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  土壤学报  2020, Vol. 57 Issue (2): 273-283  DOI: 10.11766/trxb201812210567
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引用本文  

胡瑾, 慈恩, 王术芳, 等. 重庆市更新统沉积物发育土壤的特性及分类. 土壤学报, 2020, 57(2): 273-283.
HU Jin, CI En, WANG Shufang, et al. Genetic Characteristics and Classification of Soil Derived from Pleistocene Sediments under Cultivation in Chongqing. Acta Pedologica Sinica, 2020, 57(2): 273-283.

基金项目

国家科技基础性工作专项(2014FY110200)、中央高校基本科研业务费专项(XDJK2017B027)和西南大学科技创新“光炯”培育项目(2016001)资助

通讯作者Corresponding author

慈恩, E-mail:cien777@163.com

作者简介

胡瑾(1999-), 女, 云南昭通人, 硕士研究生, 主要研究方向为土壤发生与分类。E-mail:hujin0421@163.com
重庆市更新统沉积物发育土壤的特性及分类
胡瑾 , 慈恩 , 王术芳 , 连茂山 , 翁昊璐 , 陈林     
西南大学资源环境学院, 重庆 400715
摘要:选取重庆市境内分别由夹卵石黄色黏土(PC)、黄色黏土(YC)、红色黏土(RC)等更新统沉积物发育的6个典型旱地和水田土壤剖面为研究对象, 探讨其土壤特性及系统分类归属。结果表明, PC发育的旱地土壤富含砾石且无铁锰斑纹, YC发育的旱地土壤不含砾石但有铁锰斑纹, RC发育的旱地土壤耕作层以下黏粒淀积明显。在PC和YC发育的水田土体内, 上部土层的有机质累积明显且彩度较下部低, 游离铁在下部土层有明显聚积, 而母质为RC的水田土体内游离铁则迁移不明显。3个旱地土壤分别被划归为普通简育湿润雏形土、普通铁质湿润雏形土和红色铁质湿润淋溶土3个亚类, 3个水田土壤则分别被划归为普通铁聚水耕人为土和普通简育水耕人为土2个亚类, 共可建立6个土族和6个土系。YC发育的普通铁质湿润雏形土有铁锰斑纹存在, 这是古水文条件的反映, 现已完全脱离地下水的影响, 故不再具有潮湿土壤水分状况; 沉积物特征、区域气候等会影响旱地土体内黏粒的淋溶淀积, 进而影响其土纲划分; 水耕活动使更新统沉积物发育的雏形土和淋溶土演变为水耕人为土; 地块筛选、坡改梯、拣拾等人为活动会显著减少PC发育的水田土体内砾石含量, 影响其土族控制层段的颗粒大小级别判定。
关键词更新统沉积物    耕作条件    土壤特性    土壤系统分类    重庆    

更新统的陆相沉积物按沉积相的不同主要分为风积黏土、冲积黏土等,研究其土壤发生与演变规律对地质变迁、古气候变化和土壤资源的管理有重要意义[1-5]。我国已有学者在辽宁省[6]、湖北省[7]和湖南省[8]等区域开展了更新统沉积物发育土壤的类型归属等相关研究。由于耕作环境、耕作方式和模式等存在明显差异,旱地和水田在人为耕作下的成土环境、成土过程和发生特征均有所不同,从而导致土壤特性和类型不同。韩光中等[9-10]研究了母质对南方丘陵区水耕人为土属性演变的影响,认为水耕对成土过程有重要作用。重庆市地貌以山地和丘陵为主,大部分土壤较浅薄,但境内水系发达,河谷两侧的丘陵和山间平坝常遗留有大量古河道,在其形成的高阶地上常有更新统地层零星出露[11-13],而更新统沉积物发育的土壤则较为深厚,土地利用率高,是重庆市重要的农业土壤资源。土壤分类是土壤学最基础的研究领域,以诊断层和诊断特性为基础、以定量化为特点的土壤系统分类目前已成为国际土壤分类的主流[14-15]。近年来我国在土壤系统分类领域发展迅速,取得了诸多成果[16-23]。重庆市对紫色土、冲积物发育土壤和中山区土壤已开展了相关工作[16-18],但未见更新统沉积物发育土壤的分类及耕作条件对其特性影响的相关研究。为此,本文探讨了耕作条件下重庆市几类更新统沉积物发育土壤的特性及分类,旨在推动重庆市土壤定量化分类的进程,为更深入地认识土壤演变机制及合理利用每一类土壤提供重要思路和理论依据。

