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The contact angle has an important influence on the hydraulic properties of the soil. In order to understand the contact angle intuitively, a more realistic Soil-Water Characteristic Curve should be established. In this study, silty soil, red clay and expansive soil were selected for testing, and a sample preparation method for measuring the contact angle of hydrophilic soil particles was proposed, namely deposition-adhesion method of adhering to a viscous flat surface to obtain the test sample and then measuring its contact angle by the Sessile drop method. The measurement results were compared with that of capillary rise method and the Wilhelmy plate method. The results show that when expansive soil is measured by capillary rise method, due to the violent expansion of expansive soil in contact with water, its internal pore volume is reduced or even closed, resulting in the measured value of expansive soil contact angle of about 79°, and the error of the measurement result is huge. The Wilhelmy plate method is affected by capillary infiltration, and the wetting front migration distance is inconsistent with the immersion depth. The sample preparation method of the test sample is difficult to ensure uniform reproduction, resulting in fluctuations in the contact angle measurement results. Through the deposition-adhesion method, a thin layer surface with uniform distribution of soil particles can be obtained, which can effectively reduce the capillary dispersion of droplets on the surface of soil particles, and the droplets can be stably formed on the surface of the sample, and the measurement of contact angle and dynamic contact angle can be achieved on one sample at the same time. The method can be applied to different types of soil.
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In order to explore the effect of intermittent drip irrigation with different mineralization level farmland drainage on the spatial distribution of soil moisture and salinity, a soil column test was conducted with two farmland drainage mineralization levels (2 g/L and 4 g/L) and three drip irrigation intervals (0 h, 0.5 h and 1 h between irrigation 2 h) for six treatments to compare and analyze the effect patterns of different treatments on soil water infiltration and spatial distribution of water and salt. The results showed that soil water infiltration under intermittent irrigation followed the power function variation rule. Increasing the irrigation interval time and irrigation water mineralization can increase the extension of soil horizontal and vertical wetting fronts. The spatial distribution of soil moisture was more uniform with increasing irrigation interval time. The effects of both single and two-factor interactions on the desalination rate of the soil desalination zone were statistically significant. The mean desalination rate increased by 25.04% in the 2 g/L treatment compared to the 4 g/L treatment, by 6.78% in the 0.5 h irrigation interval compared to the non-intermittent irrigation treatment, and by 17.05% in the 1 h irrigation interval compared to the non-intermittent irrigation treatment. The highest average water content, the lowest average salinity and the highest desalination rate in the soil wetted body were found in the irrigation water mineralization level of 2 g/L and in the irrigation interval of 1 h treatment.
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In order to obtain a reasonable application scheme of biogas slurry instead of chemical fertilizer under different deficit irrigation conditions, in this study, the water/biogas slurry integration technology was adopted, with greenhouse tomato as the research object, two season field experiments were carried out in the autumn of 2020 (2020A) and spring of 2021 (2021s). In the experiments, three irrigation levels of 0.5 Ep (W1), 0.7 Ep (W2) and 0.9 Ep (W3), and three fertilization schemes of soil mixed with biochar with biogas slurry (F1), chemical fertilizer (F2) and biogas slurry (F3), a total of 9 treatments were used to explore the effects of different irrigation and fertilization schemes on the growth, water use efficiency, yield and quality of greenhouse tomato. The comprehensive nutritional quality and comprehensive benefits of tomato were evaluated and analyzed by principal component analysis and TOPSIS. The results showed that W2F3 treatment could effectively promote the formation of tomato plant height, stem diameter and dry matter mass, and could obtain higher water use efficiency under the premise of high yield. Under the same fertilization method, the tomato plant height and stem diameter have a parabolic relationship with the irrigation amount, and reaches the maximum when the irrigation level is 0.7 Ep; the total dry matter mass and yield of tomato are proportional to the irrigation amount under the F1 and F2 fertilization methods, while increased first and then decreased with the increase of irrigation amount under the F3 fertilization method. Under the same irrigation level, fertilization scheme F3 could obtain the best fruit quality. The W3F2 treatment (0.9 Ep, fertilizer) achieved the highest yield, but the W2F3 treatment achieved the best water use efficiency with only a 0.3% (fall) and 0.9% (spring) reduction in yield. The analysis results of principal component analysis method and TOPSIS method show that W2F3 treatment can obtain the best comprehensive quality and comprehensive benefit. It is recommended to popularize and apply W2F3 treatment as the optimal deficit irrigation mode of water/biogas slurry integration.
