Effects Of Soil Strength Research Articles

Effect of Soil Strength and Soil Physical Properties on Performance of Tillage Machines

Effect of Soil Strength and Soil Physical Properties on Performance of Tillage Machines

Bond behaviour of bamboo splints in cement-stabilised rammed earth blocks

This paper represents an effort to study the bond characteristics of plain and noded bamboo splints embedded in cement-stabilised rammed earth (CSRE) blocks. A series of CSRE pullout test specimens and two species of bamboo, namely Melocanna Baccifera and Bambusa Balcooa having an average tensile strength of 384 and 310 MPa, respectively, were fabricated using 4–10% Portland cement. These bamboo species are commonly available and widely used for construction in the north-eastern part of India. Besides considering the effects of soil strength, cement content, splint size and type on bond force and slip, the effect of embedded area was also briefly considered as part of the test programme. The test result showed that pullout bond resistance is correlated to rammed earth compressive strength, splint size and type, and embedded area.

Upper Bound Solution for Ultimate Bearing Capacity of Foundation Based on Unified Strength Theory

Based on unified strength theory, an upper bound solution for bearing capacity of foundation is established considering the strength of soil above the basement by using Prandtl slip model. The proposed method could be degenerated to classical slip-line method in some certain situations. A series of results could be presented by means of changing the parameters of unified strength theory. The results obtained by this proposed method are greater than those by Terzaghi method, which is mainly because the positive effects of soil strength above foundation base. Since unified strength theory could be simplified to Mohr-Coulomb strength theory in a certain situation, the results are close to those obtained by Meyerhof method. This proposed solution can consider the effects of intermediate principal stress so that we can make full use of the potential capacity of soil, which is a rigorous upper-bound solution. Other solutions are special cases of this proposed solution.

Soil Aggregate Size and Mycorrhizal Colonization Effect on Root Growth and Phosphorus Accumulation by Berseem Clover

The effects of soil aggregate size and mycorrhizal colonization on phosphorus (P) accumulation and root growth of Berseem clover (Trifolium alexandrinum L.) were studied. Root length and dry weight decreased with increasing aggregate diameter. Colonization of clover plants by arbuscular mycorrhizae (Glomus intraradices Schenck and Smith) improved root growth and P accumulation in all aggregate‐size classes. Although total root length of either mycorrhizal or nonmycorrhizal plants decreased with increasing aggregate diameter, the length of living external hyphae was not affected by aggregate size. Thus, colonized root length was improved by 20% as soil aggregate diameter increased. Total P accumulation per plant decreased with increasing aggregate size. However, total P accumulation per unit root length improved as the size of soil aggregate increased. In our study, mycorrhizal colonization improved total P accumulation and root growth in soil with large aggregates and compensated, in part, for the effect of soil strength.

The effect of soil strength on the yield of wheat

Although it is well-known that high soil strength is a constraint to root and shoot growth, it is not clear to what extent soil strength is the main physical stress that limits crop growth and yield. This is partly because it is difficult to separate the effects of soil drying and high soil strength, which tend to occur together. The aim of this paper is to test the hypothesis that for two different soil types, yield is closely related to soil strength irrespective of difference in soil water status and soil structure. Winter (Triticum aestivum L., cv. Hereward) and spring wheat (cv. Paragon) were grown in the field on two soils, which had very different physical characteristics. One was loamy sand and the other sandy clay loam; compaction and loosening treatments were applied in a fully factorial design to both. Crop growth and yield, carbon isotope discrimination, soil strength, water status, soil structure and hydraulic properties were measured. The results showed that irrespective of differences in soil type, structure and water status, soil strength gave a good prediction of crop yield. Comparison with previous data led to the conclusion that, irrespective of whether it was due to drying or compaction (poor soil management), soil strength appeared to be an important stress that limits crop productivity.

Scale- and location-dependent correlations of soil strength and the yield of wheat