1 材料与方法 1.1 研究区概况

重庆市地处四川盆地东部,属我国陆地地势第二级阶梯;全市大致可分为渝东北中山区、渝东南中山区、渝西方山丘陵区和中部平行岭谷区(低山、丘陵区)等4个地貌分区;全市属亚热带湿润季风气候,具有夏热冬暖、光热同季、湿润多阴、无霜期长、立体气候显著等特点;其年均气温为17.5℃,年均降水量为1 125 mm,年均相对湿度为80%,年均日照时数为1 000 h~1 400 h,日照百分率仅为25%~35%,为全国年日照最少的地区之一[16]。在重庆市境内,有多种更新统沉积物分布,其中,夹卵石黄色黏土和黄色黏土(两者俗称“老冲积物”)主要分布在嘉陵江及其主要支流两岸的高阶地上,红色黏土主要分布在秀山县境内的喀斯特平原及部分槽谷平坝上,另有极少量的黄土或黄土状土(巫山黄土)则仅零星分布于巫山县城一带[11],目前已基本被人造建筑物覆盖。夹卵石黄色黏土、黄色黏土和红色黏土是重庆市更新统沉积物中最为主要的3种分布类型,为此本文仅选取以上3种更新统沉积物发育的典型土壤为研究对象。在中国土壤发生分类中,夹卵石黄色黏土、黄色黏土和红色黏土等3种母质发育的典型旱地土壤分别为黄壤土类的卵石黄泥土、面黄泥土和红壤土类的黄红泥土3个土种,其发育的水田土壤分别为水稻土土类的卵石锈黄泥田、老冲积黄泥田和黄红泥田3个土种。

1.2 样品采集与分析

选择重庆市境内更新统沉积物出露且同时有旱地和水田的区域为采样区域,参照实际情况,控制水田与旱地的母质相同,之后选取旱地和水田的采样点。供试土壤的成土环境如表 1所示,所处海拔范围为189~395 m,其成土母质分别为夹卵石黄色黏土(PC)、黄色黏土(YC)和红色黏土(RC),剖面数字编号01为旱地,02为水田。其中,剖面PC01和PC02采于合川区境内的嘉陵江干流的高阶地上,剖面YC01和YC02采于铜梁区境内的嘉陵江主要支流涪江的高阶地上,剖面RC01和RC02采于秀山县喀斯特平原。上述6个供试土壤的土种归属分别为:卵石黄泥土(PC01)、卵石锈黄泥田(PC02)、面黄泥土(YC01)、老冲积黄泥田(YC02)、黄红泥土(RC01)和黄红泥田(RC02)。参照《野外土壤描述与采样手册》(简称《手册》)[24],挖掘标准土壤剖面,开展成土环境调查(表 1)、剖面形态观察、土壤比色[25]以及相关记录工作,分层采集土壤分析样,确定其测定指标[26]及方法:pH—水浸提法;土壤有机碳(SOC)—重铬酸钾-硫酸消化法;颗粒组成—吸管法;黏粒阳离子交换量(黏粒CEC)—NH4OAc(pH7.0)交换法;交换性盐基—NH4OAc(pH7.0)浸提,原子吸收光谱法和火焰光度法;全铁(Fet)—HF、HClO4酸溶比色法;游离氧化铁(Fed)—DCB浸提比色法;土壤矿物组成及黏土矿物含量—X射线衍射法。

