Undisturbed Soil Research Articles

The Effects of Soil Salt Stress on the Nitrogen Uptake, Yield Response and Nitrogen Use Efficiency of Cotton in Arid Areas

Soil salinity is a major soil threat, causing severe environmental problems. Soil salt stress limits N uptake and cotton growth, especially in arid regions. However, the mechanism underlying stress tolerance in cotton plants under different soil salinity levels has not been fully elucidated. Therefore, the aim of this study was to examine the proportion and mechanism of cotton N uptake and transport under salt stress using the 15N isotope labeling technique. Cotton plants were grown in four undisturbed loamy soils (CK, non-salinity, <2 dS m−1; C1, low salinity, 2–4 dS m−1; C2, mid-salinity, 4–8 dS m−1; and C3, high salinity, 8–15 dS m−1) in the test pit experiments. The findings indicated that the cotton N uptake was limited by the soil salt stress and total N content, and the cotton 15N use efficiency decreased by 25–27% with increasing salinity (>4.0 dS m−1). The N transported to cotton from the 0–20 cm soil layer in C1 treatment was higher than from the 40–60 cm layer. Furthermore, the cotton fruit cultivated in C1 exhibited a notably elevated dry matter content compared to those cultivated in the control treatment. As the soil salt stress increased from the control treatment to C1, the cotton stems and fruits demonstrated a gradual enhancement in their N uptake and regulatory capabilities, albeit with a slight decrease observed in the leaves. These findings emphasize that soil salt stress diminishes cotton nitrogen uptake and transport, potentially exacerbating nitrogen pollution in the absence of optimized nitrogen fertilization.

Trichoderma Diversity in Mexico: A Systematic Review and Meta-Analysis

Trichoderma is a genus of cosmopolitan fungi with more than 375 species described today. Despite its global significance in agriculture, ecosystems, and industry, few studies have focused on studying the diversity and distribution of this genus in Mexico. In this systematic review and meta-analysis, we aimed to understand the diversity and distribution of Trichoderma species in Mexico, both in ecosystems and agroecosystems. For this systematic review, we used the PRISMA methodology. We reviewed forty-one scientific articles, two book chapters, and the GBIF database. We recorded a total of 1082 isolates, revealing the presence of 57 species of the genus Trichoderma in 29 states of Mexico. We found that species from the genus Trichoderma were reported in 20 agroecosystems and 6 ecosystems. T. harzianum was the predominant species in both agricultural and undisturbed soil. Tabasco and Veracruz were the states with the highest species diversity, with 20 and 14 species reported, respectively. Chiapas had the highest diversity indices (Menhinick had 3.20, Simpson had 0.89, and Margalef had 4.16). The coffee crop was the agroecosystem with the highest diversity, with 12 species reported. In the undisturbed ecosystems, tropical rainforests featured 12 different species. This study highlights the distribution of the genus Trichoderma as a cosmopolitan genus. We argue for the importance of the species that comprise the genus and its applications for social benefits.

Evaluate the effectiveness of soil and water conservation interventions in the upper Awash Basin, Ethiopia

AbstractThe central highland of Ethiopia is facing significant challenges due to land degradation, which resulted in changes to the soil's physicochemical properties. This study aims to assess the effectiveness of different conservation methods in enhancing soil physicochemical properties, reducing soil loss and erosion, and maximizing land productivity in Ankober District of Kenseta watershed. For this study, two land uses (conserved and non‐conserved land), three slope positions, and three replication with the soil depth of 0–30 cm were used for undisturbed and disturbed soil samples data collection and analysis. The survey data were collected and evaluated from 106 randomly selecting respondents' households. The results showed significant variation in the mean value of soil physical properties (bulk density, soil moisture content, soil texture) within and between conserved and non‐conserved land. The chemical properties, including pH, EC, exK, CEC, OC, OM, and available P, also changed significant across land management types and along slope position (p < 0.05). Soil managed with stone face soil bund demonstrated significant improvement in soil physicochemical properties. The results were statistically significant difference at (p < 0.05) level of significance. Majority of the respondents' households explained the soil loss and rate of soil erosion were declined and land productivity status increased after the adoption of soil and water conservation practices in the study area. Therefore, proper conservation practices are vital in minimizing the rate of soil loss, ameliorating physical and chemical properties of the soils, and enhancing land productivity.

