Phases and rates of iron and magnetism changes during paddy soil development on calcareous marine sediment and acid Quaternary red-clay

Laiming Huang,Ming’An Shao,Liumei Chen,Ganlin Zhang,Guangzhong Han,Xiaoxu Jia

doi:10.1038/s41598-017-18963-x

Abstract

Dynamic changes in Fe oxides and magnetic properties during natural pedogenesis are well documented, but variations and controls of Fe and magnetism changes during anthropedogenesis of paddy soils strongly affected by human activities remain poorly understood. We investigated temporal changes in different Fe pools and magnetic parameters in soil profiles from two contrasting paddy soil chronosequences developed on calcareous marine sediment and acid Quaternary red clay in Southern China to understand the directions, phases and rates of Fe and magnetism evolution in Anthrosols. Results showed that paddy soil evolution under the influence of artificial submergence and drainage caused changes in soil moisture regimes and redox conditions with both time and depth that controlled Fe transport and redistribution, leading to increasing profile differentiation of Fe oxides, rapid decrease of magnetic parameters, and formation of diagnostic horizons and features, irrespective of the different parent materials. However, the initial parent material characteristics (pH, Fe content and composition, weathering degree and landscape positions) exerted a strong influence on the rates and trajectories of Fe oxides evolution as well as the phases and rates of magnetism changes. This influence diminished with time as prolonged rice cultivation drove paddy soil evolving to common pedogenic features.

Highlights

Iron (Fe) is the fourth most abundant element in Earth’s crust (6.7 wt %)[1] and serves as an essential micro-nutrient for almost all living organisms[2]
Total Fe concentration remained relatively constant in both uncultivated pedons, ranging from 28.22 to 30.34 g kg−1 in P0-MS derived from marine sediment and from 46.64 to 49.39 g kg−1 in P0-RC derived from Quaternary red clay (Table 1).The higher total Fe concentration in P0-RC than P0-MS was attributed to the differences in parent materials
The weighted-mean total Fe concentration within 120 cm profile increased across the calcareous paddy soil chronosequence developed on marine sediment (P0-MS, 29.50 g kg−1; P50-MS, 36.55 g kg−1; P300-MS, 37.69-MS g kg−1; P700, 39.72-MS g kg−1; P1000-MS, 42.51 g kg−1), but decreased across the acid paddy soil chronosequence developed on Quaternary red clay (P0-RC, 44.45 g kg−1; P60-RC, 40.38 g kg−1; P150-RC, 35.68 g kg−1; P300-RC, 36.62 g kg−1)

Summary

Introduction

Iron (Fe) is the fourth most abundant element in Earth’s crust (6.7 wt %)[1] and serves as an essential micro-nutrient for almost all living organisms[2] It has a variety of different forms in soil systems, such as primary silicate minerals, pedogenic clay minerals, Fe (oxyhydr)oxides with different degrees of crystallinity, as well as in organic complexes[3,4]. Our objectives were to (i) investigate the dynamic changes in different Fe pools and magnetic properties during anthropedogenesis of paddy soils; (ii) identify the underlying mechanisms and processes controlling the phases and rates of Fe oxides and magnetism changes; and (iii) establish the influence of parent material and time span on Fe and magnetism evolution in paddy soils

Objectives

Methods

Results

Conclusion