表 1 供试土壤剖面的成土环境 Table 1 Soil-forming conditions of the tested soil profiles
2 结果 2.1 土壤形态特征

表 2可见,由供试PC发育土壤的剖面色调均为7.5YR,其中剖面PC01通体均一,明度为4~6,彩度为3~4,而剖面PC02的明度为5~7,水耕表层彩度为2~3,下层彩度为6,剖面YC01的色调为10YR,明度为5~7,耕作层彩度为4,下层彩度为6,而剖面YC02其水耕表层和Br1层的色调演化为2.5Y,下层色调为10YR,明度为5~7,水耕表层和Br1层彩度为4,下层彩度为6~8,剖面RC01的色调为5YR,通体均一,明度为4~7,彩度为6,而剖面RC02色调向10YR演化,明度为5~7,彩度为3~4;供试剖面PC01的砾石含量在耕作层为10%,下层为25%~60%,剖面PC02的砾石含量通体低于剖面PC01,耕作层为2%,下层为5%~10%;此外,6个供试土壤剖面均无亚铁反应;剖面PC01中无铁锰斑纹,剖面YC01除耕作层外均有铁锰斑纹,且剖面下部有少量铁管,剖面RC01除耕作层外有大量黏粒胶膜,而剖面PC02、YC02和RC02均有铁锰斑纹,且在水耕表层之下至少有一个土层存在灰色腐殖质-粉砂-黏粒胶膜;供试的旱地和水田土壤均为块状结构,且水田土壤逐渐演变为大块状结构,向棱柱状结构演化。

表 2 供试土壤的剖面形态特征和理化性质 Table 2 Morphological characteristics and physico-chemical properties of the tested soil profiles
2.2 土壤理化性质

表 2可见,供试的水田土壤Ap2层容重为Ap1层容重的1.13倍~1.39倍,而旱地土壤耕作层之下的土层其容重未明显增加。在6个供试土壤剖面中,剖面PC01的质地为壤土类,而剖面PC02为黏壤土类;剖面YC01为壤土类和黏壤土类,而剖面YC02为黏壤土类和黏土类;剖面RC01和RC02均为黏土类。此外,如图 1a所示,剖面PC01和YC01无黏粒淀积现象,剖面RC01的黏粒含量随土层深度增加而增加,且剖面中含有大量黏粒胶膜。

图 1 供试土壤剖面化学性质随土层深度的变化 Fig. 1 Changes in soil chemical properties with depth in the tested soil profiles

图 1b所示,剖面PC01和YC01的盐基饱和度均随深度先增大后减小,剖面PC02和YC02均在Br2及其下层的盐基饱和度明显高于上层,剖面RC01的盐基饱和度随深度先减小后增大再减小,有复盐基化的趋势,剖面RC02在25~75 cm处的盐基饱和度明显高于上层和下层,故更新统沉积物的旱地土壤表层盐基淋失淀积于剖面中部,而PC和YC的水田土壤其盐基淋失淀积于剖面下部,RC的水田土壤其盐基淋失淀积于剖面中部。如图 1c所示,剖面PC01和RC01的黏粒CEC含量变化较均一,剖面YC01内部变异较大,而水田剖面黏粒CEC含量内部变异大,在耕作层下部会出现一个极低值。供试的更新统沉积物发育的土壤的全铁含量在34.98~103.20 g·kg-1之间,游离氧化铁含量在15.35~69.34 g·kg-1之间,3种更新统沉积物发育土壤的全铁含量RC>YC>PC。如图 1e所示,剖面PC01的游离氧化铁含量内部变异小,剖面PC02在Br1(28~45 cm)及下层的游离氧化铁含量明显高于上层;剖面YC01的游离氧化铁含量在Br3(70~82 cm)及下层明显低于上层,剖面YC02在Br2(47~75 cm)及下层的游离氧化铁含量明显高于上层,剖面RC01和RC02的游离氧化铁含量内部变异小。如图 1d图 1e所示,供试土壤的全铁含量变化趋势与游离氧化铁含量十分相似,这表明重庆市更新统沉积物发育土壤的游离氧化铁对全铁的贡献大于硅酸盐铁。如图 1f所示,剖面PC01的铁游离度内部变异均一,而剖面PC02的Br1(28~45 cm)及下层的铁游离度明显高于上层;剖面YC01的铁游离度在Br3(70~82 cm)及下层明显低于上层,而剖面YC02的Br4(47~75 cm)及下层的铁游离度明显高于上层;剖面RC01和RC02的铁游离度随深度的变异不大,剖面RC01的铁游离度高于剖面RC02。

