Seasonal freezing and thawing soils play an important role in the management of water and land resources in arid and semi-arid regions in northern China. Hetao Irrigation District is a typical seasonal frozen soil area in China's soil salinization development. Under the influence of seasonal soil freezing and thawing, it not only formed the special soil water and salt redistribution and groundwater dynamic distribution in winter and spring, but also caused the soil moisture during ablation. The strong evaporation leads to the return of salt in spring, which has become an important factor in the secondary salinization of the soil in the irrigation area. On the other hand, for a long time, according to the data recorded by the researchers on the soil moisture recorder placed in the experimental field, the autumn water storage irrigation that is widely valued by Hetao people has a great influence on the freeze-thaw and even thaw in winter and spring. After the return of salt and sensation in the soil, many new problems were raised for agricultural production and monitoring of water and salt in irrigation areas. Understanding the distribution of soil water and salinity before and during the two key periods before the autumn irrigation and summer irrigation has a profound effect on the agricultural production and soil improvement in the Hetao Irrigation District, and it also has a representative representation of the spatial-temporal variation of water and salt dynamics during the interannual period. Zhejiang Top Instrument Co., Ltd. not only carries out advanced research and development of agricultural instruments, but also includes the production and sale of agricultural instruments such as automatic nitrogen determination instruments and seed cleanliness worktables. Click here to learn more about the instrument.
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Since the 1970s, the use of geostatistical theory to quantify the spatial variability of soil characteristics as a research hotspot has been of concern to scholars. Not only all kinds of geostatistical methods, including ordinary Kriging, cooperative Kriging, pan-Kriging, and conditional simulation, have been successfully applied in this field, but also the research content has expanded from the physical properties of soil to the nutrients of soil and Salt, etc., has made great progress regardless of breadth or depth. However, soil surveys are still mainly focused on smaller sampling scales (generally less than 10 m), while less spatial variability of soil characteristics on larger sampling scales (eg 100 m).
The spatial variability of soil moisture and salinity in Hetao Irrigation District on the larger scale before and during the summer irrigation was analyzed using geostatistical methods and recorder data, and the distribution map was drawn. This study has implications for monitoring and predicting the dynamic changes of soil moisture and salinity over large areas of seasonal freeze-thaw areas and for understanding the effects of freezing and thawing on soil water and salt redistribution processes (or spatial variability).
Overview of the pilot area The Hetao Irrigation District in Inner Mongolia has a gentle terrain with a ground slope of about 1/8000, and the groundwater runoff is extremely unsmooth. In this area, the use of autumn water as an irrigation salt and irrigation as the main means of water storage for crop germination in the following spring is generally used. The increase in groundwater level is relatively consistent, with regional underground lateral runoff absent or extremely weak. Therefore, in the Hetao Irrigation District, the soil water and groundwater movements in the unsaturated zone from the autumn to the summer of the next year are vertical evaporation-infiltration recharge.
The experimental area is located in the Changsheng Experimental Area of ​​Hetao Irrigation District. The average annual temperature is 7.1°C. The average temperature in January is the lowest at -12.4°C, and the freezing index is 624.4 to 1739.0°C·d. The average annual rainfall is 139-222 mm, and the average annual evaporation is 1999-2346 mm. The wind speed is 2.5 m/s, and the wind direction is mostly southwest and northwest winds. The shallow depth of groundwater in the irrigation area is mainly affected by irrigation leakage. In short, the region is characterized by arid climate, shallow groundwater depth, and poor horizontal drainage, which is a typical area for the development of saline soil in China.
The sampling grid design and the area of ​​the results test area are regular rectangles, with an area of ​​(500 m × 1100 m) 55 hm2. Before the autumn of 1998 (mid-September) and the summer of 1999 (late April), the profile of the test area was used. Method to collect soil samples. Before the summer irrigation (before the first irrigation of the year) sampling was not yet done in the test area, and the crop (the whole test area was sunflower) was being harvested before sampling in the autumn, and water was stored in the autumn in early November. The sampling plan is as follows: Within 1 m depth of the surface layer (in 5 layers: 0-20, 20-40, 40-60, 60-80, 80-100 cm) in the east-west and north-south direction along the test area, every 100 m. The soil samples form a large-scale grid of 100 m×100 m. Sample analysis results include soil total salt content, soil (mass) water content, EC value, pH value, and 8 main ion contents of the soil. The variability of soil moisture and salt content in the experimental area was studied using the average soil water content and average total salt content on the entire section (0 to 100 cm).
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