典型耕作土壤团聚体力稳性的区域分异特点及其影响因素

土壤团聚体力稳性直接影响根系生长和农业耕作等过程。为探究不同类型土壤团聚体力稳性的区域分异规律,自北向南选取典型农业种植区耕作土壤(黑土、褐土、红壤和砖红壤),通过抗压试验测定不同粒径团聚体(1～2、3～5、>5～8、>8～10 mm)的抗张强度、破碎能量和易碎性指数,分析其与土壤理化性质和气候因子间关系。结果表明:抗张强度和破碎能量自北向南逐渐减小,并随团聚体粒径增大而减小,但具体变化特征因土壤类型而异。易碎性指数自北向南先增大后减小,其中红壤最大(0.87),黑土最小(0.47);相比温带地区黑土和褐土,亚热带和热带的红壤和砖红壤易碎性指数的粒径分异更为明显,表现为其小粒径团聚体易碎性指数(1.10和0.76)显著高于大粒径团聚体(0.65和0.58)。抗张强度和破碎能量与蛭石呈极显著正相关关系(r=0.73和0.70,P<0.01),与年均降水量呈极显著负相关关系(r=-0.72和-0.72,P<0.01);易碎性指数与年均降水量呈极显著正相关关系(r=0.66,P<0.01),与蛭石、碳氮比、非晶形氧化锰呈极显著负相关关系(r=-0.75～-0.6...     

水保措施对红壤旱地团聚体及其特性的影响

研究了水土保持措施对红壤荒坡旱地土壤机械组成、团聚体及其特性的影响,分析了水稳团聚体及其特性与土壤侵蚀量、地表径流和花生产量的相关关系。结果表明:(1)水土流失主要引起红壤旱地粘粒部分流失,水保措施能减少12.67~24.40%的粘粒流失;(2)与CK相比,水保措施1 mm风干团聚体和0.5 mm水稳团聚体含量增加,团聚体分形维数(CFD)、稳定性指数(ASI)和平均重量直径(MWD)均显著升高,升高的幅度分别为0.38~0.76%、1.44~2.88%、15.50~18.75%;(3)土壤侵蚀量和地表径流与2 mm、1~2 mm粒级的水稳团聚体呈极显著负相关(p0.1),与0.25~0.5 mm粒级的水稳团聚体呈极显著正相关(p0.1),花生产量与0.5~1 mm和0.053 mm粒径的水稳团聚体显著负相关(p0.5)。基于此,研究红壤旱地土壤团聚体及其特性可以指导红壤旱地水土保持研究工作。     

不同修复措施下红壤水稳性团聚体中有机质分布特征

试验设置作物对照(CK)、作物+PAM(聚丙烯乙酰)(C1)、作物+稻草覆盖(C2)、作物+带状牧草(C3)、作物+PAM+带状牧草(C4)和作物+稻草覆盖+带状牧草(C5)6个处理,分别于种植花生前(A)、花生收获后(B)和小麦收获后(C)采集表层土样,研究不同修复措施下鄂东南侵蚀红壤团聚体的稳定性及水稳性团聚体中有机质的分布特征。结果表明,C时期各处理>0.25mm水稳性团聚体含量的平均值比A时期提高了24.78%,以C2处理的水稳性团聚体含量最高。不同时期土壤和各级水稳性团聚体中有机质含量表现为B>C>A。随着团聚体粒径(>4mm,4～2mm,2～1mm,1～0.5mm,0.5～0.25mm)减小,水稳性团聚体中有机质含量逐渐降低。土壤有机质含量与各粒径水稳性团聚体有机质含量呈线性正相关,小粒径(2～0.25mm)水稳性团聚体的有机质含量与土壤有机质含量呈极显著正相关(相关系数为0.779 2～0.828 6)。综合考虑土壤有机质含量和团聚体稳定性2个因素,稻草覆盖措施对侵蚀红壤的修复效果较好。     