2.3 土壤系统分类 2.3.1 诊断层和诊断特性

表 4可知,根据《中国土壤系统分类检索(第三版)》[15](简称《检索》)对6个供试土壤剖面的成土条件和各项指标进行检索,共鉴定出1个诊断表层、3个诊断表下层和4个诊断特性。结果如下:诊断层有:(1)水耕表层:剖面PC02、YC02和RC02在淹水耕作条件下符合水耕表层的检索条件。(2)雏形层:剖面PC01和YC01在风化成土过程中形成的无或基本上无物质的淀积,有结构发育的B层,符合雏形层的鉴定条件。(3)水耕氧化还原层:剖面PC02、YC02和RC02符合水耕氧化还原层的检索条件。(4)黏化层:依照黏化层的鉴定条件[15],剖面RC01由黏粒的淋溶淀积所形成的黏化层。诊断特性有:(1)土壤水分状况:剖面PC01、YC01和RC01年干燥度 < 1,为湿润土壤水分状况;剖面PC02、YC02和RC02在耕作条件下,耕作层被灌溉水饱和,符合人为滞水土壤水分状况。(2)氧化还原特征:剖面PC02、YC01、YC02、RC01和RC02均有铁锰锈斑纹,符合氧化还原特征。(3)土壤温度状况:本文中各剖面土壤年平均土温位于15~22℃之间,符合热性土壤温度状况。(4)铁质特性:剖面PC02、YC01、YC02、RC01和RC02的整个B层部分DCB浸提游离氧化铁≥20 g·kg-1,符合铁质特性。

表 4 供试土壤的系统分类归属 Table 4 Attribution of the tested soils in the Chinese Soil Taxonomy
2.3.2 系统分类单元归属

根据供试土壤的诊断层和诊断特性(表 3),依照《检索》[15]划分其系统分类高级单元(表 4),再依据“中国土壤系统分类土族和土系划分标准”[27]确定供试土壤的控制层段,选择供试土壤土族控制层段的鉴别特征—颗粒大小级别、矿物学类型、石灰性和酸碱反应类别和土壤温度等级(表 5),通过比土、评土,最后确立典型土壤个体的基层分类单元(土族-土系)。矿物组成分析表明,RC01土族控制层段黏粒部分的高岭石及其他非膨胀的2:1型层状矿物含量> 50%,但其非膨胀的2:1型层状矿物(伊利石)含量要明显高于高岭石含量,故其矿物学类型被定为伊利石混合型,而不是高岭石型;RC02土族控制层段黏粒部分的高岭石及其他非膨胀的2:1型层状矿物(伊利石)含量> 50%,且其非膨胀的2:1型层状矿物(伊利石)低于高岭石含量,故其矿物学类型被定为高岭石型。依据供试土壤的土族鉴别特征(表 4),可建立6个土族,其中PC01为粗骨壤质硅质型非酸性热性-普通简育湿润雏形土,PC02为黏壤质硅质混合型非酸性热性-普通铁聚水耕人为土,YC01为黏壤质硅质混合型非酸性热性-普通铁质湿润雏形土,YC02为黏质伊利石混合型非酸性热性-普通铁聚水耕人为土,RC01为极黏质伊利石混合型酸性热性-红色铁质湿润淋溶土,RC02为黏质高岭石型非酸性热性-普通简育水耕人为土;每个土族仅对应1个典型土壤个体,故可建立6个土系(表 4)。

