Dry Bulk Density Values Research Articles

Direct Shear Strength Characteristics in Unsaturated Compacted Soil Surface Coverage on Pb(II)-Polluted Tailings Reservoir under Low Normal Stress

Mining activities generate a large amount of solid waste called tailings, and it often contains a certain number of heavy metals, depending on the different types of minerals. To avoid disasters caused by the diffusion of tailings and their infiltration into surface water, mines often use tailings ponds as a surface coverage structure. This study mainly focused on the shear strength of surface coverage isolation layer soil under low normal stress. The soil isolation layers with different values of dry bulk density, water content, bentonite content, and Pb(II) ion concentration were treated with direct shear strength under normal stress at 12.5, 25, 50, and 100 kPa. It was found that when the dry bulk density was increased from 1.1 g/cm3 to 1.3 g/cm3, the shear strength increased by 49.3%~117.2%, and when the water content was decreased from 24% to 16%, the shear strength increased by one to three times. With the addition of bentonite in proportions from 18% to 30%, shear strength increased by 1.9 to 116.9 kPa, and the degree of improvement was related to both dry bulk density and water content; the specimens with bentonite added were more sensitive to Pb(II) ion concentration, and when the specimen with 24% bentonite addition was compared with the specimen without the addition of bentonite, both under a Pb(II) ion concentration of 5 mg/L, the shear strength decreased by 8.1~35.6 kPa, the internal friction angle decreased by 0.5~9.7°, the cohesion force decreased by 5.8~37.7 kPa, and the shear modulus decreased by 5~12 kPa/mm. Therefore, in order to maintain good mechanical properties in the surface covering structure, it is necessary to maintain a high dry bulk density, low water content, and bentonite content of no less than 24%.

Soil Sustainability: Analysis of the Soil Compaction under Heavy Agricultural Machinery Traffic in Extensive Crops

Crop establishment depends mostly on the soil preparation and sowing methods used. Our main goal was to evaluate soil compaction and its effects on wheat (Triticum aestivum L.) and soybean (Glycine max L.) yields and seedling emergence with two different tillage methods: no-tillage (NT) and conventional tillage (CT). The study was done in the Western Pampas Region during three cropping seasons. The soil of the study site is a Mollisol. The variables measured were: (1) cone index (CI), (2) dry bulk density (DBD), (3) seedling emergence (SE), and (4) crops yield (CY). For both crops, seedling emergence was slower in NT than in CT, but results were similar 22 days after sowing. After 3 years, the results show that in NT the DBD and CI reached values of 1653 kg m−3 and 3210 kPa, respectively (between 275 and 300 mm). While in CT the values of DBD and CI reached were 1540 kg m−3 and 2300 kPa respectively at the same depth. The highest yields were found in CT (3.31 and 4.10 tons/ha−1, for soybean and wheat, respectively) compared to NT (2.91 and 3.53 tons/ha−1). Topsoil horizon has to be tilled to improve crop yields. In spite of the high number of equipment passes in CT, both tillage systems caused subsoil compaction.

Carbonate strength classification based on depositional textures and fossil content of the Lower Eocene Drunka Formation, Assiut Area, central Egypt