侵蚀红壤中结合态腐殖质及其与水稳性团聚体的关系

以亚热带地区3种侵蚀程度(依据其植被、坡度以及土层厚度不同分为轻度、中度和严重侵蚀)的红壤为供试材料,利用湿筛法获得粒径4、2~4、1~2、0.5~1、0.25~0.5 mm的水稳性团聚体,分析侵蚀红壤和团聚体中3种结合态(紧结态、松结态和稳结态)腐殖质含碳量的分布特征,及其对0.25 mm团聚体稳定性的影响。结果表明:随着红壤侵蚀程度的增强,3种结合态腐殖质的含碳量均逐渐减小。在轻度侵蚀的红壤中,随着团聚体粒径的增大,其紧结态和松结态腐殖质的含碳量逐渐升高,稳结态腐殖质的含碳量逐渐降低;但是在中度和严重侵蚀红壤中,不同粒径团聚体的3种结合态腐殖质的含碳量基本相同。侵蚀红壤的紧结态、松结态腐殖质的含碳量与其0.25 mm水稳性团聚体的含量均呈极显著正相关(r分别为0.88,0.74),说明土壤中腐殖质与矿物质的结合方式和松紧程度不一样,其对侵蚀红壤的结构具有不同的影响。     

土地利用方式对土壤水稳性团聚体有机碳的影响

对福建省建瓯市山地红壤的农业用地(坡耕地、茶园、桔园)、林地(杉木、木荷、封育)不同土层(0-10,10-20 cm)土壤团聚体有机碳含量与贮量进行研究.结果表明:林地开垦作为农地后,>2 mm土壤大团聚体的数量明显下降,<0.25 mm团聚体含量显著上升.不同土地利用方式的土壤大团聚体呈现粒径越大,团聚体有机碳含量越高的趋势,林地不同粒径团聚体有机碳含量都显著高于农业用地.林地随着团聚体粒径增大,土壤碳贮量增加;而农地正好相反,随着团聚体粒径增大,土壤碳贮量反而下降.土壤总有机碳增加主要受到大团聚体有机碳增加的影响,其中>2 mm和0.5～2 mm粒径土壤团聚体对土壤总有机碳贡献最为突出.因此亚热带山地红壤内林地开垦为农业用地会导致富含碳的土壤大团聚体有机碳含量大幅度下降,团聚体的稳定性也随之下降.     

不同植烟年限对土壤团聚体稳定性的影响及其相关因素分析

通过野外调查、取样和室内分析,对凉攀地区不同植烟年限的土壤团聚体稳定性及其有机碳含量等相关影响因素进行研究。结果表明:水稳性团聚体在植烟0~5 a期间被显著破坏,红壤、紫色土和水稻土团聚体MWD值分别下降68%、64%和52%;非水稳性团聚体的破坏集中在植烟3~5 a期间,3种土壤团聚体MWD值依次分别下降31%、9%和17%。有机碳含量影响团聚体水稳定性,尤以水稻土和紫色土表现显著。有机碳主要分布在5 mm和0.25 mm粒径团聚体中,随植烟年限的增加,紫色土和水稻土各粒径团聚体有机碳含量显著降低,且5 mm和0.25 mm粒径团聚体下降最明显,各粒径团聚体中有机碳分布越均匀。烤烟不宜连作,连作紫色土和水稻土烟地(田)可增施有机肥,保护土壤团聚体。     

桂西北喀斯特地区典型土壤在不同筛分强度下团聚体的稳定性

采用AS 200筛分仪分析了不同有机碳含量下3种喀斯特典型土壤(红壤、棕色石灰土、黑色石灰土)的团聚体颗粒在不同筛分强度(1.5,2和2.5mm振幅)的分级特征。结果显示,3种土壤平均重量直径(MWD)从大到小为:黑色石灰土棕色石灰土红壤(p0.05)。随筛分强度由小到大,棕色石灰土和黑色石灰土的团聚体颗粒分级变化较小,红壤团聚体颗粒分级由大颗粒(8,8~5,5~2mm)团聚体为主逐渐变为中间粒径颗粒(5~2,2~1mm)。红壤团聚体结构最易被筛分过程破坏,其次是棕色石灰土,最后是黑色石灰土。研究表明石灰土团聚体机械稳定性强于红壤,且筛分强度直接影响团聚体分级结果。从团聚体聚合角度来看,喀斯特石灰土土壤稳定性较强。     

