Saturation Stress Research Articles

Experimental study on water saturation effect on coal sample permeability under different effective stresses

During the drainage and production of coalbed methane (CBM) wells, the constant changes in stress and water saturation of reservoir restrict the dynamic change of the reservoir permeability. By carrying out stress sensitivity experiments with different water saturations in coal, the correlation between permeability and the coupling of effective stress and water saturation was analyzed. The water saturation sensitivity and stress sensitivity of reservoir were evaluated by the stress sensitivity index (S), permeability damage rate (PDR), and stress sensitivity coefficient (αk), and the change law of coal permeability under different stresses with different water saturations was revealed. The results showed that the coal reservoir permeability decreased with increasing stress following a negative exponential function and decreased nearly linearly with increasing water saturation. In addition, the coal water saturation sensitivity was positively correlated with effective stress, and the coal stress sensitivity was positively correlated with water saturation. Finally, a mathematical model for predicting coal permeability that considered the impacts of water saturation and effective stress was established, revealing the controlled mechanism affecting the permeability change.

Influence of thermal ageing on tensile-plastic flow and work hardening parameters of Indian reduced activated Ferritic Martensitic steel

The present study investigates the influence of thermal ageing (873K/5000h) on the microstructure, tensile-plastic flow behavior, and work hardening parameters of normalized and tempered (N&T) 1.4W-0.06Ta Indian Reduced Activated Ferritic Martensitic (INRAFM) steel. To comprehensively understand the tensile-plastic flow response of the INRAFM steel across a broad temperature spectrum of 300-873 K, the Hollomon, Ludwigson and Voce equations were employed. The results reveal an augmentation in the strain hardening exponent following the ageing process, attributed to the heightened work hardening capability of the aged steel, while the strain hardening coefficient exhibited a decline post ageing. To elucidate the dislocation debris structure?s formation and movement within both the N&T and thermally aged specimens, transmission electron microscopy (TEM) specimens were procured in close proximity to the tensile tested specimens at varying temperatures of 300, 573 and 873 K. The tensile plastic flow behavior at diverse temperatures was aptly described by Hollomon, Ludwigson, and Voce equations. The fitting accuracy of these equations was determined using the goodness of fit, as indicated by the lowest ?2 values. The constitutive Voce equation successfully captured the yield strength (YS) and ultimate tensile strength (UTS) with the initial stress and saturation stress acting as fitting parameters. Distinct patterns of initial stress and saturation stress variations were observed concerning both N&T and aged steel in relation to temperature. Furthermore, absolute value of the Voce strain component (nv) demonstrated a reduction consequent to ageing, manifesting a two-stage behavior corresponding to temperature elevation. Notably, the deceleration of the recovery process during high temperature conditions was more pronounced in the thermally aged steel when contrasted with the N&T steel. Conclusively, the Voce relation proved efficacious in predicting the yield stress (YS) and ultimate tensile strength (UTS) of both the thermally aged and N&T INRAFM steel at varying temperatures.

Hysteresis behavior of EQ56 high strength steel: Experimental tests and FE simulation

The probability of offshore platforms suffering to extreme cyclic loads, such as storm surges and typhoons, increases highly at deep sea. It is essential to achieve the hysteresis behavior of steel material for evaluating the dynamic response of offshore platform under cyclic load. A total of 18 coupons are fabricated from the EQ56 high strength steel (HSS) plate to investigate the monotonic and cyclic behaviors. Loading protocols include monotonic tension, constant amplitude and changing amplitude strain-controlled cyclic loadings. It is revealed that the visco-plastic behavior of EQ56 HSS is insignificant under the monotonic tension at room temperature. The EQ56 HSS presents obvious Bauschinger effect, non-masing rule, stress hardening/softening behavior and strain history memory effect under strain-controlled cyclic loading. The prior loading history at low strain-amplitude levels has little effect on the saturation stress of EQ56 HSS while stress hardening can be reactivated to a new saturation level when the applied strain-amplitude is increased. The monotonic and the cyclic hysteresis curves of EQ56 HSS were compared, and hysteretic skeleton curves are fitted using the Ramberg-Osgood model. The essential parameters of the Chaboche combined hardening model are calibrated to describe the cyclic behavior of EQ56 HSS. The comparison between FE simulation and test results demonstrates that this model cannot characterize effectively the hysteretic behavior of EQ56 HSS because the strain history memory effect and coupled behavior of cyclic stress softening and hardening are ignored in its constitutive equation.