The present study reports petrographic and physico-mechanical analyses conducted on the lower Drunka Formation in the Assiut Area of Central Egypt. The study investigated the percentage of carbonate content and percentage of allochems “Ach” and their impact on the petrophysical features using correlation and multivariate regression analyses. This study analyzes the petrophysical characterization of Drunka Formation rocks and the effect of fossil content on them. The carbonate rock samples derived from the lower Drunka Formation were studied to evaluate the compressive strength , dry and saturated unit weight, porosity, and acoustic wave velocities. The petrographic examination of the rock samples was conducted to understand the facies characteristics, size and percentage of grains, matrix type and extent of diagenesis . Various microfacies associations were also detected within the examined samples, such as lime-mudstone, echinoidal bioclastic wackestones, nummulitic/miliolid wackestones, bioclastic peiodal packstone, echinoidal packstone and nummulitic grainstone . Petrophysical analyses displayed a wide range of porosity and dry bulk density values from 1.3 to 2.75% and 2.31–2.48 g/cm 3 , respectively. The wet bulk density and grain densities are between 2.33˗2.50 and 2.35˗ 2.57 g/cm 3 , respectively. The dry ultrasonic wave velocity “V p” was observed between 2926 and 5549 m/s, whereas the saturated ultrasonic wave velocity “V p “was estimated between 3067 and 5875 m/s. The Unconfined Compressive Strength (UCS) of the tested samples was 22 ≤ UCS ≤ 82 MPa while the slake durability index was recorded as 94.37 ≤ SDI ≤ 98.7%. The Brazilian test indices characterized the studied rock samples as highly porous rocks and showed the values of 1.47 ≤ Brazilian ≤ 5.13 MPa. Finally, for all tested facies, the Böhme test data have a minimum, maximum, and an average of 12.98, 25.95, and 19.04 cm 3 /50 cm 2, respectively. The study's findings showed that, except for the mineral grain scale, the physico-mechanical properties are highly dependent on the petrographic characteristics. The study also revealed that the Ach% and the rock's carbonate content significantly affect the rock's petrophysical and mechanical properties under investigation. The mechanical properties such as UCS, tensile and point load test. increase with increasing carbonate content and decreasing with increasing Ach% of the rock. This paper presents an extensive dataset of physical parameters of a carbonate formation in Egypt; many empirical relationships are presented for predicting mechanical properties. This provides site-specific predictive value; the relationships can be used for all carbonate rocks worldwide with broader international significance. • Classification of strength from texture is proposed based on fossil and carbonate content. • This study analyzes the petrophysical characterization of Drunka Formation rocks and the effect of fossil content on them. • This paper introduces a new strength classification of carbonate rocks based on allochems and carbonate content. • The depositional texture of carbonate rocks has a significant impact on variations of physico-mechanical properties of rocks. • Diagenesis has a remarkable effect on rock strength.

Carbon sequestration potential of Avicennia marina (Forssk.) Vierh. and Rhizophora mucronata Lam. along the Western Red Sea Coast of Egypt

Increased levels of global atmospheric carbon dioxide (CO2) and further consequences of climate change derived more research efforts to emphasize the actual role of the ecosystems of higher significance in this task. Mangrove ecosystem received a great interest in the demonstration of its potential to sequester atmospheric CO2. Sampling process from the sediment of mangrove ecosystem extended some 600 km along the Egyptian western coast of Red Sea, starting from Abu Monquar Island (27.216250° N, 33.876288° E) at the north near Hurghada to Sharm El-Madfa’a (22.895165° N, 35.717757° E) near the Egyptian–Sudanese frontiers. This work compares the pure population of Avicennia marina (Forssk.) Vierh. and Rhizophora mucronata, Lam. as well as the mixed population of both species. Mean values of dry bulk density (DBD) were 1.2 ± 0.02, g cm−3 for pure A. marina, 0.8 ± 0.06 g cm−3 for pure R. mucronata, and 0.7 ± 0.04 g cm−3 for mixed sites. In addition, the values of mean soil organic carbon (SOC) were 10.2, 51.7 and 89.0 g C kg−1 for pure A. marina, pure R. mucronata and mixed sites, respectively. On the other hand, the mean values of soil organic carbon pool (SOCP) were 258.0, 604.7 and 1049.3 Mg C ha−1 for pure A. marina, pure R. mucronata and mixed sites of both species, respectively. The carbon sequestration potential (CSP) of pure A. marina, pure R. mucronata, and mixed sites of both species were 0.8, 2.2, 3.4 Mg C ha−1 year−1, respectively.