The relationship between soil strength and crop yield may be summarized by a linear correlation coefficient (usually negative). It is likely, however, that this over-simplifies a complex situation in which the relationship between these variables depends on spatial scale and location. We used the wavelet transform to assess this scale- and location-dependence. We established a transect on an arable field in Eastern England, and studied the correlations of soil strength (top- and subsoil) with crop yield. The transect comprised 267 contiguous 0.72 m × 0.72 m plots. Measurements were taken during two consecutive growing seasons of winter wheat (harvest dates of August 2004 and 2005). Soil strength was measured with a penetrometer in the spring of each growing season. As expected, the overall correlation of soil strength with yield was negative but weak. Wavelet analysis revealed that, at fine spatial scales, topsoil and subsoil strength were correlated more or less equally with yield; however, at coarse spatial scales, topsoil strength had a stronger correlation with yield than did subsoil strength. The correlation of topsoil strength with yield at fine spatial scales (corresponding to about 1 m on the ground) was negative. A likely source of this fine-scale variation was the soil compaction associated with tractor wheelings. The correlation of topsoil strength with yield at the coarsest spatial scale (corresponding to about 50 m on the ground) was positive. This correlation was temporally stable, and might have reflected how soil strength can act as a proxy for other soil attributes. In the 2005 growing season, we found evidence that, at intermediate spatial scales, the correlation of soil strength with yield changed depending on the position on the transect. This was probably due to an interaction between the compaction associated with tractor wheelings and the local soil conditions. There was no evidence of such location-dependence in the correlation of soil strength with yield in the 2004 growing season. In summary, the effect of soil strength on crop yield was not expressed in a constant negative correlation across all spatial scales and locations: the negative correlation occurred mainly at fine spatial scales, and the correlation changed according to the position in the landscape and the prevailing local soil conditions.

Why are laterals less affected than main axes by homogeneous unfavourable physical conditions? A model-based hypothesis

When plants develop in strong soils, growth of the root system is generally depressed. However, branching and elongation of branches are often less affected than growth of the main axes, whenever the whole root system encounters even-impeded conditions. On the basis of a model simulating root growth and architecture as related to assimilate availability, we propose a simple hypothesis to explain such behaviour. In the model, growth of each root depends on its own elongation potential, which is estimated by its apical diameter. The potential elongation rate-apical diameter relationship is the same for all the roots of the system and is described by a monomolecular function. Our hypothesis is that the effect of soil strength can be simulated by introducing an impedance factor in the definition of root maximum potential elongation rate, common to the whole root system. When such impedance factor is applied, it affects more the potential of larger roots (main axes) than that of thinner roots (secondary and tertiary branches). Simulations provided in high impedance conditions led to root systems characterised by short taproots, whereas growth of secondary roots was unaffected and growth of tertiary roots was enhanced. Actual branching density was also higher, although branching rules have been unchanged. Such simulated systems where similar to that observed in strong soils. Friction laws or pore size can be involved in the larger reduction of the potential growth of main axes. Moreover, when growth of main axes is restricted, assimilate availability becomes higher for branches and that could explain that their growth could be increased in a homogeneous strong soil.

The effect of soil strength on the growth of pigeonpea radicles and seedlings

The effect of soil strength on the growth of pigeonpea radicles and seedlings was investigated in cores of three clay soils prepared at different water contents and bulk densities in the laboratory. Radicle elongation directly into soil cores was reduced from 50–70 mm d-1 at strengths less than 0.5 MPa to 0 mm d-1 at 3.5–3.7 MPa. The response to soil strength was affected by the water content of the soil, presumably as a result of reduced oxygen availability in wetter soil. This effect was apparent in soils wet to air-filled porosities less than 0.15 m3 m-3. Radicles were more sensitive to high soil strength (>1.5 MPa) than were seedling roots which encountered the same conditions at 60 mm in the profile. Radicle growth ceased at 3.5 MPa which reduced seedling root growth by only 60%. Despite a 60% reduction in root length in the high strength zone, seedling roots compensated in zones of loose soil above and below the compacted layer, and total root length and shoot growth were unaffected. There was no evidence of a ‘root signal’ response which results in reduced shoot growth in some species in response to high soil strength. The proliferation of roots in surface layers and the delayed penetration of the root system to depth in compacted soil are likely to expose seedlings to a greater risk of water-deficit in the field, particularly under dryland conditions where plants rely on stored subsoil water for growth.

Three-dimensional, finite element interaction between soil and simple tillage tool

ABSTRACT A non-linear, three-dimensional, finite element model was used to study soil-tool interaction. The model included both effects of soil strength and soil-metal friction behavior. An interface element between the soil and the tool surface was established based upon a hyperbolic model. Laboratory tillage tests were conducted in a soil bin to verify the results of the finite element model. The results showed that the finite element analysis predicted an accurate draft force for a simple tillage tool. The relative prediction error ranged from 0.8% to 10.5%. KEYWORDS. Tillage, Draft force. Finite element model.