Discrete Element Simulation on Macro-Meso Mechanical Characteristics of Natural Gas Hydrate-Bearing Sediments under Shearing

In order to study the macro-meso shear mechanical characteristics of natural gas hydrate-bearing sediments, the direct shear simulations of natural gas hydrate-bearing sediment specimens with different saturations under different normal stress boundary conditions were carried out using the discrete element simulation program of particle flow, and the macro-meso shear mechanical characteristics of the specimens and their evolution laws were obtained, and their shear damage mechanisms were revealed. The results show that the peak intensity of natural gas hydrate-bearing sediments increases with the increase in normal stress and hydrate saturation. Hydrate particles and sand particles jointly participate in the formation and evolution of the force chain, and sand particles account for the majority of the force chain particles and take the main shear resistance role. The number of cracks produced by shear increases with hydrate saturation and normal stress. The average porosity in the shear zone shows an evolutionary pattern of decreasing and then increasing during the shear process.

Water Saving Using Thermal Imagery-Based Thresholds for Timing Irrigation in Potatoes under Drip and Furrow Irrigation Systems

Under the current water crisis in agriculture, irrigation methods for saving and conserving water are necessary. However, these methods must guarantee an appropriate yield with a concomitant economic benefit and a reduced environmental impact. In this study, two irrigation thresholds for irrigation timing (IT) based on thermal imagery were analyzed with the UNICA potato variety in three trials under drip (DI) and furrow (FI) irrigation during 2017–2018 in Lima, Peru. The control (T1) remained at >70% of soil field capacity. For other treatments, thresholds were defined based on stomatal conductance at light saturation (T2: 0.15 and T3: 0.05 mol H2O m−2s−1) and crop water stress index (T2: 0.4 and T3: 0.6) based on canopy temperature. An integrated index (IIN) was established for the valuation of treatments using the criteria of high fresh tuber yield (FTY) and a low total amount of irrigated water, production cost (PC), and total C emissions (TE) and using criteria of a score. FI-T2 (0.69–0.72) and DI-T3 (0.19–0.29) showed the highest and lowest IIN value, respectively. FTY in T2 was not significantly reduced under FI, resulting in a lower PC regarding DI–T2 and emphasizing the usefulness of thermal imagery in determining watering schedules in potatoes under furrow irrigation systems.

Micromechanical response of pure magnesium at different strain rate and temperature conditions: twin to slip and slip to twin transitions

The strain rate (ε˙) and temperature (T) dependent mechanical response of single crystal magnesium (Mg) micropillars compressed along the [2¯110] direction (a-axis) is investigated from room temperature to 573 K and from 10-3 to 100 s-1. The loading direction was chosen to disfavour basal slip activation by a low Schmid factor, allowing the investigation of the rate-sensitivities of extension twinning and prismatic slip. For T ≤ 423 K, the plasticity was governed by extension twinning for the entire range of the applied strain rates. At T > 423 K and for ε˙ ≤ 10 s-1, extension twinning did not occur and a continuous plastic flow induced by prismatic dislocation mediated plasticity was observed: the twin to slip transition takes place due to the decrease of the critical resolved shear stress of non-basal slip. For ε˙ > 10 s-1, however, the accommodation of the plastic deformation by activation of prismatic slip is not enough to match the applied deformation rate, favouring again deformation twinning. The first part of this work provides a complete overview of the mutual effects of T and ε˙ on the transition points of deformation modes in Mg at the microscale. In a second stage, the influence of thermal and kinetic contributions on the evolution of the flow stress leading to the slip to twin transition at 573 K has been assessed in more detail. Within the slip-dominated plasticity regime, this work provides a quantitative assessment of the increases in the saturation stress (stage III) with ε˙ at high temperature, showing how the strain rate dependency of the dislocation generation rate in the pillar and escape rate at the free surfaces of the structure controls the stress evolution in Mg microcrystals.