Changes in selected physico-chemical properties of floodplain soils in three different land-use types after flooding

This article provides information on selected physico-chemical properties, including soil colour, texture, electrical conductivity, pH<sub>H</sub>2O, pH<sub>CaCl</sub>2, content of total carbon and Q<sub>4/6</sub> quotient, of the topsoil and subsoil of former flood sediments at three diverse vegetation plots in a floodplain and in two reference plots unaffected by floods, and changes of some soil properties caused by a new subsequent flood. Aggradation of flood sediments in the area was controlled both by local terrain morphology and vegetation type cover. Differences in the properties of sediments in the individual plot types were caused by the different production of litter, root biomass and carbon cycling before the new flood. Vertical distributions and inventories of <sup>137</sup>Cs in soils revealed the position and proportion of modern sediments in soil profiles, man-made filling of former erosion grooves and ploughing depths. The new flood of a lower hydrological power aggraded a thin layer of organo-clay sediment on the soil surface but showed minor effects on the investigated soil properties. The lowest dry bulk density and highest total porosity values were found in the topsoil of woody and grassy plots after the flood implying no substantial break down of soil aggregates by the flood. The highest dry bulk density values in the subsoil of fields indicated soil compaction from agricultural machinery. No increased soil salinity was found after the flood. The flood did not significantly affect the pH<sub>H</sub>2O of the topsoil and subsoil; however, a significant increase in pH<sub>CaCl</sub>2 was found for the topsoil of grassy plots and for all topsoil samples from the park. No significant increases in total carbon (C<sub>tot</sub>) contents were found in topsoils of any plot types after the flood in spite of an accumulation of thin organo-clay material on the soil surface after the flood. However, significant increases in C<sub>tot</sub> in subsoils of all plot types indicate the vertical migration of colloidal and dissolved organic carbon in soils during the flood. C<sub>tot</sub> contents positively correlated with electrical conductivity values and negative correlated with pH values. The relatively minor changes in soil physico-chemical properties found after the flood can be explained by the short duration and small dynamic power of the flood, and the timing of sampling when the flood had receded and soil aeration was already being restored.

ESTUDO DE MEIO REATIVO PARA BARREIRAS REATIVAS PERMEÁVEIS (BRP): ENSAIOS LABORATORIAIS

Esse manuscrito apresenta resultados de estudos laboratoriais para avaliar a adequabilidade de zeólitas como meio reativo de Barreiras Reativas Permeáveis (BRPs), em 3 faixas granulométricas (4,0x10-4 a 1,0x10-3 m, 1,0x10-3 a 2,0x10-3 m e 1,0x10-3 a 3,0x10-3 m). Estudos foram desenvolvidos por meio da caracterização física, química, mineralógica, permeabilidade e de sorção. A zeólita caracterizada é da espécie Clinoptilolita, com peso específico dos sólidos de 22,87 kN/m3, razão Si/Al de 6,8 e capacidade de troca catiônica de 180 cmolc/kg. Os diferentes arranjos volumétricos das partículas geraram valores de peso específico aparente seco de 10,01 a 11,00 kN/m3 e condutividades hidráulica saturada de 1x10-5 a 3x10-4 m/s, o que compatibiliza os arranjos com diferentes meios geológicos. Em termos de sorção, a isoterma do tipo Langmuir ajusta com r2 de 0,997 e, quanto a cinética de adsorção, o comportamento ocorre por meio do compartilhamento de elétrons entre zeólita e soluto, com coeficientes de reação de primeira ordem variando de 0,06 a 0,4h-1 em função do tempo de percolação. Os resultados mostram que as zeólitas nas faixas granulométricas estudadas são adequadas para uso como meio reativo de BRP em espessuras economicamente viáveis para áreas contaminadas inseridas em materiais geológicos relativos à Formação Botucatu.

