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Chapter 57 Soil Density and Porosity

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... After the experiments, the oven-drying method (Rabot et al., 2018) measured the total porosity (n). In many cases, media porosity varies in solute transport, because of the consolidation effects of clays and other fine and coarse-grained materials (Ahfir et al., 2017;Hao et al., 2019). This means that the impacts of changing porosity (n) on solute transport parameters can also be seen in various saturated porous media. ...
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This study explains the importance of layered soil, the solute storage regions, and their residence time for groundwater remedy. A one-dimensional layered soil column experiment was conducted in clay, silt sand, fine sand, coarse sand, and very coarse sand, to investigate the mobile-immobile (MIM) solute transport and their residence time (RT). The Two Region Model (TRM) and Continuous Time Random Walk (CTRW) were used to simulate breakthrough curves (BTCs) and transport parameters were estimated by best fitting the experimental breakthrough curves (BTCs). Numerous significant results were found. Higher hydraulic conductivity (K) values in Snad layers indicate a more effective medium for solute transport. The early long-time tailing in fine sand, coarse sand, and very coarse sand showed an increase in the dispersion coefficient (D) estimated by TRM and larger values in mobile water fraction (φ) and mass transfer coefficient (ω) than those obtained for clay and silt sand layers. This indicates a larger solute residence time (RT) in fine sand, coarse sand, and very coarse sand layers than in clay and silt sand. These variations are also credited to the effect of immobile water. The average tracer velocity (Vψ) greater than the pore water velocity (V) indicates that the solute concentration is higher in the mobile region. Smaller values of β in the mobile region indicate that the solute transport was relatively faster with an average shorter residence time (RT) than that was in the immobile regions. The study will help us minimize the threat of subsurface water contamination. Graphical Abstract
... Porositas tertinggi 70,89 % pada perlakuan P2, karena bobot isi paling rendah (Tabel 1) dan tanah porous (Guo et al., 2021). Porositas tanah ditentukan oleh bobot isi tanah, makin naik bobot isi tanah makin rendah persentase prosositas tanah (Hao et al., 2019). ...
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Research to determine the effect of OST ingredients and manure from chicken manure on the physical properties of Ultisol was carried out with a completely randomized design with factorial patterns. The experimental treatment consisted of giving OST, namely P0 = without OST, P1 = 5 g/pot, P2 = 10 g/pot combined with manure, B0 = without manure, B1 = 40 g/pot and B2 = 80 g/pot repeated 3 times. The results showed that bulk density, porosity, soil pore distribution and aggregate stability were affected by OST material, while manure only affected aerase pores, unavailable pore water and aggregate stability.
... Porositas tertinggi 70,89 % pada perlakuan P2, karena bobot isi paling rendah (Tabel 1) dan tanah porous (Guo et al., 2021). Porositas tanah ditentukan oleh bobot isi tanah, makin naik bobot isi tanah makin rendah persentase prosositas tanah (Hao et al., 2019). ...
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Research to determine the effect of OST ingredients and manure from chicken manure on the physical properties of Ultisol was carried out with a completely randomized design with factorial patterns. The experimental treatment consisted of giving OST, namely P0 = without OST, P1 = 5 g/pot, P2 = 10 g/pot combined with manure, B0 = without manure, B1 = 40 g/pot and B2 = 80 g/pot repeated 3 times. The results showed that bulk density, porosity, soil pore distribution and aggregate stability were affected by OST material, while manure only affected aerase pores, unavailable pore water and aggregate stability.
... La densidad real, es un parámetro dependiente de la composición mineralógica, el contenido de materia orgánica e influenciado por el tamaño de partículas debido al cambio gradual de la composición mineralógica (Brogowski et al. 2014). Así en el suelo Fr.A., con fracciones dominantes de arena (70%), compuesto eminentemente de cuarzo de densidad de 2,65 g.cc -1 y menor contenido de materia orgánica, tendrá una densidad real ligeramente mayor respecto del Fr.Ar.A. que poseen menor arena y mayor material fino como arcilla y materia orgánica, en razón a que la densidad real, representa el promedio compuesto de la densidad de todas las partículas que componen el suelo (Hao et al. 2019). Los resultados son comparables a los hallados por Schojoning 2017, quienes demuestran que hay una clara disminución de la densidad de partículas, con el aumento del contenido de materia orgánica, es decir un compuesto de baja densidad real (1.3 a 1.5 g.cc -1 ). ...
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Debido a la necesidad de optimizar el agua, se estudia a la diatomita, poco explorado en agricultura. La diatomita, roca sedimentaria de origen orgánico, aporta sílice y posee elevada porosidad y superficie específica. En Ayacucho la diatomita o “Quicato” de elevado contenido de silicio, porosidad superior al 80% y muy poco contaminante, podría emplearse en la actividad agrícola. Se evaluó en condiciones de laboratorio la aplicación de dosis de diatomita (0, 5, 10 y 15% v/v) de 2 mm, en dos suelos, de textura franco arcillo arenosa (Fr.Ar.A.) y franco arenosa (Fr.A.) de Luricocha - Huanta, a fin de valorar sus efectos sobre las propiedades físicas entre ellas la capacidad de campo, densidad aparente, densidad real y porosidad total de los suelos. Luego de incubar conservando a capacidad de campo los suelos durante seis meses, se encontró que incorporar 5, 10 y 15 % (v/v) de diatomita, aumenta significativamente la capacidad de campo en 2.87%, 8.39%, 9.87% (Fr.Ar.A) y 3.14%, 6.46%, 9.77% (Fr.A.), respecto al testigo. 15% (v/v) de diatomita en suelo Fr. A, disminuye respecto al testigo en 5.20%, la densidad aparente y en 9.66% la porosidad total. En suelo Fr.Ar.A., no influyen significativamente en ambos parámetros, sin embargo, muestra tendencia creciente en poros totales. La densidad real en ambos suelos, disminuye linealmente con las dosis de diatomita, de 2.56 a 2.38 g.cc-1 en Fr.A. y 2.48 a 2.40 g.cc-1 en Fr.Ar.A.
