Increase In Penetration Resistance Research Articles

Effect of CO2 mixing on the rheological and electrochemical properties of fresh mortar at the early age

The study aimed to elucidate the mechanism behind rheological modification due to CO2 mixing at the mixing and post-mixing stages from an electrochemical perspective. The results indicated that CO2 mixing reduced the flowability while increasing penetration resistance and static yield stress. The electrostatic attraction between particles with opposite surface charges and the bridging effect of calcium carbonate constitute the primary factors for influencing the rheological properties of mortar at an early age. The altered surface charge of carbonized cement particles, primarily resulting from CO2 injection lowering the pH and ion concentration, reversed the zeta potential of particles from the traditionally negative charge (-3.59 mV) to a positive value (+13.3 mV). Furthermore, CO2 mixing further enhanced the dissolution of cement particles and accelerated the hydration process, thereby increasing the rate of structural build-up. CO2 mixing was demonstrated to be a potential rheological modifier for 3D-printed concrete applications.

Effects of reduced tillage and prolonged cover cropping in maize on soil quality and yield

Maize (Zea mays L.) is the most common arable crop on sandy soils in the Netherlands, and it is often grown for several consecutive years after temporary grassland. For the maize-growing years, reduced tillage intensity and prolonged growing period of cover crops could limit declines in soil organic matter (SOM) and soil biota while maintaining soil structure and maize yield. We measured soil parameters and maize yield in an eight-years field experiment on sandy Gleyic Podzol. Treatments included four cropping systems differing in tillage intensity but with conventional sowing dates (conventional inversion tillage (CT), non-inversion tillage (NIT), strip tillage (ST) and no-till (NT)), and two cropping systems (CT-prolonged and ST-prolonged) with prolonged growing period of a winter rye-winter pea cover crop combined with a late sown short-season maize (18 weeks growth). After eight years, we found no evidence for differences in SOM or total carbon content between the treatments. However, in the reduced-tillage treatments, SOM content was higher in the top (0–15 cm) than in the bottom (15–30 cm) of the plough layer, while in CT and CT-prolonged, this stratification was inverted. We observed differences in earthworm abundance, biomass and functional group distribution. In comparison to CT (100 %), the earthworm abundance was 153 % in NIT, 235 % in ST and 206 % in NT whereas earthworm biomass was 269 % in NIT, 325 % in ST and 475 % in NT. Epigeic earthworms were more affected by tillage than endogeic earthworms. Compared to CT, earthworm biomass was higher in CT-prolonged. The initially low earthworm population recovered during the course of the experiment independent of tillage intensity.Higher soil penetration resistance was observed in the reduced tillage systems compared to CT, independent of prolonging the cover crop. Despite the increased penetration resistance, the maize yields in NIT and ST were similar to CT. The maize yields were lower in NT, CT-prolonged and ST-prolonged compared to CT, but no differences were observed between CT-prolonged and ST-prolonged. The biomass of the harvested prolonged cover crop closed the yield gap in relation to CT in four out of six years in which cover crop biomass in CT-prolonged and ST-prolonged was quantified. Based on our results, we recommend strip tillage for continuous maize-cropping systems on Dutch sandy soils. In the case of severe compacting of compaction prone soils, we recommend conventional tillage with a prolonged cover crop and short-season maize variety.