The role of brush mats in mitigating machine-induced soil disturbances: an assessment using absolute and relative soil bulk density and penetration resistance

Forest soils often exhibit low bearing capacities and as a result are often incapable of withstanding high axle loads. In New Brunswick, Canada, five different brush amounts (0, 5, 10, 15, and 20 kg·m–2) were applied as brush mats on machine operating trails during a cut-to-length harvesting operation in a softwood stand to analyze soil disturbance as a result of off-road forest harvesting machine traffic. Soil absolute and relative bulk density and soil penetration resistance measurements were completed below the varying brush mats both before and after forwarding. The mean differences between pre- and post-impact absolute soil dry bulk density values recorded on track areas were 0.24 g·cm–3 for 5–20 kg·m–2 of brush and 0.33 g·cm–3 for 0 kg·m–2 of brush. On average, 40.5%, 17.9%, 14.3%, 15.5%, and 3.6% of all post-forwarding measurements exceeded the threshold for growth-impeding soil bulk density (80% standard Proctor density) for 0, 5, 10, 15 and 20 kg·m–2 of brush, respectively. Soil penetration values >3.0 MPa represented 23.7%, 15.0%, 9.4%, 4.6%, and 0.7% of all post-forwarding test plots with 0, 5, 10, 15, and 20 kg·m–2 of brush, respectively. The results suggest that softwood brush mats of 10 to 20 kg·m–2 placed on machine operating trails play a considerable role in reducing forwarder-induced soil compaction and penetration resistance.

Practical Considerations & Good Protocol for the Interpretation of Ultramafic & Mafic Rock Physical Property Data

An increase in the availability of inexpensive and easy-to-use geophysical tools has led to an interest in the development of larger rock physical databases. These data are often interpreted at face value, with little consideration given to the selection of representative samples, sample preparation, or even the practical limitations of measuring tool. Consequently, wide-ranging data are often observed. This may lead to incorrect interpretation. Magnetic susceptibility and density measurements are now routinely made on drill-core specimens. These data are often amalgamated with historical measurements in an effort to make localised physical property databases more robust. Two practical considerations regarding these data are discussed: 1) The evaluation of dry bulk density data, and inherent issues with measuring dimensions or applying volume assumptions; 2) The appropriateness of using commonly employed inductive electromagnetic tools, i.e. handheld magnetic susceptibility meters, to resolve induced magnetisation.Changes in core-diameter due to coring and rock swelling are studied, as are the effects of core volume loss due to cutting. A comparison between empirical measurements and volume estimations has shown that up to 7% and 30% of variability may be attributed to changes in drill-core diameter and split-core geometry, respectively. Dry bulk density data that have been calculated using estimated volumes may be in extreme error and therefore inappropriate to use. Orientation markings or bottom-of-hole lines have shown to correlate with reduction in variability of core volume loss caused by cutting. The use of an Almonte core-holder, or similar, is shown to produce an even lower and less variable core volume loss. The reliability of historical dry bulk density values may be ranked based on the presence of orientation or bottom-of-hole line, or known implementation of a core cutting holders.Bulk magnetic susceptibility measurements made on ultramafic and mafic diamond drill-core using a handheld instrument are evaluated. Comparisons with Qmeter magnetisation data show that handheld bulk magnetic susceptibility values may be in the error of several orders of magnitude. Anisotropy is hypothesised to be the principal cause of variation. Furthermore, conductivity effects that are induced by handheld meters, e.g. frequency dependence, may contribute to an under-reporting of values.

