Levels Of Soil Compaction Research Articles

Impacts of Soil Compaction and Phosphorus Levels on the Dynamics of Phosphate-Solubilizing and Nitrogen-Fixing Bacteria in the Peanut Rhizosphere

Soil properties, including soil compaction and the nutrient content, influence the composition and functions of rhizosphere microbial communities. There is limited information on how soil compaction and phosphorus application affect phosphate-solubilizing (PSB) and nitrogen-fixing bacteria (NFB). This study aimed to examine the responses of PSB and NFB in the rhizosphere of peanut (Arachis hypogaea L.) plants under varying soil compaction and phosphorus application levels. To address this, pot experiments were conducted to assess the composition and assembly processes of rhizosphere PSB and NFB in peanut cultivar Hua Yu 22 under two soil compaction levels (T1, 1.25 g/cm3 compaction, and T2, 1.00 g/cm3 compaction) and two phosphorus (P) levels (P0, no P applied, and P1, 1.2 mM P/kg soil applied). The results showed that PSB community shifts were closely correlated with the content of soil available phosphorus, soil acid phosphatase activity, soil nitrogenase activity, and soil compaction. Additionally, the content of soil available phosphorus and soil compaction were correlated with changes in operational taxonomic units of NFB. A network analysis revealed that the complexities of PSB were significantly higher than those of NFB. A stronger negative relationship was identified among NFB communities. The assembly of PSB communities was primarily driven by drift processes, whereas NFB communities were influenced by a combination of homogenizing selection and drift. Both PSB and NFB community compositions were significantly affected by phosphorus limitations and soil compaction. These findings enhance our understanding of the impacts of soil compaction and phosphorus application on PSB and NFB communities, with implications for optimizing peanut crop production. Our results will provide reference for crop cultivation in compacted and low-phosphorus soils. The important phosphate-solubilizing and nitrogen-fixing bacteria screened in the interaction network in this study will become candidate microbial agents for alleviating soil compaction and low phosphorus levels.

Measurements and predictions of seedling emergence forces

Quantifying seedling emergence pressure or forces (soil impedance to seedling) during the process of plant emergence is difficult in a practical setting. In this study, a mechanical seedling testing device was designed and calibrated to measure seedling emergence pressures experienced by conical or spherical mechanical seedling in soil with varying compaction levels. The data were analysed to generate regression models for predicting seedling emergence forces. Results showed a high correlation between the seedling emergence pressure and soil resistance. The resultant regression model produced a coefficient of determination (R2) of 0.99. After incorporating the morphological characteristics of soybean cotyledon and maize coleoptile into the model, the predicted seedling emergence forces increased with the soil compaction level. During the emergence process, average emergence force of the soybean seedlings was 11.8 N for the lowest compaction level and 28.5 N for the highest compaction level, and the corresponding values of the maize seedlings were 0.2 N and 0.6 N. In a non-compacted field plot, maize crop had a 95.4% emergence rate and soybean crop had 97.2%, whereas for a compacted plot, the corresponding emergence rates were decreased to 19.1% and 60.5%. Inferences made from the study provide information on the dynamics of soil-seedling interaction, which have important implications for managing soil compaction in crop production.

The Effects of Soil Compaction on the Growth and Architecture of the Seedlings of Species Commonly Used for Afforestation in Iran

The aim of the present study was to elucidate the effects of soil compaction on the seedlings of two species of deciduous (Acer velutinum and Alnus subcordata) and evergreen trees (Pinus eldarica and Pinus nigra) in terms of above- and below-ground morphology in a greenhouse. Six soil compaction levels were applied: the lowest intensity (control), very low, low, moderate, heavy, and very heavy. The results showed that there were different effects according to the species. These effects were on lateral root length, stem diameter, leaf dry biomass, SSL (specific stem length), SRL (specific root length), LMR (leaf mass ratio), RMR (root mass ratio), SMR (stem mass ratio), and R/S (root-to-shoot ratio). The results showed that soil penetration resistance (SPR) had a significant effect on seedling variables such as lateral root length, stem diameter, leaf dry biomass, and SRL (p < 0.05). A. velutinum seedlings have the highest values of growth variables compared to three other species, followed by A. subcordata seedlings. The two evergreen species, Pinus eldarica and Pinus nigra, have the lowest values of these growth variables. It is worth noting that we found that deciduous species had enhanced growth up to a moderate compaction level (1.3 MPa), while the growth decreased at an SPR that was higher than this value.

