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Distribution of Water and Salt Ions in a Saline–Alkali Wheat Field under Freeze–Thaw Conditions

Author(s): Li Xiaoshuang, Dang Hongkai, Song Ni, Feng Di, Sun Jingsheng

In order to make clear the distribution characteristics of soil, water and salt in a saline–alkali wheat field under freeze–thaw conditions, field experiment was conducted in Cangzhou during 2015 to 2018. The experiment were selected three key periods, early stage (December 13) and late stage (March 3) of freeze–thaw period, and salt accumulation stage (April 1). The distribution of soil salt ions prior to sowing was regarded as the background. Results showed that the spatial distribution of soil moisture in the 0–100 cm soil layer varied in the different periods. In the early stage of the freeze–thaw period, the soil moisture content decreased with the increase of soil depth in 0-40 cm soil layer, and then increased with the increase of soil depth. The minimum moisture content was found in the 30–40 cm soil layer. Soil electrical conductivity (EC) in the 20–30 cm soil layer was higher than that in other soil layers. Meanwhile, soil pH value increased with the increase in soil depth. SO42–, Ca2+, Cl and Mg2+ all aggregated to the surface. After freezing and thawing, the moisture content in the 0–60 cm soil layer increased with the increase in soil depth. The moisture content dropped precipitously in the 60–80 cm soil layer, and then the moisture content quickly rebounded to the soil layer below 80 cm. Soil EC increased with the increase of soil depth. With increase depth of soil layer, the pH value appeared peak in the 10-30 cm soil layer and then decreases. The pH value of the soil below 40 cm gradually increased with the increase of soil depth. SO42–, Ca2+, Mg2+ and Na+ showed a trend of large at surface and deep soil layers, and samll in the middle soil layer. HCO3– accumulates at 0-30 cm soil layer. Cl was increase with the increase of soil layer. During the salt accumulation period, the moisture content in the 0–20 cm soil layer was significantly lower than that in the soil layer below 20 cm. Various ions accumulated in the 0–20 cm soil layer, and the soil EC was also significantly higher than that in the soil layer below 20 cm. At this period, roots of wheat were densely distributed in the 0-20 cm soil layer. Therefore, timely irrigation could alleviate the dual stress of drought and salt damage on winter wheat. The redistribution characteristics of water and salt ions before and after the freeze–thaw period could be used as the theoretical basis for the prevention and improvement of salinised soil.

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