浙西3类石灰岩发育土壤有机碳和团聚体稳定性的研究

选择浙西地区黑色石灰土、棕色石灰土和红色石灰土等3类石灰岩土壤,通过物理和化学性状的鉴定,研究了它们的有机碳组成和团聚体稳定性,并与当地质地同为黏土的典型红壤进行了比较。结果表明,石灰岩发育的这些土壤因同时含有较高的黏粒(350~450 g kg~(-1))、游离氧化铁(27.46~51.26 g kg~(-1))、交换性钙(8.55~25.77 cmol(+)kg~(-1)),其水稳定性团聚体(特别是大粒径水稳定性团聚体)数量和水稳定性团聚体平均重量直径明显高于红壤。由黑色石灰土至棕色石灰土到红色石灰土,随着土壤脱钙与风化程度的增强,矿物类型由伊利石、蛭石、蒙脱石的组合向高岭石、伊利石、蛭石的组合转变,碳酸钙、交换性钙、p H和阳离子交换量降低,土壤水稳定性团聚体数量趋向下降。同时,石灰岩发育土壤因风化较弱,p H较高,并含有高量的交换性钙和阳离子交换量,有利于有机胶体与无机胶体发生作用,土壤有机碳稳定性较高。水提取态有机碳占全有机碳的比例及易氧化态有机碳占全有机碳的比例均是黑色石灰土棕色石灰土红色石灰土红壤,而稳定性有机碳的比例及H/F比为黑色石灰土棕色石灰土红色石灰土红壤。模拟试验表明,由自然风化和施肥等引起的土壤酸化可引起石灰岩发育土壤水稳定性团聚体数量的下降,但酸化对红壤团聚体稳定性的影响较小。研究证实,石灰岩土壤因含有丰富的无机胶体和交换性钙,有利于有机碳的积累和水稳定性团聚体的形成,但土壤酸化可明显降低石灰岩土壤水稳定性团聚体的数量。     

丹江典型小流域有机碳在土壤团聚体不同粒级的分布研究

选取丹江鹦鹉沟小流域典型土地利用类型进行土样采集,研究不同土地利用类型下土壤团聚体的粒径分布特征和团聚体有机碳含量与粒径的相互关系,运用情景模拟法计算不同土地利用类型下的土壤团聚体有机碳储量转移矩阵。结果表明:不同土地利用类型土壤团聚体含量大致呈现伴随粒径的减小而减小的趋势,且主要集中于大粒径(2~10mm)的范围内。经ANONA检验,农地与林地,林地与草地之间土壤团聚体不同粒级有机碳含量存在显著差异(P0.05),其典型用地之间的土壤团聚体有机碳粒径分布的变异性属于中等变异,且团聚体有机碳与小粒径(1mm)的土粒结合更加紧密,有机碳储量的粒径分布呈现出近似正态分布的状态。     