Comparison of various single-disc type furrow openers used in no-till seeders in terms of furrow properties and acting forces

The purpose of this study was to examine the impact of various single-disc type furrow openers used in no-till seeders on furrow aspects and forces acting on the discs at various soil moisture contents, soil compaction levels, and seeding depths in soil bin. Factors included plain, notched, wavy, concave, and fluted types of disc coulters, two soil moisture levels (12-18%), two soil compaction levels (2-3 MPa), and two seeding depths (50-75 mm). According to the results, the plain, notched, and fluted type discs had the lowest vertical, draft, and side force, while the wavy type disc had the maximum vertical force, draft force, and side force and the concave type disc had the highest side force. The vertical, draft, and side force requirements of all furrow openers were found to be lower in loose soils with low moisture content and greater in compacted soils with high moisture content. Fluted, concave, and wavy-type discs produced the best results in terms of the specific vertical, specific draft, and specific side forces, respectively. While the highest furrow cross-sectional area was obtained in the wavy disc, this furrow opener was followed by concave, notched, fluted, and plain-type furrow openers, respectively.

Assessment of different agricultural soil compaction levels using shallow seismic geophysical methods

A well-developed soil structure is crucial for a fertile soil and rules its influence on the ecosystem. Slight variations in the way soil components are organized and connected can greatly impact the soil mechanical and hydraulic characteristics. However, these features are challenging to measure at a scale that is relevant for agricultural management. In this study, we assess the capability of two seismic geophysical methods, i.e. Seismic Refraction Tomography and Multichannel Analysis of Surface Waves, to monitor the effects of compaction on agricultural bare soil. The purpose is to highlight the different mechanical response caused both by soil plastic deformation and soil water distribution due to increasing compaction. Results demonstrate that both geophysical techniques provide sufficient information to capture the effects of soil compaction and distinguish its significance, while traditional direct measurements, being punctual, lack sufficient spatial coverage. P-wave velocities carry a strong imprint of soil compaction, provided by seismic refraction, incorporating the information given by the multiphase medium in its entirety. On the other hand, S-wave velocity derived from Surface Waves discriminates the effect of solid matrix structure. This work, moreover, aims to pave the way for seismic methods to spatially characterize compaction at field scale, illustrating its potential and suggesting possible developments.

Comparative Measurement of Horizontal Penetrometry with a Focus on the Degree of Soil Compaction in Real Work Conditions

Potential soil production is closely related to the physical and mechanical properties. The aim of this paper was to evaluate the effect of different levels of soil compaction created by tractor chassis. The total area of the experimental plot was 13.22 ha. Up until 2019, a conventional tillage system had been used. The measurements were carried out with an innovative measuring device that allows for the continuous measurement of the horizontal penetrometry for comparative measurements while driving, which was designed at the Slovak University of Agriculture in Nitra. The measuring device measured the soil resistance in the tire track (On-track) and out of track (Off-track) as well as in three (50 s) sequences within one tractor pass. Three lines were chosen, where in each a pair of combinations was made. The results were subjected, in addition to graphical evaluation, to single factor ANOVA analysis. When comparing individual passes (PH1 to PH6), the statistical analysis showed that the results of the horizontal resistance measurements proved to be statistically significant (p < 0.05) with respect to the weight, number of passes, and tire underinflation. The highest compaction was caused by the first pass, while the higher weight of the tractor during the next pass had a smaller effect. Underinflating the tires ensured a reduction in compaction. Reducing the tractor tire pressure to 0.15 MPa resulted in a reduction in soil compaction of up to 16%.

Alfalfa Responses to Intensive Soil Compaction: Effects on Plant and Root Growth, Phytohormones and Internal Gene Expression.

