首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 468 毫秒
1.
为探究不同生物炭混掺量对微咸水蒸发特性的影响,采用离心机试验和室内土柱模拟试验,设置3个生物炭质量添加比例(B0、B2、B4)和4个微咸水矿化度(W0、W1、W3、W5),分析不同处理对微咸水蒸发下的土壤水分特征曲线、孔隙分布、累积蒸发量、盐分运移、土壤温度日变幅的影响,并应用蒸发模型进行拟合分析。结果表明:生物炭和微咸水联合应用下能提高土壤持水能力,增加土壤中的较大孔隙和较小孔隙的比例;土壤累积蒸发量随着生物炭混掺量的增加先减少后增加,生物炭混掺量为2%时可以更好地抑制微咸水蒸发;Rose蒸发模型可以较好地拟合微咸水蒸发;土壤中混掺生物炭可以降低盐分表聚,使其在土壤中均匀分布;混掺生物炭可以有效降低土壤温度日变幅;相同生物炭施用量下,矿化度为3 g/L的微咸水,可以降低0—10 cm土层土壤平均温度,提高10—50 cm土层土壤平均温度。综合考虑各项指标,处理B2W3的生物炭和微咸水更适宜农田施用,为西北干旱地区更好地利用微咸水灌溉提供理论依据。  相似文献   

2.
A kaolinitic soil was treated chemically to remove iron and quartz. Before and after treatment the properties of the soil were, respectively: iron content, 7 and 1%; quartz content, 21 and 0%: water content at saturation (water/kaolin content, g/g), 0.40 for both, of which 0.34 was in pores for which the Kelvin radius rj, was ≤35 nm. Porosity and pore size distribution (PSD) up to this pore size were studied using nitrogen sorption, mercury injection, pressure membrane equilibration and low temperature scanning microcalorimetry (DSC). These analyses justified interpretation in terms of kaolinite content alone. The PSD was unaffected by the removal of iron or quartz or the moisture content of this soil. New DSC techniques show that the pore spaces within the treated samples (rj≤ 35 nm) are largely unconstricted, and thus, an experimental curve relating temperature depression for melting to pore size is possible using only one sample.  相似文献   

3.
The water retention characteristic provides the traditional data set for the derivation of a soil's pore‐size distribution. However, the technique employed to achieve this requires that assumptions be made about the way pores interconnect. We explore an alternative approach based on stray field nuclear magnetic resonance (STRAFI‐NMR) to probe the water‐filled pores of both saturated and unsaturated soils, which does not require information relating to pore connectivity. We report the relative size distributions of water‐occupied pores in saturated and unsaturated samples of two sets of glass beads of known particle size, two sands, and three soils (a silty loam, a sandy loam and a loamy sand), using measurements of the NMR T1 proton relaxation time of water. The T1 values are linearly related to pore size and consequently measured T1 distributions provide a measure of the pore‐size distribution. For both the sands and the glass beads at saturation the T1 distributions are unimodal, and the samples with small particle sizes show a shift to small T1 values indicating smaller voids relative to the samples with larger particles. Different matric potentials were used to reveal how the water‐occupied pore‐size distribution changes during drainage. These changes are inconsistent with, and demonstrate the inadequacies of, the commonly employed parallel‐capillary tube model of a soil pore space. We find that not all pores of the same size drain at the same matric potential. Further, we observe that the T1 distribution is shifted to smaller values beyond the distribution at saturation. This shift is explained by a change in the weighted average of the relaxation rates as the proportion of water in the centre of water‐filled pores decreases. This is evidence for the presence of pendular structures resulting from incomplete drainage of pores. For the soils the results are similar except that at saturation the T1 distributions are bimodal or asymmetrical, indicative of inter‐aggregate and intra‐aggregate pore spaces. We conclude that the NMR method provides a characterization of the water‐filled pore space which complements that derived from the water retention characteristic and which can provide insight into the way pore connectivity impacts on drainage.  相似文献   

