Magnetic Difference Between Deep and Surface Soil Within an Agricultural Area in Southern China: Implications for Magnetic Mineral Transformation During Pedogenic Process Under Subtropical Climate

Mineral magnetism is proved as a sensitive method of pedogenesis by numerous studies. However, formation pathways of magnetic minerals and subsequent magnetic response are quite different under different climate. In order to improve the understanding of magnetic assemblages in paddy soil layers in relation to soil formation conditions, a systematic magnetic investigation was performed for surface and its corresponding deep soil collected from 70 sampling sites within a paddy soil area under subtropical climate, south China. Rock magnetic results showed that superparamagnetic, single‐domain, and multiple domain maghematite and hematite were produced during ferrallitization pedogenic processes. Some fine superparamagnetic and single‐domain ferrimagnetic particles were dissolved during late gleyization of paddy soil formation with increased organic matter and reductive condition. As a result, magnetism of surface soil was weaker than that of deep soil despite basically consistent magnetic mineral composition. Key Points Maghemitization and hematization are main transformations of Fe‐bearing minerals during pedogenic process under hot and humid conditions Fine superparamagnetic and stable single‐domain ferrimagnetic particles are dissolved during gleyization of paddy soil formation Magnetic difference between deep and surface soil is a combination result of ferrallitization and gleying pedogenic processes