红壤不同粒径团聚体对草甘膦农药降解动力学的影响

草甘膦农药的大量喷施,使其在环境特别是土壤中的残留-累积风险日益突出,从团聚体粒径角度研究红壤不同粒径团聚体中草甘膦的降解动力学及其相互作用特征仍鲜有报道。基于此,本研究通过干筛筛分、室内控制培养、液质联用定量分析相结合等探究草甘膦降解残留,并进一步分析团聚体理化性质与草甘膦降解的关系。结果表明:1)不同粒径团聚体中,草甘膦残留量随降解时间不断减小,且粒径之间降解动力学差异不显著。降解半衰期为15.8～20.6 d,粒径最小的团聚体(0.25 mm)中草甘膦的降解半衰期最长,为20.6 d。草甘膦在土壤中的主要降解产物氨甲基磷酸(AMPA)的含量随着降解时间的增加而增加,且在第5d达到峰值,而后不断减小;不同粒径团聚体间AMPA含量差异显著(P0.05)。2)相关分析及主成分分析发现,草甘膦残留量与红壤团聚体中速效磷含量呈显著正相关(P0.05),而其降解产物AMPA含量与团聚体中酸性磷酸酶活性及N-乙酰氨基-β-葡萄糖苷酶活性呈显著正相关(P0.05)。团聚体粒径与草甘膦残留量间没有显著相关性,但与AMPA含量显著正相关(P0.05)。此外,草甘膦降解过程中,团聚体中有机质含量及β-葡萄糖苷酶、N-乙酰氨基-β-葡萄糖苷酶、酸性磷酸酶活性与团聚体粒径为显著负相关关系(P0.05)。由此表明:红壤不同粒径团聚体影响草甘膦降解速率,粒径最小的团聚体(0.25 mm)中草甘膦农药的降解速率最慢,但试验结束时,各粒径红壤团聚体中的草甘膦和AMPA含量均较高,可能会影响土壤健康及生态环境安全;此外,草甘膦降解与土壤磷素密切相关,后续研究需探讨磷亏缺或丰盈条件下,草甘膦农药的土壤环境特征,为后续农田草甘膦环境风险评估提供依据。     

Aggregate Stability and Its Relationship with Some ChemicalProperties of Red Soils in Subtropical China

The stability of aggregates in the surface soil is crucial to soil erosion and runoff generation. Thus, to understand the stability and the breakdown mechanisms of soil aggregates as well as the relationship between aggregate stability and selected soil chemical properties, such as different forms of Fe and A1 oxides, organic matter, CEC and clay content, the aggregates of slightly and severely eroded red soils derived from Quaternary red clay in subtropical China were analyzed using the routine wet sieving and the Le Bissonnais methods. The results indicated that the aggregates of the severely eroded soils were more stable than those of the slightly eroded soils. Different aggregate breakdown mechanisms resulted in different particle size distribution. The slaking from entrapped air in aggregates severely destroyed the soil aggregates,especially in the slightly eroded soils. Meanwhile, mechanical breakdown and microcracking had little effect on the aggregates compared to slaking. The fragments resulting from slaking were mainly microaggregates that increased in size with increasing clay content. The main fragment size of the slightly eroded soils was 1.0-0.2 mm, while for the severely eroded soils it was 5.0-2.0 mm and 1.0-0.5 mm. Overall, more than 20% of the fragments were smaller than 0.2 mm.In addition, aggregate stability was positively and often significantly correlated with Fed, Ald, Feo and clay content, but significantly and negatively correlated to SOC.     

Effect of sodicity and salinity on disaggregation and tensile strength of an Alfisol under different cropping systems

The influence of electrolyte concentration (EC) and sodium adsorption ratio (SAR) on the tensile strength and aggregate stability via flocculation and dispersion behaviour of an Alfisol varying in organic carbon content due to different cropping systems was assessed using a split-split plot experiment involving eight soils, three levels of EC and seven levels of SAR.

Generally, at a given SAR value, mean weight diameter (MWD) increased with organic matter status of the soil in the following order: virgin pasture>wheat>wheat-fallow. As MWD decreased, the amount of dispersible clay increased at a given SAR indicating that more surfaces exposed due to slaking of aggregates led to more clay dispersion. Statistical analysis of changes in tensile strength with various factors showed that an increase in organic matter decreased the magnitude of changes in strength induced by sodicity because organic matter tends to increase aggregate stability (higher MWD). While individual soils had significant relationships between the tensile strength of the aggregates and the amount of spontaneously dispersible clay, this relationship was poor when the results of all soils were pooled together. The amounts of dispersible clay from dry aggregates were higher than from wet aggregates and dispersive breakdown of the aggregates of sodic soils occured irrespective of the mode of wetting. The most important factor in determining the soil strength was the amount of clay dispersed during wet-sieving analysis followed by MWD.     

