Root Tensile Strength Research Articles

Mechanisms of root-soil reinforcement in bio-embankments of sloping farmland in the purple hilly area, China

Bio-embankment is an important soil and water conservation measure in the purple hilly area in China, which can effectively improve the ability of cultivated soil layers to resist rainfall erosion and runoff scour. In contrast, the ecological effect of bioembankment depends on the stability of the earth bank. Taking the natural grass bank as a control (CK), the root distribution, root tensile properties and shear resistance of root-soil composites for 3 typical soil and water conservation bio-embankments, namely, Morus alba Linn (Morus), Zanthoxylum bungeanum Maxim. (Zanthoxylum) and Medicago sativa (Medicago) were analysed. The results included the following: (1) The root system of the bio-embankments generally decreased in extent with the soil depth; fine roots in the 0–10 cm depth were most prevalent and significantly higher than those at the other depths, and coarse roots were mainly distributed in the 0–30 cm layer. (2) The stress-strain curves of the roots of each bio-embankment were single-peak curves without clear strain softening phenomena. The smaller the root diameters were, the smoother the stress-strain curves, and the lower the capability of the earth bank to resist collapse. The larger the root diameters were, the lower the tensile strength. The average root tensile force was highest for Zanthoxylum (73.91 N), followed by Medicago (68.07 N) and Morus (61.88 N), and the average root tensile strength showed the same trend, 16.52 MPa for Zanthoxylum, 16.08 MPa for Medicago and 13.02 MPa for Morus. (3) The bio-embankment measures significantly improved the soil shear resistance, especially under vertical loads of 100 kPa and 200 kPa. The soil internal friction angle showed a significant log-positive correlation with root morphological parameters of root length density (RLD), root surface area density (RSAD) and root weight density (RWD), while the soil cohesion force showed a positive linear correlation with these parameters. The results provide effective parameters supporting for the design of bio-embankments and promoting the use of soil reinforcement with suitable species selection in protective earth banks for stability in the purple hilly area.

Effect of the root biotechnical characteristics of Alnus subcordata, Paulownia fortunei and Populus deltoides on the soil mechanics

The effect of root reinforcement depends on the biotechnical characteristics of the root system including the tensile strength of individual roots, the root density and the distribution of the root system in the soil. This research was conducted in the Hyrcanian forest in Iran, where shallow landslides are frequent due to road construction. The effect of the root biotechnical characteristics of Alnus subcordata, Paulownia fortunei and Populus deltoides each one in 2-, 10- and 15-year-old plantations was assessed. The profile trenching method was used in this study to obtain the root area ratio of individual species by counting the number of roots and measuring the root diameter. For each species, single root specimens were sampled and tested for tensile tests in the laboratory using the standard Instron apparatus. The natural moisture content (two weeks after rainfall), Atterberg limits, shear strength of the soil were determined for plantations, stable and unstable sites. Results of this study indicated that plastic index and internal friction angle decreased with increasing root diameter rate. Moreover, internal friction angle and cohesion increased with increasing root area ratio and root diameter and density index. Tensile strength of roots decreased with increasing stand age. The highest and the lowest tensile strengths among species were observed for Paulownia fortunei and Populus deltoides, respectively. The findings of this research contribute to expanding the knowledge of root biotechnical properties of some tree species and to the choice of the most appropriate species for improving plastic index and shear strength in landslide prone areas.

The effect of drying temperature on chemical composition of chitosan powder from fishbone waste to hydroponic Deep Water Culture (DWC) application

The purpose of this study is to increase the added value of fishery waste, especially cork fish bones that have not been optimally utilized. The benefits of chitosan powder from cork fish bones can be used as a nutrient solution containing calcium in the DWC hydroponic system. The results of this study of cork chitosan bone powder obtained 22.65% Calcium Levels, 2.33% Moisture Content, 0.69% Ash Levels, Protein Levels 92.61%, 140 µm Particle Size, and 93.72% white degrees with microscopic properties obtained density ρ = 0.1 Kg / m3, Porosity P = 61%, Strength of Pressure chitosan powder in water σ = 0.13 Pa, Tensile strength of plant roots σ = 100.63 N / m3 Plant strain of ε = 6.14, and Young’s Modulus E = 16.39 N / m3. The hydrolysis process is carried out to obtain purer calcium chitosan powder with finer size fish so that it is easily absorbed by hydroponic plants.