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In order to explore the impact of different soil water treatment modes in different growing periods on citrus quality in the reservoir area, a citrus water control experiment was conducted in the Cangwubang experimental base of Three Gorges University from 2019 to 2021. And 27 kinds of water treatments were used in the young fruit period, the expansion period, and the color changing and sugar increasing period. The volume water content in the young fruit stage was low water (18%~21%), medium water (21%~24%), high water (24%~27%), and the water content in the expansion period was low water (17%~21%), middle water (21%~24%), high water (24%~27%), and water content in color conversion and sugar increasing stage is low water (16%~20%), middle water (20%~23%) and high water (23%~26%). Ten quality indexes, including whole fruit weight, fruit juice rate, edible rate, average fruit shape index, soluble solid matter, soluble total sugar, titratable acid, VC, solid acid ratio, and sugar-acid ratio, were measured. Based on the principal component analysis, a comprehensive evaluation model of citrus fruit quality under different soil water content treatments in each growth period was established. The results showed that under different water treatments, the coefficient of variation of fruit juice rate was the smallest, and the coefficient of variation of vitamin C was the largest. Three principal components were extracted based on principal component analysis, and the cumulative contribution rate of the first three principal components accounted for 87.028%, of which PC (principal component) 1 was the taste factor, PC2 was the edible factor, and PC3 was the nutritional factor. Through the comprehensive evaluation of fruit quality under different treatments, it is found that T10 (soil moisture content in each growth period is 21% ~ 24%, 17% ~ 21%, 16% ~ 20%) has the highest comprehensive score, and T27 (soil moisture content in each growth period is 24% ~ 27%, 24% ~ 27%, 23 ~ 26%) has the lowest score. The appearance quality of citrus is the best when the soil moisture content is in the range of 24%~27% in the expansion period, and the flavor quality of citrus is the best when the soil moisture content is in the range of 16%~20% in the color changing and sugar increasing period. In conclusion, the water change in the expansion period and the color changing and sugar increasing period have the most critical impact on the quality of citrus.
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In order to solve the problems of poor compatibility, low integration and unreasonable biogas slurry irrigation concentration, an integrated biogas slurry water-fertilizer machine was designed in this study, and cabbage was used as experimental materials. Under six different biogas slurry concentrations, namely 0% (CK), 20% (T20), 40% (T40), 60% (T60), 80% (T80) and 100% (T100), the differences of soil available nutrients and yield and quality of cabbage were compared, and the appropriate biogas slurry irrigation concentration was optimized. The results showed that the integrated biogas liquid water-fertilizer machine has the advantages of strong integrity, high intelligent level and good adaptability. Biogas liquid application based on the machine was beneficial to increase the content of soil available nitrogen, phosphorus and potassium, and the greater concentration of biogas slurry led to more obvious increase. The content of soil available nitrogen, phosphorus and potassium measured after cabbage harvest under T100 treatment was the highest, and were 119.7, 17.8 and 171.1 mg/kg respectively. Among the biogas slurry irrigation treatments, the yields of T80 and T60 were at a high level, and the aboveground yields reached 4710 and 69.9 t/hm2 respectively, with no significant difference (p>0.05). The application of biogas slurry reduced the nitrate content of Chinese cabbage leaves and increased the content of Vc and soluble sugar. The comprehensive cabbage quality of T60 was the optimal. Considering the yield, output value and quality, 60% is recommended as the suitable biogas slurry irrigation concentration for Chinese cabbage.
