海南岛北部玄武岩区土壤母质均一性及相对年龄判定

【目的】时间序列法是定量研究土壤发生过程、演变速率及其变化阈值的重要手段,构建可靠的土壤时间序列需对土壤母质均一性和相对年龄进行判定。【方法】以海南岛北部不同喷发期玄武岩发育土壤所构成的成土时间序列（0.09、0.146、0.64、1.12、1.81、2.30 Ma B. P.）为对象,利用各种土壤属性参数（包括剖面形态、颗粒组成、稳定元素含量、风化发育指数和元素变化率等）对该时间序列母质均一性和土壤相对年龄进行判定。【结果】各剖面颜色、质地、结构等形态总体呈均一、渐变的特征,去除黏粒后的粗粉粒含量、稳定元素Ti/Zr比值在剖面内和剖面间变化均较小,表明时间序列土壤的起源母质相同。随着成土年龄的增加,黏粒含量和剖面发育指数呈线性增加的趋势,土壤风化强度指标（B指数、CIW指数、CIA指数和ba值）服从对数函数变化规律,在土壤相对年龄的判定中具有较好的指示意义。【结论】研究区土壤母质来源相同,土壤相对年龄可通过相关土壤属性体现出来,为定量研究土壤发生阈值奠定了基础。     

土壤时间序列的构建及其在土壤发生研究中的意义

土壤时间序列在研究土壤演化速率与方向、建立土壤发生演化模型上具有重要的价值,并且能为土壤发生学理论的验证提供宝贵的信息。为了获得可靠的结果,时间序列的构建必须包括剖面内与剖面间母质均一性或母质不连续性的判定以及土壤的绝对或相对年龄的判定这两个重要过程。本文综述了土壤时间序列的类型及其构建方式,详细论述了在时间序列建立过程中母质不连续性的判定方式与土壤定年方法,并阐明了土壤时间序列方法在土壤发生研究中的重要意义,旨在为正确建立土壤时间序列、深刻理解土壤发生中的时间因素提供较为详尽的参考。     

新嵊盆地玄武岩发育土壤的母质均一性判定

成土母质的均一性判定是土壤发生研究的必要起点,也是构建土壤时间序列和评价土壤质量变化的先决条件。选取浙江省新嵊盆地典型玄武岩发育土壤剖面为研究对象,采用土壤地理学和元素地球化学方法,通过对土壤剖面的形态特征、颗粒组成、母质不连续性系数、稳定元素Ti与Zr比值以及稀土元素分布模式等指标的分析,进行不同土壤剖面母质均一性的判定。研究结果表明,土壤颜色、结构、根系等土壤剖面形态自下而上呈现均一、渐变特性特征,且所有剖面没有发现异源堆积特征,可以初步直观判定研究剖面的母质均一性;土壤颗粒组成及扣除黏粒后的粗粉粒/中粉粒含量等指标都比较均一,并沿剖面垂直方向呈现较好的渐变趋势;Ti/Zr比值和稀土元素配分模式在不同层次间的分布也没有明显的差异;母质均一性系数均介于?0.6 ~ 0.6之间。因此,研究剖面内与剖面间母质来源相同。     

热带地区玄武岩发育时间序列土壤中石英颗粒微形态特征

利用扫描电镜研究了热带地区雷州半岛和琼北地区不同年代喷发的玄武岩上发育的时间序列土壤中石英颗粒的表面形态特征,结果表明:①同一剖面中表层土壤中石英的风化程度相对较大。②从新成土到铁铝土阶段(0.01~1.33 Ma),石英颗粒表面风化程度逐渐加深,机械作用形成的特征完全消失。成土时间较长的铁铝土(6.12 Ma)中石英颗粒出现裂解现象。③本研究一方面证实Darmody评估方法在研究我国热带地区土壤石英颗粒表面风化程度的可行性,同时也说明在相同母质和环境条件下发育的土壤中,石英颗粒表面的风化状况在一定程度上可以指示土壤的相对发育程度。     

辽宁省白浆化土壤中白土层的特征及其形成

本文以辽宁省浑河在不同历史时期形成的阶地上的黄土状物质发育的土壤为研究对象,通过对剖面形态学特征、基本理化性质和母质均一性判定等研究,探讨了浑河三级阶地白浆化土壤的白土层特征及其形成机制。结果显示:(1)土壤粉粒中的稳定元素钛与锆分析结果表明在三级阶地上的21-003、21-009、07和21-076剖面和二级阶地上的21-001、21-200、03和04剖面的母质均一;(2)由于土体发育程度不同,一级阶地土体中无淀积层;二级阶地土体中有淀积层且无白土层,尚未出现白浆化现象;三级阶地土体中淀积层和白浆化现象明显,出现了白土层,其形成以黏粒的机械淋溶和潴育淋溶为主;三级阶地上土壤比二级阶地和一级阶地发育时间长,但尚未达到漂白层的标准。     