Impact of stockpile depth and storage time on soil microbial communities

Soil removal and stockpiling prior to mining activities have adverse effects on soil health, which raises concerns about the suitability of stockpiled soils as a reclamation substrate. Due to the fundamental roles microbes play in ecosystem function and services, they can be used as indicators of soil health and quality. We analyzed the prokaryotic microbial communities in a chronosequence of 0.5–28-year-old stockpiles at increasing depths (0–300 cm), in two oil-extraction locations in northern Alberta. Our results indicate that the microbial communities of the seven stockpiles examined were more similar to each other than to the undisturbed soils used as reference, which might indicate that stockpiling shifts the microbial community composition outside the range of natural variability. Furthermore, while microbial communities in younger and older stockpiles were dissimilar to the reference soils, the communities of intermediate-age stockpiles were more similar to those in the reference soils. We interpret these divergences in similarity to indicate that initial disturbance leads to a shift in the microbial community, which then recovers following several years of storage, but eventually, long-term storage leads to a secondary divergence from the range of natural variability. Additionally, the bacterial diversity decreased significantly with increasing stockpile depth, which could be attributed to the harsh conditions of the deeper stockpile layers and the scarcity of nutrients. Our findings provide important insights into the impact of soil stockpiling on microbial communities and complement those of earlier studies highlighting the importance of stockpile depth and storage time as predictors of variability of soil microbial diversity and community composition. Furthermore, due to the crucial functions played by microbes in soils, our conclusions should serve for reclamation agencies to modify the stockpiling protocols in order to mitigate the impact of stockpiling on soil microbial communities.

Can natural undisturbed revegetation restores soil organic carbon to levels under native climax vegetation under tropical semiarid climate?

AbstractLand‐use change has driven soil carbon stock losses in ecosystems worldwide. Implementing agricultural crops and exploiting forest resources trigger the breakdown of soil aggregates, thus exposing organic matter to microbial decomposition and enhancing carbon dioxide emissions, especially in biomes more susceptible to climate extremes as in the tropical semiarid regions. This study was based on the hypothesis that the undisturbed soil from the dry forest (Caatinga biome under natural revegetation in Brazilian semiarid) would have an improvement in the mass of macroaggregates and recover more than 50% of the soil C stock within 10 years. Thus, a field experiment was conducted to investigate soils from the Caatinga biome under native vegetation, “cowpea cropping” for over 30 years, and soil under natural revegetation for over 10 years, after conventional soil cultivation of maize and cowpea, to determine soil and soil‐aggregates carbon stocks and to estimate the recovery rate of these stocks. The proportional mass of aggregates of different sizes and the total stock of particulate organic carbon (POC) were also quantified. The results showed that soil under preserved native vegetation of dry forest Caatinga biome had higher total soil C stock (50.9 Mg ha−1) than that under cowpea cropping (23.2 Mg ha−1) and natural revegetation (45.1 Mg ha−1). The proportional mass of large macroaggregates was higher in soil under native vegetation for all depths. However, soil under cowpea cropping had lower C stocks in macroaggregates, and recovered roughly 63% of the original C stocks, while revegetation recovered 78% of the stock in 10 years. Although the conventional management system for cowpea monoculture aggravated losses in soil carbon stock by more than 50% of the original C stocks, dry forest under natural revegetation recovered 79% of this stock and almost 100% of POC stock in 10 years (~12 Mg ha−1). Furthermore, soil under undisturbed Caatinga dry forest achieved C stock levels equivalent to that of the global average range for semiarid tropical environments. The high recovery rate of C stock in forest soil under natural revegetation indicates the resilience potential of organisms responsible for structural protection of aggregates and the encapsulated soil organic matter content.

