原状土与扰动土导气率、导水率与含水率的关系

为分析土壤导气特性与土壤导水特性间的关系,该文通过研究陕西杨凌小麦试验田士样导水率和导气率随含水率的变化特征,比较原状土与扰动土导气和导水特征,分析相对导水率和相对导气率与饱和度的关系,结果发现导水率随含水率的增加而减小,且无论导水率还是导气率原状土都比扰动土大,证实土壤结构及孔隙特征对水和气的传输有巨大的影响,扰动土和原状土变化趋势虽然基本相同,但曲线不重合,说明扰动土和原状土的孔隙连接性和弯曲程度不尽相同.     

不同黏粒含量对黄土渗透系数影响的试验研究

[目的]开展不同黏粒含量对黄土渗透系数影响的试验研究,揭示黏粒含量对渗透系数的影响及其微观机理,为黄土及其渗透性相关的理论与工程实践提供科学依据。[方法]通过自制负压湿筛装置筛取不同黏粒含量的黄土试样,利用激光粒度仪对土样的黏粒含量进行跟踪测定,采用静压法将不同黏粒含量的黄土试样制成天然干密度水平下的不同含水率试样进行饱和渗透试验。[结果]黏粒含量对黄土渗透性能有较大影响,在同一含水率条件下,随黏粒含量的增多,黄土的渗透性逐渐降低,渗透系数与黏粒含量呈指数函数负相关关系;在黏粒含量一定时,渗透系数随着初始含水率的增加而减小,呈指数函数负相关关系;SEM分析结果表明,随着黏粒含量的增加,黄土试样微观结构由分散结构变为致密结构,部分颗粒的接触方式由支架接触变为镶嵌接触,颗粒连接由葱皮连接或桥接变为嵌埋连接,相应地孔隙则由支架大孔变为黏粒间微小孔隙,从而一定程度上降低了黄土的渗透性。[结论]黄土渗透系数受黏粒含量、含水率的影响规律相似,可通过微观结构对其影响机理进行解释。     

土石混合介质导气率变化特征试验

土壤中碎石的存在改变了土壤结构和孔隙分布,进而影响土壤通气性能。该文通过对碎石单粒径土石混合介质导气率变化特征研究,旨在探讨单粒径土石混合介质导气内在机理,为进一步研究复杂的野外土石混合介质的导气特性提供基础。为了研究土石混合介质中碎石对导气率的影响,该文通过试验研究,分析土壤颗粒小于2mm的样本(砂土、砂壤土、黏壤土)、碎石质量分数(10%、20%、30%、40%、50%)和碎石粒径(2～3、>3～5mm)对土石混合介质导气率的影响。结果表明:在土壤颗粒小于2mm的样本条件下,土壤导气率呈砂土>砂壤土>黏壤土;在相同碎石质量分数的土石混合介质中导气率呈砂壤土>砂土>黏壤土;碎石的存在改善黏壤土的导气性能,使黏壤土碎石混合介质的导气率大于黏壤土的导气率;降低了砂壤土和砂土的导气性能,且砂土的降低幅度远大于砂壤土;在砂壤土中碎石粒径2～3mm的导气率大于>3～5mm的导气率;在砂土中碎石质量分数30%之内,碎石粒径>3～5mm的导气率稍大于2～3mm的导气率,在40%则相反,但两种粒径下混合介质导气率差异不是很明显。     

马兰黄土渗气性试验研究

利用改进的ZC-2015型渗气仪对不同类型的原状风干和重塑的马兰黄土进行渗气试验,分析土样体积、渗径、干密度、取样深度等对渗气率ka的影响,并利用扫描电镜(SEM)试验得到的孔隙结构参数解释黄土渗气特性。结果表明:渗气率ka不仅是气体渗透特性的衡量指标,也是描述非饱和马兰黄土孔隙和结构特征的重要参数。不同体积的土样由于尺寸效应,其渗气率随着土样体积的增大而增大。另外,渗气率随着渗径、干密度的增大而减小。对比3种不同类型黄土的透气性试验结果和电镜照片,并结合统计的孔隙结构参数,得出渗气率在区域和深度上有一定的规律,区域上黄土颗粒中黏粒含量增高,总孔隙和大孔隙面积减小,土体有效渗气孔隙减少,重塑黄土的渗气率随着取土深度的增加有微小的减小。     

THE INFLUENCE OF IRON AND ALUMINIUM HYDROXIDES ON THE SWELLING OF Na-MONTMORILLONITE AND THE PERMEABILITY OF A Na-SOIL

Hydroxy Fe and A1 interlayers reduce the swelling of Na-montmorillonite in NaCl solutions. A deposit of sesquioxide round an aggregate or orientated flake of clay restricts swelling until the sesquioxide coating is broken by the swelling pressure of the clay. A1 is more effective than Fe. The effect of sesquioxides on the permeability to NaCl solutions of an alkali soil depends on the control of clay swelling in a manner expected from the above results. A sesquioxide coating round a soil aggregate stabilizes the structure until the coating is broken by the swelling pressure of the clay in the aggregate.     