Effect of soil strength on numerical simulation : Sargand, S M; Janardhanam, R Proc 6th International Conference on Numerical Methods in Geomechanics, Innsbruck, 11–15 April 1988V1, P529–535. Publ Rotterdam: A A Balkema, 1988

Effect of soil strength on numerical simulation : Sargand, S M; Janardhanam, R Proc 6th International Conference on Numerical Methods in Geomechanics, Innsbruck, 11–15 April 1988V1, P529–535. Publ Rotterdam: A A Balkema, 1988

Effect of soil strength on root growth under different water conditions

The objective of this study was to determine the effects of soil water and soil strength on root growth in situations where the individual effects of both of these factors were important. Three grain legumes were grown from pre-germinated seeds for five days on 50-mm compacted columns of two major soils of Sri Lanka. Four or five levels of bulk density (1.1 to 1.8 Mg.m−3) and five or six levels of matric potential (−0.02 to−2.0 MPa) were used.

Effects of Soil Strength on the Relation of Water-Use Efficiency and Growth to Carbon Isotope Discrimination in Wheat Seedlings

The ratio of carbon accumulation to transpiration, W, of wheat (Triticum aestivum L.) seedlings increased with increasing soil strength, measured as soil penetrometer resistance, and this was already apparent at the two leaf stage. The ratio was negatively correlated with carbon isotope discrimination, in accord with theory. This means that decrease in intercellular partial pressure of CO(2) accounted for an important part of the increase in W with increasing soil strength. Despite a lower CO(2) concentration in the leaves at high soil strength, assimilation rate per unit leaf area was enhanced. Greater ribulose 1,5-bisphosphate carboxylase activity confirmed that photosynthetic capacity was actually increased. This pattern of opposite variation of assimilation rate and of stomatal conductance is unusual. The ratio of plant carbon mass to leaf area increased markedly with increasing soil strength, mainly because of a greater investment of carbon into roots than into shoots. A strong negative correlation was found between this ratio and carbon isotope discrimination. For a given increase in discrimination, decrease in carbon mass per leaf area was proportionally larger than decrease in assimilation rate, so that relative growth rate was positively correlated to carbon isotope discrimination.

The effect of soil strength on germination and emergence of wheat (Triticum aestivum L.). I. Low shear strength conditions

Experimental studies of the germination and emergence of wheat as affected by soil shear strength are reported. A fine sand under saturated conditions was used as the seed bed and the shear strength of the seed bed was increased to 10 kPa (0.1 bar) by externally applied loads. From the results it is concluded that the initial soil shear strength in this range has little effect on germination. However, coleoptile growth and root elongation are markedly reduced in the range 0-2.2 kPa such that total emergence is reduced to 7% at 9.3 kPa in this fine sand. The results clearly show that coleoptile elongation is more affected than root elongation by the same mechanical stress. Roots are found to be thicker and coleoptile thinner under increasing soil shear strength conditions.

The effect of soil strength on germination and emergence of wheat (Triticum aestivum L.). II. High shear strength conditions

Experimental studies on limiting soil strength conditions for germination and emergence of wheat are reported. From the experimental results in a fine, dense sand a quantitative estimate of the stresses at the organ/soil interface that will prevent seed and seedling expansion and hence prevent germination and emergence is made using the Spherical Cavity Expansion Theory of Vesic. Interfacial stresses of 3.0, 2.3, 1.7 and 0.8 MPa (=30, 23, 17 and 8 bar) are found to be limiting to germination, root elongation, coleoptile elongation and emergence of wheat respectively. These results are discussed in terms of a range of soils with different mechanical properties. The limiting stresses are interpreted in terms of the results obtained by the torsional shear box.

Effects of soil strength on seedling emergence, root growth and crop yield: H. M. Taylor. Compaction of Agricultural Soils. ASAE Monograph (1971), pp. 292–305, 3 figs.

Effects of soil strength on seedling emergence, root growth and crop yield: H. M. Taylor. Compaction of Agricultural Soils. ASAE Monograph (1971), pp. 292–305, 3 figs.

Effect of Soil Temperature, Strength, and pH on Cotton Seedling Root Elongation1

AbstractCotton (Gossypium hirsutum ‘Empire’) seedlings were grown in glass‐fronted boxes in a growth chamber with varying soil temperature, pH, and compaction levels. Root elongation rate increased rather gradually as temperature increased, reaching a maximum at 32 C, then falling sharply as temperature was increased further. The effect of temperature was amplified at low levels of soil strength and at high pH. Temperature interacted with both strength and acidity on root elongation rate, but the effects of soil strength and acidity on roots were exerted independently.

Effect of Soil Strength on Corn Root Penetration

Effect of Soil Strength on Corn Root Penetration