Wind affects the growth, root anchorage and tensile strength of Australian pine (Casuarina equisetifolia) seedlings

ABSTRACTAustralian pine (Casuarina equisetifolia Forst.) is an important introduced reforestation species in windbreaks for agroforestry and ecological engineering. Nevertheless, the adaptive mechanism of its roots to withstand wind has not yet been fully investigated. In this study, a wind tunnel test was applied to investigate the effects of wind on growth, root architecture, root anchorage and tensile strength of Australian pine seedlings using root excavation method, pullout test and tensile test. After eight months of treatment with simulated wind load (8.2 m s−1) during the day, the non-wind-stressed control seedlings developed taller height (118%), larger stem base diameter (110%), root biomass (100%), shoot biomass (228%), and longer taproot length (56%) than those of wind-stressed seedlings. Furthermore, the wind-stressed seedlings distributed more roots at the windward side than at the leeward side, whereas the control seedlings distributed their root systems in all directions. The average maximum pullout resistance (0.25 ± 0.11 kN) of the control seedlings was significantly higher than that of the wind-stressed ones (0.08 ± 0.04 kN). Additionally, the control seedlings had significantly higher root tensile strength than the wind-stressed ones in 0–1, 1–2 and 2–5 mm root diameter classes, respectively. These results demonstrate that wind stress significantly decreases growth performance, root anchorage capability and tensile strength of Australian pine seedlings.

Evaluating the potential slope plants using new method for soil reinforcement program

Herbaceous plants are effective in reinforcing soil in the hilly area of northern China. It is a challenge to select dominant herbaceous species for soil reinforcement. In this study, investigation of plant plots, survey of plant root distribution and tests of root tensile strength were carried out in the north hilly area of Taiyuan city, Shanxi Province, North China. Species importance values (SIV) of nine herbaceous plants were calculated using the four parameters: relative frequency, relative density, relative aboveground coverage and relative underground coverage of the plants. SIV of Lolium perenne L. (32%), Vetiveria zizanioides L. (17%) and Paspalum notatum (14%) accounted for >50% of the total SIV of all species. Root area ratio and tensile strength of the three species were measured, and root cohesion was then evaluated using the Wu-Waldron model. According to the relative root cohesion (RRC) index combining with SIV and root cohesion, the dominant order of the three plants for soil reinforcement was: Lolium perenne L. (1.71 MPa) > Vetiveria zizanioides L. (1.12 MPa) > Paspalum notatum (0.74 MPa). This study provides a new method and data basis for guiding soil reinforcement in restoration projects using herbaceous plants.

Influences of plant spacing on root tensile strength of Schefflera arboricola and soil shear strength

Mechanical root reinforcement depends not only on root biomechanical properties but also on root biomass. Although it is known that plant spacing can affect root growth, it is not clear how it affects root tensile strength. We interpreted a set of field data to study the effects of spacing of Schefflera arboricola on root area ratio (RAR), root tensile strength and their combined effects on soil shear strength (also termed root cohesion). S. arboricola was transplanted into compacted silty sand at a spacing of 0.5 m, 0.8 m and 1.1 m. After 20 months of growth in the field, the root systems were excavated for root tensile testing and post-test trait measurements. Plant spacing affected the growth and tensile strength of roots. More closely spaced plants had higher RAR but lower root tensile strength, especially for roots 0.5–2 mm in diameter. According to the existing root breakage and fibre bundle models used in this study, which calculate root cohesion as the product of RAR and root tensile strength, the effects of plant spacing on root cohesion were minimal for most soil depths apart from 0.4- to 0.5-m depth.