WATER MOVEMENT IN DRY SOILS

hysteresis that occurs in the micro-hydrological characteristics of a soil (conductivity and diffusivity) as functions of water content and water potential between sorption and desorption is examined for three soils (sand, loam, and clay) and sepiolite. These materials, all aggregated, are sufficiently dry that both the vapour and liquid components of water movement are important. any water content or water potential the vapour conductivity is always bigger when wetting than when drying though differences may be small. There is hysteresis in water (vapour+liquid) conductivity as a function of water content when vapour flow but not liquid flow is dominant. Conversely, there is hysteresis in water conductivity as a function of water potential when liquid flow but not vapour flow is dominant. Both forms of this hysteresis are small. Hysteresis in diffusivity as a function of both water content and water potential exists, but is complicated. Variations caused by hysteresis, though real, are likely to be negligible in practice, swamped by effects caused by changes in the soil environment (e.g. temperature) or by changes in soil management (e.g. structure).     

AIR AND WATER PERMEABILITY OF COMPACTED UNSATURATED COHESIVE SOIL

The air and water permeabilities of unsaturated cohesive soils have been measured in a modified triaxial cell permeameter which maintains separate continuity of both the air and water phases during permeation. Three different cohesive soils have been tested and the results interpreted in terms of the cluster concept of soil structure, which recognizes the existence of both macro- and micro-pores. Both air and water permeability are shown to be dominated by the geometry and degree of saturation of the intercluster macro-pores. Compression of the soil always reduces the air permeability but can increase the water permeability by increasing the membrane flow around the clusters. The relations between soil suction, occlusion of the air channels, and compaction water content have also been studied.     

基于微观球体颗粒模型的土水特征曲线研究

When variations occur in the water content or dry bulk density of soil,the contact angle hysteresis will affect the soil-water characteristic curve(SWCC).The occurrence of the contact angle hysteresis can be divided into slipping and pinning.It is difficult to determine the effect of pinning existence on SWCC by tests.In this study,the effect of contact angle hysteresis on SWCC was analyzed either in the case of no variations in soil dry bulk density with changes in soil water content or no variations in soil water content with changes in soil dry bulk density.In both cases,soil particles were simplified to the spherical particle model.Based on the geometrically mechanic relationship between the particles and connecting liquid bridges,a physical model for predicting the SWCC was derived from the spherical particle model.Adjusting parameters made the model applicable to various soils,that is,the cohesive soil was considered as micron-sized spherical particles.Through the simulations on SWCC test data of sand,silt,clay,and swelling soil,it was confirmed that the physical model possessed good reliability and practicability.Finally,the analysis of rationality of contact angle was performed based on the basic assumptions of the model.     

Gas diffusion through soil crumbs: the effects of wetting and swelling

Gas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg¹, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter-crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter-crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra-crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the measurements.     

四种不同母质发育的红壤水分状况研究

在相同的地形和气候条件下,研究了我国东南部地区红砂岩、花岗岩、玄武岩和第四纪红粘土发育的4种典型红壤水分状况及其透水性能。结果表明,4种红壤的持水和透水性能存在不同程度差异,其原因是不同成土母质的土壤机械组成、土壤结构的变化造成的。除玄武岩和红砂岩发育红壤的某些层外,其他土壤各层的土壤渗漏量不随时间变化而变化。4种土壤含水量的年动态变化一般可划分为3个时期:土壤湿润期、土壤水分耗竭期和土壤水分恢复期,但不同年份的时间划分也不尽相同。     

EXCHANGEABLE SODIUM AND YIELDS OF COTTON ON CERTAIN CLAY SOILS OF SUDAN

Within Sudan there are extensive areas of Vertisols in the Nile River valley south of Khartoum. These soils have clay contents ranging from 40 to 60 per cent, very slow permeability, exchangeable sodium percentages up to 35 or more in the upper 60 cm, and pH values between 8.0 and 9.6. Under present management, satisfactory yields of long staple cotton are obtained under irrigation on soils having exchangeable sodium percentage (ESP) of up to 35 in the upper 60 cm. It is proposed that soil characteristics such as type of clay, cracking and exchangeable sodium in the hot, dry climate of Sudan influence soil structure and water availability and thus the yields of cotton.     