Soil compaction due to agricultural machinery impact: A systematic review

AbstractSoil compaction is generally viewed as one of the most serious soil degradation problems and a determining factor in crop productivity worldwide. It is imperative to understand the processes involved in soil compaction to meet the future global challenges of food security. In this work, we used co‐occurring keyword analysis to summarize 3491 papers on soil compaction over the past 40 years, elaborating on the main research focuses such as the causes, influencing factors, and effects of soil compaction on crops, and the mitigation and prevention of soil compaction. This review provides a comprehensive discussion of the effects of soil compaction, including altering soil structure, increasing bulk density (BD) and penetration resistance (PR), and reducing porosity and soil hydraulic properties. Notably, based on the 387 data points of 11 papers about BD, our results demonstrated soil compaction on average, increased BD by 7.6%, 6.9%, and 3.2% in the medium‐, coarse‐, and fine‐textured soils, respectively. Based on the 264 data points of 18 papers, in the 0–30 cm soil layer, compaction increased penetration resistance (by 91% in the coarse‐textured, 84.2% in the medium‐textured, and 8.8% in the fine‐textured soils). Compacted soil limits the access of crop roots to water and nutrients, leading to poor root development and reduced crop productivity. There was a difference in soil compaction sensitivity between the different crops, but crop growth and yield showed an overall worsening trend with increasing degrees of compaction. This review collected data points on 142 crop yields and found that wheat, barley, corn, and soybean yields decreased by an average of 4.1%, 15.1%, 37.7%, and 22.7%, respectively, in the BD range of 1.1–1.8 Mg/cm3 after compaction. Additionally, the effectiveness of different compaction mitigation measures, including natural, tillage, and biological, is systematically discussed. Compared with soil compaction mitigation measures, prevention should be the top priority although there is still a lack of practical prevention methods. Soil conditions and agricultural machinery type are the main factors affecting the risk of soil compaction in the process of soil compaction. Therefore, it is particularly important to optimize the soil working conditions in the field and the type of farm machinery used to reduce the risk of soil compaction. This initiative is pivotal for ensuring sustainable systems for food production and recovering crop productivity from compacted soil.

Influence of spent liquor obtained from SO2–ethanol–water (SEW) fractionation of Eucalyptus on drifting sands stabilization

Abstract The utilization of mulch stands as a paramount approach in the management of wind erosion and the stabilization of soil and drifting sands. This study aimed to explore the impact of various concentrations of spent liquor (20 %, 30 %, and 50 % v/v) derived from SO2–ethanol–water (SEW) fractionation of Eucalyptus wood on the physical and mechanical properties of sand. These properties encompassed moisture content, thickness, temperature, electrical conductivity (EC), wind erodibility, penetration resistance, and seed germination. The findings revealed that the highest compressive strength (0.76 MPa) was attained with mulch consisting of 50 % SEW spent liquor, resulting in a 3.3-fold increase in penetration resistance compared to the control treatment. Furthermore, the 20 % concentration of spent liquor did not adversely affect the germination of black saxaul (Haloxylon ammodendron), whereas the lowest seed germination rate was associated with the 50 % concentration. Based on the measured parameters, the optimal mulch treatment for stabilizing drifting sands was identified as mulch with a 50 % (v/v) concentration. This study underscores the efficacy of SEW spent liquor in dust control and mitigating its environmental impacts, thus highlighting its potential in sustainable soil management practices.

Soil Compaction and Productivity Evolution in a Harvested and Grazed Mediterranean Scots Pine (Pinus sylvestris L.) Forest

The effects of machinery and livestock on forest soil compaction have mostly been studied at short-term and local scales. A better understanding of the long-term effects of compaction in mature stands at the management scale is needed, especially in hot and dry climates. This study aims to analyze (1) soil compaction in a Mediterranean Scots pine (Pinus sylvestris L.) forest subjected to mechanized logging and grazing for more than 50 years and (2) forest productivity trends during these 50 years of disturbance. Soil penetration resistance (0–10 cm and 10–20 cm) and soil moisture (0–12 cm) were measured in 181 randomly selected points affected by “high machinery traffic”, “high cattle traffic” or “low traffic”. Decennial forest inventory data on density, timber volume, and recruitment were collected and analyzed over the five decades preceding soil measurements. Soil penetration resistance exceeded 2500 kPa at a significant portion of the sampled points, although the highest levels of compaction tended to be concentrated in the subsurface layer of the high-traffic areas. Cattle and machinery caused significant compaction in these areas and increased penetration resistance in the range of 350–450 kPa. However, despite the long period of disturbance and the increase in penetration resistance observed, no signs of productivity decline were detected in the forest.