Effects of Land-use Systems and Depths on Organic Carbon Storage and Texture-related Properties of Soil at Umuahia, Nigeria

Soil condition as influenced by land use systems and depths is relevant in the efforts to optimize crop production. This research examines the effect of land-use systems and depths on organic carbon storage and texture-related properties of soil. It was a 2-factor factorial experiment laid out in randomized complete block design (RCBD). The factors were land-use systems at four levels [arable farm land (AFL), 3 – years fallowed grassland (FGL), forest land (FL) and oil palm plantation (OP)] and depths at five levels (0 – 20, 20 – 40, 40 – 60, 60 – 80 and 80 – 100 cm). Twenty (4X5) treatments combinations were obtained and replicated nine (9) times. Soils were collected in a simple random sampling technic, and were prepared and analysed in the laboratory. Data generated was subjected to analysis of variance using GenStat software package version 14. The results showed that the lowest bulk density (BD) in range of 1.26 – 1.60 mg/kg were obtained under OP at 0 – 100 cm. The most rapid hydraulic conductivity (Ksat) in range of 3.62 – 1.90 cm/hr was obtained under AFL at 0 – 60 cm. The oil palm plantation had the highest range of organic carbon (OC) storage of 51.92 – 30.81 ton/ha at 0 – 40 cm, while at 40 – 100 cm, FL had the highest range of OC storage of 22.33 – 13.42 ton/ha. The undisturbed soils had higher OC storage and reduced BD at the various depths. Minimum tillage, cover cropping and shifting cultivation should be encouraged to enhance soil conditions for increased productivity.

Exploring limitations in the induced polarization versus surface conductivity relationship in the case of wetland soils

Recent induced polarization studies suggest that the real part of surface conductivity ([Formula: see text]) scales linearly with the imaginary conductivity ([Formula: see text] = [Formula: see text]) or normalized chargeability (Mn) for a range of soil types. The coefficients of this relationship l and l_Mn ( l = [Formula: see text]/[Formula: see text] or l_Mn = Mn/[Formula: see text]) allow the separation of the surface and electrolytic conductivities from the bulk conductivity. However, the dependence of these constants on varying soil physicochemical properties, including under unsaturated conditions, is yet to be assessed. Using estimates of [Formula: see text] from 18 undisturbed soil samples from a restored wetland and [Formula: see text] measured over a frequency range of 0.01 Hz to 10 kHz, the [Formula: see text] and [Formula: see text] were compared with the laboratory measurements of soil properties. Also, l and l_Mn were calculated for each soil sample and regressed them against the soil properties. We find an apparent dependence of l on soil texture, bulk density, organic matter, and moisture contents, with coefficients of determination ([Formula: see text]) ranging from 0.5 to 0.65 at low frequencies (e.g., 1 Hz) but not at high frequencies (e.g., 936 Hz). This dependence of l on soil texture results from the insensitivity of [Formula: see text] at low frequency to [Formula: see text] and, by implication, to the soil properties controlling [Formula: see text]. In contrast, l_Mn indicates no correlation with the soil properties because Mn is linearly correlated with [Formula: see text] and correlated with the soil properties controlling [Formula: see text]. Our results call for caution on the application of [Formula: see text] at a single frequency as a proxy of [Formula: see text] because [Formula: see text] is not necessarily correlated with [Formula: see text] across all soil types. Although using l_Mn derived from multifrequency measurements overcomes this limitation, field acquisition of spectral information (e.g., up to 1000 Hz) remains a challenge.

Performance evaluation of the Generalized Bounding Surface Model in the simulation of Cajicá clay subjected to monotonic loading

Different constitutive models, based on principles of mechanics and experimental evidence, have been developed over several decades to represent and predict the stress-strain behavior of soils subjected to various loading conditions. The Generalized Bounding Surface Model (GBSM) is one of them and is defined as a fully three-dimensional elastoplastic constitutive model for saturated cohesive soils that employ the bounding surface plasticity in conjunction with a nonassociative flow rule and a soil microfabric-inspired rotational hardening rule. The GBSM has been successfully validated on numerous laboratory reconstituted soils, but not on natural or undisturbed soil samples. Hence, in this paper the predictive capabilities of the GBSM are evaluated in the simulation of the monotonic behavior of an undisturbed cohesive soil called “Cajicá clay” from the high plain of Bogotá in Colombia. In the first instance, an isotropic consolidation test and a set of axisymmetric triaxial compression and extension tests are conducted using an automated triaxial equipment, to experimentally describe the response of the undisturbed soil. From experimental data, the parameters associated with the GBSM model are calibrated to finally evaluate its capabilities in the simulation of a cohesive natural soil. A comparison between experimental data and numerical simulations is presented to show both performance and advantages of the GBSM model.