Deformation mechanisms of a NiTi alloy under high cycle fatigue

In this paper, high-cycle fatigue mechanisms of a pseudoelastic NiTi shape memory alloy (SMA) under different mean strains are investigated. The uni-axial cyclic tensile tests with small amplitude of 0.25% are operated at three different states, i.e. austenite/elastic region, austenite and martensite coexisted region and martensite/elastic region with a pre-strain. Mechanical results indicate that the cyclic deformation strain is mainly in the inhomogeneous deformation band when the sample cycling in the B2 + B19′ phase coexist status. Cyclic deformation in the B2 + B19’ phase showed cyclic hardening effect. With increasing of the mean strain, the saturation stress is decreased, and saturation rate is reduced. The mean strain effect on the high-cycle fatigue life of NiTi is attributed to the inhomogeneous transformation of martensite. High resolution electron microscopy (HREM) observations and atomic simulations showed that partial dislocations with the Burgers vectors of 1/2<110> are induced on (001)M twin planes, the interaction of dislocations and edge dislocations in martensite results in cyclic hardening in martensite. While cyclic softening in martensite at the upper plateau of stress–strain (S–S) curve is attributed to the grain reorientation/rotation phenomenon. It suggests that newly generated stress-induced martensite at the interface of martensite and austenite could increase the high-cycle fatigue of NiTi SMA.

Gas permeability variation during methane hydrate dissociation by depressurization in marine sediments

Accurate acquisition of permeability change in hydrate-bearing sediments (HBSs) is the key to predicting reservoirs' multiphase fluids distribution and production capacity. Hydrate saturation and effective stress present significant effects on reservoir permeability. Thus, the influence of hydrate saturation and effective stress on gas permeability change of remolded core during decompression was studied. The results showed that effective stress compression and hydrate decomposition determine the flow channel structure within hydrate sediments. Under unconsolidated and low effective stress(σ' = 1.2 MPa) conditions, the gas permeability increased gradually as the decomposition of hydrate, and the magnitude of permeability variation before and after decomposition increased with increasing hydrate saturation, indicating that the effect of hydrate saturation on permeability dynamic change dominated at low effective stresses. When σ′ was increased to 3.2 MPa and 5.2 MPa, the results were contrary, indicating that the effective stress variation on gas permeability dynamic change dominated at higher effective stresses. In addition, it was found that compression led to higher heat transfer efficiency in high-saturation samples. When hydrate saturation was increased from 23.37% to 48.7%, the effect of increasing effective stress on gas production changed from inhibition to facilitation.

Analysis and Modeling of Stress-Strain Curves in Microalloyed Steels Based on a Dislocation Density Evolution Model.

Microalloyed steels offer a good combination of desirable mechanical properties by fine-tuning grain growth and recrystallization dynamics while keeping the carbon content low for good weldability. In this work, the dislocation density evolution during hot rolling was correlated by materials modeling with flow curves. Single-hit compression tests at different temperatures and strain rates were performed with varying isothermal holding times prior to deformation to achieve different precipitation stages. On the basis of these experimental results, the dislocation density evolution was evaluated using a recently developed semi-empirical state-parameter model implemented in the software MatCalc. The yield stress at the beginning of the deformation σ0, the initial strain hardening rate θ0, and the saturation stress σ∞—as derived from the experimental flow curves and corresponding Kocks plots—were used for the calibration of the model. The applicability for industrial processing of many microalloyed steels was assured by calibration of the model parameters as a function of temperature and strain rate. As a result, it turned out that a single set of empirical equations was sufficient to model all investigated microalloyed steels since the plastic stresses at high temperatures did not depend on the precipitation state.