Seven decades of Atlantic rainforest conversion to slash-and-burn agriculture: Effects on soil’s physical properties

Slash-and-burn agriculture is a millennia-old no-till farming technique that is still widely practiced in developing tropical countries. This practice is currently employed in Brazil by subsistence family farms, Indigenous groups, and maroons, in a primitive manner, using only cutting, fire, and fallow as soil preparation techniques for food production. In recent years, this practice has been drastically reduced. However, the fallow periods have become even shorter. Therefore, there is a need to understand how the recurrence of fire with the reduction of fallow time affects the soil. This study aims to evaluate the cumulative effects of fire recurrence in slash-and-burn agriculture for seven decades on the physical properties of the soil and the minimum fallow times for post-burn resilience. Using a chronosequence approach, different fallow periods: a) native forest (control); b) recently burned (30 days after fire); c) 2-year fallow; d) 5-year fallow; e) 7-year fallow; f) 12-year fallow were considered. In each area, six disturbed and six undisturbed samples were randomly collected at 0–5 cm and 5–10 cm depths each to estimate: soil bulk density, soil total porosity, penetration resistance, aggregate stability, mean weight diameter, and soil water retention capacity. The results show that the seven decades of slash-and-burn agriculture affected the topsoil (0–5 cm deep) more prominently. Curiously, soil bulk density and total porosity were not affected at any time between the areas. The fire increased penetration resistance immediately after burning in the 0–5 cm layer by 162.5%, showing resilience after five years of fallow. Soil aggregate stability showed a delayed effect, with a significant increase in two years after the fire by 64.2%, remaining high after 12 years of fallow, indicating the influence of other mechanisms and reactions in the soil after the fire. The mean weight diameter did not change at any time while soil water retention increased immediately after burning by 25.2% with resilience after a two-year fallow. Most physical properties were not directly affected by fire heating but by post-fire environmental conditions and the interaction of various mechanisms during the fallow period. In general, most physical parameters showed good resilience over an average of five years of fallow, with cumulative effects only for aggregate stability.

Did cover crop or animal manure ameliorate corn residue removal effects on soil mechanical properties after 10 years?

Crop residue removal may negatively affect soil mechanical properties, which are key components of soil quality. To evaluate potential long-term effects, we assessed the 10-yr impact of corn (Zea mays L.) residue removal (59 % of non-grain biomass annually) on surface soil mechanical properties (0–20 cm). We also evaluated whether adding carbon (C) amendments, such as using a winter rye (Secale cereale L.) cover crop or surface-applying cattle manure (24 Mg ha−1 biannually) can ameliorate the effects of crop residue removal. This long-term study was under irrigated no-till continuous corn on a silt loam soil in south-central Nebraska, USA. Measurements included soil penetration resistance, field bulk density, aggregate strength, Atterberg limits (liquid limit, plastic limit, and plasticity index), Proctor maximum bulk density, and the water content at which the Proctor maximum bulk density (critical water content) occurs. Reduction in soil organic carbon (SOC) concentration explained most of the changes in soil mechanical properties. Long-term corn residue removal increased penetration resistance (+40 %) for the 0–20 cm depth, and reduced aggregate strength (−44 %), plasticity index (−22 %), and critical water content (−13 %) in the 0–5 cm depth. Residue removal also reduced field bulk density (−5%), liquid limit (−12 %), and plastic limit (−10 %) in the 0–10 cm depth, but increased Proctor maximum bulk density (+8 %) in the 0–5 cm depth. Winter rye cover crop reduced field bulk density (−5%, 0–15 cm depth) and increased penetration resistance (+52 %, 0–20 cm depth). Surface-applied manure amendments increased the near-surface soil liquid limit (+8 %) and plastic limit (+8 %) in the 0–5 cm depth. Given the high rate of residue removal used in this experiment, our findings support that excessive corn residue removal over the long-term (∼10 years) negatively affects near-surface soil mechanical properties, but that use of winter rye cover crop or surface-applied manure can minimally to partially ameliorate these effects.

CHARACTERISATION OF POLYMER MODIFIED BITUMEN

This study focuses on characterizing Polymer Modified Bitumen (PMB) using Ethyl Vinyl Acetate (EVA) as the modifier. The objective of the research is to investigate the effects of EVA modification on the properties of bitumen, including penetration, softening point, ductility, and specific gravity. The study aims to compare the performance of the modified bitumen with conventional bitumen and provide insights into its potential applications in road engineering. experimental work utilized standardized test methods (IS 1203 for penetration, softening point, and ductility, and IS 1202 for specific gravity) to evaluate EVA-modified bitumen. Samples with 2% and 4% EVA concentrations were prepared. Results showed significant enhancements compared to basic bitumen, including increased penetration resistance, Keywords-: Bitumen, Ductility, Penetration, Softening Point, Speicfic Gravity