4.
Numerous experimental data obtained by different methods confirm the theoretical ideas about the electric nature of the interaction between the solid and liquid soil phases, which were first suggested by the Maxwell-Boltzmann-Helmholtz-Gouy and Deryagin-Landau-Verwey-Overbeek theories about the double electric layer in two-phase disperse systems. The interaction between the solid phase and water in the diffuse part of this layer may be described by the theoretically derived equation lnP w = A − BW, where P w is the soil moisture pressure, W is the ratio between the masses of the water and the solid phase in the soil, and A and B are physically grounded parameters. The exponential form of this equation first predicted by the out-standing researcher Gouy 100 years ago results from the exponential distribution of ions in the diffuse layer near the electrically charged surface of the solid soil phase.  相似文献   

5.
残膜量对膜孔灌土壤水氮运移特性的影响   总被引：1，自引：0，他引：1  
为探究土壤残膜量对膜孔灌肥液入渗土壤水氮运移特性的影响,通过室内土箱模拟试验设置0,90,180,360,720 kg/hm~2的5个残膜量水平,分析不同残膜量下膜孔灌肥液入渗累积入渗量、湿润锋运移距离、湿润体特征和水氮分布规律。结果表明:残膜对膜孔灌肥液入渗具有阻渗作用,残膜土累积入渗量较无残膜土减少10.63%～30.77%,Kostiakov模型对残膜土单位膜孔面积累积入渗量与入渗时间有较好地拟合效果;入渗前30 min,不同残膜量的垂直湿润锋运移距离差异不显著,随着入渗时间推进,残膜量与湿润锋运移距离、湿润体体积呈负相关关系。入渗结束时,含残膜土湿润体体积减小18.09%～41.96%。垂直湿润锋距离、湿润体体积与入渗时间均呈显著的幂函数关系,R~2均0.98;除膜孔中心处,相同位置含残膜的土壤含水率低于无残膜,30%高含水率区域减小。湿润体内同一深度土壤NO_3~--N和NH_4~+-N含量随残膜量增加而减小,减小幅度为4.20%～16.27%。研究结果可为残膜土下膜孔灌技术提供理论参考。  相似文献   

6.
In order to determine if soil hydraulic properties present a direction‐dependent behavior, undisturbed samples were collected at different horizons and orientations (vertical, diagonal [45°], and horizontal) in structured soils in the Weichselian moraine region in northern Germany. The water‐retention curve (WRC), the saturated hydraulic conductivity (kf), and the air permeability (ka) were measured. The air‐filled porosity (?a) was determined, and pore‐continuity indices (ka/?a, ka/?a2, N) and blocked porosities (?b) were derived from the relationship between ka and ?a. The development of soil structures with defined forms and dimensions (e.g., platy by soil compaction or prismatic up to subangular‐blocky by swelling–shrinkage processes) and the presence of biopores can induce a direction‐dependent behavior of pore functions. Although the pore volume as a scalar is isotropic, the saturated hydraulic conductivity and air permeability (as a function of air‐filled porosity) can be anisotropic. This behavior was observed in pore‐continuity indices showing that the identification of soil structure can be used as a first parameter to estimate if hydraulic properties present a direction‐dependent behavior at the scale of the soil horizon.  相似文献   

7.
By examining the symmetry between the distributions of particle‐size (PSD) and pore‐size (POD) in a soil, as hypothesized by early pore‐solid fractal (PSF) models, we found significant discrepancies in fractal dimensions between the PSD and the water retention curve (WRC) of a soil. Therefore, we developed an asymmetry‐based PSF model to estimate better the WRC directly from the PSD data of a soil. To do so, we adopted the concept of a microscopic arrangement of different‐sized particles to address such asymmetry, and evaluated the performance of the modified PSF model on five soil textural classes (coarse‐, moderately coarse‐, medium‐, moderately fine‐ and fine‐textured soils) using experimental PSD and WRC data from the UNSODA database (159 undisturbed soils for model calibration and 70 undisturbed soils for model validation). The fit of the symmetry‐based PSF model to the calibration dataset showed that the fractal dimension of the WRC (Dp) was slightly larger than that of cumulative mass distribution of particles (Ds) for most soils. The asymmetry‐based PSF model performed better than the symmetry‐based PSF model. In addition, the asymmetry‐based PSF model reduced the tendency to under estimate soil water content for a given matric head and the performance of the asymmetry‐based model was consistent irrespective of soil texture, indicating that the adoption of asymmetry between the PSD and the POD was adequate in predicting the WRC of a porous, particulate system such as soil.  相似文献   