表 3 供试土壤的诊断层和诊断特性 Table 3 Diagnostic horizons and diagnostic characteristics of the tested soils

表 5 供试土壤的土族鉴别特征 Table 5 Soil family characteristics of the tested soils
3 讨论 3.1 沉积物特征对更新统沉积物发育土壤特性及类型的影响

虽然3种供试母质均为更新统沉积物,但不同类型沉积物的物质来源、分布位置、颗粒组成、颜色以及其他理化性质等存在明显差异。第二次土壤普查资料认为PC和YC母质系更新统冰水沉积物[28, 29],较之PC母质,供试的YC母质样点海拔较低,位于涪江下游沿岸阶地的较平缓地段,可能是因沿河搬运距离的延长导致流水挟砾能力的下降,使得其以黏土等细颗粒物质沉积为主而无卵石分布;此外,两者间的砾石含量差异也可能与沉积相不同有关,PC母质可能是古河床相沉积,富含卵石和其他粗颗粒物质[1, 11],而YC母质可能是古河漫滩相沉积,受古河流分选作用的影响,该沉积物以粒径较小的黏土类物质为主,故无卵石存在。PC发育的土壤砾石含量很高、透水性较好,不易形成水分饱和且呈还原状态的土壤层次或区域,土体内的铁锰氧化物难以发生还原迁移和再氧化,使得土壤结构体面上无明显铁锰斑纹存在;与PC母质发育的土壤相比,YC母质发育的土壤更黏、透水性较差,受古水文条件(如地下水位等)的影响,土体内易出现水分饱和并呈还原状态的土壤水分状况—潮湿土壤水分状况,故使其发育的旱地土壤剖面上有明显的铁锰斑纹和少量铁管存在。然而,受新构造运动的影响,河流不断下切,使老冲积物(PC和YC母质)的分布位置由河床和河漫滩逐渐演变为高阶地,其发育的土壤已完全脱离了现代地下水的影响,YC母质发育的土壤已不再具有潮湿土壤水分状况,其土体内存在的铁锰斑纹和铁管仅仅是其古水文条件或古土壤水分状况的反映,因此本文将剖面YC01归为普通铁质湿润雏形土亚类。在重庆市境内,更新统沉积物RC母质则主要是由石灰岩风化发育而成,在湿热的气候条件下,经溶蚀、冲积、洪积等作用后,最终堆积于秀山县境内的喀斯特平原或槽谷区域[1, 11, 28],在地势较低或汇水区域(如水田),其发育的土壤复盐基作用较为明显,这使得水田土壤的pH明显高于旱地土壤(图 1b);RC母质富含黏粒,其发育的土壤质地黏重,加上所处地域的降雨量较为丰富[13],导致该类母质发育的旱地土体中水分向下运动频繁,使得其耕作层以下土体内出现了明显的黏粒淀积;受RC母质的游离氧化铁含量及其色调的影响,其发育的旱地土壤游离铁含量较高,且色调较老冲积物(PC和YC母质)发育的旱地土壤更红,一般为5YR且在140 cm深度范围内明度和色度的变异较小,故被划归为红色铁质湿润淋溶土亚类。

