Objective  The analysis of the variation characteristics of regional soil magnetic susceptibility can obtain the soil evolution and characteristics of soil environmental change, and provide a basis for regional soil resource management.

  Method  This study analyzed the differences in the magnetic susceptibility of soil profiles in Chengdu Plain for different agricultural land-use patterns and parent material types based on 675 sample data from 174 soil profiles, and evaluated the effects of agricultural land-use changes on magnetic susceptibility of the farmland soil profile by using the space-time substitution method.

  Result  The results showed that the magnetic susceptibility of soil decreased with the increase of soil depth. Soil magnetic susceptibility in 0 ~ 20 cm soil layer (23.30  ×  10⁻⁸ m³ kg⁻¹) was significantly higher than that in 20 ~ 40 cm and 40 ~ 60 cm soil layers (20.42  ×  10⁻⁸ m³ kg⁻¹ and 19.36  ×  10⁻⁸ m³ kg⁻¹). In general, the magnetic susceptibility of each soil layer for rice-vegetable rotation was significantly higher than that for traditional rice-wheat/rapeseed rotation and afforested land, which were 1.57 ~ 2.15 times than that in the latter two agricultural land uses. While there was no significant difference in the magnetic susceptibility of each soil layer between the afforested land and the traditional rice-wheat/rapeseed land. However, the differences in the soil magnetic susceptibility between rice-vegetable rotation land and afforested land and traditional rice-wheat/rapeseed rotation land varied with soil parent material types. For soils formed from the Q3 old alluvium and Q4 grey-brown alluvium, the magnetic susceptibilities of the four layers in the rice-vegetable rotation land were significantly higher than that in the traditional rice-wheat/rapeseed rotations (P < 0.05). But for soils formed from the Q4 grey alluvial, the soil magnetic susceptibilities in the rice-vegetable rotation land were significantly higher than that of the rice-wheat/rapeseed rotation land only in the 40 ~ 100 cm soil layers (P < 0.05). The magnetic susceptibilities of the soil profile in the afforested land were slightly higher than that of the traditional rice-wheat/rapeseed rotation land for soils formed from the Q3 old alluvial soil, but lower than that of the traditional rice-wheat/rapeseed rotations for soils formed from the Q4 grey and grey-brown alluvial soil. Additionally, for the traditional rice-wheat/rapeseed rotation land, the magnetic susceptibilities of all the soil layers formed from the Q4 gray and gray-brown alluvial soils were significantly higher than that of soils formed from the Q3 old alluvial soils (P < 0.05), but there is no significant difference in the soil magnetic susceptibility among soils formed from all the three parent material types on the afforested land (P < 0.05).

  Conclusion  These results indicated that the effect of land use change on magnetic susceptibility of soil depends on parent material. The transformation from traditional rice-wheat/rapeseed rotations to rice-vegetable rotations and afforested land changed the magnetic characteristics of soil profile. Compared with the traditional rice-wheat/rapeseed rotations, the rice-vegetable rotations enhanced the magnetic properties of soils formed from the Q3 old alluvial and Q4 grey-brown alluvial soils, but only increased the magnetic properties of the 40 - 100 cm soil layer formed from the Q4 grey alluvial. While afforestation obviously reduced the magnetic properties of soil profiles formed from Q4 grey alluvium and Q4 grey-brown alluvium.