The perennial legume alfalfa (Medicago sativa L.) is of high value in providing cheap and high-nutritive forages. Due to a lack of tillage during the production period, the soil in which alfalfa grows prunes to become compacted through highly mechanized agriculture. Compaction deteriorates the soil's structure and fertility, leading to compromised alfalfa development and productivity. However, the way alfalfa responses to different levels of soil compaction and the underlying molecular mechanism are still unclear. In this study, we systematically evaluated the effects of gradient compacted soil on the growth of different cultivars of alfalfa, especially the root system architecture, phytohormones and internal gene expression profile alterations. The results showed that alfalfa growth was facilitated by moderate soil compaction, but drastically inhibited when compaction was intensified. The inhibition effect was universal across different cultivars, but with different severity. Transcriptomic and physiological studies revealed that the expression of a set of genes regulating the biosynthesis of lignin and flavonoids was significantly repressed in compaction treated alfalfa roots, and this might have resulted in a modified secondary cell wall and xylem vessel formation. Phytohormones, like ABA, are supposed to play pivotal roles in the regulation of the overall responses. These findings provide directions for the improvement of field soil management in alfalfa production and the molecular breeding of alfalfa germplasm with better soil compaction resilience.

Performance of seedlings and yield of soybean genotypes under soil compaction

AbstractThe identification of soybean genotypes tolerant to soil compaction makes it possible to reduce productivity loss under stress conditions. Added to this, the prior selection of these genotypes will result in greater assertiveness in the positioning of cultivars in the field. Thus, the objective was to evaluate the susceptibility of soybean genotypes to compaction in greenhouse and field conditions; verify which characteristics of seedlings under high resistance to root penetration are correlated with crop production in compacted soil; and to validate the substrate mechanical impedance method for evaluating the susceptibility of plant genotypes to soil compaction. Seeds of 20 genotypes were sown in a substrate mechanical impedance system under controlled conditions. The characteristics evaluated were total root length, total root surface area, mean root diameter, total root volume, taproot length, shoot length, root dry matter and seedling shoot dry matter. In the field experiment, half of the planting area was compacted, constituting two treatments, soil with and without compaction. The percentage of seedling emergence, initial plant height, stem diameter, number of nodes, internode length, number of lateral branches, shoot dry matter, final plant height, absolute and relative growth rate, number of pods, weight of 100 seeds and grain yield. In addition, the number of days between soybean sowing until plant flowering and grain harvest was recorded according to genotype and soil compaction level. In a controlled environment, genotypes tolerant to soil compaction show greater plasticity of root characteristics and smaller alterations in the shoot of seedlings. In the field, these genotypes show smaller reductions in growth rate, height, number of pods and grain yield. The shoot dry matter and the root dry matter of soybean seedlings in a mechanical impedance system present a positive and negative correlation, respectively, with soybean yield in compacted soil, indicating that the genetically determined susceptibility to soil compaction stress was similar throughout ontogenesis. The substrate mechanical impedance system used to evaluate the performance of soybean seedlings under stress, facilitates the decision‐making in breeding programs focused on identifying genotypes expressing soil compaction tolerance.

Soil disturbance caused by timber harvesting in a natural forest, West Sumatera Indonesia

Logging operations in natural forests generally use bulldozers. Bulldozers skid logs from the stump site to the landing site. The bulldozer maneuvers in the felling area cause skid trails and soil compaction. Soil compaction is one of the negative impacts of logging operations. The research aim is to analyze the level of soil compaction in various bulldozer skidding intensities after logging operations. The research occurred at a natural forest area in Siberut West Sumatera, Indonesia. The results of the study showed that there was a relationship between skidding intensity and the level of soil bulk density. The more a bulldozer moves at the same skid trail, the higher the soil bulk density. The range of soil bulk density is from 0.82 g cm−3 to 1.31 g cm−3. The bulk density increases markedly after the bulldozer’s first, second, and third passes. After the fourth pass, the bulk density is relatively constant. The porosity of the soil decreases with the increase of the bulk density. On skid trails where the soil is very compact, seeds that fall on skid trails will have difficulty growing well. Requires planting on primary skid trails. Soil damage in the form of soil compaction by bulldozers needs serious attention in the Reduce Impact Logging technique.