Sunflower (Helianthus annuus L.) harvest: Tractor and grain chaser traffic effects on soil compaction and crop yields

AbstractPrevious studies have defined compaction as an important degradation process of agricultural soils. However, there is very little information (under field conditions) on the effects of tractor and grain chaser traffic during harvest operations on soil cropped for 15 years under no‐till cultivation methods. The aim of this study was to quantify the effects of two different total loads of tractor and grain chaser traffic on soil physical properties and sunflower (Helianthus annuus L.) yields. The treatments included a control plot with no tractor or grain chaser traffic (T1), a plot with tractor and grain chaser traffic with a total load of 275.8 kN (94.35 kN km−1 ha−1; T2), and a plot with tractor and grain chaser traffic with a load of 332.2 kN (123 kN km−1 ha−1; T3). Soil physical properties and sunflower yields were analysed over three growing seasons in the western part of the Pampa region, Argentina. In the topsoil (0 to 200 mm), the results showed that after one pass of T2 and T3, infiltration decreased significantly compared with that in T1; a similar trend was observed for total topsoil porosity. Cone index values in T3 were >2.5 MPa and between 3.33 and 4.90 MPa in the subsoil (200 to 600 mm). Dry bulk density values in T3 were >1.70 Mg m−3 in the topsoil and in the subsoil. This study also demonstrated that as the wheel load and ground contact pressure increase, sunflower yields decrease and subsoil compaction increases, even in soils with a high bearing capacity.

Assessment of ground-based skidding impacts on the horizontally rate and extent of soil disturbance along the margin of the skid trail

Skidding operations significantly influenced soil physical properties up to a 2-m distance from the wheel ruts in a forest ecosystem. The most significant changes in soil properties were identified within a 0.5 m to 1 m transitional zone. The main purpose of this investigation was to determine how far into a forest stand changes in soil physical properties were evident due to skidding operations. Treatment plots with three replications included combinations of four distance zones at 0.5 m intervals (0 to 2 m in distance) on both sides of skid trail edges to the forest, three slope gradient levels were applied (gentle 20 %) and two levels of traffic intensities 20 and 40 passes (with a rubber-tyred skidder, model HSM 904). A total of 576 soil samples were used in this study. Results showed that the physical properties of soil were significantly changed by each traffic intensity in the first distance zone, where the slope was >20 % compared to soil changes at a slope of 20 % after 20 and 40 skidding cycles. Dry bulk density values reached its maximum levels in the first 0.5 m from the skid trail on slopes >20 % after 40 skidding cycles.

Nursery Growing Media: Agronomic and Environmental Quality Assessment of Sewage Sludge-Based Compost

There is a stringent need to reduce the environmental impact of peat in the plant nursery production chain. In this experiment, the use of different rates of sewage sludge compost in the preparation of growing media for potted Bougainvillea was evaluated to assess its efficiency for the replacement of peat and to quantify the environmental impact of such alternative substrates by the life cycle assessment (LCA) method. Five substrates containing increasing proportion of composted sewage sludge to peat (0%, 25%, 40%, 55%, and 70% v/v) were used, and their physicochemical properties were measured. Bougainvillea plant growth, biomass production, and macro- and micronutrient absorption were also determined. The main results were that compost addition improved the plant nutrient and increased the substrate pH, electrical conductivity (EC), and dry bulk density values. Globally, the results showed that compost could be used at up to 55% by volume with no negative effects on plant growth. The LCA showed that use of compost reduced the environmental loads of the growth media, except the Global Warming Potential value (GWP100). Environmental implications of the use of compost in the plant nursery chain are discussed.

Impact of land use on the hydraulic properties of the topsoil in a small French catchment