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In order to explore the effects of soluble organic fertilizer on the growth, quality and yield of greenhouse tomatoes, a total of seven treatments were set up in this experiment, including CK without fertilization, T1: Low amount of inorganic fertilizer (N 150 kg/hm2, P2O5 60 kg/hm2, K2O 120 kg/hm2), T2: Medium amount of inorganic fertilizer (N 300 kg/hm2, P2O5 120 kg/hm2, K2O 240 kg/hm2), T3: High amount of inorganic fertilizer (N 450 kg/hm2, P2O5 180 kg/hm2, K2O 360 kg/hm2), M1: Low amount of inorganic fertilizer with low amount soluble organic fertilizer (75 kg/hm2), M2: low amount inorganic fertilizer with medium amount soluble organic fertilizer (225 kg/hm2), M3: Low amount inorganic fertilizer with high amount soluble organic fertilizer (375 kg/hm2). The plant height, stem thickness, leaf area index(LAI), relative chlorophyll content (SPAD value), yield and fruit quality of tomato were determined. The results showed that the plant height, stem thickness, leaf area index, SPAD value and yield of tomato increased with the increase of fertilizer application, and there was no significant difference between T3, M2 and M3. In terms of fruit quality, the increase in the amount of inorganic fertilizer application will increase the titrable acid and nitrate content in the fruit and adversely affect the quality of the fruit, while the increase of soluble organic fertilizer will increase the soluble sugar, vitamin C and lycopene in the fruit, improve the sugar-acid ratio of the fruit, and significantly improve the quality of tomato fruit. Based on the various indicators, the tomato under the M3 treatment had good growth, higher yield and the best fruit quality, which was the best application method in the experiment.
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Under the condition of drip irrigation, it is a major problem to accumulate salt in the moist body within the scope of root development. This paper puts forward a new technology to expand the scope of root desalination. Taking Lycium barbarum as the test plant, according to the rule of salt accumulation on the edge of wet body, the method of three capillary tubes with staggered drippers and delayed dripping was adopted to expand the desalting range of root system and save water consumption. The results show that when the three capillary tubes lag in dripping, they gradually chase the salt in the root system development range, push the salt out of the root system development range, and press the salt locally, thus saving the amount of pressed salt water 3 times a year. The reduction of wetting salt in the body is related to not only irrigation times, but also soil properties, initial salt content of soil and water quality. The research results can provide a basis for the quantification of water consumption for salt pressing and scientific improvement of saline-alkali land.
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The aims of this work are to analyze the fractal dimension of soil particle size and soil hydraulic properties in the aquatic-terrestrial ecotone of the Lijiang River and to provide references for the simulation of soil migration, deposition and soil hydrological cycle. Taking five typical aquatic-terrestrial ecotone plots in Lijiang River as the research object, the basic physical properties and hydraulic parameters of soil were measured, and the fractal dimensions of soil particle size were calculated. The relationships between the fractal dimensions and the hydraulic properties were discussed based on correlation analysis, redundancy analysis and stepwise regression analysis. The results showed that the soil particle size in the aquatic-terrestrial ecotone of the Lijiang River mainly ranged from 0~400 μm, with fine soil particles and high clay content. The soil particles with large volume fractions were dominant in the particle size distribution range. Soil particle size was mainly distributed in dense areas, but the soil particle size was more sensitive to environmental factors in sparse areas. The single fractal dimension (D),information dimension (D(1)),correlation dimension (D(2)), information dimension/volume dimension (D(1)/D(0)) andspectral width (?α) were significantly negatively correlated with the saturated water content, field capacity, total porosity, saturated water content fitted by the VG model and the BC model (VG-θs, BC-θs), while significantly positively correlated with the bulk density. D, D(1), D(2) and D(1)/D(0) were extremely significantly negatively correlated with the sand content, while extremely significantly positively correlated with the specific surface area of soil particles, clay content and silt content. The basic physical properties of soil can explain 95.84% variation of fractal dimension. Sand content and total porosity were the main controlling factors of D. Sand content was the main controlling factor of D(1), D(2) and D(1)/D(0). The distribution of soil particle size in the aquatic-terrestrial ecotone of the Lijiang River has typical fractal characteristics, and the fractal dimensions can be used as indicator parameters for numerical simulation of soil water movement.