Engineering properties of SBS and crumb-rubber modified bitumen – a design of experiment approach

Purpose Cracking, deformation and rutting are the most prevalent types of pavement distress, and these deformations and flow characteristics greatly distress the pavement features while also limiting its use. In India, on the other hand, more than 300 million scrap tyres are generated each year, and their disposal has become a severe environmental issue. Furthermore, the scrap generated by the used tyre must be disposed of properly. Hence, this study presents the experimental investigations of bitumen incorporating with Crumb rubber as main additive along with SBS polymer, to enhance the engineering property. Design/methodology/approach Crumb rubber (CR) was used as an additive along with styrene–butadiene–styrene (SBS) polymer to enrich the engineering qualities of the bitumen to reduce the disposal problem of scrap tyres and reduce the risk of environmental pollution. Because SBS polymer is expensive, response surface methodology modelling's central composite design (CCD) was used to optimise the number of tests. CCD modelling's input factors (process variables) were the inclusion rates of SBS and CR, which ranged from 2% to 5% and 4% to 10%, respectively, by total weight. Furthermore, the influence of SBS polymer and CR on the characteristics of modified bitumen was prioritised. Findings The addition of SBS and CR enhanced the bitumen's penetration resistance at service temperatures. Furthermore, increasing the SBS and CR concentration affected the flow characteristics of the modified bitumen and enhanced its viscosity. The addition of SBS and CR as bitumen modifiers increased penetration resistance by 24.06%. The Dynamic Shear Rheometer test demonstrated that the complex modulus of virgin bitumen increases with increasing SBS and CR content, which is consistent with the shifting softening point trend. The dosing rate of up to 3.5% SBS and 11% CR considerably contributed to the creation of polymer link networks, which increased the complex modulus of the bitumen by 16.5%. The CCD model's analysis of variance and Pareto bar chart demonstrated that the dose of CR is significant in improving the engineering features of the virgin bitumen rather than the SBS. Originality/value The utilisation of CR as a bitumen modifier may solve the problem of waste tyre disposal while also lowering the risk of environmental damage. Furthermore, because the presence of CR increased the engineering properties, particularly the complex modulus of virgin bitumen, the use of CR in combination with SBS polymer can be an efficient and cost-effective strategy to improving bitumen qualities.

Thirteen‐year stover harvest and tillage effects on soil compaction in Iowa

AbstractCorn (Zea mays L.) stover is an abundant biomass source with multiple end‐uses including cellulosic biofuel production. However, stover removal may increase soil compaction by reducing organic matter inputs and increasing vehicle loads during harvest. While numerous studies have reported stover removal impacts on soil physical quality, few have assessed the role played by traffic compaction. Our objective was to quantify subsurface soil compaction after 13 years of chisel plow versus no‐till management and no, moderate (3.5 ± 1.1 Mg ha−1 year−1), or high (5.0 ± 1.7 Mg ha−1 year−1) stover harvest rates. Penetration resistance was measured in most‐ and least‐trafficked interrow spaces. Chisel plowed plots with moderate and high levels of stover removal had higher penetration resistance in trafficked areas relative to least‐trafficked areas, whereas there was no evidence of traffic compaction when stover was retained. Traffic compaction did not negatively impact yields, which were greater with high levels of stover removal compared to no removal. The no‐till practice led to very small increases in penetration resistance with wheel traffic and had no evidence of increased compaction with residue removal. This lack of traffic compaction indicated soils under no‐till practice have a higher load‐bearing capacity than soils under chisel plow practice. Overall, there were no yield‐limiting effects of tillage practice or stover removal, and no evidence of soil compaction below the plow layer, suggesting stover removal with both tillage practices can be effectively employed without detrimental effects on plant or soil health.