Micromechanical properties of low-carbon martensitic stainless steel by microtensile experiments

This paper presents a detailed experimental approach to extract the critical resolved shear stress (CRSS) and the saturation stress of the elementary constituents of the microstructure of quenched S41500 martensitic stainless steel by conducting various microscopy observations and microtensile testing. To the authors' knowledge, the direct extraction of micromechanical properties of a single martensite variant by tensile testing has never been performed. However, the literature does propose studies that measured the mechanical properties of the bulk or small volumes containing a few variants. In this work, a particular attention is dedicated to the preparation of the specimens from the macro to the microscale, where final machining of test specimens was made using a Gallium Focused Ion Beam (Ga-FIB). In the present work, the CRSSs of {110}, {211} and {123} plane-related slip systems were directly measured. The post-experiment analysis showed no significant difference between the slip resistance of those planes. To relate this effort with previous work, a comparison with results from the literature was made using a similar testing procedure in lath martensite, revealing similar values of CRSS. The slip resistance saturation was also measured on different slip systems, and the data suggest a very similar hardening behavior for most of the samples tested. Finally, cross-slip remains, in this alloy, a very potent mechanism to reduce the strain hardening that can arise from clusters of nanoparticles observed by TEM.

Constitutive analysis of stress–strain curves in dynamic softening of high Nb- and N-containing austenitic stainless-steel biomaterial

High N-containing austenitic stainless steels have long been used as materials in orthopedic implants. For almost three decades, research has shown that ASTM F-1586 steel is an alternative for orthopedic applications involving severe loads and long implant survival rates in the human body. However, several studies have detected impaired mechanical strength of prostheses during use as a result of manufacturing processes. In this research work, the dynamic softening of this material is characterized based on a constitutive analysis of the stress–strain curves under conditions resembling those of industrial manufacturing, obtained by continuous isothermal hot torsion tests at different temperatures (900ºC-1200 °C) and strain rates (0.01–10s−1). The results indicate that the hot deformation apparent activation energy (Qdef = 594 kJ/mol) is high compared to other types of 300 series stainless steel, as are the ratios between critical (σc), peak (σp), steady state (σss) and saturation (σsat) stresses: σo/σp = 0.69, σc/σp = 0.94, σss/σp = 0.68 and σsat/σp = 1.01. These high values suggest competition between the mechanisms of work hardening (WH), dynamic recovery (DRV) and dynamic recrystallization (DRX), with delay in the onset and progression of DRX kinetics, significantly affected by the moderate stacking fault energy (γsfe ∼ 68.7 mJ/m2), solute atoms (Nb,N) and by fine Z-phase precipitates (CrNbN) at the grain boundaries, which favor softening with intense DRV. Thus, as can be seen, the parameters of WH (h), DRV (r) and DRX (t0.5, n) determine the shape of the stress–strain curves.

Changes and significance of retinal blood oxygen saturation and oxidative stress indexes in patients with diabetic retinopathy.