Вариативность поверхностных горизонтов почв города Тюмени (Россия)

Urbanization is one of the main trends of the modern world. The growth of the urban population, and, as a consequence, the increase in the area of urban landscapes, leads to a significant transformation of the environment due to comprehensive human economic activity or anthropogenesis. Such changes affect not only natural landscapes as a whole, but also their individual components, such as soil cover. Anthropogenically transformed soils occupy significant areas within urbanized territories. The nature of the anthropogenic impact on soils is determined by the type of land use and is reflected in the profile of urban soils in the form of formation of corresponding anthropogenic horizons or changes in the properties of surface horizons. Field work was carried out within the boundaries of the city of Tyumen (57°09′ N, 65°32′ E), including both the core of dense urban areas and peripheral agricultural and recreational areas. The object of the study in this work is anthropogenically modified soils of the city of Tyumen. The description and diagnostics of horizons and characteristics were carried out on the basis of the “Classification and Diagnostics of Soils of Russia” [2004], taking into account proposals for the introduction of urban soils into the soil classification system of Russia. The research methods included morphological analysis of soils, determination of acidity, organic carbon content by the titrimetric method, soil texture by sedimentation method with pyrophosphate preparation. Statistical analysis of the data was carried out using the STATISTICA 12 “StatSoft” package (USA). The results showed that natural surface horizons are typical only for undisturbed soils of the recreational area. The soils of other functional zones demonstrated signs of anthropogenic impact, which were expressed in the form of changes in both the soil profile as a whole and surface horizon. The direction and intensity of anthropogenic impact correspond to the severity of the transition from natural to anthropogenic landscapes. The reaction of the surface horizons varies from acidic to strongly alkaline. The largest area within the city is occupied by alkaline soils. The Corg values fluctuate within 0.01-22.84%, with an average value of 2.7%. Loamic and siltic varieties predominate, among which silt loams are the most widespread. The composition of the major oxides is consistent with the soil texture. The contents of Fe2O3 and Al2O3 vary between 0.7-7.7 and 1.5-13%, their increased values are typical for soils on cover and loess-like loams. The SiO2 content in most urban soils is 60-70%. Within the urban area of Tyumen, 5 districts are distinguished according to with the morphology and properties of surface soil horizons. In the city center, urban stratified soils on sandy and silty loamy technogenic deposits with elevated pH and average content of Corg predominate. The northern part of the city is occupied mainly by peat soils on the site of mined-out areas of the Tarman bog massif with an alkaline reaction and а high content of Corg. In the western part on the city periphery, agrogenically transformed and postagrogenic soils with slightly acidic and neutral reaction and average content of Corg on loess-like loams can be found. In the northeast of the city alkaline agricultural soils predominate. In the southeastern part within the lacustrine-alluvial deposits, slightly altered soils with low pH values and low Corg content can be found.

Wooded biocorridors substantially improve soil properties in low-altitude rural benchlands

This study examines soil properties in 30- and 60-year-old agricultural biocorridors and provides a comparative overview with neighbouring farmland. Both mixed and undisturbed soil samples were collected from six farmland/biocorridor study areas to assess a wide spectrum of physical, hydrophysical, chemical and biological soil properties. Biocorridor soils were characterised by higher water retention capacities, porosity, aeration and soil carbon stock, the latter increasing with depth. On the other hand, biocorridor bulk density under forest vegetation cover was lower, indicating progressive soil restoration. Slightly lower soil reactions in biocorridor soils disproved the hypothesis that nutrient-rich soils under biocorridors would form substrates with a high base cation content, leading to soil acidification. Biological activity, expressed through respiration coefficients, was generally low due to unfavourable physical conditions (clayey or silty-clay substrates), with the lowest levels in biocorridors. Nevertheless, biocorridor soil microbiota displayed more effective utilisation of organic matter as a carbon and nitrogen source, with lighter-textured soils tending to show more effective organic matter utilisation after excluding the influence of land use. Our results confirm biocorridors as an important landscape component, contributing to both soil stability and local revitalisation of soil environments and further emphasising their potential as climate-change mitigation tools in their role as carbon sinks.