土粒表面电场对土壤团聚体破碎及溅蚀的影响

团聚体是土壤结构的基本单元,其稳定性是评估土壤抗侵蚀能力的重要指标。土壤团聚体破碎是降雨溅蚀发生的关键一步。土粒表面电场对团聚体稳定性具有重要影响,必然也会深刻影响降雨溅蚀过程。该文以黄土母质发育的黄绵土和塿土为研究对象,采用不同浓度的电解质溶液定量调控土粒表面电场,研究不同电场强度对团聚体破碎及溅蚀的影响。结果发现:1)随电解质浓度的降低,土粒表面电位升高,表面电场增大,黄绵土和塿土团聚体平均重量直径减小,团聚体稳定性降低,降雨溅蚀量增大。2)电解质浓度小于10-2 mol/L,黄绵土和塿土表面电位绝对值分别高于202.0和231.6 mV,此时团聚体稳定性和溅蚀量变化不明显,表明表面电位202.0和231.6 mV分别是影响黄绵土和塿土团聚体稳定性及溅蚀的关键电位。3)随着土粒表面电场的减弱,团聚体破碎后释放的<0.15 mm微团聚体含量减小,>0.25 mm大团聚体含量增加,团聚体倾向于破碎为更大粒级的团聚体。4)电场作用下团聚体的破碎特征对降雨溅蚀具有重要的影响,溅蚀量与团聚体破碎释放的<0.15 mm微团聚体含量呈显著正相关,与>0.25 mm大团聚体含量呈显著负相关。上述结果表明,当降雨进入土壤后,对于干燥的土壤而言,土壤溶液电解质浓度被迅速稀释,土粒表面产生强大的电场,该电场通过影响团聚体破碎程度进而影响降雨溅蚀。该研究有助于加深对降雨溅蚀的科学认识,同时也为土壤团聚体稳定性及降雨溅蚀的人为调控提供了一定的理论依据。     

Soil structure and microbial activity dynamics in 20‐month field‐incubated organic‐amended soils

Soil structure formation is essential to all soil ecosystem functions and services. This study aims to quantify changes in soil structure and microbial activity during and after field incubation and examine the effect of carbon, organic amendment and clay on aggregate characteristics. Five soils dominated by illites, one kaolinitic soil and one smectitic soil were sieved to 2 mm, and each soil was divided into two parts and one part amended with ground rape shoots (7.5 t ha^?1) as an organic amendment. Samples were incubated in the field for 20 months with periodic sampling to measure water‐dispersible clay (WDC) and fluorescein diacetate activity (FDA). After incubation, WDC and FDA were measured on air‐dried 1–2‐mm aggregates. Tensile strength was measured on four aggregate classes (1–2, 1–4, 4–8 and 8–16 mm) and results used to assess soil friability and workability. Intact cores were also sampled to determine compressive strength. During incubation, the amount of WDC depended on soil carbon content while the trends correlated with moisture content. Organic amendment only yielded modest decreases (mean of 14% across all sampling times and soils) in WDC, but it was sufficient to stimulate the microbial community (65–100% increase in FDA). Incubation led to significant macroaggregate formation (>2 mm) for all soils. Friability and strength of newly‐formed aggregates were negatively correlated with clay content and carbon content, respectively. Soil workability was best for the kaolinite‐rich soil and poorest for the smectite‐rich soil; for illitic soils, workability increased with increasing organic carbon content. Organic amendment decreased the compression susceptibility of intact, incubated samples at smaller stress values (<200 kPa).     

雨滴机械打击和消散作用对土壤团聚体的破坏特征

土壤团聚体是土壤结构的基本单元,其稳定性是描述土壤抵抗侵蚀过程中破坏作用的重要指标。但溅蚀过程中,雨滴对团聚体的消散和机械打击两种破坏作用的相对贡献及其破坏机制尚未明晰。利用酒精和超纯水作为雨滴形成材料,模拟机械打击单独作用及消散和机械打击共同作用,分别在五个高度(0.5、1、1.5、2和2.5 m)对塿土和黄绵土进行溅蚀实验。结果表明:当降雨动能相同时,塿土的溅蚀率均小于黄绵土。同时,超纯水雨滴对土壤的机械打击和消散共同作用所导致的溅蚀率均大于酒精雨滴单一机械打击作用的溅蚀率。随着降雨动能增加,两种雨滴对两种土壤的溅蚀率均呈幂函数增加;团聚体因消散破坏作用和机械打击作用的溅蚀率均亦随之增加。但两种土壤的消散破坏作用和机械打击作用的贡献率分别随着降雨动能增加而减小和增加。在相同降雨动能时,塿土消散破坏作用的贡献率均大于黄绵土,而机械打击作用贡献率均小于黄绵土。研究结果对深入理解溅蚀过程中团聚体破坏机理及评价溅蚀过程中团聚体稳定性具有重要意义。     