8.
Sun  Wen-Jing  Li  Ming-Yu  Zhang  Wen-Jie  Tan  Yun-Zhi 《Journal of Soils and Sediments》2020,20(11):3875-3883
Purpose

Biochar has the characteristics of loose porosity, high specific surface area, and strong adsorption properties. Recently, the compacted biochar amended clay has been proposed as a sustainable alternative material for the final cover of landfills. However, the effect of biochar on saturated hydraulic conductivity (ksat) is not yet conclusive. The objective of this study was to determine the influence of biochar content on the permeability of biochar-clay mixed soils.

Materials and methods

The clay used in the study belongs to the low liquid limit clay. The biochar is produced by heating the rice straw under an oxygen-deficient condition at a temperature of 500 °C. To study the effect of biochar content on the permeability of biochar-clay mixed soils, the biochar-clay mixed soils with the mass percentage of biochar being 0%, 5%, 10%, 15%, and 20% were used. The saturated hydraulic conductivity of the biochar-clay mixed soils was measured by the head pressure control permeameter. Meanwhile, the micro-pore structure of the saturated biochar-clay mixed soils was obtained by the nuclear magnetic resonance (NMR) technique.

Results and discussion

It can be observed that the saturated hydraulic conductivity ksat of biochar-clay mixed soils increases linearly as the biochar content increases. The NMR results show that the T2 distribution curve of pure clay is a unimodal pattern, while the T2 distribution curve of biochar-clay mixed soils presents the bimodal pattern, where T2 is the transverse relaxation time, reflecting the pore size of the soil specimens. With the increase of biochar content, the T2 spectrum of the mixed soils moves slightly to the right, and T2 at main peak increases gradually, correspondingly the most probable pore size of biochar-clay mixed soils increases.

Conclusions

The pore size distribution of the soil was changed by the addition of biochar and subsequently affects the permeability of biochar-clay mixed soils. This study provides some useful suggestions for optimizing the pore structure of the biochar amended clay anti-seepage layer in the final cover of landfills.

  相似文献   

9.
Soil pore size distribution(SPSD) is one of the most important soil physical properties. This research investigated the relationships of location and shape parameters of the SPSD curves with plant-available water(PAW) and least limiting water range(LLWR) of the light-textured soils at the Torogh Agricultural Research Station in north-eastern Iran. Soil moisture release curve(SMRC), PAW and LLWR in matric heads of 100 and 330 h Pa for the field capacity and location and shape parameters of the SPSD curves of 30 soils with different texture and organic carbon contents were determined, and the variable relationships were statistically analyzed. The results showed that the median equivalent pore diameter(de), mean de, standard deviation(SD*), and skewness of the SPSD curves were significantly correlated with PAW(PAW330) and LLWR(LLWR330) measured in a matric head of 330 h Pa. Decrease in deand increase in the diversity of soil pore size(SD*) increased PAW330 and LLWR330. The SD* values of all the soil samples were lower than the optimal ranges suggested in literature. Neither PAW nor LLWR values were significantly different in the soils with the optimal modal deand those with non-optimal modal de. Optimal values of median and mean equivalent pore diameters and kurtosis of SPSD curves led to a significant improvement of PAW330 and LLWR330 as soil physical quality indicators. It was recommended to revise the optimal ranges for SD* and modal defor future studies.  相似文献   