Laboratory evaluation of sampling quality of a new A+ sampler for natural fine soils

This paper presents a comparison of sampling disturbance measured by consolidation tests between two high quality samplers and stationary piston samplers. University G. Eiffel and Cerema have used their université Laval sampler and a new sampler on a soft organic clayey soil experimental site. This paper present first the new sampler designed to sample almost undisturbed soil specimens. The objectives of this sampler are to collect natural fine soils such as clay or silt, normally to medium overconsolidated for depths up to 10 m. This sampler is designed to preserve the saturation state of the specimen. An inner diameter of 150mm core barrel allow to keep the sampler relatively compact, even with the size of a ball valve used to close the sampler. Tests on Pont de Cran clayey site are presented and laboratory tests results on specimen sampled using both samplers show the quality of the specimen and the efficiency of the samplers using void ratio criteria.

The population structure of the Fusarium brachygibbosum species complex in the grassland biome of South Africa

Fusarium brachygibbosum Padwick is a phytopathogen with a widespread distribution, infecting various host plants. In South Africa, there is a limited number of studies on the genetic diversity of fusaria, particularly in undisturbed soils. In the current study, the genetic diversity of F. brachygibbosum was investigated using inter-simple sequence repeat (ISSR) and mating type genes. The F. brachygibbosum isolates were collected from four different geographic regions within the grassland biome of South Africa. A total of ten ISSR primers produced 64 distinct and reproducible amplicons, with 100% polymorphism. The ISSR markers revealed high levels of intraspecific variation, which is depicted by various genetic diversity indexes. In the analysis of mating type genes, the MAT1-1-2 gene was found among the four populations, but the MAT1-2-1 gene was only present in the population from the Groenkloof Nature Reserve. The data from this study will contribute substantially to knowledge of grassland fusaria of South Africa and their population structure in the grassland biome.

Geotechnical conditions of in-field road design in northern territories of Yamalo-Nenets Autonomous Okrug (Tomsk)

The Yamal-Nenets Autonomous District is the largest hydrocarbon resource base, supplying up to 300–330 billion m3/year of gas and up to 10–15 million t/year of liquid hydrocarbons. Mineral extraction is accompanied by the development of engineering infrastructure, namely: cluster pads, oil storage tanks, pumping stations and automobile roads that link both within and between sites. The area is unique in terms of complexity of geotechnical conditions due to permafrost soils in particular in the upper open-cast. The assessment of geotechnical conditions of the field development as well as adverse processes, hazards, risks and impacts on designed, constructed and operating roads to the cluster pads is undoubtedly relevant.Purpose: The evaluation of geotechnical conditions of design, construction and operation of in-field roads in the Severo-Komsomolsk field.Methodology/approach: The analysis and generalisation of materials of geotechnical surveys for design and construction documentation of the cluster pad 11 in the Severo-Komsomolsk oilfield, performed by AO "TomskNIPIneft". Determination of composition and physical properties of undisturbed soils taken when equipping observation posts, performed in the Laboratory of Ground Science and Soil Engineering, TSUAB.Research findings: Natural and geotechnical conditions of the Yamal-Nenets Autonomous District includes areas with hard frozen soil and areas with complete or partial absence of permafrost soils. In the first case, the subgrade design envisages that the upper permafrost horizon is not lower than the embankment bottom and remains at this level during the entire period of the road operation. In the second case, the design implies preliminary thawing of frozen soil lenses and road drainage prior to the subgrade construction. In the first case, the position of perennially frozen soils is evaluated by the appropriate embankment height, when non-cemented road-building materials are used, and by arranging heat-insulating layers (peat, polystyrene foam, hard frozen soil) with their thermotechnical calculation. The first principle implies the subgrade construction only in winter. To prevent deformation of embankment slopes, it is recommended to build peat benches fixed with a geosynthetic material. Land reclamation in the road construction zone should be avoided to prevent erosion of the soil cover.

Anisotropy of soil hydraulic properties induced by repeated machinery traffic in a Typic Argiudoll of the Argentinean Pampas Region

