Relative Bulk Density Research Articles

Legume N mineralization: Effect of aeration and size distribution of water-filled pores

The relative importance of air-filled porosity and the size distribution of water-filled pores to the mineralization of legume N and soil N were assessed. Seven soils, with or without added legume, were packed to two relative bulk densities and incubated at a constant water potential. Mineralization was measured over 70 d. The accumulation of inorganic N in the amended treatment was described using a two-pool model and in the control using a one-pool model. Biomass C was measured in both treatments. Mineralization was found to be influenced by both the air-filled porosity and the distribution of the volume fractions of pores (VFP) that were water-filled and the relative importance of each was assessed using stepwise variable-selection regression procedures. The parabolic dependence of mineralization on air-filled porosity that has been observed when soils are incubated at different potentials was not obvious in soils equilibrated at a constant potential. Air-filled porosity was positively related to the rate constant of the labile pool and negatively related to the size of the resistant pool in the amended treatment. The rate constant of the control was parabolically related to air-filled porosity, but did not give rise to a predicted maximum in N accumulation within the experimental range of air-filled porosities. The VFP with dia < 3 μm was selected most often in the stepwise regression analyses. Pore characteristics had a larger influence on the labile pool than on the resistant pool of the amended treatment. The size of the labile pool and its rate constant decreased with the VFP < 3 μm dia. The size of the potentially mineralizable pool of the control treatment varied with the VFP in manner similar to the labile pool of the amended treatment. Biomass C in the amended and control treatments increased with the VFP < 1.5 μm dia, and in the amended treatment decreased with the VFP 10–20 μm dia. The role of pore size on the space inhabited by soil flora and their predators suggests that protection of soil flora in pores < 3 μm contributed to decreased mineralization from the labile pool.

Physicochemical properties and garification (gari yield) of selected cassava cultivars in Rivers State, Nigeria.

Gari was processed from six different cassava cultivars TMS 3575, TMS 3044, hormone treated variety (HTV), TMS 30555, TMS 40944 and TMS 30572. Chemical analyses of the gari samples showed pH values of: 4.0, 4.0, 3.9, 3.6, 3.4, 3.6 and total titratable acidity of 0.99, 0.99, 0.98, 0.85, 0.96, 0.85 (% lactic acid) for TMS 3575, 3044, HTV, 30555, 30572, and 40944 respectively. Physical characteristics of the samples showed the swelling index of 264.5%, 223.5%, 364.0%, 321.3%, 241.3% and 232.7%, water absorption capacity of 1.0 ml/g, 0.8, 1.5, 1.9, 1.7, 1.9 ml g(-l) sample, relative bulk density of 0.29, 0.30, 0.15, 0.17, 0.15 (g/cm3) and gari yield of 34%, 21%, 33%, 24%, and 23%, for cultivars, TMS 3575 (2), 3044, HTV, 30555, 30572, 40944 respectively. Sensory evaluation showed a significant difference (p < 0.05) in quality and overall acceptability among the samples while Tukey test showed a difference (p<0.05) between HTV and between 3575 and 3044. The cassava pulp from the cultivars and their corresponding gari had HCN content (mg/100 g) ranging from 7.9 to 9.3 for pulp and 1.1 to 1.5 for gari, respectively. The 72 hours fermentation period reduced the HCN in all cultivars by 85%, which is considered to be a safe level for human consumption.

Management versus inherent soil properties effects on bulk density and relative compaction

Bulk density ( D b) is a soil physical parameter used extensively to quantify soil compactness. The D b varies with management as well as with inherent soil properties. Because of its dependence on inherent soil properties, measurements of D b are of limited value as a measure of the effect of management on soil compaction when soils with different inherent characteristics are compared. Researchers have used the concept of relative compaction or relative bulk density, ( D b-rel), the ratio of the D b of a soil to the D b under some standard compaction treatment ( D b-ref), in order to compare the response of different soils to stresses arising from management. This research was conducted to determine D b, D b-ref and D b-rel across a range of soils under different tillage practices and to assess the relative importance of texture, organic matter content and management on these parameters. Thirty-six paired sampling sites were located along two parallel transects in a side by side comparison of no-tillage and conventional tillage treatments. The transects crossed three soil types: Aquic Hapludalfs, Psammentic Hapludalfs, and Typic Hapludalfs. Clay content (CLAY) varied from 5.8 to 42.3%, and organic matter (OM) varied from 1.4 to 11.6%. Multiple regression analyses showed that D b was related ( R 2 = 0.83) with CLAY, OM, tillage, position, and the interactions OM∗CLAY and tillage∗position, whereas the D b-ref was related ( R 2 = 0.86) with OM, CLAY, and tillage. Normalizing D b with respect to D b-ref, effectively eliminated the influence of CLAY, OM and their interaction on D b-rel. The analyses indicated that it is possible to quantify the separate effects of inherent soil properties and management on D b, when soils derived from similar parent materials and under similar climatic conditions are considered, either by using multiple regression analyses to describe D b, or by normalizing D b with respect to D b-ref.