湘北地区典型水稻土的发生特性及其在中国土壤系统分类中的归属

选取湘北地区7个发育于2种母质的水稻土剖面样点,通过对其成土环境、剖面形态特征以及土壤理化性质进行野外观测和室内分析,按中国土壤系统分类方案,检索出诊断层和诊断特性,确定其在中国土壤系统分类中的归属,并评述土系的生产性能。结果表明:供试水稻土归属于水耕人为土亚纲下的简育和铁聚水耕人为土2个土类,底潜简育水耕人为土、普通简育水耕人为土、普通铁聚水耕人为土、漂白铁聚水耕人为土4个亚类;进一步按照土族和土系划分标准,划分出7个土族和7个土系。在相同成土环境下,同种母质发育的水耕人为土,土壤系统分类比土壤发生分类具有更强的划分能力。其划分的基层土壤单元(土族和土系),对农业生产、土地资源利用更具有指导意义。     

太湖地区水耕人为土中漂白层的成因探讨

采集太湖地区4个具有漂白层的水耕人为土剖面(E-A1、E-A2、E-A3、E-A4)及1个发育于相同母质上的一般水耕人为土剖面作为参照(Ref),描述了土壤剖面的形态特征,分析了土壤颗粒组成、黏粒矿物组成、铁氧化物以及大量和微量元素等,并探讨了漂白层成因。5个剖面土壤颗粒组成以粉粒为主,在60%~75%之间,且剖面中各层次变异系数较小,小于10%;大量元素和微量元素在剖面各层次间变异系数也小于10%,指示漂白层与上覆和下伏土层发育在相似物质来源的土壤母质上;而E-A1剖面漂白层中较高的粉粒含量(75.04%)、较大的中细粉粒和中细粉粒/粗粉粒比值的变异系数(38.05%、61.85%)表明该剖面母质具有不均一性。说明E-A2、E-A3、E-A4、Ref剖面土壤性质的变化主要是由于成土作用形成的,而E-A1剖面土壤的性质变化除受成土作用影响外,还受沉积环境的影响。E-A2、E-A3、E-A4剖面的漂白层中蒙脱石和蛭石、粉粒和粗粉粒、SiO2、CaO、Zr等含量高于上下土层,而水云母和绿泥石、游离铁、Al2O3、Rb、Li、Ba、稀土元素(Rare earth element,REE)等则相反;同时,参照剖面亦有与E-A2、E-A3、E-A4剖面类似的特点,只是漂白作用出现在耕作层,不能定义为漂白层;而E-A1剖面的部分性质则显示出空间上的不一致性,其粉粒含量并非漂白层最高,而是随剖面土层深度向下越来越大。这些变异表明,太湖地区水耕人为土漂白层的形成,可以由黄土性泻湖相沉积物经过水耕过程中水分的周期性淹水和排干,通过机械淋洗和活性铁的淋溶而形成(剖面E-A2、E-A3、E-A4),也可以是母质沉积的过程中受湖水水面升降,导致机械淋溶,然后水耕过程叠加活性铁的淋溶而形成(剖面E-A1)。     

红壤性水稻土稀土元素组分分布与变异性研究

测定了具有代表性的 4种母质发育、3种水育型的红壤性水稻土及起源土壤的∑REE、∑LREE和∑HREE ,分析了其分布特点和剖面变异性 ,表明 :(1)红壤性水稻土的∑REE平均水平和离散性均大于全国水稻土平均水平 :(2 )不同母质发育的供试土壤的∑REE和∑LREE的平均水平依玄武岩母质土壤系列 >石英闪长岩母质土壤系列 >黑云母花岗岩母质土壤系列 >凝灰岩母质土壤系列顺序递减 ;(3 )土壤剖面稀土组分体系的变异程度为 :∑LREE >∑HREE >∑REE ;而在不同水育类型上则依起源土壤、潜育型水稻土、渗育型水稻土、潴育型水稻土顺序增大。 (4 )∑LREE和∑HREE在渗育型水稻土的E层和潴育型水稻土的Br层具有显著的分馏作用     