Logging Machinery Traffic Has Greatest Influence on Soil Chemical Properties in the Amazonian Rainy Season

Abstract In the forests of Amazonia each year, previously unentered stands are logged, which usually results in some degree of soil compaction. Consequently, the soil chemical properties in compacted areas are altered. The aim of this study was to determine how these changes may help or hinder site recovery in the context of seasonal variation and increased levels of compaction. To investigate these changes, an experiment was established in the Central Amazon. This consisted of tractor trails compacted at three incrementally increasing traffic intensities of one, three, and twelve machine cycles in the wet and dry seasons. Results revealed that elevated moisture in the wet season combined with heavy compaction from twelve machine cycles had the greatest impact on soil chemical properties. This was indicated by diminished total nitrogen, organic carbon, available phosphorus, cation exchange capacity, and elevated ammonium and Fe2+. Nevertheless, heavy compaction in the wet season led to lower Al3+ and higher base saturation, which could be beneficial for future site recovery. Study Implications: Annually, vast swathes of old-growth forest are logged for the first time in Amazonia. These areas require an extensive skid trail network to facilitate movement of logging machinery and subsequent log skidding. Skid trails always entail some level of soil compaction, especially in the heavily used primary skid trails. This compaction influences the soil chemical properties. Some impacts are only apparent in the wet season and may not be present in the dry season. Therefore, to reduce overall impacts to soil chemical properties, skid trail coverage should be planned to reduce the coverage of the logging site.

Dissecting chickpea genomic loci associated with the root penetration responsive traits in compacted soil.

Soil compaction reduces root exploration in chickpea. We found genes related to root architectural traits in chickpea that can help understand and improve root growth in compacted soils. Soil compaction is a major concern for modern agriculture, as it constrains plant root growth, leading to reduced resource acquisition. Phenotypic variation for root system architecture (RSA) traits in compacted soils is present for various crops; however, studies on genetic associations with these traits are lacking. Therefore, we investigated RSA traits in different soil compaction levels and identified significant genomic associations in chickpea. We conducted a Genome-Wide Association Study (GWAS) of 210 chickpea accessions for 13 RSA traits under three bulk densities (BD) (1.1BD, 1.6BD, and 1.8BD). Soil compaction decreases root exploration by reducing 12 RSA traits, except average diameter (AD). Further, AD is negatively correlated with lateral root traits, and this correlation increases in 1.8BD, suggesting the negative effect of AD on lateral root traits. Interestingly, we identified probable candidate genes such as GLP3 and LRX for lateral root traits and CRF1-like for total length (TL) in 1.6BD soil. In heavy soil compaction, DGK2 is associated with lateral root traits. Reduction in laterals during soil compaction is mainly due to delayed seedling establishment, thus making lateral root number a critical trait. Interestingly, we alsofound a higher contribution of the GxE component of thenumber of root tips (Tips) to the total variation than the other lateral traits. We also identified a pectin esterase, PPE8B, associated with Tips in high soil compaction and a significantly associated SNP with the relative change in Tips depicting a trade-off between Tips and AD. Identified genes and loci would help develop soil-compaction-resistant chickpea varieties.

Linking horizontal crosshole GPR variability with root image information for maize crops

AbstractNon‐invasive imaging of processes within the soil–plant continuum, particularly root and soil water distributions, can help optimize agricultural practices such as irrigation and fertilization. In this study, in‐situ time‐lapse horizontal crosshole ground penetrating radar (GPR) measurements and root images were collected over three maize crop growing seasons at two minirhizotron facilities (Selhausen, Germany). Root development and GPR permittivity were monitored at six depths (0.1–1.2 m) for different treatments within two soil types. We processed these data in a new way that gave us the information of the “trend‐corrected spatial permittivity deviation of vegetated field,” allowing us to investigate whether the presence of roots increases the variability of GPR permittivity in the soil. This removed the main non‐root‐related influencing factors: static influences, such as soil heterogeneities and rhizotube deviations, and dynamic effects, such as seasonal moisture changes. This trend‐corrected spatial permittivity deviation showed a clear increase during the growing season, which could be linked with a similar increase in root volume fraction. Additionally, the corresponding probability density functions of the permittivity variability were derived and cross‐correlated with the root volume fraction, resulting in a coefficient of determination (R2) above 0.5 for 23 out of 46 correlation pairs. Although both facilities had different soil types and compaction levels, they had similar numbers of good correlations. A possible explanation for the observed correlation is that the presence of roots causes a redistribution of soil water, and therefore an increase in soil water variability.