Soil Physicochemical Properties and Caper (Capparis spinosa L.) Growth in Response to Various Mulches

ABSTRACT One of the sustainable and the most effective methods for controlling wind erosion is protecting the ground surface by mulching and vegetation cover. This study was done to assess the effect of organic and inorganic mulches and also compaction levels on soil properties and growth characteristics of caper plants, as one of the important shrubs to combat desertification in hot-humid areas. Results suggested that sugarcane bagasse and palm waste compost mulches significantly increased soil organic carbon (OC), nutrients (available nitrogen, phosphorus, and potassium), and moisture, and decreased soil electrical conductivity (EC), pH, and temperature. Petroleum mulch increased soil penetration resistance (69.50 kPa) and temperature (25.50). Petroleum and cement-slag mulch, and also their combination (petroleum-cement mulch) decreased soil moisture to the minimum extent. For either compaction level, using petroleum mulch increases penetration resistance. Compaction decreased soil moisture by 0.96% and increased total neutralizing value (TNV) and bulk density (BD) by 1.52% and 0.31 g cm−3, respectively. For either compaction level, soil porosity increased with the application of sugarcane bagasse mulch and palm waste compost. Using sugarcane bagasse mulch and palm waste compost increased stem length, leaf number, above ground and root weight, and shoot to root ratio of caper plant. Soil temperature (a = −0.70, R2 = 55.70%, P ≤ 0.001), EC (a = −0.87, R2 = 42.49%, P ≤ 0.001) and penetration resistance (a = −1.32, R2 = 17.03%, P ≤ 0.01) decreased with increasing soil moisture. BD (a = −1.20, R2 = 37.08%, P ≤ 0.001) decreased with increasing soil OC. Findings suggested the significant effect of organic mulches on improving some soil properties and growth characteristics of caper plants.

Implications of crop residue removal on soil physical properties: A review

AbstractCrop residues are often removed for livestock and biofuel production, but how such removal impacts soil physical properties has not been widely discussed. The objectives of this paper were to discuss: (a) the impacts of crop residue removal on soil physical properties, (b) factors affecting residue removal effects on soils, (c) threshold level of residue removal, (d) strategies to offset the removal negative effects, and (e) research needs. We compiled 66 studies on crop residue removal and soil physical properties published prior to 17 Aug. 2021. Residue removal may not affect bulk density and water infiltration rate but increases penetration resistance by 55% and soil temperature by 1.8 °C in spring. However, it reduces wet aggregate stability by 31%, dry aggregate stability by 44%, and water retention at –33 kPa by 24% in most studies, indicating residue removal can increase erosion risks and reduce soil water storage. Residue removal rate is the leading factor that explains changes in soil physical properties. Residue removal at rates above 50%, in general, adversely affected soil physical properties, which correlates to retaining about 4 Mg ha–1 of residue. Cover crops and manure application may partially offset adverse effects of residue removal on soil physical properties, but studies are too few to make a strong conclusion. Consistency of soil sampling depths, accurate reporting of residue removal rates, and additional data from long‐term experiments are needed. Overall, high rates of residue removal can increase erosion potential and reduce soil water but have mixed impacts on other physical properties.

Influence of Plants on the Spatial Variability of Soil Penetration Resistance

Abstract Soil penetration resistance is an informative indicator to monitor soil compaction, which affects a range of ecological processes in floodplain ecosystems. The aim of the investigation was to reveal the influence of vegetation cover on the spatial variability of penetration resistance of floodplain soils. The study was carried out in the elm oak forest in the floodplain of the Dnipro River (Dniprovsko-Orilsky Nature Reserve, Ukraine). The study of the soil profile morphology was performed in accordance with the guidelines of the field description of soils FAO. The soil penetration resistance was measured in the field using the Eijkelkamp manual penetrometer to a depth of 100 cm at 5-cm intervals within the polygon consisted of 105 sampling points. Vegetation descriptions were made in a 3×3-meter surrounding from each sampling point. The soil penetration resistance was found to regularly increase with increasing depth. The changes in resistance values were insignificant until 25–30 cm depth. After that, there was a sharp increase in penetration resistance up to the depth of 70–75 cm, after which the indicators plateaued. In the three-dimensional aspect, the spatial variation of soil penetration resistance can be fractionated into broad-scale, medium-scale, and fine-scale components. Tree vegetation induces a broad-scale component of soil penetration resistance variations, which embraces the whole soil profile. The herbaceous vegetation induces a medium-scale component, which embraces the upper and middle parts of the soil profile. The fine-scale component is influenced by pedogenic factors.