... Sediment bulk density (ρd) was calculated based on dry weight divided by the volume. The void ratio (e) was then estimated using bulk density, particle density (ρp = 2.65 g/cm 3 ), and water density (ρw = 1.0 g/cm 3 ) [37]. Porosity (n) was derived from the void ratio [38]. ...
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Connectivity of landslide sediment to and within fluvial systems is a key factor affecting the extent of mobilization of hillslope material. In particular, the formation of landslide dams and the transformation into landslide-induced debris flows represent “end members” of landslide sediment mobility. To quantify sediment connectivity, we developed a two-segment flume representing tributary inflow and the main channel. Mobility of sediment was examined by combinations of various topographic factors, such as tributary inflow angle (0 to 90° in 30° increments) and main channel gradient (10° and 15°), as well as water content of sediment (0 to 100% in 20% increments). We also examined differences of mobility among sediments derived from various lithologies (sand and shale, pyroclastic sediment, weathered granite, and weathered sedimentary rock). Mobility of sediment differed, depending on the water content of sediment, particularly less than saturation or greater than saturation. When all types of unsaturated landslide sediments entered the channel at inflow angles of 60° and 90°, substantial deposition occurred, suggesting the formation of landslide dams. At low inflow angles (0° and 30°) in a steep channel (15°), >50% of landslide sediment was transported downstream, indicating the occurrence of a debris flow. The amount of sediment deposited at the junction angle was greater for pyroclastic sediment followed by weathered granite, weathered sedimentary rock, and finally, sand and shale. Our connectivity index suggests that a threshold exists between landslide dam formation and debris flow occurrence associated with topographic conditions, water content, and types of sediment.
... Soil samples from each plot represented a composite of five 5.25 cm-diameter soil cores collected at five depths (0-5, 5-10, 10-20, 20-30 and 30-40 cm). Soil samples were used for soil bulk density analysis with the method described by Hao et al. (2008). ...
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Background and aims Relevant soil properties and nutrient distributions influencing crop root growth might be different under no-till (NT) and mouldboard plough (MP) management. The possible different root systems within different managements might have key impact on crop nutrient uptake and consequently crop production. Our objective was to assess the long-term combined effects of tillage and phosphorus (P) fertilization on corn (Zea mays L.) root distribution and morphology. Methods Corn root and soil samples were collected during the silking stage at five depths (0–5, 5–10, 10–20, 20–30 and 30–40 cm) and three horizontal distances perpendicular to the corn row (5, 15 and 25 cm) under MP and NT with three P fertilizations (0, 17.5, and 35 kg P ha−1) for a long-term (22 years) experiment in eastern Canada. Root morphology and soil properties were determined. Results NT practice decreased corn root biomass by −26 % compared to MP, mainly by decreasing the primary and secondary roots. Additionally, corn roots in NT tend to be more expansive on the surface layer with higher root length and surface densities for the depth of 0–5 cm at two sampling distances of 15 and 25 cm. The 35 kg P ha−1 rate increased the root biomass by 26 and 41 % compared to the 0 and 17.5 kg P ha−1 rates. Conclusions No-tillage practice and low rates of P fertilization reduce corn roots. This is probably caused by the weed competition in NT and the continued downward P status with low P rates over 22 years.
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Characterization of soils in selected potato growing farms of Molo, Nakuru County in Kenya was compelled by the decline in potatoes acreage yields observed in the study area over the years. In the pursuit of reasons behind the decline, this study determined levels of some key soil fertility indices in soil samples obtained from selected farms. Four farms that have been in intensive potatoes farming were used. The soil was randomly collected from a depth of 0-10 cm separately for all the investigated sites. Collected site-wise samples were air-dried, ground, and passed through a 2 mm sieve and stored in plastic containers ready for analysis. Analytical techniques employed were Walkley black for carbon, Kjeldahl for nitrogen, standard wet chem soil analysis, saturation method for water porosity, glass electrode determined soil pH, bulk density, particle density, water holding capacity were determined by methods of Keen box. The mean levels of essential soil fertility indices obtained were; soils pH (5.46 ± 0.43), soil bulk density (g/cm3) (1.03 ± 0.01), particle density (2.51 ± 0.08), water holding capacity (%) (36.07 ± 2.57), porosity (0.59 ± 0.01), exchangeable cations (uS/cm) (83.63 ± 14.22), cation exchange capacity (meq/100g) (18.48 ± 0.89), organic carbon (%) (3.50 ± 0.24), total nitrogen (%) (0.17 ± 0.03). Mean micro and macronutrients available (mg/Kg) were; phosphorous (7.92 ± 4.10). These findings reveal the extent of some fertility indices depletion in the soils and will form a base for decreased acreage yield of potatoes in this region. The results further form the baseline for future research on the working acreage of key soil fertility indices required for remediation.
