【Journal of Soils and Sediments】Pedogenetic evolution of clay minerals and agricultural implications in three paddy soil chronosequences of south China derived from different parent materials

Purpose

This study aims to understand how clay minerals change sequentially with paddy cultivation age and how parent materials (or original soils) affect the clay mineral behavior of paddy soils.

Materials and methods

Three paddy soil chronosequences in the hilly regions of South China derived from purple sandy shale (PS) Quaternary red clays (RC) and red sandstone (RS) were selected to explore the dynamic changes in clay mineralogy by comparing physical chemical and mineralogical properties of soil sequences.

Results and discussion

For RC and RS soils both of which have a low K content there was little change in the clay minerals. Long-term paddy cultivation can promote formation of illite-like minerals; however this form of K storage was limited under present farming conditions. In PS soils which are abundant in K-bearing minerals the depotassication was strong accompanied by marked transformation of clay minerals. Kaolinite-like minerals gradually decreased with paddy cultivation age; by contrast derivative clay minerals such as secondary chlorite and halloysite gradually increased. Strong depotassication mainly occurred in the nonclay fractions. The rate of depotassication and the generation of clay fractions were much faster than in natural soils.

Conclusions

The clay minerals of paddy soils mainly followed the feature of their original soils. Their evolutions could be distinguished based on their constituents which are greatly affected by their parent materials. Moreover paddy cultivation is able to modify clay mineralogy according to the original mineralogy and paddy soil management.