Sorption and desorption of triadimefon by soils and model soil colloids

Sorption-desorption of the azole fungicide triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2, 4-triazol-1-yl)-2-butanone] on eight soils and a series of single, binary, and ternary model soil colloids was determined using the batch equilibration technique. Regression analysis between Freundlich sorption coefficients (K(f)) and soil properties suggested that both clay and organic C (OC) were important in triadimefon sorption by soils, with increasing importance of clay for soils with high clay and relatively low OC contents. Triadimefon sorption coefficients on soil were not significantly affected by the concentration of electrolyte or the presence of soluble soil material in solution, but they were highly dependent on the soil:solution ratio due to the nonlinearity of triadimefon sorption on soil. Freundlich sorption isotherms slopes were very similar for all soils (0.75 +/- 0.02). Desorption did not greatly depend on the concentration at which it was determined and showed higher hysteresis for more sorptive soils. Results of triadimefon sorption on model sorbents supported that both humic acid and montmorillonite-type clay constituents contribute to triadimefon retention by soil colloids.     

Hysteresis of the Water Retention Curve: Wetting Branch Simulation Based on the Drying Curve

Hysteresis of the soil water retention curve (SWRC), manifested as a difference between equilibrium curves of soil wetting and drying (hysteresis loop), is a phenomenon specific to soil hydrology, which is of practical importance for calculating irrigation norms. We have attempted to derive a model of the wetting curve from the drying curve. Modeling was based on parameters proposed by van Genuchten [6] and certain soil physical characteristics. SWRC hysteresis characteristics were obtained experimentally using capillarimetric measurements for wetting and drying curves at soil water pressures ranging from 0 to –800 cmH₂O. Two models, М-1 and М-2, based on the hypothesis of dissimilarity of parameters α for wetting (α_w) and drying (α_d) and the constancy of other parameters of the van Genuchten SWRC approximation for both curves of the hysteresis loop, have been developed for wetting curve assessment based on the drying curve. The M-1 error (RMSE = 0.05 cm^–1) was less than that of M-2 (RMSE = 0.06 cm^–1), which used clay content and soil density as predictors, as well as that of the well-known model proposed by Kool and Parker [11]. This approach to derive the wetting curve from the drying curve for a presumed correlation between the values of one parameter and equal values of the other parameters, can be used to predict an estimate of the SWRC hysteresis for a specific soil.     

THE EFFECT OF THE CONCENTRATION AND MOVEMENT OF SOLUTIONS ON THE SWELLING, DISPERSION, AND MOVEMENT OF CLAY IN SALINE AND ALKALI SOILS

Changes in permeability of a soil containing montmorillonite, and the swelling of orientated aggregates of extracted clay have been measured for a range of exchangeable sodium percentages and electrolyte concentrations. The concentrations at which clay moved out of the soil in the percolates have been found and compared with the concentrations at which aggregates dispersed in stationary solutions, and the concentrations at which soil suspensions dispersed when shaken. The results indicate that: (a) permeability begins to decrease at the same concentration as the clay begins to swell, (b) the changes in permeability are directly controlled by the swelling of clay until clay dispersion and movement begins, (c) the concentration at which clay disperses depends on the mechanical stress applied, (d) when small mechanical stresses are applied, the proportion of the clay which swells and disperses depends directly on the exchangeable sodium percentage, and (e) large mechanical stresses may disperse most of the clay even at low exchangeable sodium percentages.     

Effect of potassium on soil structure in relation to hydraulic conductivity

The effect of exchangeable K⁺ on soil structure and permeability has been studied. A loamy sand, a light clay and a heavy clay soil were leached with solutions adjusted to potassium adsorption ratios (PAR) of 0.0, 0.72, 3.74 and ∞. Exchangeable K⁺ percentage (EPP) and hydraulic conductivity (HC) were measured on the leached soils. SEM observations on undisturbed soil samples were used to evaluate changes in soil structure and pore size.

EPP values for the three soils ranged as follows: 0.8–1.3, 5.5–9.2, 16.0–21.0 and 58.0–76.0 for PAR's of 0.0, 0.72, 3.74 and ∞, respectively. HC incrased slightly (20%) up to EPP values of about 20% for the loamy sand and heavy clay soil, while a decrease in HC corresponding to any increase of EPP was observed for the light clay soil. This soil was richer in illite and also exhibited higher affinity for K⁺. At the highest EPP values (58.0–76.0) HC of the three soils decreased to about 20% of the values measured for the Ca²⁺ saturated soils.

