Soil Horizons Research Articles

How magnetism-based fractional spinels contribute to the bioavailability of geogenic chromium in serpentine soils of Taiwan

Serpentine soils are highly rich in geogenic chromium (Cr), typically associated with spinel minerals. The high resistance of these minerals to weathering has raised concerns regarding their contribution to Cr bioavailability in serpentine soils. This study collected soil horizon samples from two pedons (Entisol and Ultisol) in eastern Taiwan and applied a two-step magnetic separation method to divide the bulk soils into strongly magnetic (SM), weakly magnetic (WM), and nonmagnetic (NM) fractions. The basic characteristics of the bulk soils were examined. To characterize the mineralogy and geochemistry of the fractions and determine their quantitative contribution of bioavailable Cr in serpentine soils, we analyzed their mineral composition, magnetic properties, and elemental composition and valence by using various spectrometric techniques, such as X-ray diffraction, electron probe microanalysis, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, as well as vibrating sample magnetometry. The results indicated the main Cr-bearing minerals were magnetite and chromite in the SM and WM fractions, with minor occurrences in layer silicates, such as serpentine and chlorite, in the NM fraction. The total Cr content decreased in the following order: SM > WM > NM. The SM fraction had the lowest weight proportion, and this proportion was lower for the Ultisol than the Entisol. This observation indicated that the weathering of Cr spinels is associated with the substantial cation substitution of Al, Ca, Mn, and Ni for Fe and Cr in broken mineral grains and increases in the Fe(III) and Cr(VI) concentrations in magnetite. The SM fraction, mainly consists of magnetite and chromite, exhibited the highest concentration of bioavailable Cr extracted by 0.1 M HCl. However, the Cr-bearing layer silicates represented the largest potential pool of bioavailable Cr in the bulk soils because the weight proportion of the NM fraction was higher than those of the other fractions and increased during pedogenesis.

Factors of winter moisture movement in arable soils of the Ishim steppe

Based on the materials of long-term field observations in the southern regions of the Omsk region, the influence of the main factors on the winter movement of moisture in arable soils of the Ishim steppe was traced. The penetration depth of 0 °С determines the lower boundary and vertical thickness of the moisture freezing layer. The distance between its lower edge and the penetration depth of 0 °С is 20–40 cm. The penetration depth of 0 °С is predetermined by the air temperature and the thickness of the snow cover and reaches 170–240 cm. The forms of moisture dominant in the soil are associated with the granulometric composition. Film moisture prevails in the heavy loamy, highly silty soil-ground strata of the Ishim steppe. The content of capillary-backed and free gravitational water does not exceed 6% of the soil volume at full moisture capacity, which determines the small volume of moisture freezing (up to 50 mm). Thermogradient migration of moisture is determined by field methods in highly moistened soil-ground strata. High humidity of the soils and rocks of the Ishim steppe is associated with their granulometric composition and the close occurrence of groundwater. If in the second ten days of October groundwater is recorded at a depth of less than 3 m, the layer of moisture freezing at the end of March is noted in the depth range between 40–80 and 160–200 cm, the volume of cryogenic accumulation is 30–50 mm, including in the upper meter layer – 10–25 mm. If groundwater is detected at a depth of more than 3 m in the autumn, the freezing layer is fixed at 80 to 160–200 cm, the moisture gain in it is 15–30 mm, in the 0–100 cm layer the moisture content does not change. The role of cryogenic accumulation in replenishing the post-vegetation moisture deficit in the root layer of spring grains is modest. This process is significant for the formation of conditions for anaerobiosis and the development of modern hydromorphism in the lower soil horizons and in the subsoil strata.

Effects of Deficit-Regulated Irrigation on Root-Growth Dynamics and Water-Use Efficiency of Winter Wheat in a Semi-Arid Area

Water management is critical for wheat production under extreme drought conditions, and the mechanisms by which root dynamics and soil water utilization affect wheat yield are uncertain. This study was conducted in 2023–2024 under a mesophilic semi-arid climate with a two-factor partitioned experimental design, aiming to assess the response of different irrigation amounts in winter wheat crops on root growth and development, soil water utilization, and yields in different soil horizons. The results showed that variety and irrigation volume had significant effects on the spatial and temporal distribution of root and yield components, with irrigation volume having the greatest effect on yield. Compared with CK, deficit-regulated irrigation significantly promoted root penetration to deeper layers and delayed root senescence. DRWD, RLD, RSA, and RV decreased gradually with increasing soil depth, and the peaks of RLD, RSA, and RV appeared at the tassel to flowering stage, respectively; and under deficit-regulated irrigation, the contribution of the A2W4 treatment to stable yield was greater. Therefore, A2W4 is an effective water-saving irrigation method to improve grain yield and water-use efficiency under deficit-regulated irrigation.