Biomechanical properties of plant root systems and their ability to stabilize slopes in geohazard-prone regions

Vegetation is widely used for reinforcing slopes, and thus controlling shallow landslides, because plant root systems can increase soil shear strength by anchoring soil layers and modifying hydrological characteristics. However, limited information is available regarding the vertical variation of soil reinforcement by roots at the slope scale, and how slope stability is influenced, especially in plantation areas. In this paper we examine the biomechanical effects on slope stability of the roots of Populus tomentosa, Robinia pseudoacacia and Olea europaea in a geohazard-prone region in China. Root density, variation in root area ratio (RAR) with depth, root tensile strength and root peak tensile force are measured, along with calculating the contribution of root cohesion to the factor of safety. The Wu-Waldron model and fiber bundle model are used to estimate static stress and dynamic stress adherence of plant roots to soil during debris flows and landslides, and a two-dimensional finite element model is used to calculate the increase in the factor of safety caused by additional root cohesion. The results show that RAR is higher for P. tomentosa than for R. pseudoacacia and O. europaea. The vertical soil profile of R. pseudoacacia roots has the highest soil water content (7.06%). The additional cohesion provided by R. pseudoacacia roots (10.35–15.12 kPa) is greater than that provided by P. tomentosa roots (6.19–10.26 kPa) and O. europaea roots (2.31–5.06 kPa). The stable area is also larger on a slope planted with R. pseudoacacia compared with the other two species. Young growth roots (8 years) are shown to affect the distribution of soil water and are limited by soil water in the semi-humid region. R. pseudoacacia roots provide significant additional cohesion by both static and dynamic stress for slope stability. This study aims to increase current understanding of the biomechanical properties of plantation species roots and their efficacy in soil reinforcement.

Influence of root suction on tensile strength of Chrysopogon zizanioides roots and its implication on bioslope stabilization

Root tensile strength is an important factor controlling the performance of bio-slope stabilization works. Due to evapotranspiration and climate factors, the root moisture content and its suction can vary seasonally in practice and may not equal soil suction. The influences of suction and root moisture contents were investigated on Chrysopogon zizanioides (vetiver grass) root tensile strength. The root specimens were equilibrated with moist air in different suction conditions (0, 10, 20, and 50 kPa), prior to root tension tests. The root-water characteristic curve or relationship between root moisture and suction, was determined. The increase in suction resulted in decreased tensile strengths of the grass roots, particularly those with diameter of about 0.2 mm, which constituted 50.7% of all roots. For 1 mm roots, the tensile strength appeared to be unaffected by suction increase. The average root tensile strengths were used to estimate the root cohesion in slope stability analysis to find variation of safety factors of a bioengineered slope in different suction conditions. The analysis showed that the critical condition of slope with the lowest factor of safety would happen when the soil suction was zero and the root suction was high. Such condition may occur during a heavy rain period after a prolonged drought.

Soil fixation and erosion control by Haloxylon persicum roots in arid lands, Iran

Vegetation roots contribute to soil fixation and reinforcement, thus improving soil resistance against erosion. Generally, the amount of soil fixation presented by roots mainly depends on root density and tensile strength. In the present study, we conducted the research in order to further understand the biotechnical properties of Haloxylon persicum and also to quantify its role in increasing soil cohesion in arid lands of Iran. Ten H. persicum shrubs were randomly selected for root distribution and strength investigations, in which five samples were set on flat terrain and other five samples on a moderate slope terrain. The profile trench method was used to assess the root area ratio (RAR) as the index of root density and distribution. Two profiles were dug around each sample, up and downslope for sloped treatment and north and south sides for flat treatment. The results showed that RAR increased with increasing soil depth and significantly decreased in 40–50 cm layers of downhill (0.320%) and 50–60 cm for uphill (0.210%). The minimum values for the northward and southward profiles were 0.003% and 0.003%, respectively, while the maximum values were 0.260% and 0.040%, respectively. The relationship between the diameter of root samples and root tensile strength followed a negative power function, but tensile force increased with increasing root diameter following a positive power function. The pattern of increased cohesion changes in soil profile was relatively similar to RAR curves. The maximum increased cohesion due to the presence of roots in uphill and downhill sides were 0.470 and 1.400 kPa, respectively. In the flat treatment, the maximum increased cohesions were 0.570 and 0.610 kPa in northward and southward profiles, respectively. The analysis of variance showed that wind and slope induced stresses did not have any significant effect on the amount of increased cohesion of H. persicum. The findings served to develop knowledge about biotechnical properties of H. persicum root system that can assist in assessing the efficiency of afforestation and restoration measures for erosion control in arid lands.