Use of Impact Penetrometer to Determine Changes in Soil Compactness After Entracon Sioux EH30 Timber Harvesting

Wood harvesting with the use of wheeled harvesters is now common in Polish and Czech forests. While moving in the forest, the wheels of these machines affect the forest soil and the extent of this impact is interesting. The paper presents the results of measurements of the changes that occur in the soil on the operational trails after the timber harvesting using the Entracon Sioux EH30 thinning harvester. The measurements were taken on fragments of three operational trails, in and between the ruts and at a distance of 1.0 m off the trail. An impact penetrometer was used to measure the penetration resistance, soil samples were collected to determine the bulk density and moisture content, and soil deformations on the trail were measured with a profile meter. Unit pressures exerted by harvester wheels on the ground were determined. It was shown that in the places where the harvester wheels pass, even of a small weight (5.73 tons, 8 wheels) and with unit pressures of the wheels on the ground <50 kPa, changes in soil parameters occurred. A statistically significant increase in penetration resistance in relation to the control occurred at a depth of up to 35 cm, while at a depth of up to 5 cm the increase was more than 2-fold. There was also a slight decrease in soil moisture content (up to 7.9%) and an increase (up to 8.4%) in bulk density in the ruts, while rut depths were small and reached 4 cm. As it was shown, the impact penetrometer, simple in design, which was assumed to be used for measurements, and which is not used in this type of research in forestry, despite its limitations, can be used to determine the compactness of the soil and its changes resulting from machine work.

Macroaggregates of loam in sandy soil show little influence on maize growth, due to local adaptations of root architecture to soil heterogeneity

AimsRoot hairs and lateral growth are root traits among many which enable plants to adapt to environmental conditions. How different traits are coordinated under local heterogeneity, especially when two or more environmental factors vary in space, is currently poorly understood. We investigated the effect of heterogeneity on root system architecture of maize in response to the presence of loamy macroaggregates, which come along with both, increased penetration resistance and nutrient availability, i.e., two important environmental factors shaping root system architecture. The comparison between a mutant with defective root hairs and the corresponding wild type made it possible to investigate the importance of root hairs in the adaptation strategies of plant roots to these factors.MethodsChanges in root growth and root distribution with respect to macroaggregates were investigated using X-ray computed tomography. The wild-type of Zea mays L. was compared with the root hair defective mutant (rth3) to investigate the importance of root hairs in addition to adaption of root architecture.ResultsThe presence of aggregates lead to increased root length and branch densities around aggregates, while only a few roots were able to grow into them. Thereby, wildtype and rth3 were influenced in the same way. Aboveground biomass, however, was not affected by the presence of macroaggregates, as compared to controls with homogenously distributed loam.ConclusionsMacroaggregation of loam in sandy soil shows little influence on maize growth, due to local adaptations of root architecture to the heterogeneity in nutrient availability and penetration resistance caused by the aggregates.

Installation design of a large tubular caisson in the spatially varying seabed

The installation of large steel tubular caissons, used as protection for underwater production systems, is still a challenge. To evaluate the reliability of installation, soil spatial variability is accounted for in this study through two-dimensional random field establishments and Monte Carlo simulation. As vertical random parameters are identified by field CPT data, the effect of the horizontal scale of fluctuation (δh) is explored, which becomes significant due to the extremely large diameter of the caisson. Probability distributions of self-weight penetration, inclination angle, and the ultimate soil resistance with various δh are derived from conventional installation analyses with spatially varying soil domains. It shows that increasing δh reduces the likelihood of over-tilt, yet raises the possibility of vibratory drivability refusal (failure probability). The effect of stiffeners during caisson installation is also studied, including an increase in penetration resistance and failure probability. This analysis sheds light on the impact of the soil correlation distance as well as caisson stiffeners and is useful to the reliable installation design of the large tubular caisson, particularly in layered soil.

Reversible and irreversible root phenotypic plasticity under fluctuating soil physical conditions

Roots grow in a highly heterogeneous physical environment due to the spatial complexity of soil structure. Thereby, the root growth zone repeatedly experiences soil physical stress such as hypoxia or increased penetration resistance. To mimic the highly variable physical environment surrounding the root growth zone, we subjected pea and wheat seedlings to periodic soil physical stress. One day of soil hypoxia or increased penetration resistance reduced root elongation rate of both species by at least 20 %. Upon stress release, root elongation rate of pea could recover within one day, while no such recovery occurred in wheat. Similarly, the diameter of the root elongation zone in pea increased by 15 % and 20 % due to hypoxia and increased penetration resistance, respectively, but decreased again once the stresses were released. In contrast, the diameter of the elongation zone of wheat roots started to decrease with the onset of soil physical stress and this trend continued upon stress release. Hence, root responses to short-term soil physical stress were reversible in pea and irreversible in wheat, indicating reversible and irreversible root phenotypic plasticity, respectively. This suggests that strategies to cope with periodic soil physical stress may vary among species. The differentiation between reversible and irreversible phenotypic plasticity is crucial to advance our understanding on soil exploration, resource acquisition, whole plant growth, and ultimately crop yield formation on structured soil.