Clay Dispersion of Hardsetting Inceptisols in Southeastern Nigeria as Influenced by Soil Components

Abstract

Hardsetting soil properties are undesirable in agricultural soils because they hamper moisture movement and soil aeration. The soils of the floodplain of Niger River in eastern Nigeria hardsets upon drying, following dispersion, puddling, and slaking during the waterlogged period. Ten soil samples collected from a depth of 0–20 cm were analyzed for their properties. The soils are classified as Fluvaquentic Eutropepts or Dystric Gleysol (FAO). The objective was to investigate the influence of some soil properties on water‐dispersible clay (WDC) of the soils, which is the precursor of the hardsetting process. The total clay content (TC) correlated significantly with WDC (r=0.94??), whereas the water‐dispersible silt (WDSi) was higher than its corresponding total silt content. The WDC showed a positive correlation with dithionite extractable Fe (Fed), Al (Ald), and oxalate extractable Fe (Feo) (r=0.75?, 0.89??, and 0.76? respectively). Exchangeable Mg²⁺ correlated significantly with WDSi (r=0.70). Principal component analysis of the soil variables indicates that 15 soil components, which influence WDC as hardsetting properties, were reduced to 5 orthogonal components. The parameters that influence hardsetting properties are exchangeable Na⁺, K⁺, Ca²⁺, Mg²⁺, Fed, Alo, and Feo. Other soil properties are kaolinite, smectite, illite, and WDC, including soil organic carbon (OC), electrical conductivity (EC), and ESP. Therefore, those soil properties, which explain hardsetting characteristics most, are exchangeable Na⁺, Fed, OC, Mg²⁺, and Alo. There are negative consequences on the erodibility, runoff, infiltration and tillage of the soils at both submerged and dry conditions due to clay dispersion, low OC, and hardsetting behavior of the soil.     

中国亚热带红壤团聚体稳定性与土壤化学性质的关系

The stability of aggregates in the surface soil is crucial to soil erosion and runoff generation. Thus, to understand the stability and the breakdown mechanisms of soil aggregates as well as the relationship between aggregate stability and selected soil chemical properties, such as different forms of Fe and Al oxides, organic matter, CEC and clay content, the aggregates of slightly and severely eroded red soils derived from Quaternary red clay in subtropical China were analyzed using the routine wet sieving and the Le Bissonnais methods. The results indicated that the aggregates of the severely eroded soils were more stable than those of the slightly eroded soils. Different aggregate breakdown mechanisms resulted in different particle size distribution. The slaking from entrapped air in aggregates severely destroyed the soil aggregates, especially in the slightly eroded soils. Meanwhile, mechanical breakdown and microcracking had little effect on the aggregates compared to slaking. The fragments resulting from slaking were mainly microaggregates that increased in size with increasing clay content. The main fragment size of the slightly eroded soils was 1.0-0.2 mm, while for the severely eroded soils it was 5.0-2.0 mm and 1.0-0.5 mm. Overall, more than 20% of the fragments were smaller than 0.2 mm. In addition, aggregate stability was positively and often significantly correlated with Fe_d, Al_d, Fe_o and clay content, but significantly and negatively correlated to SOC.     

