Magnetic Susceptibility Characteristics And Its Environmental Significance Of Farmland Soils In Weishan Yellow River Irrigation Area

Weishan Yellow River Irrigation area is the largest Yellow River irrigation area in the downstream Yellow River and main grain producing area,and the quality of farmland soils is closely related to the quality of agricultural products and human health.However,due to factors such as human production and life activities,the composition and fertility of farmland soils have changed greatly.As an important indicator of environmental magnetism,soil magnetic susceptibility can effectively evaluate the quality of farmland soils and has been widely applied to the soil research.This paper determined magnetic susceptibility?MS?,grain size and organic carbon of farmland soils sampled from the Weishan Yellow River irrigation area,analyzed the characteristic of farmland profile of soil MS,grain size and organic carbon and their correlation,discussed the influence factors of farmland soil MS and analyzed the environmental significance of the soil MS.The main results are as follows:?1?The soil low frequency magnetic susceptibility(?_lf)of farmland profiles in research area ranged from 35.37×10^-88 m³/kg to 97.20×10^-88 m³/kg,and with the increase of soil depth,the soil?_lff decreased and was higher at 0²0 cm.The soil frequency-dependent magnetic susceptibility(?_fd)ranged from 0.65%to 22.14%,and with the increase of soil depth,the soil?_fdd fluctuated smoothly in some ranges and was on an ascending trend.The soil?_lff had no abvious correlation with the soil?_fdd at 0²0 cm,however,the soil?_lff was significant positive correlation with the soil?_fdd at 20⁸0 cm.?2?The soil?_lf ranged from 38.63×10^-88 m³/kg to 95.03×10^-88 m³/kg,and the soil?_fdd ranged from 0.76%to 12.61%,and the average values of?_lf and?_fd were 66.18×10^-88 m³/kg and 6.53%,respectively.The analysis indicated that the values of farmland soil?_lf and?_fdd were low in southern study area,mainly affected fluvial sediments discharged by irrigation;the values of farmland soil?_lf and?_fdd were high in central and eastern study areas,mainly affected by lowland terrain between river and rich moisture conditions;the values of farmland soil?_lf and?_fdd were low in northwestern study area,mainly influenced by deposition of the ancient river channel.?3?The content of clay?<4?m?ranged from 3.20%to 27.16%,the content of slit?4⁶3?m?ranged from 35.82%to 90.23%,the content of sand?>63?m?ranged from 1.95%to 58.52%,the average content of clay?<4?m?,slit?4⁶3?m?and sand?>63?m?was9.07%,68.94%,21.99%,respectively.The average value of median grain size was 34.94?m,the minimum was 9.56?m,the maximum was 72.86?m.With the increase of soil depth,the clay?<4?m?and the slit?4⁶3?m?increased,and the sand?>63?m?and the median size decreased.The soil?_lff was significant negative correlation with the slit?4⁶3?m?and significant positive correlation with the sand?>63?m?,however the soil?_fdd was positive correlation with the clay?<4?m?and significant negative correlation with the slit?4⁶3?m?at 0⁸0 cm and 20⁸0 cm.?4?The soil organic carbon ranged from 0.67 g/kg to 15.97 g/kg,and with the increase of soil depth,the soil organic carbon decreased.The soil organic carbon was higher and decreased faster with the increase of soil depth in cultivated layer at 0²0 cm,however,the organic carbon was lower and had no obvious changes with the increase of soil depth at20⁸0 cm.The soil?_lff was significant positive correlation with organic carbon and the soil?_fdd had no obvious correlation with organic carbon at 0⁸0 cm.At 0²0 cm the soil?_lff was significant positive correlation with organic carbon but the soil?_fdd had no abvious correlation with organic carbon.At 20⁸0 cm the soil?_lff had no abvious correlation with organic carbon and the soil?_fdd was positive correlation with organic carbon.?5?The soil MS can be used to indicate the change of the quality of farmland soils in Weishan Yellow River Irrigation area.The research area is located in the Alluvial Plain Region of Yellow River,and the terrain is flat,the distribution of soil parent material is more uniform,and the MS of soil parent material is lower.So there are two main reasons for the soil MS enhancement,one is soil parent material and soil-forming process,and the other is human factors.At 0²0 cm the soil MS is enhanced and the value is higher due to human activities such as irrigation and fertilization.At 20⁸0 cm the soil MS is lower,which indicates that pedogenesis is not obvious to promote the enhancement of soil MS,and the soil MS is mainly related to the soil parent material.