3.2 人类活动对更新统沉积物发育土壤特性及类型的影响

人类活动使3种更新统沉积物发育土壤的特性及分类存在明显差异,PC和YC发育的水田土壤其上部彩度降低,结合表 2可知,彩度降低的土层较旱地土壤更厚,这类土层有机碳含量较下部土层更高,游离氧化铁和全铁含量较下部土层更低,这可能是水耕作用使得其长期处于淹水厌氧状态,有机碳易在土壤表层积累后向下迁移,且土壤上部游离氧化铁被还原为低价铁,随水向下淋溶淀积于土壤下层。因此,表层有机碳积累并向下迁移以及铁元素淋溶共同导致PC和YC发育的水田土壤上部彩度降低,由此可通过抛荒土壤上部土层彩度降低的厚薄来判断PC和YC发育土壤从前的耕作条件,这与已有的研究结果一致[30-33]。此外,人类活动会导致PC发育的水田土壤其砾石含量低于旱地土壤,原因如下:(1)造田时人为筛选卵石含量相对较低的地块进行开垦;(2)该类型土壤分布于高阶地上,在坡改梯、挖高填低形成梯田和后期水耕的过程中,人为拣拾较深土层的卵石(笔者调查与推测至少为1 m),才能使水田形成滞水层。故PC01的颗粒大小级别为粗骨壤质,PC02的颗粒大小级别为黏壤质。剖面PC02的Br1层砾石含量较高,是因为最初耕作时耕作层的卵石被压在犁底层,犁底层容重增加(表 2),后期在水耕过程中,受周围土壤的淤积作用,耕作层变深,犁底层上升,之前的犁底层变为Br1层。

在老冲积物(PC和YC)发育的水田土壤其下层的游离氧化铁含量和铁游离度明显高于上层,而在红色黏土RC发育的水田土壤其游离氧化铁含量和铁游离度的内部变异较小,故水耕作用使得PC和YC发育的水田土壤其游离氧化铁在剖面上部被还原为低价铁,向下淋溶淀积于土壤下层,在耕作层以下发生游离氧化铁聚积,故被划归为普通铁聚水耕人为土;而RC的水田土壤由于所处地形部位和耕作时间影响,在人为水耕作用下其游离氧化铁聚积均不明显,故被划归为普通简育水耕人为土。剖面RC01的矿物学类型为伊利石混合型,剖面RC02的矿物学类型为高岭石型,原因如下:(1)该类沉积物的矿物分布不均匀;(2)水耕作用会导致RC发育的水田土壤其次生矿物伊利石等缓慢脱盐基而逐步减少[34]。由表 2图 1b可见,剖面R C01的pH较低,盐基饱和度较低,RC02的pH较高,盐基饱和度较高,是由于RC发育的旱地土壤在复盐基作用后风化溶蚀过程中淋失较多盐基离子,而其水田土壤在水耕作用下,复盐基化持续发生,故剖面RC01的石灰性和酸碱反应类别为酸性,RC02的石灰性和酸碱反应类别为非酸性。

4 结论

在重庆市境内,夹卵石黄色黏土(PC)、黄色黏土(YC)和红色黏土(RC)等3种更新统沉积物发育的典型旱地土壤分别归为普通简育湿润雏形土、普通铁质湿润雏形土和红色铁质湿润淋溶土3个亚类,老冲积物(PC和YC)和红色黏土(RC)发育的典型水田土壤则分别归为普通铁聚水耕人为土和普通简育水耕人为土2个亚类。YC发育的普通铁质湿润雏形土有铁锰斑纹存在,这是其古水文条件的反映,现已完全脱离地下水的影响,故不具有潮湿土壤水分状况;沉积物特征、区域气候等会影响旱地土体内黏粒的淋溶淀积,进而影响其土纲划分,使得PC和YC发育的旱地土壤划分为雏形土,RC发育的旱地土壤为划分为淋溶土;水耕活动使更新统沉积物发育的雏形土和淋溶土演变为水耕人为土;地块筛选、坡改梯、拣拾等人为活动会使得PC发育的水田土体内砾石含量较低,影响其土族控制层段的颗粒大小级别判定。