Effect of Rib Root Shape on the Rib Root Tensile Strength of Press and Injection Hybrid Molded Products Made with CF/PA6 Random Prepreg Sheet

Effect of Rib Root Shape on the Rib Root Tensile Strength of Press and Injection Hybrid Molded Products Made with CF/PA6 Random Prepreg Sheet

Assessment of the potential of semi-arid plants to reduce soil erosion in the Konartakhteh watershed, Iran

Soil erosion is a major environmental problem in arid and semi-arid areas. Although bioengineering is important in preventing soil erosion, plant architecture and mechanical properties in these areas are rarely studied. In this study, in order to evaluate the potential of native plants to reduce soil erosion in semi-arid regions, their above-ground (e.g., stem density, radius of the stem, etc.) and below-ground (e.g., root area ratio, root tensile strength, etc.) characteristics were measured in the field and laboratory. Five indicators, namely, stem density (SD), sediment obstruction potential (SOP), plant stiffness (MEI), relative soil detachment (RSD), and root cohesion (Cr), were taken into account. Each indicator was scored according to a five-point scale (0 = low, 4 = high), and then, the score of each indicator was represented on an ameba diagram. Finally, for understanding traits of plants and evaluating their potential to control rill and gully erosion, the area occupied by the ameba diagram was studied. The results indicated that the shrub Ziziphus spina-christi (MEI = 108.35 N, RSD = 0.398, Cr = 8.34 kPa, SOP = 0.097, and SD = 0.00270) is a very suitable native plant species for controlling both the gully and rill erosion. In addition, Scariola orientalis is effective for sediment obstruction, but its low scores on the MEI and RSD indicators imply that it is not able to control gully development. Furthermore, Noaea mucronata, Platychaete glaucescens, Astragalus gummifer, Alhagi persarum, Lycium shawii, and Prosopis farcta have a distinct potential to reduce the rate of gully erosion. These results have wide applicability for adopting soil conservation measures to other semi-arid environments.

Root moisture content influence on root tensile tests of herbaceous plants

Root tensile strength controls root reinforcement, but a range of factors including root moisture and diameter have such a large impact that it is difficult to make predictions. In this study, we measured how variable root moisture content affects the relationship between root diameter and root tensile strength of herbaceous plants. Fresh roots of two herbaceous plants, Heteropappus altaicus and Poa sphondylodes were divided into four groups: (i) saturated in water, (ii) kept fresh, (iii) or dried for 6 h or (iv) 12 h in air. Root diameter and mechanical failure under tension before and after the moisture treatment were measured. Tensile strength and tensile force of both species decreased linearly while mean root diameter increased linearly with increasing root moisture content. Root moisture content has a large impact on the variability of root tensile strength. This emphasizes the need to avoid desiccation during testing. In field impacts of soil water potential on root strength requires further study. We recommend soaking roots in water before testing to decrease this source of error.

Effects of root dehydration on biomechanical properties of woody roots of Ulex europaeus

AimsEffects of root water status on root tensile strength and Young’s modulus were studied in relation to root reinforcement of slopes.MethodsBiomechanical properties of woody roots, Ulex europaeus, were tested during progressive dehydration and after thirty-day moisture equilibration in soil with contrasting water contents. Root diameter, water content and water loss were recorded and root water potential versus water content relation was investigated. Tensile stresses induced by root contraction upon dehydration were measured.ResultsRoot tensile strength and Young’s modulus increased abruptly when root water content dropped below 0.5 g g−1. The strength increase was due to root radial and axial contraction induced by root water potential drop. Diameter decrease and strength gain were the largest for thin roots because of the relatively larger evaporative surface per volume of thin roots. Largely negative water potentials in dry soil induced root drying, affecting root biomechanical properties.ConclusionRoot water status is a factor that can cause (inappropriately) high strength values and the large variability reported in literature for thin roots. Therefore, all root diameter classes should have consistent moisture for fair comparison. Testing fully hydrated roots should be the routine protocol, given that slope instability occurs after heavy rainfall.