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Measuring the tempospatial variability of saturated hydraulic conductivity (Ks) is time consuming, expensive, and encounters many uncertainties. This work aimed to develop a new model (REPM, Relative Effective Porosity Model) that estimates Ks from relative effective porosity (φer) and then compare it with a model (EPM, Effective Porosity Model) that estimates it from effective porosity (φe). The effective porosity (φe) is defined as the total porosity minus field capacity (FC), and the relative effective porosity (φer) is defined as effective porosity (φe) divided by FC. Both φer and φe can be estimated from FC and bulk density (Bd). Data from 11 homogeneous textural-class mean soils and several international and American soils were used to evaluate REPM and EPM. For the 11 textural-class mean soils, log (Ks) was highly correlated to log (φer) as well as to log (φe). For the international soils, log (Ks) was highly correlated to log (φer) (r2 = 0.77), but the correlation was less pronounced between log (Ks) and log (φe) (r2 = 0.58). The saturated hydraulic conductivity of soils from an international database was more accurately predicted by REPM (RMSE of 539 cm d-1) than by EPM (RMSE of 733 cm d-1), while both of them performed as well for American soils. The slope and the intercept of REPM and the slope of EPM were independent of soil. These results suggest that our new model gives reasonable estimates of Ks for different soils.
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Intrinsic permeability to air of macropore space (ka) is related to macroporosity (ɛ) and organization of macropore space (O). Organization is defined as ka/ɛ. The use of ka for estimating saturated hydraulic conductivity (Ka) is also considered. The relationship between Log (O) and ɛ (Oɛ characteristic) can be used to describe changes to the macropore space of clay soils by amelioration and compaction. The effects of dominant macropore shape can also be identified and calculated as an empirical index of the efficiency of the pore organization E (E=log (O)/ɛ). Intrinsic permeability can then be related to E in a E:ka characteristic. Intrinsic permeability is the parameter most sensitive to structural change and E is mainly influenced by the dominant shapes of the macropores. Thus, the E:ka characteristic is suggested as a basis for studying differences in macropore space as may occur in response to external and internal stresses upon the soil and different systems of soil management, for example increases of packing pores by cultivation or of fissures by gypsum application and loss of packing pores by compaction. Empirical data indicate that Ks of the B horizons of Australian red-brown earths can be estimated from ka of macropore space at a standard potential.
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An improved technique for measuring soil water desorption curves of a large number of soil cores was tested. A procedure for improving contact between the soil and a "tension medium" resulted in rapid extraction of water from 7.6 × 7.6-cm cores at pressure heads from 0 to −500 cm of water. The data for clay and sandy loam cores showed that equilibrium was reached in less than 200 h at all pressure heads. The "tension medium," used essentially as a large porous plate, was carefully chosen with a narrow pore size distribution. This provided a high hydraulic conductivity and high air-entry values, both necessary for efficient desorption over the pressure head range 0 to −500 cm of water. A tensiometer-pressure transducer combination for establishing equilibration time proved more reliable than the traditional weight-loss criterion. The consistency and reproducibility of desorption curves was demonstrated using data for hysteretic loops as well as standard deviations of water contents at each pressure head on similar soils.
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mine the three-dimensional distribution of solids and water in laboratory soil cores (Phogat et al., 1991, Ro- The partitioning of the soil volume between water, solids, and air gasik et al., 1999). Applications of these techniques are strongly influences many soil processes. In this paper we demonstrate a new approach to nondestructively measure this partitioning. A limited to laboratory settings and are further limited by thermo-time domain reflectometry (thermo-TDR) probe was inserted lack of access to the equipment. The limitations of cur- into sandy loam soil and used to apply thermal and electromagnetic rent techniques create a need for new techniques to pulses and to monitor the transport of these pulses through the soil. measure the partitioning of the soil volume between We used the resulting data to determine the soil water content, air- water, solids, and air. filled porosity, and volume fraction of solids, as well as degree of Our new technique for determining the , vs, and the saturation and bulk density. When calibrated for this soil, the standard volume fraction of air in soil (na) follows from a unique errors between thermo-TDR measurements and gravimetric measure- combination of two widely accepted theories. The first ments were 0.02, 0.07, and 0.05 m 3 m 3 for water content, volume theory is that the thermal properties of a system are fraction of solids, and air-filled porosity, respectively. The standard related to the volume fractions of the individual compo- error for degree of saturation was 0.08 m 3 m 3 , and for bulk density
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Soil saturated hydraulic conductivity (Ks) is an important soil physical property. Some laboratory and field methods are expensive, time consuming and labour intensive. Indirect methods such as pedo-transfer functions (PTF) are available. Effective porosity or macroporosity (Øe) is approximately equals to porosity minus volumetric soil water content at the field capacity. According to Kozeny–Carman equation, Ks could be evaluated using Øe. Franzmeier estimated the Ks from Øe based on Ahuja et al. He found a strong relationship between Øe and Ks. This paper presents results of a study to characterize the effective porosity in lowland paddy fields and to show the possibility of using the effective porosity (Øe) in estimating the saturated hydraulic conductivity (Ks). Soil in lowland paddy fields forms its horizon as topsoil, hardpan and subsoil. Soil samples were collected randomly within a 2300-ha rice cultivation area where there are five dominant soil series. A total of 408 soil samples were taken from 136 sampling points and at three depths, namely, the topsoil, hardpan and subsoil. Ks values were measured in the laboratory using the falling head method. Soil bulk density and moisture content at −66 kPa were determined. The Øe was then calculated using the difference of the total porosity (Ø) minus the volumetric moisture content at −66 kPa. The Ks values ranged from 5.35×10−4 to 8.77×10−2 m day−1. The Db varied from 0.62 to 1.91 Mg m−3, and the values of the Dp ranged from 1.10 to 2.89 Mg m−3. The Ø ranged from 0.17 to 0.68 m3 m−3. The results of the Øe of the samples in this study were obtained by calculating the difference of the total porosity and volumetric moisture content at field capacity. For clayey soils, field capacity is taken at the suction of −66 kPa. The Øe varied from 0.05 to 0.55 m3 m−3, with the mean value of 0.24 m3 m−3. The regression equation of a power function shows a highly significant regression coefficient, r2 of 0.50 (n=400). This indicates that there is a strong relationship between Ks and Øe for the lowland paddy soils in the study area.