10.
Soil hydraulic properties as related to soil structure   总被引：5，自引：0，他引：5  
  相似文献   

11.
Abstract

Soil texture, aggregates in different size classes and water retention at several water potentials were measured in the top layers of 12 Danish soils. Size frequency curves of dispersed and aggregated soil particles and of soil pores were calculated using numerical differentiation of sum curves, which were obtained from measured data through interpolation procedures. Soils which originated from water sediments had narrow peaks with approximately lognormal distribution of dispersed soil particles and of soil pores, reflecting the sorting action of the water. Moraine soils appeared to have broad and flat frequency curves of dispersed soil particles, some of which were bimodal or skewed. These soils exhibited a typical bimodal size distribution of soil pores. Degree of aggregation was determined primarily by the soil content of clay, 10% or more creating stable macroaggregates of 2–6 mm diameter. A comparison of the frequency curves for soil pore size to a generalized four-parameter mathematical expression relating matric potential and volumetric water content revealed that the model fitted the empirical data reasonably well for the well-sorted water-sedimented soils, while in the case of the bimodal pore size soils a deviation of differing magnitude was observed. From the investigation it is recommended that in most cases, quantities of particles and pores in soil should be related to size with frequency rather than cumulative expressions.  相似文献   

12.
The physical characteristics of the soil surface are of extreme importance in relation to energy and matter transfer processes between the atmosphere and the soil. Soil internal structure changes can be due to natural or artificial causes and one important natural process is the alternation of wetting and drying (W–D) processes, which induce swelling and shrinking of soil particles, causing modifications in pore size and shape. To study the consequence of these W–D events on possible modifications in pore size distribution, pore number, and pore shape of soil samples collected in metal rings pore image analysis was used. Samples were taken from profiles of three soils of different characteristics, named as Geric Ferralsol (GF), Eutric Nitosol (EN), and Rhodic Ferralsol (RF). Confined volumetric samples (50 cm3) were submitted to none (T0), three (T1), and nine (T2) subsequent W–D cycles. Image cross sections of resin impregnated soil permitted the micrometric and macrometric characterization of changes in soil structure induced by sequences of W–D cycles. Duncan's statistical test indicated that there were significant differences (α = 0.05) among treatments for all soil samples. General conclusions indicate that total pore area increased for all soils after repeated W–D processes, specifically 19.0 to 28.9% for GF, 5.9 to 11.7% for EN, and 13.0 to 17.2% for RF. Main changes of pore diameter occurred in pores larger than 500 μm, and minor changes were observed in the total number of these pores. It is demonstrated that soil samples undergo important changes in their structures after repeated W–D cycles. The information presented here is very important for the evaluation of soil water retention curves and other soil hydric properties, because soil samples used in these procedures are collected in rings and frequently submitted to several W–D cycles.  相似文献   

13.
The spatial and temporal nature of the precise interactions between soil fungi and roots and their subsequent role in developing soil structure is still a subject where our understanding is limited. This research examines the relationship between three species of arbuscular mycorrhizal fungus (AMF) and soil structural characteristics. Plantago lanceolata was inoculated with one of: Glomus geosporum, Glomus mosseae or Glomus intraradices, and every combination of the fungal species. Infectivity was similar for each individual species, but G. mosseae and G. intraradices together resulted in the lowest per cent root length colonised. Despite the lower percentage colonisation, this combination induced the greatest mycorrhizal growth response. Aggregate stability and aggregate size distribution were unaffected by AMF but were increased by the presence of roots. Microbial biomass-C was also enhanced by roots. Pore size, pore size distribution and nearest neighbour distance were all reduced by G. mosseae and increased by G. intraradices. All AMF inocula containing G. intraradices resulted in greater distances between pores within the experimental soils. Porosity (%) was increased by G. mosseae suggesting that more, smaller pores with less distance between them enhanced overall porosity.  相似文献   

14.
The relationship between structure and the hydraulic conductivity of soil   总被引：7，自引：0，他引：7  
A random fractal matrix comprising a hierarchical aggregation of primary structural elements is used to capture the characteristics of a heterogeneous soil structure with a tortuous pore space. The influence of heterogeneity of both the solid matrix and the pore space, as well as the shape of the pore boundary, on the saturated and unsaturated hydraulic conductivity is studied. For such random structures, the fractal (Hausdorff) dimension alone is not enough to characterize the structure from the point of view of fluid flow and additional characterizations are introduced. The porosity, ρp, of the primary elements has a critical value, ρc. With probability 1, both the saturated and unsaturated conductivities are found to be dependent as a power law on the length scale, L, at which the measurement is made when ρp>ρc. When ρp<ρc, only the unsaturated conductivity is scaling in length scale, while the saturated conductivity becomes dominated, with probability close to 1, by the conductivity of the largest connecting pores in the structure, i.e. preferential pathways. The relationships between the parameters of the power laws and structure are derived and are found to depend on the fractal (Hausdorff) and spectral dimensions of the solid matrix, denoted dm and respectively. A discussion of the importance of these results for the interpretation and extrapolation of measurements is presented, and the implications for variability and predictability of the hydraulic properties of soil is discussed.  相似文献   

