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Soil moisture is one of the most important components in the land-air coupling system. Acquisition of soil relative moisture in high precision can benefit to the finer monitoring and assessment, as well as prediction and warning for drought and waterlogging. This study aims to assess drought and waterlogging using data fusion of soil water in multiple dimensions. Daily soil relative moisture was derived from China Meteorological Administration Land surface data assimilation system (CLDAS). Hourly soil relative moisture was observed from automatic soil moisture stations during April and November from the year of 2020 to 2023. The dataset also included the land use, soil properties and geographic information. A dynamic fusion model was constructed to correct the bias of relative soil moisture from between automatic soil moisture stations and CLDAS. Random forest and support vector machine models were used to take the latitude, longitude, altitude, soil sand, soil silt and soil clay as the inputs. Given that daily fusion relative soil moisture was constructed, the intensity, area and duration index were proposed to monitor and assess drought and waterlogging disasters at the multiple dimensions. The results showed that the values of determination coefficient between observed and corrected soil relative moisture by random forest model were 0.79, 0.81 and 0.80, respectively, and relative root mean square errors were 13.81%, 11.40% and 9.50%, respectively, at the length of 0-10, 0- 20 and 0-50 cm. Comparatively, the determination coefficient was 0.56-0.57 and relative root mean square error was 17.72%- 23.63% between observed and corrected relative soil moisture by support vector machine model. Thus, random forest model was accepted to effectively correct the bias of relative soil moisture between automatic soil moisture stations and CLDAS. Daily fused relative soil moisture was then generated as well. At the spatial scale, the days percent of water deficit increased from southeast to northwest in the period of April-November. Moreover, the days percent of water deficit in the central-western areas of Inner Mongolia and majority of Northwest China was greater than 70% and even 80%, while 50%-70% was found in northeastern Inner Mongolia, central-northern North China and central-western Southwest China, even less than 40% in major central-eastern areas. The days percent of soil overwetting decreased from southeast to northwest, with the value of greater than 50% only in eastern and southern South China, southern Southeast China and northeastern Northeast China. According to the water deficit index, overwetting, moisture, the area and duration index, drought and waterlogging conditions were dynamic assessed in the quantitative and finer characteristics at the intensity-area-duration dimension, especially in the typical disaster process, such as typical heat and drought event in Yangtze River in the year of 2022, typhoon Dusuri and Khanun in the year of 2023. Typically, the soil water deficit was tended to intensify in Yangtze River in the summer of 2022. The overwetting index was much lower during April-July in Huang-Huai-Hai region, whereas, there was the significant increase in late July by typhoon Dusuri, which was characterized by 12.3%-70.1% area exposed to waterlogging in 3-5 days. In Northeast China, the area exposed to overwetting or waterlogging in a large extent during 2-4th August in Heilongjiang and Jilin by typhoon Dusuri. After that, there was some decrease in 5-9th August, but it enlarged to 27.4%-41.8% in 10-13th August by typhoon Khanun. Of course, further investigation should be explored to consider more inducing factors on soil moisture. [ABSTRACT FROM AUTHOR]

A long-term in situ measurement cannot fully meet the requirements of soil nitrate measurement in recent years, due to the high cost and the inability. In this study, a measurement method was proposed to collect the soil solution using the titanium sintering filter cartridge, in order to detect the nitrate concentration in the soil solution under near-infrared spectroscopy. Correspondingly, the detection device was also designed in this case. Therefore, it was demonstrated that the nitrate was suitable for the analysis at 1 250 to 1 860 nm. The commercially available Near-Infrared (NIR) Light-Emitting Diode (LED) products were combined with the 940, 1 050, 1 200, 1 310, 1 350, 1 450, and 1 550 nm NIR LED. Simulated experiments of soil solution collection were carried out using self-made soil columns. Titanium sintering filter cartridge was selected as the soil solution sampler to collect the soil solution. The results show that the soil solution collection was positively correlated with the water content of the soil, but negatively correlated with the burial depth and the clay content of the soil. It infers that the titanium sintered cartridge was suitable for sandy or clayey soils with low clay content. Once the soil moisture content exceeded 20 %, the collection time was selected as 30 min. But the collection time needed to be extended, when the moisture content was low. A systematic evaluation was made to consider the volume of solution required for the test chamber and the vertical distribution characteristics of soil nitrogen. More importantly, the optimal collection time of the soil solution was required over 60 min, where the burial depth was 10 to 40 cm. In addition, the comparative tests confirmed that the titanium sintered cartridge presented a greater capacity for