Study of the effect of the compaction level on the hydrodynamic properties of loamy sand soil in an agricultural context

Agricultural soil compaction adversely affects crop water use and yield performance and should be avoided or remediated through appropriate soil management strategies. The investigation of the impact of different levels of soil compaction on its hydrodynamic properties remains a crucial step in improving water use and crop yields. We examined five compaction levels of silty sand soil sampled from a potato field in the agricultural regions of northern Quebec (Canada). Soil hydraulic characteristics (saturated and unsaturated hydraulic conductivity, soil water retention capacity) were measured using the constant head method, the HYPROP device, and a WP4C dew point potentiometer. The sixteen hydraulic models integrated into the HYPROP software were fitted to the soil water retention curve (SWRC) data for the studied compaction levels. Statistical parameters such as the mean bias error, mean absolute error, correlation coefficient, and root mean square error were used to measure the performance of the models. The results show that saturated and unsaturated conductivity decreases with increasing soil compaction. The lowest saturated hydraulic conductivity (Ks) value is observed for the highest level of soil compaction, reflecting a solid medium with less pore space and connectivity. Among the hydraulic models, the Peters-Durner-Iden (PDI) variant of van Genuchten's unconstrained bimodal model (VGm-b-PDI) outperformed all other models for SWRC simulation of different soil compaction levels and was, accordingly, selected as the optimal model. This model was implemented in HYDRUS-1D to estimate the amount of irrigation for different compaction levels. We simulated irrigation scenarios with the dual-porosity model. The results indicated that soil compaction can strongly influence soil hydraulic properties and water differently. However, the amount of irrigation for the potato crop was optimal at a moderate level of soil compaction. Overall, combined HYPROP and HYDRUS 1D can provide helpful information on the soil hydraulics properties dynamics and a rigorous simulation for irrigation planning and management in potato fields.

Load-Bearing Capacity of an Oxisol under Burned and Mechanized Harvest Sugarcane Crops

The change in land use and the expansion of mechanized sugarcane production systems have led to an increase in soil compaction levels. Preconsolidation pressure may be used as a useful measure for soil mechanical state, management, and planning of mechanization systems. This study aimed to assess the soil compressive behavior, soil physical properties, and spatial variability of preconsolidation pressure of an Oxisol in sugarcane fields under burned harvest and mechanized harvest and the effects of land use change. The physical soil attributes (granulometry, soil water content, bulk density, total porosity, and macro and microporosity) and preconsolidation pressure were evaluated at 0.00–0.10-m, 0.10–0.20-m, and 0.20–0.30-m layers. The soil load-bearing capacity models were constructed from σp values for soil water contents. We mapped the assessed soil attributes from crossing points in a sampling mesh with regular 10 m intervals in each area and evaluated them via geostatistics. Land-use change towards sugarcane production systems promoted soil compaction. The mechanized harvesting system increased the soil load-bearing capacity in the water range corresponding to the friability region in subsurface layers. The preconsolidation pressure and soil water content exhibited spatial dependence in the sugarcane areas, regardless of the management system employed in the harvesting operations.

Soil Density in Traditional Mouldboard Tillage

Abstract Until recently, mouldboard ploughing was used as the main tillage in almost the entire territory of Ukraine and Russia. However, mouldboard technologies contribute to the formation of a “plough pan”, which contributes to additional soil compaction. The intensity of agricultural production exacerbated the problem of soil compaction by machine and tractor units. The over-consolidation of soil results in stunted plant root growth, lack of oxygen, and water and nutrient restrictions. Soil compaction can be reduced by deep local chiselling. The aim of the study was to determine the density of the soil at different depths during continuous traditional cultivation (reverse ploughing). The density of the soil was evaluated by resistance to penetration into the soil in a vegetable-forage crop rotation on an experimental field with continuous traditional tillage. The measurement of penetration resistance was carried out using an automatic electronic hardness tester “DATAFIELD”. The boundaries of the experimental field were determined, a computer map of the experimental field was compiled with automatic “grid” of plot sizes, two-dimensional mapping was carried out, and the sequence and place of measurements were developed. As a result, the level of soil compaction at different penetration depths and resistance to root growth was determined. It has been established that with constant traditional reverse tillage, the soil at a depth of more than 10 cm is sufficiently compacted. At a depth of 15 cm, a strong compaction of the soil is observed, which indicates its physical and hydrological degradation.

