Soil genesis along a paddy soil chronosequence in a millennium scale.

A paddy soil chronosequence consisting of five profiles derived from calcareous marine sediments ranging in paddy cultivation history from 0 to 1000 years was studied. The general soil physical and chemical properties, magnetic properties, clay mineral and major elements of the soil samples were measured, in order to investigate the dynamic change of different soil properties, and to understand the response rate of soil properties over different time scales. The results showed that soil properties including surface soil organic carbon, CaCO 3, MS(magnetic susceptibility), IRM s(soft isothermal remanent magnetization), had notable changes within the initial stage (50 yrs) of paddy cultivation. Clay content, free iron oxides, and IRMh (hard isothermal remanent magnetization), change notably when paddy cultivation history reach 700 years. However, clay mineralogy shows few changes even if the cultivation time reaches 1000 years. The results of gains and losses of major elements indicate Ca, Mg, and Na are strongly lost in the initial stage (50 yrs) of paddy cultivation and gradually depleted with increasing paddy cultivation time, Si and Al remain basically constant, while, Fe has large depth variation. In conclusion, our data demonstrate that different soil components and properties have quite different changing process and rate under paddy cultivation condition.