南方丘陵区不同母质水耕人为土发育速率的比较

如何度量水耕人为土的发育程度和发育速率是土壤发生学的一个难题。选择南方丘陵区3种常见母质(紫色砂页岩类坡积物PS、第四纪红黏土RC和红砂岩类坡积物RS)发育的水耕人为土时间序列作为研究对象,尝试利用属性距离和土壤发育指数来表征水耕人为土的发育程度,揭示母质对水耕人为土发育速率的影响。结果表明,水耕人为土剖面形态特征经定量后和属性距离一样能够表征水耕人为土发育的时间趋势,在指示水耕人为土的发育程度和估算发育速率上有重要意义。有机碳(SOC)、pH、黏粒含量和磁化率(MS)在计算发生层距离(HD)中贡献很大,而土壤颜色和湿结持性在计算发生层指数(HI)中起着重要作用。RC母质的土壤,土层较厚,颜色红,黏粒含量较高,保肥和保水状况好,土粒的黏结性和可塑性较好,SOC容易累积,发育速率最快。PS母质的土壤,土层较厚,细颗粒(黏粒+细粉粒,0.01mm)含量高,保肥和保水状况好,土粒有一定的黏结性和可塑性,SOC容易累积,发育速率次之。RS母质的土壤,黏粒和细颗粒含量均很低,土层薄,保肥和保水状况以及黏结性和可塑性差,SOC很难累积,发育速率最慢。母质对水耕人为土发育过程的影响可以通过影响其发育速率表现出来。研究同时显示,水耕人为土平均发育速率远较自然土壤快,并在人为培育下快速定向发育。但随着种稻年限的增加,水耕人为土的发育速率普遍下降,水耕人为土发育速率和成土年龄的关系大致符合对数关系。这种定量方法可以提高对水耕人为土形成过程的理解并能实现不同地区水耕人为发育速率的定量比较,有较好的使用前景。但此方法仍处于试验探讨阶段,有待更多的研究来验证和改进。     

绰墩山遗址古水稻土的一些微生物学特性研究

在江苏绰墩山遗址考古发掘中,发现了在剖面不同深度埋藏的距今约6 500 a的史前古水稻田土层(100~200 cm)和距今约3 320 a的商周时期的古水稻田土层(42~100 cm)。本研究为了解古水稻土的生物学性状及其与现代水稻土的差别,以土壤剖面P-01(包含史前古水稻土和商周时期古水稻土)与P-03(仅含商周时期古水稻土)为对象,利用土壤厌氧培养、Biolog分析和广古生菌界16S rDNA的V3区的PCR-DGGE分析,初步研究了不同土层厌氧微生物多样性、产甲烷潜势以及产甲烷古菌群落多样性的变化。结果表明,史前古水稻土仍有较多厌氧微生物存活,可达7.0×105cfu g-1干土,并且其单一碳源利用能力和多样性也显著高于其湖相沉积母质和相同时期的非水稻土(黄土母质)。与现代水稻土相比,古水稻土仅存留了很微弱的产甲烷潜势。但史前古水稻土比同期非水稻土和商周时期古水稻土的产甲烷潜势较高。PCR-DGGE结果显示,水稻土层都有其区别于非水稻土层的产甲烷古菌群落结构,而现代水稻土、商周时期古水稻土和史前古水稻土也各有不同的优势产甲烷古菌种群,不同时期的水稻耕作方式是造成这种差异的可能的重要原因之一。     

红壤稻田土壤理化及生物学性状的动态变化特征

Rice production plays a crucial role in the food supply of China and a better understanding of the changes in paddy soil fertility and the management effects is of practical importance for increasing rice productivity. In this study, field sampling in a typical red soil region of subtropical China, Jiangxi Province, was used to observe changes in the soil physical, chemical, and biological properties in a cultivation chronosequence of paddy fields. After cultivation, clay (< 0.002 mm) content in the soil, which was 39% in the original uncultivated wasteland, decreased, to 17% in the 80-year paddy field, while silt (0.02--0.002 mm) content increased. Additionally, macroporosity increased and pore shapes became more homogeneous. Soil Ph generally increased. Soil organic C and total N content of the 0-10 cm layer increased from 4.58 and 0.39 g kg-1 to 19.6 and 1.62 g kg-1, respectively in the paddy fields after 30-year cultivation and then remained stable. Soil total P content increased from 0.5 to 1.3 g kg-1 after 3 years of rice cultivation, indicating that application of phosphate fertilizer could accelerate phosphorous accumulation in the soil. Total K content in the 0--10 cm soil layer for the 80-year paddy fields decreased by 28% compared to that of the uncultivated wasteland land. Total Fe and free Fe contents declined with years of cultivation. The bacterial population increased and urease activity noticeably intensified after years of cultivation. In this chronosequence it appeared that it took 30 years to increase soil fertility to a relatively constant value that was seen after 80 years of cultivation.     