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HU Jin , CI En , WANG Shufang , LIAN Maoshan , WENG Haolu , CHEN Lin     
College of Resources and Environment, Southwest University, Chongqing 400715, China
Abstract: 【Objective】 It is of great significance to explore genetic characteristics and evolution laws of the soils derived from Pleistocene sediments to the study of geological evolution and ancient climate change and the management of the soil resources. Chongqing is a region dominated by mountains and hills, and hence known as "Mountain City", where the soil layer is thin, except for the soils derived from Pleistocene sediments, which are often quite thick in soil layer and hence high in land utilization rate, so it is the important agricultural resource of Chongqing. However, so far little has been reported on genetic characteristics and classification of the soils and effects of cultivation on evolution of their properties. Therefore, this paper addressed the issue in an attempt to promote development of quantitative classification of the soils, to provide certain theoretic bases and important ideas for rational utilization of the soils, relative to soil type.【Method】 Field soil surveys were conducted to specify six soil profiles, 3 upland soils and 3 paddy soils, derived from Pleistocene sediments of pebble-mixed yellow clay (PC), yellow clay (YC) and red clay (RC), of which soil morphological characteristics were obtained through investigations of their soil-forming environments. PC and YC (commonly known as old alluvial sediments) are mainly distributed on the high terraces on both sides of the Jialing River and its main tributaries, and RC mainly on the karst plains and some valleys in Xiushan County. Soil samples were collected from the profiles by horizon for analysis of physico-chemical properties. Based on the comparative analysis, genetic characteristics and classification of the soils relative to cultivation mode were discussed, and diagnostic horizons and diagnostic characteristics of the soils were determined, and the soils were attributed and named in CST level by level in the light of the "Chinese Soil Taxonomy (3rd ed.)".【Result】 The upland soil derived from PC was found to have a lot of gravels but no iron-manganese speckles or stripes, while that derived from YC was found to be in a reverse condition and that derived from RC to have apparent clay deposition right beneath the plow layer. In the profiles of paddy soils derived from PC and YC, organic matter accumulation was obvious in the upper part, while iron oxide accumulation was in the lower part, so the upper part was lowery the lower part in chroma. However in the paddy soil derived from RC, migration of iron oxide was not as obvious. The 3 upland soils were sorted into 3 subgroups, i.e. Typic Hapli-Udic Cambosols, Typic Ferri-Udic Cambosols and Red Ferri -Udic Argosols, and further into 3 soil families, i.e. Coarse bone loamy silica non-acid thermic -Typic Hapli-Udic Cambosols, Clay loamy silica mixture non-acid thermic-Typic Ferri-Udic Cambosols and Heavy clayey illitic mixture acid thermic-Red Ferri-Udic Argosols, separately. The 3 paddy soils were sorted into 2 subgroups, i.e. Typic Fe-accumuli-Stagnic Anthrosols and Typic Hapli-Stagnic Anthrosols, and further into 3 soil families, i.e. Clay loamy silica mixture non-acid thermic-Typic Fe-accumuli-Stagnic Anthrosols, Clayey illitic mixture non-acid thermic-Typic Fe-accumuli-Stagnic Anthrosols and Clayey kaolinitic non-acid thermic-Typic Hapli-Stagnic Anthrosols, separately. The six soils formed 6 soil series in total.【Conclusion】 The soils derived from YC have iron-manganese speckles or stripes, which are reflections of paleo-hydrological conditions, but now they are completely free from the influence of groundwater and no longer were the aquic soil moisture regime. The characteristics of sediments and regional climate do have some impact on clay deposition in the upland soils, thus affecting their classification on the soil order level. Long-term paddy cultivation would transform Cambosols and Argosols derived from Pleistocene sediments into Stagnic Anthrosols. Artificial activities, such as field screening, changing slopes into terraces, gathering pebbles et al, would reduce gravel content in the paddy soil derived from PC, which would in turn influence particle-size fractionation of the soil layers controlled by soil family.
Key words: Pleistocene Sediments    Cultivation conditions    Genetic Characteristics    Chinese soil taxonomy    Chongqing