Modelling biome‐scale root reinforcement and slope stability

AbstractRapid changes in the composition of hillslope vegetation due to a combination of changing climate and land use make estimating slope stability a significant challenge. The dynamics of root growth on any individual hillslope result in a wide range of root distributions and strengths that are reflected as up to an order of magnitude variability in root cohesion. Hence the challenge of predicting the magnitude of root reinforcement for hillslopes requires both an understanding of the magnitude and variability of root distributions and material properties (e.g. tensile strength, elasticity). Here I develop a model for estimating the reinforcement provided by plant roots based on the distribution of biomass measured at the biome level and a compilation of root tensile strength measurements measured across a range of vegetation types. The model modifies the Wu/Waldron method of calculating root cohesion to calculate the average lateral root cohesion and its variability with depth using the Monte Carlo method. The model was validated in two ways, the first against the predicted depth‐reinforcement characteristics of Appalachian soils and the second using a global dataset of landslides. Model results suggest that the order of magnitude difference in root cohesions measured on individual hillslopes can be captured by the Monte Carlo approach and provide a simple tool to estimate root reinforcement for data‐poor areas. The model also suggests that future hotspots of slope instability will occur in areas where land use and climate convert forest to grassland, rather than changes between different forest structures or forest and shrubland. Copyright © 2018 John Wiley & Sons, Ltd.

Correction to: Root tensile strength and root distribution of typical Mediterranean plant species and their contribution to soil shear strength

The original version of this article unfortunately contained a mistake. Figs. 4a and 4c were duplicated. This Figure has now been corrected.

English

Restoration of Alnus formosana (Burk.) Makino on landslide areas is important for agroforestry, forestry and soil erosion control in Taiwan. To ensure successful reforestation, A. formosana seedlings have to develop strong root system for nutrient and water acquisition as well as anchorage. Inoculating of A. formosana with symbiotic nitrogen-fixing actinobacteria Frankia may help mitigate drought and nutrient deficiencies on landslide sites. However, the effects of Frankia inoculation on growth, root architecture and mechanical properties of A. formosana seedlings are not well understood. In this research, a Frankia strain AF1 was isolated from actinorhizal nodules of local A. formosana and recognized as Frankia species, and its influences on growth performance and root mechanical properties of A. formosana seedlings were examined and analyzed. The results showed that the inoculated seedlings had significantly larger height and root biomass, longer root length, and more root tip number than that of the non-inoculated controls. Consistently, the inoculated seedlings had statistically significant higher uprooting resistance, root tensile resistance force and tensile strength than the controls. The results reveal that this native Frankia strain can promote growth performance, root system architecture, anchorage ability and root tensile strength of A. formosana. Key words: Actinorhiza, Betulaceae, inoculation, root morphology, tensile strength, uprooting resistance.

Arbuscular mycorrhizal fungi increase the proportion of cellulose and hemicellulose in the root stele of vetiver grass

Arabidopsis thaliana is the model plant that is mainly used in studying cellulose and hemicellulose (CH) biosynthesis. Unfortunately, A. thaliana does not associate with mycorrhiza and as a result there are only rare reports on the role of arbuscular mycorrhiza (AM) fungi on CH biosynthesis. This study aims to investigate the effects of AM fungi on changing the CH content in mycorrhizal plant. Three AM fungi, Glomus aggregatum, Rhizophagus intraradices and Funneliformis mosseae, were inoculated to vetiver grass (Chrysopogon zizanioides) and grown for 12 months. Roots were harvested, and the proportions of CH, lignin, lipids and hydrosoluble content were analysed. The corresponding root tensile strength (positively correlated with the proportion of CH) was measured to counter check the CH content. Plants inoculated with AM showed a higher proportion of CH (P < 0.05) compared with uninoculated ones. This increase was coupled to a 40–60% enhancement in tensile strength. Potential mechanisms for this phenomenon are discussed. This is the first study showing that the proportion of CH and tensile strength of plant root could be significantly affected by AM symbiosis. It is thus desirable that future research on CH biosynthesis uses mycorrhizal-associating plants, such as medic (Medicago truncatula) and rice (Oryza sativa).