AbstractThe hydraulic properties of the topsoil control the partition of rainfall into infiltration and runoff at the soil surface. They must be characterized for distributed hydrological modelling. This study presents the results of a field campaign documenting topsoil hydraulic properties in a small French suburban catchment (7 km2) located near Lyon, France. Two types of infiltration tests were performed: single ring infiltration tests under positive head and tension‐disk infiltration using a mini‐disk. Both categories were processed using the BEST—Beerkan Estimation of Soil Transfer parameters—method to derive parameters describing the retention and hydraulic conductivity curves. Dry bulk density and particle size data were also sampled. Almost all the topsoils were found to belong to the sandy loam soil class. No significant differences in hydraulic properties were found in terms of pedologic units, but the results showed a high impact of land use on these properties. The lowest dry bulk density values were obtained in forested soils with the highest organic matter content. Permanent pasture soils showed intermediate values, whereas the highest values were encountered in cultivated lands. For saturated hydraulic conductivity, the highest values were found in broad‐leaved forests and small woods. The complementary use of tension‐disk and positive head infiltration tests highlighted a sharp increase of hydraulic conductivity between near saturation and saturated conditions, attributed to macroporosity effect. The ratio of median saturated hydraulic conductivity to median hydraulic conductivity at a pressure of − 20 mm of water was about 50. The study suggests that soil texture, such as used in most pedo‐transfer functions, might not be sufficient to properly map the variability of soil hydraulic properties. Land use information should be considered in the parameterizations of topsoil within hydrological models to better represent in situ conditions, as illustrated in the paper. Copyright © 2010 John Wiley & Sons, Ltd.

Air Permeability in Repacked Porous Media with Variable Structure‐Forming Potential

Air permeability was measured as a function of gravimetric water content and dry bulk density for six sieved, repacked porous materials with organic matter contents ranging from 0 to 88%. The six media used were two relatively fine sandy soils, a filter sand, a peat soil, and two commercial composts made from sewage sludge and yard waste, respectively. The materials were initially wetted from air dry to the desired water content, after which measurements were done. Selected combinations of material gravimetric water content and dry bulk density were used in the permeability measurements. The combinations were selected to cover the entire possible ranges of water content and dry bulk density for each material. The six materials exhibited very different relationships between air permeability, water content, and dry bulk density, exhibiting both increasing and decreasing air permeability with water content depending on their structural behavior. All six materials had regions in their water content–dry bulk density domains where air permeability tended to increase with increasing water content, indicative of increasing structure formation in these regions. This tendency was strongest for the two sandy soils and weakest for the filter sand, which exhibited almost no structure formation. Increased structure, as indicated by increasing air permeability with increasing water content, was strongest for low values of dry bulk density in all six materials.

Changes in some physical properties of a clay soil in Central Italy following the passage of rubber tracked and wheeled tractors of medium power

The aim of this study was to evaluate the compacting effect of rubber tracked tractors in comparison to that of the traditional wheeled tractors. Macroporosity, pore shape and size distribution, bulk density, penetration resistance and saturated hydraulic conductivity were analysed in a clay soil (Vertic Cambisol) near Rome (Italy) following one and four passes on the same track of rubber tracked and wheeled tractors of medium power. The soil structure attributes were evaluated by characterising porosity by means of image analysis of soil thin sections prepared from undisturbed samples. Macroporosity decreased in the 0–10 cm layer of compacted soil, particularly after four tractor passes, due to a large reduction in the proportion of elongated pores and in their vertical continuity. The rubber tracked tractor had a more pronounced compaction effect in the surface layer (0–10 cm) than the wheeled tractor both after one and four passes; the latter treatment producing the lowest soil porosity. The same trend was observed for hydraulic conductivity, which showed a highly significant correlation with elongated pores. In the 10–20 cm layer the porosity was significantly decreased following traffic, apart from in the soil under one pass of the rubber tracked tractor. Again in this layer, the lowest values of porosity were found in soil after four passes of the rubber tracked tractor. Single and multiple passes made by the two tractors induced different effects regarding soil penetration resistance and bulk density. Increment ratio of penetration resistance after tractor passes with respect to the control was: 12.5 and 49.9% with the wheeled and 34.4 and 39.8% with the tracked after one and four passes, respectively. Increment ratio of dry bulk density values after tractor passes with respect to the control was 7.9 and 11.7% with the wheeled and 7.5 and 8.3% with the tracked after one and four passes, respectively. The tractor passes transformed the initial subangular blocky structure into a massive structure with sometimes a platy structure in the upper few centimetres. The results indicated that soil compaction following traffic with the rubber tracked tractor was generally the more pronounced. However the compacting effect of this tractor after one pass seemed to be limited to the surface layer only.