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In order to study the water replenishment needed for river ecological restoration, the QUAL-2K water quality model was used to simulate the sectional water quality and the Tennant method was used to determine the ecological flow of the river. The coupling model was established with the objectives of the water quality up to the standard, the ecological water quantity up to the standard and the minimum impact on the water source. And it was applied to a small and medium river in Sichuan Province. Under the objective of the water quality, through the evaluation and analysis of the current water quality factors of the river, the two water quality factors of ammonia nitrogen and total phosphorus were selected as the objective to reach class Ⅲ water. And these two factors were used in the simulation of the exit section. Under the objective of the water quantity, 30% and 50% of the annual average discharge were used as the ecological discharge in non-flood season and flood season, respectively. Under the objective of the water source, ecological water replenishment should not encroach on the ecological flow of water source and the water of other water users. The results show that the annual water diversion under the water quality target is 71.97 million m3 and the annual water diversion under the water quantity target is 68.08 million m3. The months of water replenishment are determined to be from January to June, and the annual water diversion is determined to be 101 million m3. The research results show that ecological water replenishment can be used as a means to improve the damaged ecosystem due to water shortage in a short term, and can provide a decision-making basis for the determination of ecological water replenishment amount of river projects.
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Accurate estimation of yield and protein is of great significance. Crop models can capture the key physiological process, simulate crop growth and N uptake, and further estimate production, protein yield and grain protein concentration (GPC). However, the existing crop models have simplified the N uptake ability of storage organs (sink process), few models have considered the effects of multiple factors on sink process. In this study, individual grain N accumulation model and SWAP were combined together to construct SWAP-pro model, which have considered the influences of temperature, water availability, nitrogen status, and genotype on sink process. Comparison between SWAP and SWAP-pro showed that SWAP could not accurately simulate the nitrogen stress of winter wheat, had a poor estimation of yield, and significantly underestimated the protein yield; SWAP-pro demonstrated good robustness when simulated leaf area index, leaf nitrogen content and biomass. SWAP-pro had a more stable and accurate simulation of nitrogen stress, performed a better estimation of yield, and had a smaller simulation error of protein yield. This study can help understand the relationship between nitrogen cycle and harvest quality of winter wheat, and provide some reference for estimation of production and protein.
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Rapid and accurate measurement of soil water content is crucial for applications in agriculture, hydrology, ecology and more. Digital image technology for measuring soil water content has become a hot research topic because of its advantages of being inexpensive, fast and non-destructive soil. In this paper, R, G, B, H, S, V and DN seven image characteristic parameters are extracted based on the digital image obtained by mobile phone camera, and the soil water content inversion model based on BP neural network and BP neural network optimized by genetic algorithm is constructed by using the image characteristic parameters R, V and DN which have great correlation with soil water content to obtain high precision soil water content. The results show that both BP neural network and genetic algorithm can improve the accuracy of soil water content measurement by digital image technology, in which the coefficient of determination (R 2) of the BP neural network soil water content inversion model can reach 0.940~0.972 and the root mean square error (RMSE) is 0.936%~1.694%; the genetic algorithm optimized BP neural network soil water content inversion model can reach R 2 of 0.976~0.993 and RMSE of 0.559%~0.878%. The BP neural network model optimized by using genetic algorithm for digital image technique inversion of soil water content has R 2 closer to 1, smaller RMSE and higher accuracy. The R 2 of the multiple linear model proposed in the same type of research is between 0.60 and 0.96, and the RMSE is between 1.11% and 7.00%. Compared with the multiple linear model proposed in the same type of research, the prediction accuracy and stability of the model proposed in this study are higher. These results show the advantages of BP neural network and genetic algorithm in the application of digital image technology to measure soil moisture content. In addition, this study shows that the digital image obtained by the mobile phone camera can be used to predict the surface soil water content under indoor conditions. Subsequent studies need to be carried out in outdoor deep soil to expand the applicability of the model.
