关键词: 水稻土（水耕人为土）, 时间序列, 母质, 黏粒矿物, 物源

Abstract:

Paddy soils (Hydragric Anthrosols) greatly differ from their parent soils and homologous Orthic Anthrosols in physical and chemical properties, owing to their special soil formation processes. This prevented discriminating their provenance by conventional means. Paddy terraces in the hilly regions of South China are an example of successively expanding cultivated lands in a sustainable system. Because of their depth, fertility and ease of irrigation, soils at the bottom of slopes were generally the first to be converted to paddy; as population pressure increased, lands upslope were progressively brought into paddy cultivation. Thus, these hillside terraces, with increasing cultivation age from the top to the bottom of the slopes, form soil chronosequences. Considering the constraints, three paddy soil chronosequences derived from the main parent materials of the region in the hilly regions of South China, namely, purple sandy shale (PS), Quaternary red clays (RC) and red sandstone (RS), were selected to explore the clay mineral assemblages and their provenance implications. The XRD pattern suggested that kaolinite-like clays were major constituents of the PS soils. Similarly, illite-like, kaolinite-like and bayeritewere major constituents in the RC soils, and 1.4 nm intergradient minerals, kaolinite-like and bayerite were major constituents in the RS soils. For RC and RS soils, there was little change in the clay minerals. Long-term paddy cultivation can promote formation of illite-like minerals. In PS soils, 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 non-clay fractions. The results also indicated the clay minerals of paddy soils mainly followed the feature of their original soils and that their evolutions could be roughly distinguished based on their constituents. For soils with a low content of K-bearing minerals, there was little change in clay mineralogy. For soils that were abundant in K-bearing minerals, depotassication was strong and the change in clay minerals was comparatively remarkable. This result suggests that the evolution of clay minerals is primarily affected or determined by their original soils derived from different parent materials. In addition, the crystallinity of illite-like minerals would be worse under the long-term paddy cultivation and periods of artificial submergence with highly activity in hydrolysis might cause the change of the ordering degree of lattice of clay minerals. However, the projections of main clay minerals for paddy soils from same parent material centralized in a lesser range and the clay mineral assemblages can reflect their parent material sources in paddy soils.

Key words: paddy soils (Hydragric Anthrosols), soil chronosequences, parent materials, clay minerals, provenance