BACKGROUNDDiabetic retinopathy (DR) is a diabetic complication that can severely affect the patients’ vision, eventually leading to blindness. DR is the most important manifestation of diabetic micro-vasculopathy and is mainly related to the course of diabetes and the degree of blood glucose control, while the age of diabetes onset, sex, and type of diabetes have little influence on it. AIMTo explore the changes in blood oxygen saturation and oxidative stress indices of retinal vessels in patients with DR.METHODSIn total, 94 patients (94 eyes) with DR (DR group) diagnosed at Jianyang people’s Hospital between March 2019 and June 2020, and 100 volunteers (100 eyes) (control group) without eye diseases, were included in this study. Arterial and venous blood oxygen saturation, retinal arteriovenous vessel diameter, and serum oxidative stress indicators in the two groups were compared. Based on the stage of the disease, the DR group was divided into the simple DR and proliferative DR groups for stratified analysis. RESULTSThe oxygen saturation of the retinal vessels in the DR group was significantly higher than that in the control group (P < 0.05). The retinal vessel diameters between the DR and control groups were not significantly different. The serum malondialdehyde (MDA) and 8-hydroxydehydroguanosine (8-OHdG) levels in the DR group were significantly higher than those in the control group (P < 0.05). The serum superoxide dismutase (SOD) and reduced glutathione (GSH) levels in the DR group were significantly lower than those in the control group (P < 0.05). The oxygen saturation of the retinal vessels in the patients with proliferative DR was significantly higher than that in the patients with simple DR (P < 0.05). The retinal vessel diameter in patients with proliferative DR was not significantly different from that of patients with simple DR (P > 0.05). Serum MDA and 8-OHdG levels in patients with proliferative DR were significantly higher than those in patients with simple DR (P < 0.05). Serum SOD and GSH levels in patients with proliferative DR were significantly lower than those in patients with simple DR (P < 0.05).CONCLUSIONIncreased blood oxygen saturation of retinal arteries and veins and increased oxidative stress damage in patients with DR may be associated with decreased retinal capillary permeability and arterial oxygen dispersion, possibly reflecting the patient’s condition.

Effect of rhenium on low cycle fatigue behaviors of Ni-based single crystal superalloys: a molecular dynamics simulation

Molecular dynamics simulations are carried out to investigate the effects of rhenium (Re) on low cycle fatigue behaviors and deformation mechanisms of Ni-based single crystal superalloys. The low cycle fatigue behaviors and deformation mechanisms at different temperatures are discussed. The results show that Re has a positive effect on the low cycle fatigue behaviors of Ni-based single crystal superalloys and the cyclic deformation mechanism is strongly dependent on temperature, which are in good agreement with the previous experimental results. The addition of Re can increase the saturation stress amplitude, reduce the cyclic hysteresis energy and dislocation density, and improve the plastic deformation resistance of the superalloys. During cyclic loading, Re atoms in γ matrix phase gradually move to the γ/γʹ interface, these enrichment of Re atoms at the γ/γʹ interface have pinning effect on dislocations, improving the microstructure stability. At the later of the saturation cycle, segregations of Re atoms prevent the dislocations from cutting into the γ′ phase by dragging dislocations, thus improving the fatigue resistance of superalloys. The simulation results also show that the deformation mechanism gradually changes from dislocations and stacking faults shearing γʹ precipitate phase to Orowan bypassing and climbing mechanism with temperature increases.

The Relationship between Understanding of Materials and Burnout with Stress Levels of Nursing Students at Bale Bandung University (UNIBBA) In E-Learning Learning During the Covid-19 Pandemic

Covid-19 has made many changes, especially in the education sector, which has shifted the learning process which is generally carried out face-to-face to e-learning. This system change has an impact on the psychosocial conditions of students who are not familiar with this method, one of which is the increase in student stress. This is caused by various factors, including an understanding of the material provided, learning boredom that arises, and so on. This study aims to determine the level of understanding of the material and the saturation of learning with the stress level of nursing students at Bale Bandung University (UNIBBA) in e-learning during the covid-19 pandemic. The research design used a cross-sectional with a correlational approach. A sample of 86 nursing students aged 17-26 years was taken by purposive sampling. The research instrument used a questionnaire sheet via a google form and a statistical test with Spearman Correlation Rank at an error rate of 5%. The results showed that most of them experienced mild stress (62.8%), almost all students were quite good at understanding the material (76.7%), and almost all of them experienced learning boredom at a moderate level (76.7%). From the results of the Spearman Rank test, it was concluded that there was a relationship between understanding of the material and stress levels (correlation coefficient -0.221, p-value 0.041), and there was a relationship between learning saturation and student stress levels (correlation coefficient 0.353 and p-value 0.001). Thus, the researcher advises students to continue to increase coping stress, especially in the e-learning learning process by controlling the emotional feelings that arise due to the stressful situation.