SEM observations were performed and Ca²⁺ saturated soils compared with the K⁺ enriched ones. Ca²⁺ treated loamy sand exhibited discrete clay aggregates located in the spaces between sand particles or attached to them. K⁺ enrichment resulted in the formation of a dense network of clay microaggregates filling up the pore space. The microaggregate structure of the two Ca²⁺ clay soils changed to a dense layer composed of much smaller particles following K⁺ enrichment. Pores were mostly smaller than 10 μm in the K⁺ soil compared to several tens of microns in the Ca²⁺ form.

SEM observations and the fact that clay content did not vary with depth suggest that dispersion of clay microaggregates and their rearrangement in situ were the major mechanisms involved in HC reduction, rather than long-range clay migration and the formation of a clay enriched layer with impeded drainage.     

人工降雨模型试验研究降雨入渗对滑坡类型之影响

台湾属海岛型气候,因而年雨量丰沛,降雨时间与空间的不均匀,对台湾大量的山坡地造成威胁。该研究系利用人工降雨系统,配合土壤模型试体探讨强降雨下滑坡破坏型态与坡体饱和度之关系,以对各种边坡稳定、边坡破坏获得更进一步的了解。研究结果得知边坡滑动主要发生在坡体趋近稳定饱和时,而坡面冲蚀则受土壤饱和度影响较小。土壤渗透率与降雨强度之关系亦影响着坡面破坏型态,降雨强度远大于土壤渗透系数时,其破坏型态以浅层滑动为主;降雨强度近似于土壤土壤渗透系数时,则主要为较深层滑动;若降雨强度小于土壤临界入渗率时,则主要为表面冲蚀破坏。     

Increased Carbon Stabilization in Australian Ferrosol with High Carbon Saturation Deficit

The concept of carbon (C) saturation implies that soils have a finite capacity to store C in a stable form, depending on their silt + clay content. We hypothesized that the stabilization of added organic C would be low in C saturated soil. We tested experimentally the influence of C saturation deficit on stabilization of added grass residue. We incubated 12 highly weathered, oxic soil samples collected from three contrasting land uses (i.e. cropping, improved pasture, and forest) with grass residue for 8 months. Carbon saturation deficit of the forest soils was lower than pasture and cropping soils. After incubation, we found increases in silt + clay associated C in grass residue treatment positively correlated with C saturation deficit of soils. Our results suggest that stabilization of added C was high in soil with low C saturation level and hence higher C saturation deficit.     

武陵山地植烟土壤酸度特征及影响因素——以湖南省湘西自治州为例

为了解多年种植烤烟的山地土壤酸度特征,研究了湘西自治州的土壤酸度指标特征及其关系以及植烟年限和土壤类型、有机质、黏粒对土壤酸度的影响。结果表明:(1)植烟年限对土壤酸度的影响大于土壤类型;随植烟年限增加,土壤pH下降,潜性酸度增加,黄棕壤土的交换性盐基、阳离子交换量和盐基饱和度下降。(2)土壤pH与交换性酸为幂函数关系,交换性铝是土壤交换性酸的主体,土壤交换性酸强度随交换性铝及其相对比例的增加而增加。(3)土壤pH与交换性盐基、阳离子交换量、盐基饱和度为二次曲线关系,当pH6时,随土壤pH增加,交换性盐基和阳离子交换量下降,盐基饱和度增加;当pH6时,随土壤pH增加,交换性盐基和阳离子交换量增加,盐基饱和度变幅小。(4)土壤交换性盐基离子主要是交换性钙,其次是交换性镁;对土壤pH影响较大的盐基离子是交换性钙。(5)有机质和黏粒主要影响土壤pH、阳离子交换量、交换性盐基和交换性钙。     

江西兴国县土壤渗透性的研究

对我国南方侵蚀较严重的三种土壤,即第四纪红土母质、花岗岩母质形成的红壤和紫色土进行了土壤渗透性测试。结果作出了渗透时间与总渗透量、渗透时间与渗透速度及渗透速度与总渗透量间的关系曲线,其关系方程分别是Y=A+BlogX、Y=Ae^B/X。对10个试验小区都作出了实测曲线的拟合方程,并对其渗透特征作了讨论。     

崩岗不同土层渗透差异及其影响因素研究

崩岗不同土层的水分渗透性能对其土壤侵蚀特征具有重要影响。研究采用“环刀法”对崩壁垂直剖面22个不同深度土层的渗透特性进行了研究。结果表明:崩岗垂直剖面的渗透特性存在较大差异,红土层的渗透性能总体上优于砂土层和碎屑层,表层0.1 m以下存在一层厚度约1 m的弱透水层。对不同土层影响渗透的因子进行回归分析可知,弱透水层影响渗透的主要因子为容重和机械组成,砂土层影响渗透的主要因子为黏粒含量,碎屑层影响渗透的因子主要为机械组成。