soil solution collection than the LLYQ-P02 soil solution sampler, suitable for lower soil moisture contents. Finally, the BP neural network was trained using a Bayesian regularisation, with the voltage data at different wavelengths as the input layer and solution nitrate-nitrogen content as the output layer. Specifically, 70 % of all data were randomly used as the training set and the remaining 30 % as the validation set to complete the training of the nitrate-nitrogen prediction model. The feasibility and stability of the detection device were tested through the performance tests (including stability, resolution, dynamic response, and field comparison tests). The results show that the voltage tended to increase with the increasing nitrate concentration, while the voltage was lower at 1 310, 1 450 and 1 550 nm. Therefore, the presence of a large absorbance confirmed that the absorption at 1 310 and 1 550 nm was influenced by the nitrate and at 1 450 nm by water. The Pearson's correlation coefficients were 0.997 and 0.995 for the training and test set of the nitrate nitrogen prediction model, respectively. The root mean square error of prediction was 3.43 during this time. The improved prediction model of nitrate nitrogen performed the best prediction than before. The relative deviations of the measuring device from the ion electrode and the colourimetric were 5.9% max. and the absolute deviation was 9 mg/L max., respectively, fully meeting the requirements for the in-situ monitoring of nitrate nitrogen in soil solution. The new device can serve as fully automatic, non-destructive (no interference with the original soil structure), long-term, and in-situ, not available with the current nitrate ion electrodes and soil nutrient quick testers. An optimal combination of operational performance was achieved, where the standard deviation of the output voltage was 0.006, and the dynamic response time for a single wavelength was 1.4 s during the long-term operation of the detection device. The finding can provide a feasible solution for the long-term automatic measurement of soil nitrate nitrogen and the construction of a water-fertilizer integration system. [ABSTRACT FROM AUTHOR]

Calcic vertisol is a typical kind of low-yield field with a total area of about 4 million hm2 in China. Calcareous concretion with particle size larger than 2 mm has been one of the representative characteristics of calcic vertisol. The limitation of soil available water is an important reason for crop failure in this region. Therefore, the curve of soil water retention dominates the estimation of available water content. However, most studies focused on the effects of calcareous concretion on soil water retention of calcic vertisol mainly under laboratory conditions. It is lacking that under field conditions. In this study, both field surveys and laboratory experiments were conducted to explore the effect of calcareous concretion distribution in 0-1 m soil profile on soil water retention. Firstly, the spatial distribution of calcareous concretion was investigated in the study plot with 150 m length, 50 m width, and 1 m depth. After then, soil profiles (0-1 m soil depth) were chosen to divide into 5 layers with a 20 cm interval. Disturbed and undisturbed soil samples were collected in each layer. Physicochemical properties were evaluated to measure the distribution of soil particle size, size and content of calcareous concretion, bulk densities of soil, and calcareous concretions. Meanwhile, the curves of soil water retention were determined using high speed centrifuge. A pressure plate method was conducted to measure water retention curves in calcareous concretion. The results showed that the mass contents of clay, silt, and sand were 30.56%-39.75%, 39.88%-45.34%, and 18.67%-24.45%, respectively, which belonged to silty clay soil in the classification standard of the United States Department of Agriculture (USDA). Clayey particles decreased, but sandy particles increased significantly with the increase of soil depth. Calcareous concretion was mainly distributed in the soil depth of >20-100 cm, where the content and size increased as soil depth increased. Calcareous concretions content in the surface soil (0-20 cm) was very low (with mass content 0.02%), where only a few calcareous concretions of 2-5 mm were discovered. The maximum content of calcareous concretion was detected at > 80-100 cm (up to 11.42%), where the calcareous concretion content was 8.04% in the size of >8-30 mm. Soil bulk density ranged from 1.23-1.61 g cm-3. The densities of calcareous concretions were 2.01, 2.21, and 2.23 g cm-3 with the size of 2-5 mm, >5-8 mm, and >8-30 mm, respectively. Soil bulk density increased along with the calcareous concretion content increasing. Water retention curves of soil and calcareous concretion were well fitted by the van Genuchten model, with the determination coefficient larger than 0.95. The saturated water content of surface soil (0-20 cm) was significantly higher than that of 20-100 cm soil. Nevertheless, the Gravitational-water content in the surface soil (0-20 cm) was much larger than that in the soil of > 20-100 cm, which was related to macropores formed during tillage. In the subsurface (>20-100 cm), soil gravitational-water content and available water-holding capacity increased with the increase of soil depth, but the field capacity and wilting point decreased. Calcareous concretion maintained a non-negligible amount of water, 0.25, 0.22, and 0.20 cm3 /cm3 in the particles with the size of 2-5 mm, >5-8 mm, and >8-30 mm, respectively. But the water-holding capacities of calcareous concretion were significantly lower than that of soil. The effects of calcareous concretion on water-holding capacity mainly occurred in the subsurface soil. Soil saturated water content, field capacity, and wilting point decreased with increasing calcareous concretion. Interestingly, calcareous concretion content was positively correlated with the soil sand content, but negatively correlated with the soil clay content. Calcareous concretion can bind soil particles together to prevent sand weathering, and thereby effectively improve soil texture. More calcareous concretion led to higher sand contents, and thus increased the available water-holding capacity in soil. This finding can provide a theoretical basis to accurately assess the soil water-holding capacity in calcic vertisol for precision irrigation and high crop productivity. [ABSTRACT FROM AUTHOR]

Accurate and rapid assessment and measurement of soil salt accumulation and spatial distribution changes are essential for preventing land degradation and improving the ecological environment. The soil Apparent Conductivity (ECa) obtained by electromagnetic induction technology can be more effective and faster to obtain soil salinity information, which helps to overcome some challenges in traditional sampling methods and reduce costs. However, the differences in soil properties among different geomorphologic types may lead to the decrease in the accuracy of EM38 in predicting soil salinity. In order to clarify the effect of soil properties on apparent conductivity under different geomorphologic types, three typical landforms (alluvial-proluvial fan edge, alluvial plain and dry delta) in Manas River Basin of Xinjiang were taken as the research objects. The apparent conductivity data of two measurement modes (horizontal mode EMh and vertical mode EMv) were obtained by using EM38 at different heights from the ground, i.e., 30 cm, 50 cm, 70 cm, 90 cm, 110 cm and 130 cm, respectively. Moreover, in each landform, 20 representative sampling points were selected for soil sample collection, with sampling depth of 0-20, 20-40, 40-60, 60-80, 80-100 cm. Soil salt content, soil moisture content, soil clay mass fraction, soil Cation Exchange Capacity (CEC) and soil organic carbon content (SOC) were determined. Firstly, path analysis method was used to analyze the influence degree and contribution rate of salt content, soil clay mass fraction, soil CEC and SOC at different depths on apparent conductivity (ECa) measured at different heights. Next, by selecting non-salinity factors with high contribution rate of ECa as auxiliary variables, a multi-factor collaborative interpretation model of soil salinity was established, and compared with the model established only with ECa as independent variable. Finally, the optimal interpretation model of soil salt content was established and the accuracy of the model was evaluated. The results showed that among the three types of landforms, soil salt content was the most important factor affecting the contribution rate of ECa, and there were significant differences in the factors affecting ECa of each soil layer under different landforms. Water content of the upper soil (0-60 cm) contributed most to ECa, whereas soil CEC content and organic carbon content of the bottom soil (60-100 cm) in the alluvial-proluvial fan edge. A high contribution was made by soil salt content at 0-20 cm layer and 40-80 cm layer, whereas CEC and clay mass fraction for 20-40 cm layer in the alluvial plain. And ECa can be significantly affected by CEC content of the upper layer (0-60 cm) and soil organic carbon content of the lower layer (60-100 cm) in the dry delta. According to the accumulative contribution rate of more than 80%, non-salt factors were selected to establish the synergistic interpretation model of layered soil salt under different landforms. The R2 adj of different soil layers under three types of landforms increased from 0.81-0.86, 0.57-0.87 and 0.27-0.47 to 0.83-0.91, 0.63-0.93 and 0.48-0.70, respectively. The accuracy verification results showed that the R2 of salt prediction models for different soil layers under three types of landforms were 0.61-0.81, 0.48-0.85 and 0.35-0.66, respectively. The research results can provide reliable theoretical basis and technical methods for rapid and accurate monitoring of saline soil. [ABSTRACT FROM AUTHOR]

The effect of high concentration sodium salt solution infiltration in reclaimed water on soil hydraulic characteristics is one of the key problems of soil ecological environment degradation caused by long-term low-quality water irrigation. In this paper, the hydrodynamic parameters of 5 kinds of subtropical soil, such as clay fluvo aquic soil, sandy fluvo aquic soil, red soil, paddy soil and purple soil, were measured by constant head penetration method and one-dimensional horizontal soil column imbibition method. The influence of sodium salt solution concentration on the hydraulic properties of soil was investigated, and the mechanism of the physical and chemical properties of soil affecting the hydraulic conductivity was analyzed. The results showed sodium slat solution infiltration could enhance soil wet front migration rate of clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil maximally by 33.0%, 32.5% and 93.5%, lower that of red soil maximally by 34.8%. The soil clay content, exchangeable iron and aluminum content mainly inhibited soil water movement, while silt content, exchangeable calcium and magnesium