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This article aims to solve the problem of residual pollution of soil inputs in irrigation areas caused by industrial development, a soil pollution monitoring and early warning system based on geographic information system (GIS) was proposed. The system combined a VOC-PF1 sensor, an STM32 master chip, and a GSM communication module to achieve efficient data collection and communication functions. The spatial analysis was carried out by the in-verse distance weighted (IDW) interpolation method, and the early warning threshold was established to realize the real-time monitoring and early warning of soil input residual pollution in the irrigation area. The experimental results show that the monitoring accuracy of the system is as high as 98%, and the monitoring time is up to 49 s, which has high practicability and efficiency. This study not only provides an effective means for the monitoring of soil input residue pollution in irrigation areas, but also provides strong support for environmental protection and sustainable agricultural development. [ABSTRACT FROM AUTHOR]

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Water resource shortage has become an important limiting factor for the agricultural production in arid areas in Northwest China. The efficient utilization of brackish water resources is of great importance significance for food safety in irrigated areas. However, the influence of irrigation with different solute type and mineralization on salty ions in soil solution during the release water process is unknown. In the study, the soil samples were collected from orchard calcareous soil in Qin’an County of Gansu Province. The content of soil organic matter was 10.52 g/kg and pH was 8.54. Soil electrical conductivity was 0.43 mS/cm. The contents of HCO3, Cl-, SO42-, Ca2+, Mg2+, K+ and Na+ were 0.85, 0.16, 0.14, 0.24, 0.06, 0.05, 0.13 g/kg, respectively. The content of calcium carbonate was 134.8g/kg. Soil texture classification was based on the U.S. Department of Agriculture system and the soil texture was a silty clay loam, which has 25.2% sand, 53.9% silt, and 20.9% clay. The influences of two sodium salts (NaCl, Na2SO4) with different mineralization degrees (1, 3, 5, 10 g/L) on salt ion composition in soil solution were explored with the dehydration centrifugal method under different water suction conditions (pF 1.01, 1.49, 2.01, 2.71, 3.49, and 4.09), distilled water was used as control. The result showed that the influences of NaCl and Na2SO4 on electrical conductivity, HCO3-, Cl-, SO42-, Ca2+, Mg2+, K+ and Na+ in soil release solution were significant (p<0.05) or extremely significant (p<0.01). The influences of NaCl and Na2SO4 with the same salinity on salt ions in soil release solution were different. The ability of Cl- to replace HCO3 was better than SO42- to replace HCO3- in soil solution of treatments with 1 g/L of NaCl and 1 g/L of Na2SO4. When soil water tension (pF) was less than 2.01, the NaCl solution with the degree of mineralization more than 3 g/L promoted the dissociation of the Ca2+ in soil solution and the promoting effects of dissociation increased with the increase of salinity. When soil water tension (pF) was more than 2.01, Cl- and SO42- in irrigation water inhibited the dissociation of HCO3- in soil solution and Cl- in irrigation water inhibited the dissociation of SO42- in soil solution, and SO42- in irrigation water inhibited the dissociation of Cl-, NaCl solution (the degree of mineralization of was 1 g/L) inhibited the dissociation of Ca2+ in soil solution. NaCl and Na2SO4 in irrigation water promoted the dissociation of Mg2+ in soil solution. Therefore, from the viewpoints of the improvement salinized soil using brackish water, for sodic-saline soils, it was possible to irrigate with brackish water containing the mostly of Cl- and SO42-. For sulfate saline soil, it was possible to irrigate with brackish water containing the mostly of Cl-. For chloride soils, it was possible to irrigate with brackish water containing the mostly of SO42-. The study could provide the basis for restraining soil salts in brackish water irrigation in arid regions. [ABSTRACT FROM AUTHOR]

Shortage of freshwater resources restricts agricultural production in arid and semiarid region. Irrigation with saline water provides an effective way to make up for the deficiency of freshwater resources. However, it is unknown about influence of irrigation with different salt ion compositions on soil physical and chemical properties. In this study, the effect of different salt ion compositions of irrigation on soil water and salt movement was investigated. The soil samples were collected from orchard calcareous soil in Qin’an County of Gansu Province. The soil electrical conductivity was 0.43 mS/cm, pH is 8.54 and soil organic matter is 10.52 g/kg. A total of 4 treatments were included: NaCl, NaCl:MgCl2 with the ratio of 1∶1, NaCl:CaCl2 with the ratio of 1∶1, NaCl:KCl with the ratio of 1∶1. The concentration of all the treatments was 3 g/L. Soil water diffusivity and salt ions movement along the horizontal distance were studied by the method of horizontal soil column infiltration. Soil pH and sodium adsorption ratio were determined. The Boltzmann function was used for simulation of soil salt movement. The relationship between soil water diffusivity and water content was simulated by an power function. The results showed that the soil water diffusivity capacity at water content of 0 was the highest in the treatment of NaCl, followed by NaCl:MgCl2, NaCl:KCl and NaCl:CaCl2. The change rate of diffusivity with water content was the highest in the treatment of NaCl:CaCl2 followed by the NaCl:KCl, NaCl:MgCl2 and NaCl only. The salt ion composition of irrigation water and soil water content both significantly affected the soil water diffusivity (P<0.01). For all the treatments, the soil salt content, calcium ions, potassium ions, sulfate ions and sodium ions all increased with the infiltration distance but the bicarbonate ion decreased with the distance. The obvious trend wasn’t found for the chloride and magnesium ions. Soil pH decreased with infiltration distance for the treatment of NaCl only. The decrease trend of soil pH fluctuated for the other treatments. The soil pH at distance of 8 and 32 cm was significantly different (P<0.05). The salt ion composition did not significantly affect the soil pH. The sodium adsorption ratio decreased obviously with the infiltration distance in the treatment of NaCl only. The sodium adsorption ratio in the treatment of NaCl was higher than the other treatments. The sodium adsorption ratio increase trend fluctuated for the other treatments. The salt ion composition of irrigation water significantly affected the sodium adsorption ratio (P<0.05). Based on the Boltzmann function fitness, the initialization value and final value were influenced by the salt ion composition of irrigation water and the treatment NaCl was higher than the other treatments. The center was similar for all the treatments (28.488-28.700). The simulation was well with the determination coefficient higher than 0.89. The study indicated that adding calcium ions in irrigation water could inhibit water movement and decrease salt accumulation in the process of irrigation with brackish water. The irrigation at one end of plot was not recommended since it may cause salt accumulation and we suggested to irrigate at both ends of the plot. The study could guide the irrigation with brackish water in arid or semiarid regions. [ABSTRACT FROM AUTHOR]