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Information in regard to nondestructive and repetitive measurements of changes in soil porosity (ϵ) that may occur during wetting and drying is limited, particularly information regarding changes on a very small scale. The objectives of this study were (i) to determine whether the changes in ϵ that may occur during wetting and drying at scales as small as 2 × 2 mm can be discriminated by computer-assisted tomography and (ii) to use a published theoretical equation to estimate surface fractal dimension (D) from ϵ and to determine whether D is sensitive to wetting and drying. Computer-assisted tomography was applied to gamma-ray attenuation to measure dry bulk density (ρ), before and after wetting, at 2 × 2-mm resolution of water-stable soil aggregates (WSA) 2 to 4, 0.71 to 1.40, and 0.25 to 0.71 mm in size and packed separately in acrylic cylinders. Columns with similar particle size were also prepared for unstable soil aggregates (USA). Before wetting, ϵ computed from ρ in WSA, ranged from 0.621 to 0.740; after wetting the range was 0.604 to 0.709. In USA, ϵ ranged from 0.489 to 0.562 before wetting and from 0.457 to 0.516 after wetting. The lack of a 1:1 relationship between the before and after wetting data for ϵ indicated there were significant differences between the two. Initial aggregate size (x), wetting, (w), and the interaction w x accounted for 74% of the variability in ϵ of USA compared with only 47% of the variability for WSA. The estimates of D, obtained using the theoretical equation and ϵ, ranged from 2.154 to 2.236 for WSA and from 2.055 to 2.12 for USA. Wetting, x, and w x accounted for 47% of the variability in D of USA compared with 69% for WSA. Pore continuity (PC), estimated using a theoretical relation involving PC, ϵ, and D, decreased from 0.45 to 0.30 after wetting in USA and from 0.60 to 0.55 in WSA.
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Long-term cultivation of soils for arable crops and without application of organic manure is thought to reduce the soil quality for crop production. We studied the porosity of two sandy loam soils from organic dairy farms with a ley cropping system and compared them with a conventionally managed dairy farm growing arable crops only and an arable soil receiving only mineral fertilizers, respectively. Saturated hydraulic conductivity, water retention characteristics, air diffusivity and air permeability were determined in the plough layer of the soil. The soil of one of the organic dairy farms contained many more earthworm burrows and had a significantly larger hydraulic conductivity than the counterpart soil of the conventionally managed dairy farm. In other respects, these two soils were much alike. The soil of the other organically managed dairy farm was less dense and had a larger volume of pores > 30 μm than the arable soil receiving only mineral fertilizers. A tube model was used to combine the air exchange measurements in a description of the soil pores. The pore system of the mineral fertilized soil consisted of continuous arterial pores with only a small volume of blocked and marginal pores embedded in the soil matrix next to the arterial pores. The porosity of the counterpart organic dairy farm soil had a considerable volume of blocked and especially marginal pores. The complexity of the latter was considered beneficial for local aeration in the soil and for derived soil properties such as fragmentation on tillage.
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Two models are presented describing the air-filled continuous pores in soil and how they change with soil water potential. In the first model (A), the pores are represented by tortuous tubes of uniform radius. The radius, length and number are calculated from air permeability, relative diffusivity and air-filled porosity measured at each soil water potential. In the second model (B), the pores are represented by tortuous tubes of three radii joined at random in series. The radii and total lengths of the tube sections are estimated by comparison of air permeability, diffusion coefficient and air-filled porosity at each water potential with values calculated for a large number of theoretical systems. The models were applied to the results from undisturbed cores of a silt loam taken from 30 to 80 mm depth. For both models, the sequences of continuous pores were estimated to be 2 to 7 times as long as the sample but shortened as the sample dried. From the second model the average pore radius in direct drilled soil, 0.3 mm, was half that in ploughed soil and the minimum radius, 0.1 mm, was one-quarter that in ploughed soil.
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A classification of structural condition in surface soils is proposed, based on the volumes of two categories of pore size, termed air capacity (pores greater than 60 μm diameter) and available water (pores of 60 to 0.2 μm diameter. Relationships of pore volumes to particle size class, organic carbon content and soil water regime are examined. Soil structural conditions are mainly affected by water regime and organic carbon and, apart from the extremes of sandy or clayey textures, less influenced by particle size distribution.
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SummaryA simple model was employed to interpret the results of a series of measurements of gas diffusion in soil cores. The model divides air-filled porosity into three functional categories: arterial, marginal and remote. Diffusion along the axis of the core occurs through arterial pores; marginal pores do not contribute to axial diffusion; remote pores are isolated from gas transport. Simulations based on the model closely resembled data acquired from real cores. Optimizing the fit between real and simulated data gave estimates of the three functional pore fractions which generally made sense (compaction or wetting of cores resulted in reduced arterial and increased marginal porosities, for example). Dividing the pores into the different classes specified by the model was functionally equivalent (i.e. observable results were identical) to the introduction of a tortuosity factor to represent pore convolution. In order to account for observed diffusion rates in terms of pore convolution alone it is sometimes necessary to invoke implausibly high tortuosities; the introduction of marginal porosity renders this unnecessary without in any way compromising the ability of the model to simulate real diffusion data.
