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The prevention and control of saline soil is of great significance to the sustainable development of agriculture in Xinjiang, and comprehensive knowledge of the Salt content of saline soil is a prerequisite for the prevention and control of salinization, so it is necessary to find an accurate and rapid method to estimate salt content information of saline soil. Ground Penetrating Radar (GPR) is widely used in geophysical and environmental assessment as a non-destructive detection technology. In recent years, this technology focuses on the detection of water content. However, the detection of soil salt is relatively weak due to the large dielectric loss in saline-alkali soil, the easily-absorbed electromagnetic wave energy the complex way to process radar signal, and even the different frequency combinations are needed to test, all of which above bring great troubles to the detection of salt. However, the rapid development of dielectric models in salinized soil makes it possible to use this technique to retrieve salt content. In order to better understand the soil salt content in drip irrigation cotton field, a typical drip irrigation cotton field was selected as the research object to be detected with a Canada's Ekko PRO series GPR multi-frequency antenna (250 MHz and 1 000 MHz). Then, the soil dielectric constant was obtained through radar amplitude envelope Average method (AEA). Soil salt content was estimated by adopting the Dobson saline soil dielectric model (Dobson dielectric model of saline soil, Dobson) as the theoretical tools. Meanwhile, the dielectric constant, soil bulk density, water content, and soil clay content were applied as the input variables of the model; Multiple Linear Regression (MLR) method was used to establish soil salinity inversion model; BP neural network (BP) was employed for simulation and prediction. Finally, the accuracy of salt content inversion by MLR model, BP model and Dobson model was evaluated based on the measured salt content. The results showed that: (l) The effective depth of GPR 250 MHz and 1000 MHz frequency antenna AEA method was 0-30 cm. (2) The dielectric constant obtained by 1 000 MHz frequency antenna AEA had a good polynomial relationship with the measured water content, and the fitting effect and accuracy of the measured water content and the inverse water content were good (R², RMSE, MER were 0.96, 1.61%, and 7.25%, respectively). (3) Among the three salt inversion models, the inversion accuracy of Dobson salinized soil dielectric model was significantly higher than that of the other two methods, with R² and RMSE of 0.91 and 0.313 g/kg respectively. Therefore, it is suitable and reliable to use GPR multi-frequency antenna AEA method to estimate soil salt content in cotton fields under drip irrigation. This method provides a new way to retrieve soil salt content and enriches the methods and means of detecting soil salt content. [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]

To evaluate reasonably the effect of reclaimed water irrigation salt in the soil environment, varying salinity in the effluent of salty solution leaching subtropical soil and the effect on soil chemical properties were analyzed. In this paper, five subtropical soils: clay fluvo aquic soil, sandy fluvo aquic soil, red soil, purple soil and paddy soil were selected as the research object. Use the constant head infiltration method to observe the differences in electrical conductivity (EC) and pH of effluent after leaching of soils with different concentrations of sodium salt solution (EC of solutions was 1.96, 4.77, 9.08, 17.25 and 25.06 dS/m, respectively). The results showed that the high concentration salt solution had weaker penetrating ability in red soil, purple soil and clay fluvo aquic soil with higher clay content than paddy soil and sandy fluvo aquic soil with low clay content. The same treatment achieved the same degree of penetration, and acidic soil (red soil, purple soil, paddy soil) can withstand more low quality water. In addition, the migration rate of salinity in the soil was mainly determined by the physicochemical properties of the soil. Soil clay content and exchangeable aluminum content significantly slowed the migration of salinity in the soil, while the soil silt content, EC, pH value and exchangeable calcium and magnesium content promoted the migration of salt in the soil. Salt can easily flow out through alkaline soil (clay fluvo aquic soil and sandy fluvo aquic soil). The maximum change rate of relative EC from the alkaline soil effluent was 36% higher than that of the acidic soil. The concentration of inflow salt had an obvious influence on the relative EC change rate and the penetration process of the red soil effluents, and it mainly affected the relative EC change rate for the purple soil, the clay fluvo aquic soil and the sandy fluvo aquic soil, which mainly affected the lag degree of the penetration process for paddy soil. The Boltzmann fitting showed the infiltration water salt concentration and soil physical and chemical properties had a significant impact on the model parameters (P<0.05). Moreover, the degree of soil chemical properties affected by the salt concentration in the infiltration solution was not only related to its own chemical properties, but also had a very significant relationship with the content of powder particles and clay in the soil texture (P<0.01). The concentration of salt solution had no significant (P > 0.05) effect on the pH value of alkaline soil, and had a greater effect on the pH value of acidic soil. The pH of the effluent decreased by 1.6-2.6 units, of which red soil had the greatest change in pH value, followed by purple soil. The influence of infiltration solution with EC higher than 4.77 dS/m on the stable pH value of soil effluent did not increase substantially. Therefore, when irrigating with low quality water, the salt concentration in the water should be sufficiently limited according to the physicochemical properties of the soil. The research results can serve as reference for reclaimed water irrigation and calculation of water and salt transport in subtropical regions. [ABSTRACT FROM AUTHOR]