Organic carbon accumulation in a 2000-year chronosequence of paddy soil evolution

Considerable amounts of soil organic matter (SOM) are stabilized in paddy soils, and thus a large proportion of the terrestrial carbon is conserved in wetland rice soils. Nonetheless, the mechanisms for stabilization of organic carbon (OC) in paddy soils are largely unknown. Based on a chronosequence derived from marine sediments, the objectives of this study are to investigate the accumulation of OC and the concurrent loss of inorganic carbon (IC) and to identify the role of the soil fractions for the stabilization of OC with increasing duration of paddy soil management. A chronosequence of six age groups of paddy soil formation was chosen in the Zhejiang Province (PR China), ranging from 50 to 2000 years (yrs) of paddy management. Soil samples obtained from horizontal sampling of three soil profiles within each age group were analyzed for bulk density (BD), OC as well as IC concentrations, OC stocks of bulk soil and the OC contributions to the bulk soil of the particle size fractions. Paddy soils are characterized by relatively low bulk densities in the puddled topsoil horizons (1.0 and 1.2 g cm^− 3) and high values in the plow pan (1.6 g cm^− 3). Our results demonstrate a substantial loss of carbonates during soil formation, as the upper 20 cm were free of carbonates in 100-year-old paddy soils, but carbonate removal from the entire soil profile required almost 700 yrs of rice cultivation. We observed an increase of topsoil OC stocks from 2.5 to 4.4 kg m^− 2 during 50 to 2000 yrs of paddy management. The OC accumulation in the bulk soil was dominated by the silt- and clay-sized fractions. The silt fraction showed a high accretion of OC and seems to be an important long-term OC sink during soil evolution. Fine clay in the puddled topsoil horizon was already saturated and the highest storage capacity for OC was calculated for coarse clay. With longer paddy management, the fractions < 20 μm showed an increasing actual OC saturation level, but did not reach the calculated potential storage capacity.     

Assessing parent material uniformity of a red and black soil complex in the landscapes

The distribution of red and black soil (Xeralfs–Xerolls) associations in the Monarto area (South Australia) is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known. The objectives of this study were (i) to assess Zr- and Ti-bearing grains as minerals resistant to chemical weathering prior to employing Zr and Ti in determining parent material uniformity, and (ii) to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) were used to study chemical weathering and elemental composition of surfaces of Zr- and Ti-bearing grains. X-ray fluorescence (XRF) analysis was used to determine elemental concentrations in various soil fractions. Results showed that Zr-bearing grains consisted of only zircon having smooth clean surfaces, which are characteristic of a mineral resistant to chemical weathering. EDAX spectra confirmed that Zr was a specific element to represent zircon, suggesting its reliability to be used in assessing parent material uniformity. On the other hand, Ti derived not only from minerals (rutile/anatase) resistant but also from minerals (ilmenite/pseudorutile, biotite) susceptible to chemical weathering. This limited the usefulness of Ti as an index mineral for soil development studies. Except for Zr:Ti ratio, all other indicators of parent material uniformity, i.e., depth distribution curves of Zr and Y in various fractions and Y:Zr ratio showed no considerable inflection and variation with depth in a Xeralf (red soil). This indicated the Xeralf derived from a uniform parent material (mica schists), thereby texture contrast within a profile is due to pedological processes. On the other hand, depth distribution curves showed clear inflection and variation in Xerolls (black soils), indicating soils developed from lithologic discontinuities, so different trends in particle size fractions between 0–48 cm for MA5 and 0–59 cm for MA3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis. The presence of complex red and black soil association in the landscape is attributed to the difference in parent materials, where the red soil developed from mica schist and the black soils from calcareous deposits.     