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A method is described for the rapid determination of water release characteristics in soil cores 75 mm diameter and 50 mm deep of field structure.A simple suction table system is described for drainage of samples to matric potentials between 0 to −20 kPa. The need for material to promote contact between sample surfaces and the suction medium is emphasised. The equilibration of samples on pressure plates to matric potentials < −20 kPa is also briefly considered.Guidelines are provided for the choice of equilibration pressures and saturation method. Errors associated with compactness, texture, wetting method, water content and disturbance at sampling and equilibration with the suction medium are discussed. Particular consideration is given to the determination of saturated water content and total porosity and their variation with soil type and condition.
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The volumetric ring and the computerized tomography (CT) techniques were applied to study soil bulk density, in order to understand the compaction of an Albaqualf soil (Planosol) of the Rio Grande do Sul State, Southern Brazil (latitude 31°52′00″S and Longitude 52°21′24″W). Among six different tillage systems and crop rotations the greatest soil bulk density was measured for the continuous irrigated rice crop system and the lowest for the no-tillage treatment under rye grass straw. The CT method enabled the measurement of bulk density variations in the soil profile and indicated critical zones not observed by the volumetric ring method that measures only the mean sample soil bulk densities. A meaningful correlation between soil bulk densities measured by both methods was found, although the CT method presented more reliable results in comparison to the volumetric ring method. A 3% variation in bulk density was observed due to method intrinsic errors, probably also correlated to different samples sizes.
Article
The variation of soil compactibility and its relationship to plasticity, texture, organic matter and particle density is considered for 156 sites and for one intensively sampled site. These sites were concentrated in east Scotland and were the locations of Scottish Agricultural College (SAC) ®eld experiments and surveys related to tillage and compaction. Compactibility was determined by a rammer method on sieved soil. The coef®cient of variability of compactibility (as maximum dry bulk density) was relatively low between sites (9.5%) and within site (4%). The soils covered a wide range of textures; sand contents ranged from 1.7 to 93.5 g 100 g À1 and clay contents ranged from 2.5 to 49.1 g 100 g À1 . However, liquid limit was more important than particle size fractions in the prediction of compactibility. Loss-on-pretreatment prior to measurement of particle soil distribution was taken as a measure of readily oxidisable soil organic matter. This fraction was more variable and more relevant than total organic matter in determining mechanical behaviour. Compactibility was predicted adequately by a combination of loss-on-pretreatment and liquid limit. Maximum dry bulk density and liquid limit were identi®ed as important characteristics of the dataset and would be suitable parameters for measurement of soil physical/ behavioural quality. Although particle density was not particularly important in predicting compactibility, it ranged from 2.36 to 2.87 Mg m À3 . Awareness of this variability is important for properties estimated by a calculation involving particle density. # 2000 Elsevier Science B.V. All rights reserved.
Article
Two regression equations describing water movement in saturated macropores in the field are compared with a theoretical expresion of the form Qma e2ma where Qma is the saturated volume flux density through a macropore system of porosity ema. The theoretical exponent of 2 agrees fairly well with the analyses of two very different sets of field experiments by Burger (1922–1940) and Ehlers (1975). It is suggested that the relationship Qma= Q*e2ma may be a useful first approximation to predict macropore flow, where Q* is an empirical coefficient that is expected to depend on the hydraulic connectivity, geometrical structure, tortuosity, roughness and other properties of the macropore system.
Article
Gas diffusivity and permeability, and air-filled porosity, were measured in undisturbed soil cores at six water potentials between -2 kPa and oven dryness. All increased as water potential fell. In silt loam at 30 to 80 mm depth, relative diffusivity and air permeability at -2 kPa were 0.0013 and 5 × 10−8cm2 after direct drilling, and were 6 and 15 times greater respectively after ploughing, presumably because of the larger volume of air-filled large pores in the ploughed soil. These pores may also have been more continuous or less tortuous than in the direct drilled soil. However, at equal air-filled porosities up to 0.18 v/v, the pores were apparently more continuous and less tortuous in the direct drilled than in the ploughed soil. In the direct drilled silt loam at any given matric potential, air-filled porosity, gas diffusivity and permeability within and below the previously ploughed layer were isotropic. In clay loam at 30 to 80 mm depth gas diffusivity and permeability at -2 kPa were greater than in the silt loam irrespective of tillage but increased less on oven drying.
Article
Relative gas diffusivity, air permeability and hydraulic conductivity were measured in undisturbed soil cores from tillage and traffic experiments. Continuity indices were taken as the quotient of relative diffusivity and air‐filled porosity, and of air permeability and air‐filled porosity (and the square of air‐filled porosity). These were applied to individual measurements or to treatment means. More general continuity indices were derived from the changes in flow or diffusion with porosity, where the variations in porosity were due to both field variability and applied changes of water potential. These indices were the exponent in the relationship between relative diffusivity and air‐filled porosity and the slope of log–log plots of air permeability and air‐filled porosity or hydraulic conductivity and degree of saturation. Some physical significance was attached to the exponents by comparison with models of soil porosity. Positive intercepts of the relative diffusivity or air permeability plots on the air‐filled porosity axes were taken as porosities blocked to gas movement. Continuity indices and flow measurements showed differences between tillage and traffic treatments which did not necessarily reflect differences in bulk density. Intrinsic permeability was better estimated from air permeability than from unsaturated hydraulic conductivity.