Experimental and Modeling Evaluation of Impacts of Different Tillage Practices on Fitting Parameters of Kostiakov’s Cumulative Infiltration Empirical Equation

The evaluation and modeling of the water infiltration rate into the soil are important to all aspects of water resources management and the design of irrigation systems for agricultural purposes. However, research focused on experimental studies of infiltration rates in clay soils under different tillage practices remains minimal. Therefore, an empirical prediction model for cumulative water infiltration needs to be created to estimate water depth under different tillage practices. Thus, the present research investigated the impacts of different tillage practices, including plow type (three tillage systems: moldboard, disk, and rotary plows), tillage depth (100 and 200 mm) and four soil compactions levels (0, 1, 3, and 5 tractor wheel passes), on cumulative infiltration behavior in a clay soil under a randomized complete design with three replications. Double-ring infiltration experiments were conducted to collect infiltration data. The research was conducted in three different stages. The first stage was performed through a field test to obtain infiltration data, the second stage involved using a Kostiakov empirical equation (Z = q × tb) for cumulative infiltration to acquire the fitting parameters of “q” and “b”, and in the last stage, we predicted the fitting parameters of “q” and “b” based on soil mean weight diameter, tillage depth, and four soil compaction levels by applying regression data mining approaches in Weka 3.8 software. The results show that the effects of relevant factors on the cumulative water infiltration depth of the soil could be statistically significant (p < 0.05). The Kostiakov model, with an average coefficient of determination of 0.939, had a good fitting effect on the cumulative water infiltration depth process of the investigated soil. The average, lowest, and maximum values of the “q” parameter were 2.7073, 2.2724, and 3.1277 mm/minb, respectively, while for the “b” parameter, they were 0.5523, 0.5424, and 0.5647, respectively. Furthermore, the evaluation of several regression data mining approaches determined that the KStar (K*) data mining approach, with a root mean square error of 0.0228 mm/minb, a mean absolute error of 0.0179 mm/minb, and a correlation coefficient of 0.997, was the most accurate method for fitting parameter “q” using the testing dataset. The most accurate method for fitting the parameter “b” estimation was determined to be the Multilayer Perceptron method, with a root mean square error of 0.0026, a mean absolute error of 0.0013, and a correlation coefficient of 0.962, using the testing dataset. Therefore, this research, which consisted of in situ field observation experiments and infiltration modeling of the infiltration process in a clay soil, provides an essential theoretical basis for improving models of the rate of cumulative infiltration. Moreover, the proposed methodology could be employed for simulation of the fitting parameters “q” and “b” for soil water cumulative infiltration processes, not only for irrigation management purposes under regular crop production conditions, but also for the selection of the most suitable tillage practices to modify the soil during the agriculture season to conserve water and prevent yield declines. The results support the understanding of the infiltration processes in a clay soil and demonstrate that tillage practices could reduce the water infiltration rate into the soil.

Measurements and DEM modelling of soybean seed expansion

The dynamics of the seed driven by its hydration status has important agronomical implications. However, little research has been done in this area. This study was devoted to the expansion and force of individual seeds hydrated in two different environments: soil and water. The expansion of a soybean seed in soil during imbibition (the uptake of water by dry seed) phase was measured using the computer tomography (CT) scanning technology (non-destructive tests). The expansion force was predicted by a model developed using the discrete element method (DEM). The model was able to predict the expansion force of a seed under different soil compaction levels (Low, Medium, and High). The force potential of a fully hydrated seed was measured. The CT scan results showed that during the imbibition process, a soybean seed continued expanding, and after 36 h, it expanded by 80% of its original length and by 37% of its original volume. The model simulation results showed that as seed expanded in soil, forces arose between the seed and surrounding soil particles. Under the same soil conditions, the expansion force of seed along its length-axis was the highest among all three axes of seed. Within each seed axis, the expansion force increased with the soil compaction level. Measurements showed that a sufficiently hydrated soybean seed was capable of generating a force of 11.3 N along the length-axis. This high force potential suggests that the expansion of soybean seed is unlikely restricted by soil particles during the imbibition process, even the soil is severely compacted. This study provides new information for understanding and improving the process of seed germination.