Effects of cryogenic and warm temperatures on quasi-static penetration resistance of carbon-aramid hybrid nanocomposites reinforced using halloysite nanotubes

The quasi-static penetration test of a composite structure aims to measure impact behavior under the out-of-plane loadings without dynamic and rate effects. In this study, carbon-aramid reinforced nanocomposites were manufactured by vacuum-assisted resin transfer molding and hand lay-up techniques and characterized by quasi-static penetration tests. Halloysite nanotubes (HNTs) were added to epoxy resin as nanofillers. Quasi-static punch shear test (QS-PST) was performed using a 12.7-mm cylindrical punch with a 50.8-mm support span. QS-PSTs tests were carried out at −50 °C, −25 °C, 0 °C, 25 °C, and 50 °C to determine the effect of temperature on quasi-static penetration behavior of neat and HNT-reinforced carbon-aramid nanocomposites. Absorbed energy values and penetration force–displacement curves were acquired from QS-PSTs for each sample. Photographs of the front and rear sides of the samples were taken and analyzed. Moreover, the samples were cut from the middle, and the damage throughout the thickness of the composite samples were examined. It was observed that for all test samples, damages increased when the temperatures decreased. For the same temperature, nanoparticle addition to the samples resulted in higher penetration force and less damage. We confirmed the possibility of increasing penetration resistance and energy absorption capacity by adding HNT to carbon-aramid fibers at cryogenic and warm temperatures.

Soil Penetration Resistance after One-Time Inversion Tillage: A Spatio-Temporal Analysis at the Field Scale

Conservation agriculture may lead to increased penetration resistance due to soil compaction. To loosen the topsoil and lower the compaction, one-time inversion tillage (OTIT) is a measure frequently used in conservation agriculture. However, the duration of the positive effects of this measure on penetration resistance is sparsely known. Therefore, the aim of this study was to analyze the spatio-temporal behavior of penetration resistance after OTIT as an indicator for soil compaction. A field subdivided into three differently tilled plots (conventional tillage with moldboard plough to 30 cm depth (CT), reduced tillage with chisel plough to 25 cm depth (RT1) and reduced tillage with disk harrow to 10 cm depth (RT2)) served as study area. In 2014, the entire field was tilled by moldboard plough and penetration resistance was recorded in the following 5 years. The results showed that OTIT reduced the penetration resistance in both RT-plots and led to an approximation in all three plots. However, after 18 (RT2) and 30 months (RT1), the differences in penetration resistance were higher (p < 0.01) in both RT-plots compared to CT. Consequently, OTIT can effectively remove the compacted layer developed in conservation agriculture. However, the lasting effect seems to be relatively short.

Liquefied strength ratio with stress densification and low stresses

This paper presents a comparison of four assumptions or approaches for using a liquefied shear strength ratio for sandy soils in cases where there has been a large increase in effective vertical stress, e.g., structure raising or remedial measure, that is outside the effective stresses of the case histories used to develop the empirical liquefied shear strength ratio and penetration resistance correlations. Changes in penetration resistance due to an increase in effective vertical stress are used in an example to illustrate the following four assumptions for determining a liquefied shear strength ratio in such a post-liquefaction stability analysis: (1) initial effective vertical stress and initial penetration resistance; (2) initial effective vertical stress and the expected increase in penetration resistance due to the increase in effective vertical stress; (3) final effective vertical stress and initial penetration resistance, which is suggested; and (4) final effective vertical stress and final penetration resistance. This paper also presents suggestions for using a liquefied strength ratio at low effective vertical stresses, e.g., approaching the toe of a dam or embankment, in a post-liquefaction stability analysis.