The increase in heavy machinery traffic due to crop sequence intensification under no-tillage (NT) management can lead to soil compaction, modifying the soil pore configuration, with negative effects on water dynamics. The objective of this work is to evaluate the residual effects of repeated machinery traffic under different soil water contents on the anisotropy of soil hydraulic properties. The residual effect of repeated machinery traffic under different soil moisture conditions (partially dry, PD, and wet, W) on soil compaction was evaluated and compared with the control treatment (no traffic, T0). Field infiltration using tension disc infiltrometer was carried out, and in laboratory, in order to analyse the anisotropy of soil hydraulic properties infiltration experiments were carried out on vertical and horizontal undisturbed soil samples. No significant differences in field soil hydraulic conductivity K(h) were observed between treatments. The W treatment showed a decrease on the transmission and storage pores in the vertical direction, as compared to T0. Anisotropic behavior of soil hydraulic properties was observed for the compacted treatments. The W treatment showed an increment in the transmission porosity in the horizontal direction. In addition, the W treatment presented higher values of transmission and storage pores in the horizontal direction as compared with the vertical direction. From laboratory infiltration experiments, it was observed a strong reduction on the hydraulic conductivity measured at 0, − 3 and − 6 cm water pressure heads (K0, K3 and K6) in the vertical direction under W treatment. An anisotropic behavior for both compacted treatments was observed, with higher values of K0 in the vertical direction under the PD treatment and higher values of K0 and K3 in the horizontal direction under the W treatment. These results show that machinery traffic under wet conditions causes a disruption in soil porosity, not only with a reduction of the pore space, but also with a change in its configuration.

Experimental study on mechanical behavior deterioration of undisturbed loess considering freeze-thaw action

To solve the problem that the mechanical behavior of undisturbed loess in seasonally frozen soil area is affected by freeze-thaw action, triaxial shear tests of undisturbed loess under freeze-thaw condition were carried out. The results show that the mechanical properties of undisturbed loess are greatly affected by factors including freeze-thaw process, water content, natural density and confining pressure. Freeze-thaw action has a certain impact on the failure surface shape and stress-strain curve. Before and after freeze-thaw, the shape of the shear failure surface is complex, including single oblique failure surface, double oblique failure surface, vertical failure surface, X-shaped failure surface, bulging failure, etc. And under the conditions of low water content, low confining pressure and high dry density, the stress-strain curve tends to be softened. Conversely, the curve tends to harden. Freeze-thaw action can make the stress-strain curve transition from softening to hardening. In addition, the freeze-thaw action significantly weakens the failure strength, shear strength, cohesion, initial tangent modulus and failure ratio of undisturbed soil, but does not change the internal friction angle obviously. Also, the heterogeneity of natural soil is also an important factor affecting the mechanical parameters, failure surface shape and stress-strain curve of undisturbed loess.

Thermal Conductivity of Loess: Experimental Studies and Empirical Model

Soil thermal conductivity is an important indicator for developing and utilizing geothermal resources. In this study, the impact of underground environmental factors on the thermal conductivity of loess was explored by studying the thermal conductivity of saturated and unsaturated loess under varying water content, dry density, and temperature using the Hot Disk thermal constant analyzer. The results show that the thermal conductivity of unsaturated undisturbed and remolded loess presents different growth trends as the water content increases. When the water content is less than 9%, the thermal conductivity of undisturbed soil increases slowly. The thermal conductivity of unsaturated loess gradually increases with temperature. When the temperature rises above 30°C, the latent heat transfer of steam gradually strengthens, accelerating the increase in thermal conductivity, which is most noticeable at intermediate saturation. However, the thermal conductivity of saturated loess rises slowly as the temperature rises. A weighted geometric average model is proposed in this study to predict the thermal conductivity of loess under temperature conditions, considering the effects of soil water content, dry density, and mineral content. The model accuracy was corroborated by the measured soil thermal conductivity and the data collected from six regions.

Experimental research on vertical straw cleaning and soil tillage device based on Soil-Straw composite model

Strip tillage is a necessary technical means to solve blockage problems during the no-tillage sowing process under the condition of total straw return to the field. However, the large amount of straw on the surface, thick stems, and slow decomposition make it difficult for the traditional straw wheel structure to effectively clean the straw out of the operating area. Based on the distribution of straw and soil characteristics on the no-tillage surface, a Soil-Straw composite model is established using the discrete element method (DEM) for undisturbed soil under straw coverage conditions. The relative error of its bonding parameters is 7.9 %, which can accurately predict the mechanical behavior of soil contact components. A vertical rotation-based straw strip cleaning and soil tillage method is proposed, and three vertical straw strip cleaning and soil tillage devices combining spring teeth (ST) and rake teeth (RT) were designed. The reasonable operating parameters are determined through trajectory analysis, with a forward velocity of 1.67 m/s and a rotational velocity of 300 r/min. Based on the Soil-Straw composite model, the combination of three ST and RT types is studied using DEM-MFBD coupled simulation technology. Regarding the straw cleaning rate, the straw cleaning rates of STb-RTb and STc-RTc are 96.66 % and 96.99 %, respectively, meeting the operational requirements. The field test results showed that the straw cleaning and soil fragmentation rates of the STc-RTc combination were 97.7 % and 96.4 %. The bench test and field test verification show that the DEM-MFBD coupled simulation technology based on the Soil-Straw model can predict the operating quality and deformation stress of the machine. This study provides a new solution for a wide range of straw cleaning in straw-covered areas.