湿润速率和粘粒含量对红壤沟间侵蚀的影响

An aggregate stability test and a simulated rainfall test were conducted on four representative Ultisols from southeastern China. The soils selected, with clay contents ranging between 117 and 580 g kg-1 , were derived from shale and Quaternary red clay. The stability of aggregates (2–5 mm in diameter) obtained from the soil samples were determined by the Le Bissonnais method. For determination of infiltration, runoff, and erosion, the soil samples were packed in 30 cm × 60 cm trays, wetted at rates of 2, 10, and 60 mm h-1 , and then exposed to simulated rainfall at 60 mm h-1 for 1 h. The results indicated that both aggregate stability and slaking caused by fast wetting increased with increasing clay content. The effect of wetting rate (WR) on infiltration and seal formation varied with clay contents. In the soil with low clay content (sandy loam), the infiltration rate was affected slightly by WR due to low aggregate stability and slaking. In the soils with medium clay content (silt clay loam and clay), WR affected infiltration significantly due to the high aggregate slaking force. In the soil with high clay content, the effect of WR on infiltration was significant, but not as evident as in the soils with medium clay content, which may be related to high aggregate stability by wetting partially compensating for slaking force. The effect of WR on soil loss was similar to that of runoff, but more pronounced. The findings from this study indicated that the relationship between wetting rate and clay content should be considered when predicting interrill erosion in Ultisols.     

五台山土壤水稳性团聚体有机碳分布特征

为揭示五台山垂直带土壤不同形态团聚体有机碳的分布特征,以五台山垂直带土壤为研究对象,于2016年8月从高海拔至低海拔对亚高山草甸土、山地草甸土、棕壤、淋溶褐土、石灰性褐土样品进行采集,并且通过湿筛法和物理分组技术获得不同土壤类型中2,2~0.25,0.25~0.053,0.053mm水稳性团聚体,进一步分析了土壤及各级水稳性团聚体的总有机碳、颗粒有机碳(POC)和矿物结合有机碳(MOC)。结果表明:亚高山草甸土、山地草甸土和棕壤均以2mm团聚体为最多,达到总水稳性团聚体的45.13%。然而,淋溶褐土和石灰性褐土中分别以2~0.25mm和0.25~0.053mm团聚体为最多,分别达到33.79%和39.95%。随着海拔高度的降低土壤有机碳含量依次降低,且不同土壤类型中,2mm和2~0.25mm团聚体有机碳含量与其对应的土壤有机碳含量呈极显著正相关关系,相关系数分别为r2mm=0.986和r2~0.25mm=0.966(P0.01)。随着土壤团聚体粒径的减小,亚高山草甸土、山地草甸土、棕壤的POC含量呈现下降趋势,而淋溶褐土和石灰性褐土的POC含量呈现升高趋势。亚高山草甸土、山地草甸土、棕壤的MOC含量都以2mm团聚体为最大,淋溶褐土和石灰性褐土分别以2~0.25mm和0.25~0.053mm团聚体的MOC含量为最大。各土壤及团聚体中MOC的含量要明显大于POC的含量,而且在土壤和各级大团聚体中二者呈现正相关关系(P0.05)。此外,各土壤POC和MOC的含量与土壤有机碳含量也呈现正相关关系(P0.05)。因此,随着海拔高度的降低,各土壤团聚体组成由大团聚体向微团聚体转变,亚高山草甸土、山地草甸土、棕壤的碳截获能力强于淋溶褐土和石灰性褐土。     

Directional strength in aggregates as affected by aggregate volume and by a wet/dry cycle

Reduction of aggregate size in the upper, tilled soil layer as a result of one wet/dry cycle was observed for sandy soil and clay soils. Bulk density of aggregates tended to increase as their size diminished for the clay after the wet/dry cycle, whereas similar changes in bulk density for the loam were observed only for aggregates smaller than 5.6 cm. Slaking and water-drop impact seem to be the major factors in reducing the aggregate size of the sandy loam, while swelling and shrinkage affect clay aggregates of all size groups, but only aggregates smaller than 4.0 mm for the sandy loam. Tensile strength of the sandy loam aggregates was related to the axis along which the stresses were applied. A definite directional dependence of tensile strength was observed, e.g. the shorter the axis, the larger the tensile strength. The directional strength dependence was apparently not affected by one wet/dry cycle.