Root reinforcement to soils provided by common Ethiopian highland plants for gully erosion control

AbstractGrasses and trees are often used to stabilize gully banks. However, the effectiveness of such biological conservation measures has not been investigated for the Ethiopian highlands. This study investigates the reinforcement that plant roots may provide to strengthen gully banks in Ethiopia. The root systems of 26 indigenous and exotic plant species of 3 plant life forms (grasses, shrubs, and trees) were sampled, and root tensile strength and distribution were determined. The RipRoot model was used to quantify the additional cohesion derived from the plant roots. Among all tested roots, Eleusine floccifolia (grass), Tephrosia vogelii (tree), and Rosa abyssinica (shrub) had the strongest roots for each life form. The root volumetric ratio (root volume divided by soil volume) in the top 0.6 m of soil ranged from 0.03% to 0.46%. Roots of Digitaria abyssinica provided the maximum added cohesion (10.6 kPa) over this depth. For a given plant species, root volumetric ratio had a greater effect on additional cohesion than root tensile strength. Plant species with a fibrous root system provided greater additional cohesion values in the top 0.6 m (on average 3.4 vs. 1.7 kPa for tap root systems) and could potentially enhance gully bank stability for shallow gullies more than plants having a tap root system. To effectively rehabilitate larger gullies, plants should be integrated with other gully rehabilitation measures, such as regrading of gully banks and structural measures such as check dams to trap sediments, thereby reducing the effective gully bank height relative to rooting depth.

The tensile root strength of five emergent coastal macrophytes

The root biomass of emergent macrophytes in coastal wetlands is essential for anchorage and erosion protection. The tensile root strength of these plants is an important component in determining the strength of coastal wetland soils. We made 1449 tensile strength measurements of roots <1.5 mm in diameter for five species of emergent wetland macrophytes (Spartina alterniflora, S.patens, Panicum hemitomon, Schoenoplectus americanus, and Sagittaria lancifolia) collected from six sites in three coastal estuaries. An analysis of variance revealed that the tensile root strength of dead and live roots for all species decreased with depth and that dead roots were stronger than live roots of the same diameter (p < 0.05). There was low variation in the mean tensile root strength among all sites. The S. alterniflora dead roots from the Barataria Basin site, however, were stronger than those from the Lake Pontchartrain site and the S. patens live and dead roots collected from Breton Sound were stronger than those from a nearby site in the same watershed. Wetland root samples exposed to partially-treated sewage effluent were considerably smaller than roots collected from the nearby reference wetland. Further investigation is warranted to ascertain the nature of the factors that causing these variations in tensile root strength with depth, between live and dead roots and with nutrient exposure

Tensile properties of seminal and nodal roots and their relationship with the root diameter and planting density of maize (Zea mays)

The tensile property of roots is an important factor for anchorage and for resistance to root lodging. In this study, a root tensile test was applied to maize (Zea mays L.) grown in the field at three planting densities, 4.5 × 104, 6.75 × 104 and 9.0 × 104 plants ha–1, to quantify the maximum tensile force (Fmax) and tensile strength (Ts) of roots at the V10 stage (tenth leaf visible) and grain-filling stage. In addition, relationships among tensile properties, diameter and turgid weight : dry weight (TW : DW) ratio of roots were investigated. The results showed that the Fmax of primary and seminal adventitious roots was lower than of nodal roots. Among nodal roots, the Fmax of roots on upper nodes was higher. Planting density significantly affected the tensile force of nodal roots of the sixth to eighth tiers; their Fmax decreased with increasing planting density. A positive linear correlation between Fmax and root diameter and a power function between Ts and root diameter was observed. In addition, there was a positive linear correlation between the TW/DW ratio and root diameter and a negative exponential correlation between Ts and TW : DW ratio. Therefore, nodal roots with a lower TW : DW ratio could have a larger Ts, because their cells are smaller and cell walls are thicker. This result suggests that nodal roots with small and thick cells benefit the tensile properties of maize.