Genesis of a So-called Ferrolysed Soil of Bangladesh

It was postulated by Brinkman (1970) that low clay contents in the surface horizon of paddy soils (Planosols) are caused by clay destruction through ferrolysis. In an effort to test this, a rice profile from the site of Brinkman's Eutric Planosol (Salna, Bangladesh) and a neighbouring forest soil (Dystric Cambisol) of the same parent material and particle-size distribution (Bhawal National Park) were investigated. The micro-structure, particle-size distribution, mineral contents, pedogenic oxides, contents of Zr, Ti and K of the fine earth and individual fractions and also the exchangeable ions were studied. The clay fraction of both soils were chloritised by interlaying of hydroxy-Al in the smectite interlayers in the surface horizons and got stabilized. As a result CEC showed some decrease. The forest profile has a loose and uniform brown-yellow surface horizon and is relatively rich in coarse sand at 62–75 cm depth which might be caused by a strong termite activity as observed during sampling. On the contrary, the frequent and alternate reducing and oxidizing conditions have resulted in gleying the top soil and forming iron-oxide films on the surface of aggregates during dry periods in the paddy soil. An evaluation of all results shows that a little clay destruction and an enrichment of silt in the top soil through vertisol formation and also through primary parent material stratification were the reasons for low clay content in epipedons. In forest soil there was a little clay migration, while the epipedon of the paddy soil had low clay in addition, because of selective erosion during heavy rains following the destruction of structure by puddling. The ferrolysis as a dominant factor for a clay-low epipedon is improbable, because the clay loss of the neighbouring forest soil can not be explained by ferrolysis.     

Soil texture affects soil microbial and structural recovery during grassland restoration

Many biotic and abiotic factors influence recovery of soil communities following prolonged disturbance. We investigated the role of soil texture in the recovery of soil microbial community structure and changes in microbial stress, as indexed by phospholipid fatty acid (PLFA) profiles, using two chronosequences of grasslands restored from 0 to 19 years on silty clay loam and loamy fine sand soils in Nebraska, USA. All restorations were formerly cultivated fields seeded to native warm-season grasses through the USDA’s Conservation Reserve Program. Increases in many PLFA concentrations occurred across the silty clay loam chronosequence including total PLFA biomass, richness, fungi, arbuscular mycorrhizal fungi, Gram-positive bacteria, Gram-negative bacteria, and actinomycetes. Ratios of saturated:monounsaturated and iso:anteiso PLFAs decreased across the silty clay loam chronosequence indicating reduction in nutrient stress of the microbial community as grassland established. Multivariate analysis of entire PLFA profiles across the silty clay loam chronosequence showed recovery of microbial community structure on the trajectory toward native prairie. Conversely, no microbial groups exhibited a directional change across the loamy fine sand chronosequence. Changes in soil structure were also only observed across the silty clay loam chronosequence. Aggregate mean weighted diameter (MWD) exhibited an exponential rise to maximum resulting from an exponential rise to maximum in the proportion of large macroaggregates (>2000 μm) and exponential decay in microaggregates (<250 μm and >53 μm) and the silt and clay fraction (<53 μm). Across both chronosequences, MWD was highly correlated with total PLFA biomass and the biomass of many microbial groups. Strong correlations between many PLFA groups and the MWD of aggregates underscore the interdependence between the recovery of soil microbial communities and soil structure that may explain more variation than time for some soils (i.e., loamy fine sand). This study demonstrates that soil microbial responses to grassland restoration are modulated by soil texture with implications for estimating the true capacity of restoration efforts to rehabilitate ecosystem functions.     

水耕年限对黄棕壤发育的水稻土的表面化学性质的影响

利用采自江苏省农业科学院果园的旱地黄棕壤(对照)和由黄棕壤发育水耕20年和60年的水稻土,研究了土壤黏粒和粉粒的矿物组成,胶体和土体的化学性质随水耕年限的变化.粉粒的X-射线衍射图谱表明,3种供试土壤发育母质相似,胶体的矿物组成随水耕年限的变化不大.动电电位和表面负电荷的测定结果也表明,胶体表面化学性质未发生明显变化.随水耕年限增加,土壤黏粒含量降低,导致土体性质发生明显变化,土壤CEC和结构电荷量随水耕年限增加显著减少.     

Fine silt and clay mineralogical changes of a soil chronosequence in the Langtang valley (Central Nepal)

Chemical and mineralogical properties of a soil chronosequence in the high mountain zone between 3857 m and 4120 m a.s.l. in Central Nepal (Langtang valley) are presented. The soils have been developed in moraine deposits which consist of acid gneisses. They were classified as Entisols, and Spodosols. XRD analyses of the clay and fine silt fraction show increasing changes with distance from the recent Lirung glacier, depending on the time of deposition, resp. soil age. Alteration of illite to interstratified minerals and to hydroxy-Al interlayered minerals or pedogenic chlorite with increasing soil development could be observed. The interstratified minerals could be identified as random and regular illite-interlayered vermiculite mixed-layer minerals. Intensification of the X-ray signals of the fine silt fraction is given compared to the clay. With increasing soil development differences between the clay and fine silt fraction seem to increase. Indications are given of interstratification of the mica-pedogenic chlorite and chloriteinterlayered vermiculite type in the more intensively weathered soils.