Article
Great Plains dryland agriculture is a risky venture because of large annual fluctuations in precipitation and high evaporation potentials. Water capture is limited by low water infiltration rates because many of our soils have relatively small aggregate size distributions, which limit infiltration, and are also susceptible to crusting and sealing. No-till management has permitted cropping intensification, which via improved water storage, has increased crop residue returned to the soil, decreased surface bulk density, and increased surface soil porosity. Our objective was to quantify the relationship between crop residue biomass generated by cropping system intensification and the physical properties of the surface soil (0–2.5-cm depth). This study was conducted within an existing long-term dryland experiment consisting of three sites in eastern Colorado that transect an evapotranspiration gradient. Each site transects a soil catena with three distinct soils arranged along a slope gradient. Only soils at the summit and toe slopes were sampled for this study. Soils are Argiustolls and Ustochrepts. Three no-till cropping systems, Wheat–Fallow (WF), Wheat–Corn–Fallow (WCF), and Continuous Cropping (CC), were sampled in the summer of 1998 after the cropping systems had been in place for 12 years. Bulk density, effective porosity, aggregate size distribution, sorptivity, and soil aggregate organic C content were measured at the surface 2.5 cm of the soil in each cropping system at the two soil positions at each site. Bulk density was reduced by 0.01 g cm−3 for each 1000 kg ha−1 of residue addition over the 12-year period. Each 1000 kg ha−1 of residue addition increased effective porosity by 0.3%. Increases in macroaggregation were associated with linear increases in the C content of the aggregates; each g kg−1 of organic C in the macroaggregates increased the proportion of macroaggregates by 4.4%. Implementation of no-till intensive cropping systems under this semiarid environment increased residue biomass, which has ultimately increased effective porosity, and thus water capture potential was increased.
Article
Investigations of the physical and chemical characteristics of macropores and mesopores at two forested sites established for subsurface transport research are summarized. The hydrologically active macroporosity (pores larger than 1 mm diameter) is a very small fraction of the total soil porosity but is sufficient to conduct a large proportion of ponded infiltration. Mesopores (pores less than 1 mm diameter that are generally drained at field capacity) are sufficient to conduct total infiltration during the majority of rain events and have a much higher surface area than macropores. The cation adsorption coefficient of macropore walls was similar to bulk soil for mineral coatings but was higher for organic linings derived from roots. The subsurface outflow from a 0.46 ha subwatershed generated by two precipitation events displayed two contrasting patterns of chemical concentration. At the time of peak discharge, the concentration of Na, K, Mg, Ca and S was close to maximum (high supply); and for Al, Fe and Mn, chemical concentration was highest prior to peak discharge (low supply). A pathlength-supply hypothesis is proposed, based on (1) changing proportions of mesopore flow path lengths with stage of the subsurface hydrograph and (2) the ability of mesopore surfaces and adjacent micropores to continue supplying chemicals to percolating soil water. Macropores are viewed as being important physical conduits in convergent flow zones of watersheds but as having little influence on water quality.
Article
The temporal variability of soil porosity, especially macropores (> 50 μm), and associated porosity factors such as pore continuity, percent water-filled pore space (%WFPS), and earthworm numbers and biomass were determined over 3 years under direct-drilling and mouldboard ploughing. The study was conducted on a Charlottetown fine sandy loam, an Orthic Podzol with a humid to perhumid soil-moisture regime.Differences in soil porosity between tillage systems were mainly confined to the surface 0–8-cm soil depth. Fissures (> 300 μm), or large pores, were reduced under direct drilling compared with mouldboard ploughing, but subject to regeneration over the winter period. The absence of soil loosening caused the volume of macropores to fall below 10% during the growing season. Tillage had a residual effect on soil porosity, maintaining the volume of macropores between 11 and 18%. Differences between tillage and ice-induced porosity influenced the degree of macropore regeneration. In general, water-storage pores were similar between tillage systems. A close relationship (r2 = 0.832) was observed between dry bulk density and macroporosity under both tillage systems. The relationship between macroporosity and pore continuity (Ksat), which differed between tillage systems, indicated that a macroporosity of between 8 to 10% (v/v) would maintain adequate soil permeability. In contrast, the %WFPS, which was closely related (R2 = 0.952) to macroporosity and soil water content, indicated that the volume of macropores should exceed 14% to provide an optimum level of air-filled pore space.Under humid soil-moisture regimes, the use of macroporosity as an index of critical soil structure or limiting density needs to be based both on adequate soil permeability and on water-filled pore space. Although direct drilling maintained adequate functional porosity, the need for an optimum aerobic environment may necessitate loosening of the surface soil on an annual basis.
Article
The effect of the application of sewage sludge on soil porosity over 28 months is discussed here. Anaerobic sludges of urban refuse waters were applied on a degraded limestone soil in a mining land by two ways. First, a previous mixture of sludge and soil was carried out; this was then applied to the target land. Second, a direct application of sludge to soil and tilling. Porosity and pore morphology were measured on thin sections prepared from undisturbed soil samples. Data were obtained from backscattered electron images and image-processing computer equipment. The application of sludge induced an increase of both soil fine microporosity (φ<50 μm) and coarse microporosity (φ>50 μm). However, this effect showed transient, since no significant differences were reported in relation to the control plot after one year from application. The incorporation of sludge and developed vegetation modified coarse micropore irregularity and orientation. On the other hand, fine micropore morphology remains unchanged.