Suggested Method of Specimen Preparation for Triaxial Tests on Partially Saturated Sand

Abstract In geotechnical engineering, triaxial testing is widely adopted to evaluate the mechanical behavior of sand. Methods of specimen preparation for triaxial tests on dry and completely saturated sand are well established in the literature, whereas very little guidance exists on the preparation of partially saturated sand at relatively high degrees of saturation (typically Sr &amp;gt; 80 %). The purpose of this study is to elucidate the suitable method of specimen preparation for partially saturated sand using sodium percarbonate and investigate the effects of partial saturation on the undrained cyclic behavior of sand. Loosely and densely packed specimens are prepared in a dynamic triaxial apparatus through dry pluviation and tamping of sand. For tests on fully saturated sand, dry specimens are flushed with carbon dioxide and deaired water and saturated applying back pressure. For tests on partially saturated sand, sodium percarbonate is used in either fine powder or aqueous solution form to create oxygen bubbles in the voids, reducing the degree of saturation of specimens. The results suggest that not only the degree of saturation but also the way partially saturated specimens are prepared affects the liquefaction resistance. At the same level of saturation and principal stress difference, specimens prepared with the aqueous solution exhibit higher liquefaction resistance than those prepared with the powder. The solution of sodium percarbonate proves to be a more reliable and repeatable technique for preparing partially saturated triaxial specimens with relatively high degrees of saturation.

Effect of stress on permeability of clay silty cores recovered from the Shenhu hydrate area of the South China Sea

Hydrate saturation and effective stress are the most important key factors in controlling permeability by altering the pore structure of hydrate reservoirs. However, the understanding of the dependence of the permeability on these factors in fine-grained hydrate reservoirs is not comprehensive due to limited experimental conditions. In this study, clay silty cores recovered from the Shenhu hydrate area of the South China Sea were used as skeletons to synthesize tetrahydrofuran (THF) hydrate-bearing sediments with hydrate saturations of 0–0.6. A series of step-by-step loading and water permeability measurements were conducted on a customized permeability measurement system. The results showed that the water permeability was in the range of 0.005–4 mD, approximately 0.03–1.47 mD near the value of the in situ effective stress of ∼2 MPa. The water permeability increased with increasing effective porosity and conformed to a modified Kozeny-Carmen equation, while the effective porosity increased exponentially with hydrate saturation and effective stress. Permeability stress sensitivity analyses showed that the normalized permeability stress sensitivity coefficient increased with the increase of hydrate saturation. Pore space compression and pore throat clogging were the important factors in the reduction in the water permeability, which dropped by approximately 95% when the effective stress increased from 0 to 8 MPa. This study provides insight into the evolution of pore space and permeability during gas recovery from hydrate-bearing clay silty sediments.

Stress dependence of the gas permeability of montmorillonite sediments in the presence of methane hydrate

The evolution of porosity and permeability of silty clay sediments in the South China Sea has significant effect on gas hydrate production due to the stress effect of submarine overburden rocks. The gas permeability of silty clay specimens under different effective stresses was measured in a cylindrical stainless steel reaction vessel. The experimental results in this paper show that application of effective stress destroys gas permeability of methane hydrate specimens. The power function relation between permeability and effective stress and exponential function relation between porosity and effective stress are given. The experimental data show that the formation of methane hydrate improves the compressible channel of montmorillonite deposits. The permeability damage rate increases with increase of effective stress, and stress sensitivity coefficient increases first and then decreases with increase of effective stress. Finally, an effective permeability equation of sediment containing hydrate saturation and effective stress parameters is established. The results are of guiding significance for the study of the stress dependence of porosity and permeability of gas hydrate silty clay reservoirs in the South China Sea. • Power law is superior to exponential law for showing permeability stress dependency. • Hydrate formation improves the compressible space of montmorillonite sediments. • Permeability damage rate increase with increasing effective stress in sediments. • Stress sensitivity coefficient show a trend of decreasing first and then increasing. • Relational expression between effective stress and permeability is proposed.