Evaluation of soybean genotypes grown under soil compaction

AbstractSoil compaction has caused negative impacts on soybean productivity due to the excessive use of machinery and heavy agricultural implements in the cultivation areas. Effects of two levels of soil compaction were investigated on 60 soybean genotypes in a field experiment. Soil properties, weather conditions in the region and changes in agronomic characteristics of the crop were evaluated. The genotypes were divided into three groups according to the relative maturity group (RMG) and classified according to stress susceptibility. Compaction increased soil density and soil mechanical resistance to penetration, varying according to the registered rainfall regime. The genotype responses to compaction in the three groups, in general, were increased seedling emergence (EME), initial height (IH), number of nodes (NN), shoot dry matter (SDM), and final height (FH) of the plants. However, there was a reduction in the relative growth rate (RCR), in the number of pods (NP), and in grain yield (PROD). From the calculation of the stress susceptibility index (SSI) it was possible to identify tolerant and sensitive soybean genotypes to soil compaction stress. SSI and the relative trait change index (RTC) indicated the responses that the tolerant genotypes present under conditions of high mechanical impedance. Therefore, soil compaction provides greater seedling emergence and vegetative growth, but significant losses in soybean yield. Soil compaction‐tolerant genotypes show smaller reductions in relative growth rate, absolute growth rate, final height, number of pods, and grain yield.

Validating Agar as an Analog of Soil to Monitor Corrosion of Pipeline Steel

Aqueous electrolyte traditionally used for electrochemical characterization of soil‐related corrosion in laboratories fails to represent the soil physical features, such as pore structure, soil heterogeneity, soil compaction, and saturation levels, in the diffusion‐controlled corrosion process. This article introduces a semi‐solid agar system to reproduce the physical structure of soil for corrosion study. For feasibility validation of the agar system, direct comparison regarding electrochemical activity, diffusion characteristics, and corrosion mechanisms has been performed on pipeline steel in aqueous sodium chloride (NaCl) solution (5 g L−1), 5 g L−1 NaCl‐containing agar, and 5 g L−1 NaCl in sand, respectively. The results indicates that oxygen diffusion in agar and sand media is similar, which significantly weakens the cathodic activity of steel specimens, but leads to distinct corrosion characteristics from those identified in aqueous NaCl solution counterparts. The high diffusion rate of chloride ions in aqueous solution also accelerates corrosion of pipeline steel in NaCl solution through extensive attack at defect sites, but the limited chloride ion movement and the diminished driving force for anodic corrosion activity reduce such attack in their agar and sand equivalents. The solid nature of agar outperforms aqueous electrolytes as soil replicate to explore soil‐related corrosion responses at laboratory scale.

Experimental Study on the Variation of Soil Dielectric Permittivity under the Influence of Soil Compaction and Water Content

The dielectric permittivity of common soils is mainly controlled by water content and porosity, while the latter is closely related to the characteristics of compaction. By studying the changes in dielectric permittivity of soil samples with different soil water content and compaction levels, the influence of the controlling factors on the relationship model between soil water content and dielectric permittivity can be evaluated. In this paper, network analyzer was used to measure the dielectric permittivity of 7 groups of soil samples with gravimetric water content ranging from 8.09% to 14.52% and dry density ranging from 1.61 g/cm3 to 1.96 g/cm3. The results show that the dielectric permittivity increases with the increase of water content and dry density, and the effect of water content on permittivity is more significant for soils with higher dry density. Furthermore, when the water content is less than or equal to the optimal water content, Topp formula and the complex refractive index model (CRIM) can better predict the soil dry density. When the water content approaches the saturated state of soil, there is a deviation between the predicted value and the actual value. At last, the modified Topp formula and the complex refractive index model (CRIM) can accurately predict soil compactness. This provides an important basis for rapid detection of water content and compactness of highway subgrade soil by ground penetrating radar.