Article
The potential suitability of a soil to accommodate growing roots was assessed on the basis of: (1) the existing pore space available for unobstructed root growth; and (2) the obstruction offered to a growing root by the soil matrix. The former was evaluated by measuring the air permeability of undisturbed soil cores, equilibrated at a chosen water tension. The latter was evaluated by measuring the spectrum of the tip resistance encountered by a slowly penetrating fine probe.The influence of cropping history on this potential suitability was examined by comparing the same soil with two different cropping sequences (corn grown continuously for five years and forages grown for three years followed by two years of corn). Measurements were started shortly before the forages were plowed under.Air permeabilities were higher for the plots on which forages had been grown, indicating greater potential suitability for unobstructed root growth. The penetration experiments showed that the average resistance to deformation of root-sized pores was equal for the two cropping patterns. The average bulk density was higher in the continuous corn plots than in the plots on which forages had been grown. After analysis of our data we postulated that the effect of the higher bulk density was offset by lower aggregate strength in the continuous corn plots. Implications of this hypothesis are discussed.
Article
Heavy agricultural machinery can cause structural degradation in agricultural subsoils. Severe structural degradation impedes plant growth. Therefore, compaction must be limited to layers that can be structurally reclaimed and remoulded with reasonable effort by tillage. The purpose of this study was to investigate the impact of a single pass with a sugar beet harvester on the soil properties of an unploughed Eutric Cambisol. Field measurements and laboratory testing were carried out in Frauenfeld, Switzerland. In addition 2D calculations of strain, stress and subsequent compaction were conducted using a three-phase (soil skeleton, pore water, and air) model for unsaturated soil incorporating a recently developed constitutive law. Model data were compared to the field measurements. Due to the pass of the machinery, the soil was compacted down to a depth of at least 0.15 m and at most 0.25 m. This compaction was indicated by an increase in soil bulk density and pre-consolidation pressure as well as by a decrease in total porosity and macroporosity. The surface displacement measured in the field was consistent with the calculated model data. The calculated and measured stresses at depths of 0.35 and 0.55 m stand in good accordance with each other, whereas at a depth of 0.15 m the pressure measured in the field exceeded the calculated pressure. In this study, we show the degree of compaction due to heavy wheel traffic and the suitability of a model approach to describe compaction processes.
Article
The aim of this study was to investigate the effects of different tillage operations on bulk density, and the hydraulic properties of a loamy sand soil of southwestern Nigeria. A replicated randomised complete block design with treatments consisting of (i) no-tillage (NT), (ii) manual tillage (MT), (iii) plough-plough tillage (PP) and (iv) plough-harrow (PH) operations established at the Teaching and Research Farm, Obafemi Awolowo University, Nigeria was used for the study. The soil bulk density, cone index of penetrometer resistance, saturated hydraulic conductivity and moisture retention characteristics were determined for each of the treatments. The cone penetration resistance was determined at the depths of 5, 10 and 15 cm while the soil moisture and suction relationship was determined on the surface (0–15 cm) soil at the suction of 4.5, 50, 100 and 150 kPa. The bulk density, penetration resistance and saturated hydraulic conductivity were determined weekly over a period of 8 weeks after tillage operations. All the tillage operations were significantly different in their effects on soil density and was in the descending order of NT > MT > PP > PH. The soil bulk density decreased with the degree of soil manipulation during tillage practices, with NT having the highest (1.28 g cm−3) and PH having the least (1.09 g cm−3). The soil bulk density also increased with increase in time after cultivation. The soil penetration resistance was consistent with bulk density data, with NT also having the highest resistance of 0.65 kg cm−2. Soil saturated hydraulic conductivity at 8 weeks after tillage decreased with increased intensity of soil manipulation by tillage. The highest conductivity was recorded under NT (7.2 × 10−3 cm s−1) and the least under PH (6.1 × 10−3 cm s−1). Regression analysis revealed a strong and positive correlation between soil saturated hydraulic conductivity and porosity within individual tillage treatments. The however weak relationship between conductivity and porosity when considered across all the tillage treatments indicates that total porosity is not the major determinant of saturated hydraulic conductivity in this soil. This was attributed to the disturbance of continuity of macropores under the conventionally tilled plots.
Article
Methods for evaluating soil conditions as influenced by tillage are often limited to analysis of bulk samples. The application of medical computed tomography (CT) to the characterization of tillage effects on soil provides an alternative tool for measurement since it is at a more detailed scale. The objective of this study was to compare soils under conventional and no-tillage (NT) systems using X-ray CT. Chisel-disk-disk (CDD) conventional tillage and NT systems were compared for a Mexico silt loam (fine, smectitic, mesic Aeric Vertic Epiaqualfs) soil. Five replicate soil cores (75 mm long by 75 mm diameter) were collected from each treatment. Two CT systems were used in this study: a medical CT scanner (MCT, 1 mm thick scans) and an ultra-high resolution CT scanner (UHCT, 0.1 mm thick scans). Significantly higher soil density was found for the NT treatment using the MCT scanner (P=0.05). Data from the UHCT scanner were used to compare the effects of scan thickness and to evaluate macropore characteristics. Macropore area was significantly higher (P<0.001) for CDD as compared to the NT treatment: 11 versus 5%. The number of macropores in the CDD treatment were twice those in NT; their perimeter was 62% longer; and their circularity was 94% of that for pores from the NT tillage treatment. The macropore box-counting fractal dimension (D) was significantly greater (P<0.001) for CDD (D=1.44) as compared to the NT treatment (D=1.26), reflecting the greater space-filling behavior of the CDD treatment. This study shows that the UHCT scanner can characterize differences in soil macroporosity more precisely than standard MCT scanners. The use of ultra-high resolution tomography can aid in the discrimination of differences between seedbeds created by different tillage systems.