The effect of soil compaction and soil physical properties on the mechanical resistance of South African forestry soils

High soil strengths frequently develop in compacted forestry soils thus limiting root development of commercial timber species. The effect of soil compaction on mechanical resistance was assessed for 29 South African forestry soils ranging widely in texture (8 to 66% clay) and organic carbon content (0.26 to 5.77%). Models are presented which show that clay content and organic carbon strongly influence the relationship between penetrometer soil strength (PSS), bulk density and water content. Organic carbon levels were not high enough to have a large effect on the PSS–compaction–water content relationship for finer-textured soils (>30% clay). However, evidence is presented to suggest that organic matter becomes more important in influencing PSS for a range of water contents and bulk densities as clay content decreases. For cohesive soils (generally those with more than approximately 20% silt plus clay) increasing clay content reduces the rate at which PSS increases with decreasing water content. Similar to clayey soils, non-cohesive soils (<20% silt plus clay) displayed slow rates of decrease in PSS as the soil dried although the magnitude of PSS was considerably less for similar matric potentials and relative bulk densities than for finer-textured soils. Thus the PSS at wilting point (−1500 kPa) increased with increasing clay content. At a matric potential of −10 kPa PSS was most strongly related to loss-on-ignition indicating that organic carbon and clay mineralogy rather than soil texture alone affect soil strength in wet soils.

Soil compaction reduction with a modified one-way disker

Tillage implements and power units for soil management bring about high risks of soil compaction. The detrimental impacts of soil compaction on crop production have been reported for years. A one-way disker was modified as a conservation tillage tool for eastern Canada conditions to reduce soil compaction. The main modification included replacing the original 500-mm-diameter disks with 610-mm, high sphericity (68 mm) concave disks to be operated at a working angle of 45°. A split-plot field layout was established on a Sainte-Rosalie clay with subsoiling (or without) as main plot units and tillage treatment combinations as subplot units. Before seeding to corn ( Zea mays L.), the modified one-way disker (MOD) was used for (1) both fall primary and spring secondary tillage, (2) fall primary tillage only followed by spring-tine cultivator and (3) as a once-over combined primary and secondary tillage tool in the spring. Conventional tillage, defined as fall moldboard plowing followed by two spring-tine cultivation operations, was also included for comparison. While a plow pan, indicated by an abrupt increase in bulk density under the tilled layer, reappeared within 2 years after subsoiling under conventional tillage, the MOD maintained a relative uniform bulk density profile without resulting in the formation of a plow pan. Furthermore, the MOD not only prevented recompaction of the subsoiled profiles, but also seemed to favor an alleviation of previous subsoil compaction. Micro-cone penetrometer data did not show the occurrence of a disk pan or soil smearing zone under the concave disks of the MOD operated at a working angle of 45°.

Application of Pressure Swing Granulation to Hardmetal Granulation Process.

A novel binderless granulation method, Pressure Swing Granulation (PSG) was applied to the granulation of waxed hardmetal powders in which the conventional spray drying (SD) technique has been facing difficulties to produce good granules. Properties of granules and green compacts from the PSG based process were examined and compared with those from the SD based process. Mechanical properties of sintered bodies were evaluated with a Cemented Carbide Industrial Standard of Japan Cemented Carbide Tool Manufacturers' Association.Spherical granules of sizes ranging 0.1-1mm in diameter were obtained with a high yield. Angle of repose and relative bulk density of granule beds were much improved compared with those of original powder beds and the bed of spray dried granules. Density of green compacts with pressures of 0.5-1.5tf/cm2 (49.0-147.1MPa) was greater than 50% of theoretical density which should be sufficient for obtaining good quality of sintered products. The sintered samples of compaction at a pressure of ltf/cm2 and sintering at 1673K in vacuum for lh showed sufficient mechanical properties for industrial use.

Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. I. Two‐dimensional case

AbstractA body of experimental evidence suggests that reinforcing fibers influence both the crystallization kinetics and morphology of those composite materials that are based on crystallizable thermoplastics. The absence of an analytical model to predict the effect of fibers on crystallization has hindered data analysis. A new approach, using computer simulation of polymer crystallization, makes it possible to study the influence that reinforcing fibers have on the crystallization kinetics and morphology of semicrystalline polymers. Fibers depress the crystallization rate relative to an unreinforced polymer since they constrain spherulitic growth by an impingement mechanism. On the other hand, reinforcing fibers can also enhance crystallization rate by providing added surface nucleation sites. This work describes a two‐dimensional simplification of the crystallization process that occurs in bulk materials. It is demonstrated that the relative bulk and fiber nucleation densities, in addition to the fiber fraction, fiber diameter, and spherulitic growth rate control the crystallization kinetics and also the spherulitic and transcrystalline morphologies that develop in reinforced thermoplastic composites. © 1993 John Wiley &amp; Sons, Inc.

A comparison of physicochemical variables across plant zones in a mangal/salt marsh community in Louisiana

Three vegetation zones were delineated in a mangal / salt marsh community at Bay Champagne, Louisiana — a zone dominated byAvicennia germinans adjacent to the bay, an inland zone dominated bySpartina alterniflora, and a transition zone between the two containing both species. Parallel transects that intersected each zone were established perpendicular to the shore of the bay and sampled to determine if these zones differed on the basis of soil texture, elevation, redox potential, and selected interstitial water variables. Redox potential and interstitial water sulfide, ammonium, P, Ca, Mg, K, Fe, Mn, Cu, Zn, pH, and salinity were measured 5 times during the year to account for seasonal variation. Factor analysis identified five factors, accounting for 80.6% of the variation in the data. These factors were interpreted as representing seawater, sulfide, nitrogen/phosphorus, Eh, and copper variables. Factor scores in theAvicennia zone were significantly different than in the other zones for the salinity and sulfide factors, with higher salinity scores and lower sulfide scores. Analysis of variance revealed highly significant zone differences for most individual variables. TheAvicennia zone was characterized by the highest relative elevation and soil bulk density. Higher concentrations of ions associated with sea water, such as potassium, calcium, and magnesium, occurred in theAvicennia zone, which also caused interstitial water salinity to be higher in that zone. The transition andSpartina zones were more biochemically reduced than theAvicennia zone, as shown by lower redox potential measurements, higher sulfide concentrations, and higher sulfide factor scores in the former. Iron and manganese were lower in the more reduced zones, probably due to precipitation with sulfide. The transition andSpartina zones only differed in interstitial water potassium and sulfide and relative elevation, with some additional seasonal differences in other variables. TheSpartina zone had a lower elevation and usually higher sulfide concentrations than the transition zone. We hypothesize that the relatively high sulfide and lower elevation of theSpartina zone may limit the establishment ofAvicennia propagules there.

Penetration resistance of fine sandy apedal soils as affected by relative bulk density, water content and texture

The major physical properties that control the penetration resistance of soils are the degree of soil compaction, water content and particle size distribution. Sandy soils with well-sorted particle size distributions and low cohesivity compact and consolidate easily under pressure. Six soil samples with predominantly fine sand fractions and clay contents varying between 8 and 20% silt plus clay were selected to determine the relationships among penetration resistance, relative bulk density and water content. Penetration resistance was measured using a constant-rate penetrometer. The relative bulk density given by the ratio between bulk density and maximum ASTM bulk density was used as the parameter representing the level of compaction. Curves relating penetration resistance to water content at different relative bulk densities and to relative bulk density at different water contents were determined for each soil. All the variables were incorporated into a multiple regression equation. This equation can be...

Calculated Vs Measured Viscosities of Sol-Gel Processed Silica

ABSTRACTThe densification of sol-gel processed silica was studied by comparing calculated and measured viscosities between 700 and 850°C. Linear shrinkage was measured in a dilatometer. From shrinkage data, relative bulk densities were determined. The densities were used in a model for viscous sintering to calculate viscosities. Beam-bending viscosimetry was used to determine viscosities directly. The deflection rate of a centrally loaded beam was measured. Both the calculated and measured viscosities had the same time dependence. The temperature dependence was also determined.