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In order to study the dynamic changes of water supply for moistube irrigation, soil moisture migration and redistribution characteristics of water content, and the expansion and contraction characteristics of wetting front under dynamic working conditions, the water content, wetting front area, and moistube pipe outflow were measured by laboratory simulation experiments. Based on the data, the movement law of soil moisture under constant water head and variable water head conditions was explored, and based on the experimental data, the wetting front transition model of wetting irrigation under constant water head was revised, and a flux-equilibrium conjugate-based microfluidic model was proposed. A model for predicting the migration distance of moist peaks was proposed by adjusting the irrigation head. The result showed that:①Under the condition of constant water head, the cumulative infiltration volume of moistube irrigation increased linearly with time, and the infiltration rate and cumulative infiltration volume were positively correlated with the pressure water head. The infiltration rate and cumulative infiltration curve growth trend of moistube irrigation changed significantly with the regulation of increasing or decreasing water head. When the water head was increased from 1 meter to 2 meters, the cumulative infiltration volume and infiltration rate increased to 1.63 times and 1.51 times, respectively, of that before the adjustment of the water head. When the water head was reduced from 2 meters to 1 meter, the cumulative infiltration volume and infiltration rate in the same time period were reduced to 33.7% and 38.63% of those before the head adjustment, respectively. The larger the variable of increasing-adjusting head, the more pronounced this trend. With the passage of time, the growth trend of the cumulative infiltration amount and the infiltration rate tended to be stable. ②When the working water head was increased, the wetting front migration rate and the average moisture content of the wetting body increased significantly. When the working head was reduced, the wetting front migration rate was significantly reduced, the average moisture content of the wet body increased slowly, The migration rate of the wetting front and the average moisture content of the wetting body tended to be stable with time. When the water head increased from 1 meter to 2 meters, the area of the wet front increased to 2.92 times within 72 h of that when the water head was adjusted. When the water head was reduced from 2 meters to 1 meter, the area of wet front increases to 1.57 times of that at the moment of water head reduction within 72 h.③The prediction model of moist front migration was constructed by using the model evaluation goodness index analysis. It can be seen that the measured value of moist front migration distance was in good agreement with the simulated value, the MRE and NRMSE values were close to 0.022, and the NSE values were all greater than 0. 890, which confirmed the goodness and good applicability of the model. The results confirm that it is feasible to artificially regulate the outflow, infiltration characteristics and water content distribution of the micro-moistening pipe by adjusting the working head of moistube irrigation. In terms of practical application, the appropriate technical parameter range and irrigation mode of different facility crops can be worked out based on the scenario simulation results of wet-body of moistube irrigation under variable water head and the water requirement law of typical facility crops' roots.
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In order to study the adsorption-desorption effect of nano-biochar on ammonium nitrogen, bulk biochar was prepared from rice straw, nano-biochar was prepared by ball milling method, and the study was carried out by adsorption and desorption experiment combined with model simulation. The results showed that the adsorption-desorption effects of nano-biochar on ammonium nitrogen showed significant advantages compared with bulk biochar. The adsorption capacity of nano-biochar for ammonium nitrogen improved with the increase of their dosage and initial solution nitrogen concentration, followed by a stable trend. The best adsorption effect of nano-biochar on ammonium nitrogen were found at pH 7 and the adsorption reaction equilibrium time of nano-biochar was 210 min. The maximum adsorption capacity of nano-biochar for ammonium nitrogen were 6.91 mg/g, which was twice that of bulk biochar under the same conditions. The isothermal adsorption and adsorption kinetics of ammonium nitrogen by nano-biochar could be better described by the langmuir equation and quasi-second-order kinetic equation. The desorption reaction equilibrium time of nano-biochar were 240 min. The maximum desorption capacity of nano-biochar was 6.051 mg/g, which was 1.9 times of that of bulk biochar under the same conditions. The dynamic desorption process of ammonium nitrogen by nano-biochar could be better described by the quasi-second-order kinetic equation. In conclusion, the adsorption characteristics of ammonium nitrogen by nano-biochar was mainly single-molecular layer adsorption, mainly in the form of chemical adsorption, and the desorption process could be regarded as the reverse process of the adsorption reaction. This study can provide theoretical basis for reducing nitrogen loss and improving nitrogen use efficiency by applying nano-biochar in field.