Composting of Green Waste Shredded by a Crush/Cut Roller Versus a Low Speed Counter-Rotating Shear Shredder

Green waste was shredded at a commercial composting site by a conventional commercial low speed counter-rotating shear type shredder and an alternative shredder, a crush/cut roller mounted on and powered by a tracked excavator. Material from both shredding systems showed similar dry weight and dry bulk density patterns across a broad particle size distribution range. The crush/cut roller produced significantly different (p < 0.05) quantities of material in the 10-25 mm and 75-100 mm particle size ranges, whilst dry bulk density values were significantly different in the 16-25 mm range only. Over a three month windrow composting period, dry weight percentage and dry bulk density values from both systems tended to increase toward the lower end of the particle size range and decrease toward the higher end of the particle size range and were, with one exception, not significantly different. These values were similar in magnitude to those for material from commercial green waste composting windrows. Temperature profiles were comparable in both systems and indicated the existence of thermophilic conditions within each windrow for over 50 days, whilst product stability, as indicated by specific oxygen uptake rates, was the same for both treatments. It was concluded that any differences in particle size distribution between the two shredding systems were not important in relation to the biological aspects of the composting process. Development of a simple compost maturity test based on particle size profiling is suggested. It is proposed that the alternative, crush/cut roller, approach to green waste shredding could potentially reduce the economic threshold for organic recycling and allow many smaller communities to benefit from this environmentally sound waste management practice.

Changes of some physical properties of a clay soil following passage of rubber- and metal-tracked tractors

The aim of this research was to evaluate the change in physical properties of an arable clay soil following passage of rubber- and metal-tracked tractors in view of increased use of tracked tractors for ploughing on clay soil in centre-south and insular Italy. Field tests were carried out on arable soil cropped to lucerne ( Medicago sativa L.) to compare two types of tracked tractors, one with rubber tracks (CAT Challenger Ch35) and one with metal tracks (FIAT FA 150) in order to establish the compacting effects resulting from one and four passes of the tractors on the same track. The following parameters were studied: soil penetration resistance, bulk density and its increment ratio, pressure distribution on soil along the length of the tracks, soil macroporosity and hydraulic conductivity. Multiple passes made by the two tractors induced very similar effects in the surface soil in regards to soil penetration resistance and dry bulk density. Mean values of penetration resistance (0 to 0.20 m depth), were 2425 kPa for rubber tracked tractor and 2415 kPa for metal-tracked tractor; dry bulk density values were 1.52 and 1.48 Mg m −3, respectively. The decrease in macroporosity, in particular that of elongated pores in the soil surface layer (0–0.10 m depth) was greater in treatments involving the rubber-tracked tractor (from 10.6% to 4.0%) than for the metal-tracked tractor (from 10.6% to 7.3%). Following traffic of the two tractors hydraulic conductivity decreased and the lowest values were found after one and four passes of the rubber-tracked tractor (1.5 and 0.08 mm h −1, respectively). A highly significant correlation between hydraulic conductivity and elongated pores and a significant correlation with total macroporosity were found. Significant exponential relationships between macroporosity and penetration resistance for one and four passes of both tractors were found in the surface soil. A significant difference was found between tractors and for correlations of penetration resistance values above control values. However, in the soil surface with respect to the higher degree of porosity, treatments involving the metal-tracked tractor showed better soil structure quality.

SINGLE-SOURCE GAMMA RADIATION PROCEDURES FOR IMPROVED CALIBRATION AND MEASUREMENTS IN POROUS MEDIA

When dual-energy gamma radiation systems are employed for measurements in porous media, count rates from both sources are often used to compute parameter values. However, for several applications, the count rates of just one source are sufficient. These applications include the determination of volumetric liquid content values in two-liquid systems and salt concentration values in water-saturated porous media. Single-energy gamma radiation procedures for three applications are described in this paper. Through an error analysis, single-source procedures are shown to reduce the probable error in the determinations considerably. Example calculations and simple column experiments were conducted for each application to compare the performance of the new single-source and standard dual-source methods. In all cases, the single-source methods provided more reliable data than the traditional dual-source methods. In addition, a single-source calibration procedure is proposed to determine incident count rates indirectly. This procedure, which requires packing under saturated conditions, can be used in all single- and dual-source applications and yields accurate porosity and dry bulk density values.