A pulse of simulated root exudation alters the composition and temporal dynamics of microbial metabolites in its immediate vicinity

Root exudation increases the concentration of readily available carbon (C) compounds in its immediate environment. This creates ‘hotspots’ of microbial activity characterized by accelerated soil organic matter turnover with direct implications for nutrient availability for plants. However, our knowledge of the microbial metabolic processes occurring in the immediate vicinity of roots during and after a root exudation event is still limited.Using reverse microdialysis, we simulated root exudation by releasing a13C-labelled mix of low-molecular-weight organic C compounds at mm-sized locations in undisturbed soil. Combined with stable isotope tracing, we investigated the fine-scale temporal and spatial response of microbial metabolism, soil chemistry, and traced microbial respiration and uptake of exuded compounds.Our results show that a 9-h simulated root exudation pulse leads to i) a large local respiration event and ii) alteration of the temporal dynamics of soil metabolites over the following 12 day at the exudation spot. Notably, we observed a threefold increase in ammonium concentrations at 12 h and increased nitrate concentrations five days after the pulse. Moreover, various short-chain fatty acids (acetate, propionate, formate) increased over the following days, indicating altered microbial metabolic pathways and activity. Phospholipid and neutral lipid fatty acids (PLFAs, NLFAs) of all major microbial groups were significantly 13C-enriched within a 5 mm radius around the microdialysis probes, but not beyond. The highest relative 13C enrichment was observed in fungal NLFAs, indicating that a significant proportion of the exuded compounds had been incorporated into fungal storage compounds.Our findings indicate that the punctual release of low-molecular-weight organic C compounds into intact soil significantly changes microbial metabolism and activity in its immediate surroundings, enhancing mineralization of native organic nitrogen. This highlights the versatility of microbial metabolic pathways in response to rapidly changing C availability and their effectiveness in increasing nutrient availability near plant roots.

Preferential flow in the shallow vadose zone: Effect of rainfall intensity, soil moisture, connectivity, and agricultural management

AbstractPreferential flow is ubiquitous in soils, and it affects water infiltration, runoff, and contaminant transport. Undisturbed soil lysimeters (n = 10; 900 cm2) were collected from an agricultural field to quantify the effect of climate, soil moisture, connectivity, and agricultural practices on water transport through the shallow vadose zone. A series of 10 rainfall simulations was conducted on each lysimeter (n = 100 events) and data were analysed within a framework of five case studies where we assessed the impact of rainfall intensity (n = 30 events), soil moisture (n = 28), and tillage (n = 21). Three lysimeters that had near‐zero flow initially were modified to investigate dynamics of direct surface connectivity through an artificial macropore in which we assessed the impacts of soil moisture (n = 12) and subsequent disruption via tillage (n = 9). Stable water isotopes were used to separate leachate into event (Qe) and pre‐event water (Qpe). Results showed that event water transport in leachate was not affected by rainfall intensity (Qe/Q = 49% ± 21% to 50% ± 24%); however, event water decreased from 65% ± 5% to 23% ± 28% with increasing soil moisture. Lysimeters with artificial macropores resulted in leachate that was nearly all event water (85% ± 12% to 92% ± 4%) irrespective of soil moisture. Tillage decreased event water transport for both lysimeters with and without an artificial macropore by ~30%. Findings show how varying initial and boundary conditions produce a continuum of preferential flow. Water and tracer flux data collected in the current study are therefore essential for predicting conditions with high relevance of preferential flow and contaminant transport when assessing or modelling long‐term hydrographs where these conditions are only met during a small proportion of the flow time.

Mechanical and microstructural characteristics of undisturbed lateritic soil subjected to alkali contamination

Mechanical and microstructural characteristics of undisturbed lateritic soil subjected to alkali contamination