15.
In the sandy soils of northeast Thailand, root development is generally limited to the topsoil (0–20 cm depth) but a simple slotting intervention (20–40 cm) significantly increased the root frequency in the slotted material (Eslot) compared with the undisturbed subsoil (E horizon). The aim of this study was to investigate the consequences of slotting on the soil structure by analysing at different scales the pore characteristics of the original soil profile and of the soil material inside the slot. These characteristics were studied using bulk density measurements, image analysis of thin sections and mercury porosimetry. Our results showed that the total porosity of the E horizon and Eslot material was similar when measured in 100 cm3 cylinders, but that the pore size distribution had been changed by slotting. The unaltered E horizon contained mainly small pores characterized by a narrow distribution related to close packing of the sand grains, associated with some biological macropores probably with poor continuity as they did not contain roots despite their size. On average, pores were larger in the Eslot material, with a broader distribution resulting from looser packing of the sand grains but with fewer biological macropores. Although slotting reduced the number of biological pores, the looser packing appeared to be more favourable to root development than the presence of macropores in the E horizon. Finally, the comparison of the porosity in the different horizons with the porosity of the Eslot material, indicated the significance of the closeness of the sand packing on root development.  相似文献   

16.
Spatial location of carbon decomposition in the soil pore system   总被引：5，自引：0，他引：5  
We sought to examine the distribution of carbon (C) decomposition within the framework of the soil pore system. Soils were sampled from a transect having a natural gradient in pore‐size distribution. After the addition of labelled wheat straw (13C) the repacked soil columns were incubated (25°C) at soil water matric potentials of either ?75 kPa or ?5 kPa and for either 4 or 90 days. Pore‐size distribution was determined for each soil column after incubation and soils were then analysed for soluble C, label‐derived residual C, label‐derived and native biomass C, nematode abundance, and ergosterol concentration as an indicator of fungal biomass. Overall, the data suggested that pore‐size distribution and its interaction with soil water give rise to a highly stratified biogeography of organisms through the pore system. This results in different rates of decomposition in pores of different size. Added plant material seemed to decompose most rapidly in soils with a relatively large volume of pores with neck diameters c. 15–60 µm and most slowly in soils with large volumes of pores with neck diameters < 4 µm. Regression analysis suggested that at matric potentials of both ?75 kPa and ?5 kPa the fastest decomposition of organic substrate occurred close to the gas–water interface. This analysis also implied that slower rates of decomposition occur in the pore class 60–300 µm. Correlations between the mass of soil biota and the pore volume of each pore class point to the importance of fungi and possibly nematodes in the rapid decomposition of C in the pores c. 15–60 µm during the early stages of decomposition.  相似文献   

17.
羟丙甲纤维素对土壤水分入渗特性及水稳性团聚体的影响   总被引：3，自引：0，他引：3  
吴军虎  任敏 《水土保持学报》2018,32(6):66-71,235
通过向土壤中施加不同含量的羟丙基甲基纤维素(简称HPMC),研究了HPMC对土壤水分入渗特性及土壤水稳性团聚体的影响。结果表明:(1)土壤中施加一定量的HPMC可以显著降低土壤入渗能力,在施加量为0～1.0g/kg范围内,累积入渗量、湿润锋运移距离和入渗率均随施加HPMC含量的增加而显著减小;利用Philip方程和Kostiakov公式对实测数据进行拟合发现,两者均能较好模拟施加HPMC后土壤的入渗过程,随HPMC施加量的增加,吸渗率S、稳渗率A和经验系数K明显减小,经验指数β逐渐增大。(2)随HPMC含量的增加,0.25mm的水稳性团聚体百分比明显增大,供试土壤的分形维数逐渐减小,其平均重量直径与水稳性团聚体含量间呈显著正相关关系,表明施加HPMC之后,土壤结构更趋于稳定,土壤抗破坏和抗侵蚀能力增强。HPMC加入土壤后具有明显的减渗效果,一定程度上可以增加水稳性团聚体含量,改良土壤结构,并提高土壤的抗侵蚀能力。  相似文献   