Compressibility of Some Trinidadian Soils as Affected by the Incorporation of Peat

The effect on compressibility of incorporating peat into four remoulded Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa using a compression machine. Air-dry peat was applied at four levels (0, 4, 8 and 12% by mass) to the soils (two sandy loams, clay loam and clay) and tested at three moisture contents close to the Proctor optimum moisture content of the soils. Compression curves (bulk density versus log applied stress) for each soil at the moisture levels tested were almost linear and parallel over the range of stresses from about 100 to 1000 kPa. Mean values of dry bulk density declined significantly at 0.001 level with increasing peat content from 1·23 to 0·87 Mg m -3. Mean bulk density values increased significantly at 0·001 level with increasing applied stress and moisture content and declined with increasing clay content. Significant interaction effects were observed between soil type and peat content and between peat content and moisture content. Peat incorporation resulted in greater soil compression, but the increases were less evident in clay than in sandy loam soils. Soil compression refers to the decrease in soil volume with the application of external load. The compression index, C (slope of the dry bulk density versus log applied stress relationship), increased significantly at 0·05 level from 0·21 Mg/m 3 in one sandy loam soil to 0·38 Mg/m 3 in the clay soil. While the C value did not differ significantly with increasing peat content in the sandy loams and the clay loam, it decreased significantly at 0·01 level in the clay soil. An equation expressing C as a function of initial soil bulk density before compression and a strain parameter was developed in order to explain the variation of C in the soils tested. A method is described that can be adopted to quantify the effect of peat on soil compressibility.

The soil condition of adjacent bio‐dynamic and conventionally managed dairy pastures in Victoria, Australia

Abstract. Physical and chemical properties were compared during 1992 in adjacent bio‐dynamic and conventionally managed Haploxeralfs under improved, summer‐irrigated pastures in the Goulburn Valley of N.E. Victoria. Intensive dairy production has been practised on both the farms since the early 1950s, and aspects of the bio‐dynamic method have been practised on one farm for the past 18 years. Particle‐size analysis showed that the soil profiles of each field are derived from similar parent materials. The bio‐dynamic soil had greater macro‐porosity to a depth of at least 420 mm, lesser soil strength at 60, 120 and 200 mm, smaller dry bulk density values between 120 and 200 mm and larger organic matter content in the upper 50 mm. Volumetric soil water content measured along three transects to a depth of 1.4 m in the summer showed that the bio‐dynamic field was drier at depths greater than 200 mm. After heavy rains during the winter, the conventionally managed soil had an air‐filled porosity unfavourable for plant roots (2%) at 200 mm depth, whereas the bio‐dynamic soil was marginal for root growth (7%). The more favourable physical and chemical properties in the bio‐dynamic soil may be attributed to less grazing pressure, longer intervals between irrigations, use of the bio‐dynamic horn‐manure preparation, intermittent compost applications, less tractor traffic and the encouragement of taller pasture growth.

AGRONOMIC USE OF CLAY SOILS FROM- ABITIBI, QUEBEC

We grew three successive crops of oats (Avena sativa L.) on Abitibi soils, either from individual horizons or from horizon mixtures. Soils were used as such or amended with 10 t of C/ha, added as peat or manure. Yield significantly decreased from the first to the third crop. In the third crop, yields of the manure-treated samples were significantly higher, at the 5% level, than those of the untreated samples. Adding an organic amendment caused a decrease of up to 9% of dry bulk density values. We also discuss the effects of cultivation on some chemical properties.