Experimental Study on the Gas Permeability of Marine Sediments with Various Hydrate Saturations and Effective Stresses

Marine methane hydrate is considered to be one of the future energy sources with the most potential due to its tremendous reserves. Permeability is a key parameter affecting the recovery efficiency and gas recovery of gas hydrate. We studied the dependence of gas permeability on hydrate saturation and effective stress using remolded core from the South China Sea. The results show that, with increasing hydrate saturation, the gas permeability first decreases, then increases, and decreases finally, which may be due to the combined effect of the growth habit of hydrates in the pores, the interaction between hydrates and particles, and the effect of effective stress. The formation and decomposition of hydrates in the sediment will cause a decrease in gas permeability. When hydrate saturation is 40.66%, the gas permeability decreases by 13 times due to hydrate formation. The gas permeability presents an approximate linear negative relationship with effective stress. The presence of hydrate significantly reduces the stress sensitivity of the sediment. A stress-sensitive critical saturation between 36.60 and 40.66% makes the ratio of permeability change to effective stress change close to a constant. This work bridges the gap of gas permeability of marine sediments between laboratory samples and natural sediments, providing reliable seepage parameters for the numerical simulation of marine hydrate exploration.

Soybean base saturation stress: Selecting populations for multiple traits using multivariate statistics

AbstractOne of the main objectives of soybean breeding programs is the search for genotypes that are both high yielding and tolerant to abiotic stresses. Brazilian Cerrado, the main grain‐producing region in the country, is characterised by naturally acidic and low fertility soils that consequently have low base saturation. Therefore, identifying genotypes with good performance for favourable and low base saturation stress conditions is of fundamental importance for crop improvement. The objective of this study was to select F3 soybean populations for multiple traits under contrasting base saturation conditions. Field experiments were carried out in two crop seasons in randomised block design with three replicates and 10 F3 populations (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10). In the first experiment, F3 populations were evaluated without base saturation correction (V = 30%, low saturation), while in the second experiment, limestone was applied 3 months before the start to raise the base saturation to 60% (recommended saturation). We evaluated physiological, nutritional, agronomic and spectral variables. Multivariate analysis was performed to know the populations’ performance and the interrelationship between variables and populations in the saturation conditions evaluated. The F3 populations showed differential performance for all traits across the conditions tested, enabling the identification of the best populations for each specific condition and both base saturation environments. Population P2 stood out under both low and recommended base saturation conditions and can be used in F4 plant selection to obtain superior lines for physiological and agronomic traits and vegetation indices.

High‐throughput phenotyping of soybean genotypes under base saturation stress conditions

AbstractThe search for high‐yielding genotypes and that are tolerant to abiotic stresses has been a major goal in plant breeding. Thus, the use of technologies such as precision agriculture associated with remote sensing tools for plant phenotyping has increased. The hypothesis of this research was that soya bean genotypes respond differently to low and adequate base saturation levels in the soil and that vegetation indexes can be efficient auxiliary tools in plant phenotyping for this purpose. The objective of this study was to evaluate the nutritional status and agronomic performance of soya bean genotypes grown in low and recommended base saturation conditions using high‐throughput phenotyping. The research was carried out in 2017/2018 and 2018/2019 crop seasons, in which two field experiments in each season were installed. In experiment I, genotypes (P1, P2, P3, P4, P5, P6, P7, P8, P9 and P10) were evaluated without soil correction (low saturation condition). In experiment II, liming was performed three months before sowing of the genotypes to raise the base saturation to 60% (recommended saturation). Canopy spectral behaviour at the following wavelengths was evaluated: green (550 nm), red (660 nm), red edge (735 nm) and near‐infrared (790 nm), and the vegetation indices (Vis) NDVI, SAVI, EVI and MSAVI were calculated. The variables evaluated were leaf calcium and magnesium contents and grain yield. The use of VI’s was efficient in assessing the performance of genotypes soya bean at different base saturation levels. The EVI showed moderate correlation with the nutritional and agronomic variables measured in each base saturation level. The approach used enabled both to identify genotypes tolerant to low base saturation soils and the ones with better response to liming.