Changes in Soil Magnetic Susceptibility and the Environmental Implications under the Conversion of Soda Saline-Alkaline Wastelands into Paddy Fields

Based on the MS (chi(lf) and chi(fd)%) and saline-alkaline indicators (e.g., total dissolved solids TDS, exchangeable sodium saturation percentage ESP, cation exchange capacity CEC, exchangeable sodium ENa) of soil, correlation analysis and structural equation modeling using maximum likelihood estimation (ML-SEM) were conducted. The results revealed that the chi(lf) and chi(fd)% of paddy soil were lower than those of soda saline-alkaline wasteland.

It's due to long-term waterlogging and human disturbances like irrigation, fertilization, and cultivation. Soda saline-alkaline soils are inherently less magnetic than other soil types. Under waterlogged and reducing conditions, ferrous magnetic minerals are destroyed, causing further magnetic attenuation during Hydragric Anthrosols' evolution.

Generally, the MS (chi(lf) and chi(fd)%) of black soils ranges from 10 < chi(lf) < 100 (x 10(-8) m(3) kg(-1)) and 2% < chi(fd)% < 10%. In contrast, research shows that chi(lf) < 14 x10(-8) m(3) kg(-1) (Mean +/- SD = 9.26 +/- 1.56) and chi(fd)% < 4% (Mean +/- SD = 2.46 +/- 1.05) are suggested to be diagnostic characteristics of the surface layer of soda saline-alkaline soils in Northeast China. The correlation analysis and ML-SEM results indicate that the main factors influencing chi(lf) in the paddy soils were the ENa, Cl-, TDS, ESP, Na+, and SO42-, with net effects of -0.990, 0.688, -0.3502, -0.3000, 0.2331, and 0.1746.

ENa, TDS, and ESP significantly inhibited the chi(lf) of paddy soils, while the Cl-, Na,(+) and SO42- contents significantly promoted it. In contrast, the chi(fd)% of the soils showed no correlation with any of these indicators. The chi(lf) of paddy soils variations can indirectly indicate the fluctuations of soil saline-alkaline indicators.

In sum, MS (chi(lf) and chi(fd)%) can serve as an alternative index for describing changes in soil salinization levels and has potential implications for soil salinization assessment.