content promoted soil water movement. Sodium salt accelerated water movement in clay fluvo aquic soil, sandy fluvo aquic soil and paddy soil. Relative soil water diffusivity increased by 22.0%, 37.3% and 39.7% respectively. Sodium salt inhibited the water diffusion of red soil and purple soil. The higher salt concentration could result in the smaller relative soil water diffusivity. At 15 g/L salt concentration, the soil water diffusivity decreased by 30.5% for red soil and 42.1% for purple soil, respectively. Relative soil water diffusivity of clay fluvo aquic soil, sandy fluvo aquic soil, red soil and purple soil fluctuated with the increase of soil water content, while the relative soil water diffusivity of paddy soil decreased with the increase of soil water content. Relative soil water diffusivity of paddy soils showed a good parabolic relationship with salt concentration (R²=0.987), while red soils and purple soils showed a good linear relationship with salt concentration (R²>0.933). The saturated hydraulic conductivity of clay fluvo aquic soil treated with sodium salt solution increased most obviously, with a maximum increase of 77.3%, followed by paddy soil, with a maximum increase of 25.1%. With the increase of salt solution concentration, the relative saturated hydraulic conductivity of soil decreased first and then increased. In the range of 1-10 g/L salt concentration, the saturated hydraulic conductivity of soil had a good parabolic relationship with the sodium salt concentration (R² was not less than 0.807), and the saturated hydraulic conductivity of soil was the smallest when the concentration of each extreme point of soil was about 5 g/L. Therefore, the salt concentration of reclaimed water should be moderately controlled to a level lower than the extreme point concentration. [ABSTRACT FROM AUTHOR]

In order to obtain the interaction parameters which can be used for discrete element simulation between the soil-engaging components and clayey black soil in northeast China, the Hertz-Mindlin with JKR Cohesion contact model in EDEM2.7 was used to simulate the clayey black soil. Aiming at the actual working environment with moisture content of 10%-20%, 2 kinds of clayey black soil with moisture content of 12.46%±1% and 17.15%±1% were prepared respectively. The rolling friction coefficient, recovery coefficient, JKR surface energy parameter and the static friction coefficient between the soil particles were used as the model calibrated parameters. The soil repose angle simulated under the simulation parameters was set as the response value. The regression model of the soil repose angle was established based on the Box-Behnken response surface method, and the regression model was optimized by using the soil repose angles under 2 moisture contents obtained by physical experiments. The optimal solution of the contact model parameters of the clayey black soil particles with 2 moisture contents was obtained. The parameter range of the discrete element contact model of clayey black soil with moisture content between 10%-20% were given. The soil repose angle and stacked shape obtained by the simulation experiment with the optimized solution had a high similarity with that of the physical test. At the same time, the static friction coefficients of 3 kinds of soil contact materials such as 65Mn plate, UHMW-PE plate and PTFE plate were tested under the conditions of 4 kinds of moisture content, which were 0, 12.46%, 17.15% and 23.5% respectively. Then for the 2 typical soil contact materials such as 65Mn and PTFE, the slope physical test bench were constructed for the clayey black soil with moisture content of 17.15%±1%. The slope simulation models of 65Mn and PTFE materials were established under the EDEM2.7 software platform. Based on the critical simulation parameters such as JKR surface energy parameter, static friction coefficient, rolling friction coefficient and recovery coefficient between soil particle and soil contact material, the simulated rolling distance of the soil ball on different soil contact materials was set as the response value. The excellent fit regression model of rolling distance for the 2 kinds of typical soil contact materials were established based on the response surface optimization method of Box-Behnkende. The 2 regression models were optimized by the sliding distance obtained by the physical experiment. Then the optimized solution of the contact model parameters of different materials was obtained. The simulation results showed that when the surface energy of JKR between soil and 65Mn was 5.5 J/m2, the recovery coefficient was 0.61, the static friction coefficient was 0.57 and the rolling friction coefficient was 0.056, the rolling distance simulation result was 153.56 mm, which was close to the average rolling distance obtained from physical experiments of 155.93 mm, and the relative error was 1.52%; When the surface energy of JKR between soil and PTFE was 4.08 J/m2, the recovery coefficient was 0.6, the static friction coefficient was 0.52 and the rolling friction coefficient was 0.045, the simulation result of rolling distance was 269.35 mm, which was close to the average rolling distance of 269.55 mm obtained from physical experiment, and the relative error was 0.07%. And the optimized parameters can be used to simulate the discrete parameters between the clayey black soil and the soil-engaging components. The study provides credible basic data for the design and simulation of agricultural machinery under clayey black soil conditions. [ABSTRACT FROM AUTHOR]