caused the deformation of droplets, as well as the horizontal velocity and landing angle; the influence degree of wind and air viscous drag varied with droplet sizes. The droplet drift model based on ballistic trajectory showed high calculation accuracy. Droplet velocity, falling height and wind speed were selected to carry out a sensitivity analysis. The results showed that droplet size was the most influential factor, followed by falling height and wind speed with droplet size smaller than 3mm, while falling height turned into the most influential factor with a bigger droplet size.

In order to explore the effects of different irrigation upper limit on the water absorption root system, yield and irrigation water utilization rate of apple trees, taking twelve-year-old dwarf red Fuji apple trees as the research object, three irrigation treatments were set (the irrigation limit was 60% of field water holding capacity, and the upper limit of irrigation T1 and T2 were 100% and 80% of field water holding capacity respectively, The upper limit of irrigation of CK for surface irrigation treatment was 80% of field water holding capacity), the root length density, root surface area density and fruit yield of the water-absorbing root system of fruit trees during the whole growth period were measured. The results showed that the water-absorbing roots of each treatment showed a trend of increasing first and then decreasing with the increase of soil depth, and the overall size showed T1>T2>CK. The water-absorbing roots of CK treatment were mainly concentrated in the soil layer of 0～60 cm, and the root length density and root surface area density at different growth stages accounted for 82.1%~85.3% and 82.1%~86.3% of the entire water-absorbent root system root length density and root surface area density respectively; T1 and T2 treatments were mainly distributed in the 20~80 cm soil layer. The root length density of different growth stages accounted for 66.3%~74.3% and 67.3%~78.1% of the entire water-absorbing root system, and the root surface area density accounted for 65.7%~73.5% and 67.3%~78.4% of the entire water-absorbing root system, respectively. The amount of irrigation water in CK treatment was 25% more than that in T2 treatment but the yield was reduced by 4.55%, and the utilization rate of irrigation water was significantly smaller than that in T1 and T2 treatments. The amount of irrigation water in T2 treatment was 33.33% less than that in T1 treatment, but the yield was only reduced by 8.82%, and the irrigation water utilization rate was significantly greater than that in T1 treatment. A comprehensive comparison showed that T2 was the optimal treatment for this experiment. The water storage pit irrigation method can induce the growth and deep penetration of the roots of fruit trees, and lowering the upper limit of irrigation can achieve the purpose of water saving and stable production.

In order to explore a high-efficiency water and nitrogen model suitable for the microporous ceramic root irrigation, the Lycium barbarum in Chaidamu of Qinghai province was selected as research object, the effects of different fertilization methods and nitrogen levels on soil moisture content, soil nitrate nitrogen content and Lycium barbarum yield under microporous ceramic root irrigation were studied. The results showed that under the same irrigation amount of water, the wetting body of microporous ceramic root irrigation was well matched with the high-density area of Lycium barbarum root, which was beneficial to water absorption of root system while reducing leakage loss. Under the condition of the same amount of nitrogen application, the yield was increased by 20.3% and 10.9%, respectively, compared with that of surface drip irrigation.When N reduction treatment was integrated with water and fertilizer for micro-porous ceramic roots, the soil nitrate nitrogen content was more evenly distributed and the utilization efficiency of N fertilizer was higher under medium and low N treatment. However, N reduction treatment would reduce the soil nitrate nitrogen content and affect the fruit production of Lycium barbarum. The yields of N reduction treatment and low N treatment were 87.7% and 79.7% of those under high N treatment, respectively. Therefore, when Lycium barbarum microporous ceramic root irrigation is performed, it is recommended to apply fertilizer in caves with a nitrogen rate of 390 kg/ hm², which is conducive to higher yield ofLycium barbarum.