Article
An index for classifying soil pore size distribution is proposed. The arithmetic mean change in percent soil water content by weight as the tension changes from zero to 1.5 bars is used as the index. This number characterizes the size distribution of pores with a radius of one micron or greater. A simple equation is presented to calculate the index from soil water contents at pressure plate settings of zero, 0.2, and 1.5 bars. Moisture release curves from 3 different soils show that the index does tend to characterize the shape of the release curve and that it is sensitive to past management which affects the distribution of large soil pores. When all other conditions are optimum, it appears that there exists a specific value of the index which indicates when the soil pore size distribution may be expected to limit plant growth. It is further suggested that the index, together with penetrometer measurements made at the 1.5-bar water content, may be used as “soil test values” for making practical management decisions and for predicting the stability of soils under varying field conditions.
Article
The percentage of soil pore space filled with water (percent water-filled pores, % WFP), as determined by water content and total porosity, appears to be closely related to soil microbial activity under different tillage regimes. Soil incubated in the laboratory at 60% WFP supported maximum aerobic microbial activity as determined by CO2 production and O2 uptake. In the field, % WFP of surface no-tillage soils (0-75 mm) at four U.S. locations averaged 62% at time of sampling, whereas that for plowed soils was 44%. This difference in % WFP was reflected in 3.4 and 9.4 times greater CO2 and N2O production, respectively, from surface no-tillage soils over a 24-h period as compared to plowed soils. At a depth of 75 to 150 mm, % WFP values increased in both no-tillage and plowed soils, averaging approximately 70% for no tillage compared with 50 to 60% for plowed soils. Production of CO2 in the plowed soils was enhanced by the increased % WFP, resulting in little or no difference in CO2 production between tillage treatments. Nitrous oxide production, however, remained greater under no-tillage conditions. Substantially greater amounts of N2O were produced from the N-fertilized soils, regardless of tillage practice. Production of CO2 and N2O was primarily related to the % WFP of tillage treatments although, in several instances, soil-water-soluble C and NO-3 levels were important as well. Calculations of relative aerobic microbial activity between no-tillage and plowed soils, based on differences in % WFP relative to maximum activity at 60%, indicated linear relationships for CO2 and N2O production between WFP values of 30 to 70%. Below 60% WFP, water limits microbial activity, but above 60%, aerobic microbial activity decreases - - -apparently the result of reduced aeration.
Article
This chapter discusses the influence of macroporosity on environmental quality. It focuses on field characterization of flow processes using relatively simple morphological and physical techniques that are accessible to agronomists and provides a descriptive characterization of macropore patterns in soil, using different morphometric techniques; relating morphology to physical flow processes; description of field techniques to characterize macropore flow; and relating macropore flow to environmental quality by analyzing some field studies. Numerous field studies have demonstrated that the occurrence of macropores in soils results in rapid, downward movement of solutes, which may lead to groundwater pollution. Some of these studies were made more than one hundred years ago and several reviews are available, in which these studies are summarized. Relatively simple soil morphological techniques that describe macropores in terms of type, size, number of occurrence, and vertical continuity can be useful in predicting the infiltration patterns of solutes in quantitative terms.
Article
Spatial and temporal measurements of shallow sub-surface soil physical properties were made within a 1 km2 upland catchment. The surface soil layer of the catchment was organic rich (>70% organic matter) with a corresponding total porosity of 81%. Monthly point observations of volumetric water content ([theta]) were combined with point estimates of total porosity ([var epsilon]) and the porosity <50 [mu]m ([var epsilon]residual), to define the ratio of water filled pore volume:pore volume in pores <50 [mu]m (=[theta]/[var epsilon]residual). Values of [theta]/[var epsilon]residual were compared with discharge to test whether mass flow occurred when [theta]/[var epsilon]residual>1. A correlation between water content and discharge was found, with discharge increasing rapidly when [theta]/[var epsilon]residual approached unity. Similar relationships between water content and catchment discharge were identified for soil units adjacent to the stream when [theta]/[var epsilon]residual approached unity. These data suggest that soil pores >50 [mu]m are of crucial importance in determining catchment discharge. Spatial and temporal variations in soil properties related to moisture content of the soil were also observed. Under dry conditions, a clear division based on aspect was noted, the west-facing side of the catchment being wettest. In wetter months, total porosity and soil water content were significantly affected by soil type and the spatial pattern of soil water content was more variable than in the dryer months. The physical quantification of soil properties in the shallow sub-surface layer proved important in explaining different initial changes in discharge from the catchment in response to a rainfall event.
Methods of Soil Analysis, Part 4 -Physical Methods
  • L E Flint
  • A L Flint
Flint, L.E. and Flint, A.L. 2002. Porosity. In J.H. Dane and G.C. Topp, Eds. Methods of Soil Analysis, Part 4 -Physical Methods. Soil Science Society of America, Madison, WI, pp. 241-254.
Spatial variability of soil physical properties in the filed
  • A W Warrick
  • D R Neilson
Warrick, A.W. and Neilson, D.R. 1980. Spatial variability of soil physical properties in the filed.