Effects Of Land Use And Soil Types On The Change Of Magnetic Susceptibility Of Paddy Soil

The dynamic change of soil magnetic susceptibility in the profile can indirectly reflect comprehensive information such as soil climate environment,hydrological status and human activity status.It is a research hotspot in recent years to master the regional soil magnetic susceptibility change information and obtain the magnetic response mechanism of environmental factors.Based on 184 paddy soil profiles in the core area of Chengdu Plain,the variation characteristics of magnetic susceptibility of paddy soil in horizontal and vertical directions were discussed by using magnetic measurement technology and geostatistical methods,and the response mechanism of magnetic characteristics of paddy soil to land use patterns and soil development was revealed.The genetic relationship between different environmental factors and magnetic parameters of paddy soils in the core area of Chengdu Plain was quantitatively analyzed by correlation analysis and regression analysis.The main results are as follows:?1?The magnetic susceptibility of the paddy soil profile in the study area ranged from 20.43 to 29.46×10^-8·m³/kg,which was generally low,and the magnetic susceptibility coefficient of the profile frequency ranged from 3.23%to 4.76%.Two magnetic parameters indicate that the content of magnetic minerals in paddy soil profile is low,and the morphology of magnetic minerals is mainly anthropogenic coarse-grained multi-domain magnetic granules..The results of semi-variance of magnetic parameters of paddy soils show that the nugget coefficient of magnetic susceptibility is 64.7%in the surface layer?0-20cm?,which indicates that the spatial variation of paddy soils is influenced by both structural and stochastic factors and mainly by stochastic factors,while the nugget coefficient decreases gradually at the section 20-100cm,and the influence degree of structural factors strengthens gradually;the nugget coefficient of frequency magnetic susceptibility is uniform in the whole section.The nugget coefficient decreases gradually with the deepening of the soil layer,which indicates that the nugget coefficient is mainly affected by structural factors,and the influence degree is gradually strengthened with the deepening of the soil layer.The spatial distribution of magnetic susceptibility of paddy soils in the study area shows the characteristics of high in Northeast?Pengzhou-Xindu area?and low in southwest?Wenjiang-Pixian area and west of Qingbai River?,while the spatial distribution of frequency magnetic susceptibility coefficient and paddy soil magnetic susceptibility in the study area shows the opposite trend,and the high and low value areas correspond and coincide with each other.?2?The correlation analysis between magnetic parameters and physicochemical properties shows that the two magnetic parameters are negatively correlated with pH and positively correlated with bulk density,and the correlation between them is gradually strengthened with the deepening of soil layer,reaching a significant correlation at 20-100 cm section.However,the content of soil organic matter was positively correlated with the magnetic susceptibility of paddy soil in each soil layer,but negatively correlated with the frequency magnetic susceptibility coefficient.The correlation analysis showed that the genetic relationship between soil magnetic properties and physical and chemical properties was the weakest in the surface layer?0-20 cm?.Combined with semi-variance analysis,correlation analysis and spatial distribution characteristics of magnetic parameters,it can be concluded that human activities have the strongest influence on the magnetic properties of surface soil?0-20cm?,and the degree of influence decreases with the increase of soil depth.?3?The magnetic properties of paddy soils were significantly affected by land use patterns in the study area.The magnetic properties of paddy soils were different under different land use patterns due to different agricultural management measures such as fertilizer application and tillage methods.The magnetic susceptibility of paddy soils was rice-vegetable>rice-oil>rice-wheat>woodland at the surface layer of the profile?0-20cm?.The main rice-vegetable rotation areas in the study area are located in Pengzhou-Xindu area.Pengzhou is one of the five major commodity vegetable production bases in China,with a long history of vegetable cultivation and cultivation.Since 1990s,the agricultural economic structure of Wenjiang and Pixian areas has changed,and a large area of arabl e land has been transformed into mixed forest land with garden land and agroforestry.The difference of magnetic susceptibility caused by different modes accords with the spatial distribution characteristics of magnetic susceptibility.Affected by plant roots,soil structure and human disturbance intensity,the magnetic susceptibility of various land use modes is generally higher in the surface layer?0-20 cm?in the profile,rapidly decreasing in the sub-surface layer?20-40 cm?,and tending to be stable in the middle layer?40-60 cm?,and rising again in the bottom layer?60-100cm?.?4?The paddy soil of different soil types in the study area has a significant effect on the magnetic susceptibility of paddy soil.The soil magnetism varies greatly in different soil types of paddy soil due to the different soil forming conditions.The magnetic susceptibility in the section surface?0²0cm?is characterized by degleyic paddy soil>percogenic paddy>waterloggogenic paddy soil>Gleyed Paddy Soil.Because of the shallow groundwater depth,the latent paddy soils are widely distributed in Wenjiang-Pixian area;the corresponding Pengzhou-Xindu area has better ventilation and drainage ability,and the delated paddy soils are well developed;the difference of magnetic susceptibility caused by different soil types in the two areas is also consistent with the spatial distribution characteristics of magnetic susceptibility.Different types of paddy soils have different water regimes in different occurrence layers,which differentiates the dynamic changes of activation,deposition and eluviation of magnetic minerals such as iron and manganese in the profiles,resulting in the unique morphological characteristics of magnetic susceptibility profiles of different types of paddy soils.The magnetic change of paddy soil profile can correspond to the corresponding development environment and degree.It can indirectly reflect the direction of paddy soil formation and development history.?5?Regression analysis showed that the main factor controlling the change of magnetic susceptibility at 0-20 cm of the profile surface was land use pattern,and its independent interpretation ability was 21.8%.In the lower part of the profile,40-100 cm structural factors gradually enhanced,and the independent interpretation ability of soil types was the strongest at 20-40 cm;in the lower part of the profile,only soil bulk density had a significant impact on the magnetic susceptibility of paddy soil;in the bottom layer of the profile,only parent material had a significant impact on the magnetic susceptibility of paddy soil,and its independent interpretation ability was 14.6%.Based on the previous analysis,it can be concluded that the magnetic characteristics of paddy soils in the study area are a comprehensive manifestation of many human and natural factors,among which the changes of soil moisture status,redox environment and pH status caused by the changes of land use patterns and soil types play a more decisive role in the magnetic properties of paddy soils.