18.
为了明确农业生产过程中耕作方式对田间土壤孔隙结构及土壤水分运动特性的影响,以广西农地蔗田为研究对象,基于土壤切片技术分析研究免耕和垄耕2种典型耕作方式蔗田的田间土壤孔隙结构特征,并结合土柱模拟入渗试验,探究土壤孔隙结构对土壤水分运动的影响,进一步揭示孔隙结构与土壤水分运动特性之间的相互作用关系。结果表明：随着土层深度的增加,免耕蔗田孔隙形态以聚集的团块状分布为主,垄耕蔗田孔隙形态以条状分布为主。与免耕蔗田相比,垄耕蔗田的土壤总孔隙度和>2.5 mm孔径的孔隙度分别增加32.5%和21.9%。垄耕蔗田在局部土层深度范围内显著增加上下土层孔隙的变异度(p<0.05),显著降低土壤孔隙的连通性(平均邻近指数为0.448)(p<0.05),土壤孔隙形态相对规则(平均成圆率为0.335)。对于土壤水分运动特性,免耕蔗田总体的土壤饱和导水率和质量流率显著高于垄耕蔗田(p<0.05),初始含水率显著低于垄耕蔗田(p<0.05),质量流率随时间变化强度相对较大,提高水流入渗能力。垄耕降低土壤孔隙结构连通性,使水分蓄存在表层土壤中,一定程度上可降低土壤水分的入渗现象,改变蔗...  相似文献   

19.
Soil physical quality (SPQ) assessment is an important part in the evaluation of soil use, management, and conservation. It can be assessed using several physical properties, hydraulic indices, and functions. Soils from tropical and temperate regions represent different physical behaviors, and the quantification of their physical properties is important to support soil evaluation and modelling. The objective of this study was to evaluate the SPQ in a subtropical field under maize crop cultivation according to its physical properties, hydraulic indices, and functions in an attempt to infer the spatial variability and to determine the behavior of soil physical structure across a spatial domain. Commonly used soil key physical variables, such as texture, bulk density, total porosity, saturated hydraulic conductivity, and organic carbon content, were measured in a regular grid with a soil sampling density of 30 points per hectare, covering an area of 0.5 ha. Saturated hydraulic conductivity varied strongly between subsamples and in the field, suggesting the heterogeneity of the soil structure regarding water drainage. The physical variables were combined with other indicators, which were based on the soil water retention curve and the pore size distribution (PSD) function. Correlation analysis was performed to verify the relationship between the measured and calculated variables, and some strong linear correlations were revealed, such as between aeration energy index and microporosity (r = 0.608) and water retention energy index with microporosity (r = 0.532) and with bulk density (r = 0.541). For most sampled locations, the shape and location parameters of PSD showed results outside of the optimum ranges, whereas the hydraulic energy indices and cumulative hydraulic energy functions presented values that were similar to those found for some tropical soils described in the literature. The spatial variability of these indices was described using semivariograms and kriged maps, indicating the variability of the SPQ in this field.  相似文献   

20.
The one-dimensional (1-D) image analysis system described in the companion to this paper (Part I) was used to analyse horizontal sections of pore space (≥ 180 μm) in four forest soil profiles with impeded drainage. Parameters were interpreted with respect to structure in the images. Mean solid intercept length is inversely proportional to extent of pore space. It was longer for blocky structures than massive structures, which had extensive, fine pore space. It decreased with decreasing ped size, increasing development and increasing intrapedal porosity. The solid intercept length distribution separated the effects of intrapedal porosity. For blocky structures, the pore intercept length distribution indicated the sizes and quantities of fissures and intrapedal pores. All profiles had an horizon with blocky structure with lower porosity owing to greater distance between interpedal pore space and low extent of intrapedal pore space. The deeper, more massive horizons had extensive, fine pore space separating fine aggregates.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号