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Self-cleaning screen filter, which is one of the most widely used equipment, is the key equipment to ensure the normal operation of micro-irrigation system. At present, most of the cleaning medium is water. The annual irrigation period has 1~2 months of flood period in Xinjiang, and the sediment content is large. Because of the water consumption, users refuse to wash continuously for a long time. The problem of water consumption for continuous cleaning can be solved by using pressurized air instead of water. With the increasing shortage of water resources, the development of the new pneumatic cleaning form of screen filter will be a new development direction. This paper puts forward an idea for the design and development of products that use air power for cleaning. Through calculations of different time node speed, pressure distribution, it is found that the pressure distribution and flow velocity distribution tend to be stable within 10~31 s. A fixed pressure vortex is formed near the upper and lower side walls of the 0~50 mm section on the inlet side, the pressure in the middle is mostly directed towards the inlet, and the distribution of velocity also shows a trend from large to small from the middle to the upper and lower sides. In the 50~80 mm section, the pressure distribution is low, and the velocity distribution is uncertain from the middle to the upper and lower sides. The computational analysis shows that the pressure vortex phenomenon exists in the initial model structure. On the 5 mm to 50 mm cross section near the upper and lower side walls, the pressure vortex phenomenon exists at the inlet end of the initial model structure. The problem of pressure vortex and pressure inequality is eliminated through the optimized design of the model and the structural parameters of this optimization are the optimal design parameters.
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The aim of this study was to investigate the transpiration water consumption and its relationship with environmental factors. A typical sand-fixing shrub Hedysarum mongolicum in Mu us Sandy Land was taken as the research object, and the transpiration process and diurnal variation of meteorological factors of Hedysarum mongolicum were monitored and recorded continuously from June to September 2021 by using a field weighing lysimeter with automatic weather observation station. The results showed that: ① the transpiration intensity of Hedysarum mongolicum showed a single peak curve in sunny days and rainy days, with obvious diurnal variation law, and the transpiration intensity in rainy days was about half of that in sunny days. ② During the study period, the rainfall was 131.02 mm, and the total transpiration water consumption of Hedysarum mongolicum was 200.65 mm. Soil water deficit was the main reason that limited transpiration intensity. ③ The order of significance of environmental factors on transpiration intensity (Ti) of Hedysarum mongolicum is as follows: solar radiation > air temperature > saturated vapor pressure deficit >10 cm soil moisture content > air relative humidity >30 cm soil moisture content >50 cm soil moisture content > wind speed. The comprehensive analysis showed that the daily variation of transpiration water consumption of Hedysarum mongolicum during the growing season was obvious, and its transpiration intensity was mainly influenced by solar radiation, soil moisture, air temperature and relative humidity.
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Based on the water balance technology and Penman-Monteith equation, the transpiration water consumption law, water demand, tree coefficient and water deficit of tree species, including Hippophae rhamnoides, Haloxylon ammodendron, Amorpha fruticosa and Caragana fruticose, in arid areas were studied in this paper. The results are as follows: the transpiration rates of the four shrubs in the growth period are all bimodal, and the peak times of seabuckthorn, Caragana and Amorpha fruticosa are the same. The peak of Haloxylon ammodendron appears around 10∶30 and 16∶30. The transpiration rate of each tree species on the sunny slope is higher than that on the shady slope. Among the four shrubs, Amorpha fruticosa consumes the most water in its growing period, and the water consumption of sunny slope and shady slope is 173.4 mm and 134.86 mm, respectively. Haloxylon ammodendron consumes the least water. The tree coefficient of each tree species in the dry area is different during the growth period. The lowest tree coefficient of Ammodendron Ammodendron on the shady slope in May is 0.16, and the highest tree coefficient of Amorpha fruticosa on the sunny slope in July is 1.33. Amorpha fruticosa has the largest water deficit, followed by Hippophae rhamnoides, and Haloxylon Ammodendron has the smallest water deficit. So Haloxylon ammodendron is the most suitable tree species, and Amorpha fruticosa is a tree species that is difficult to survive and grow in arid areas.