Geochemical Features of Organo-Accumulative Soils of Subtaiga and Subtaiga-Forest-Steppe Light Coniferous Forests of Northern Mongolia

Geochemical features of organo-accumulative (Eutric Regosols (Laomic, Ochric), Cambic Someric Phaeozems (Loamic)) soils widely distributed in the soil cover of the subtaiga and subtaiga-forest-steppe light coniferous forests forming the lower boundary of the forest belt in the mountain structures of Northern Mongolia are considered. Data on the microelement composition of soil-forming rocks are given. It was found that the paragenetic association of trace elements in them is represented by Pb, Cu, Zn, Co, V, Cr, Ni, Mn, Mo, Ba, Sr, Zr and B. It was found that, compared with the average content in the lithosphere within the subtaiga and subtaiga-forest-steppe forest-growing belt, the residual and re-deposited weathering crusts of igneous rocks are enriched with Zn, Cr, Mo, B, at the same time they contain less Pb, Co, Mn, Ba, Sr, Zr. The residual and re-deposited weathering crusts of carbonate rocks are enriched with Pb, Cu, Zn, V, Cr, Sr, B, they contain little Co, Ni, Mn, Mo, Ba, Zr. Data on the morphological structure of soils, their physico-chemical and chemical properties, as well as on the content of trace elements and their radial distribution in the soils under consideration are discussed. The data obtained indicate the accumulation of most trace elements in the surface organogenic and humus-accumulative horizons of soils, which is associated with both the heterogeneity of soil-forming rocks and the influence of soil processes that cause the accumulative redistribution of elements and their deposition on organo-sorption and carbonate geochemical barriers. It is shown that the studied soils differ not only in the absolute values of trace elements involved in the biological cycle, but also in the intensity of their involvement in biogenic migration.

Soils in Understanding Land Surface Construction: An Example from Campania Plain, Southern Italy

The contribution of sediment transport and accumulation to soil formation was investigated in an area characterized by continental sedimentary activity since the Late Pleistocene. The area was the north-eastern portion of the large Quaternary graben represented by the Campania Plain, which is rimmed to the north–east–south by the Mesozoic carbonate Apennine nappes. The plain was filled mainly by products generated by eruptions from the Phlegrean Fields, which were also distributed on the slopes bordering the plain and remobilized toward the adjacent surfaces. Five sites were selected in the area in question. They were studied using morphological features and pertinent characteristics of the mineral soil fraction >2.0 mm, such as their volume and lithological description. Soils were compared to selected lithostratigraphic sequences characterizing the studied area, which were collected from literature and reinterpreted in pedological keys. The results showed that soils derived from the emplacement of Phlegrean primary volcanic materials, such as Campania Ignimbrite (~39–40 ky B.P.) and Neapolitan Yellow Tuff (~15 ky B.P.), with the related weathering products, and from volcanic materials reworked and transported by alluvial/colluvial episodes. The latter formed contrasting soil horizons which, differing in both rock fragment content and lithological composition, testified to the presence of lithological discontinuities. The formation of the horizons in question interrupted the genetic sequence derived from the in situ alteration of the volcanic substrata, suggesting that processes of transport and redistribution of sediments from the adjacent mountain slopes contributed to soil formation. The comparison of the pedostratigraphies with the lithostratigraphic sequences indicated a strong relation between geomorphic and pedogenetic events.

Soil Formation on Loamy Deposits in Technogenic Landscapes of the Taiga Zone in the North-Eastern Part of European Russia

The paper highlights the influence of moisture on the soil formation process on loamy deposits during the primary vegetation succession. The study was carried out in the north-eastern part of European Russia (Komi Republic) in the middle taiga subzone. The authors analyzed young soils on the territory of a quarry for extraction of loamy grounds and background soils in the vicinity of it. Planting the Siberian spruce cultures on the territory of the quarry activated formation of the tree layer and thereby accelerated formation of the zonal type soils. The third succession decade in drained conditions saw formation of organic soil horizons (litters), a decrease in soil density in the upper profile part, a tendency to redistribute and differentiate the silty fraction by one-and-a-half oxides, indicating the beginning of selective podzolization. The rise in soil moisture content increased conservation of organic residues (peat formation) and made gley formation active. The quarry soils, like background soils, increased in acidity, carbon and nitrogen reserves along with the soil moisture content increase. In automorphic soil formation conditions, the rate of organic carbon accumulation in the upper 0–20-cm layer is 0.4 t· ha–1·year1; the excessive soil moisture content further increased it (1.0–1.2 t·ha–1·year1). The reserves of Corg in the upper 20-cm soil layer of young soils are by 2–4 times less than those in background soils.

Employing automated electrical resistivity tomography for detecting short- and long-term changes in permafrost and active-layer dynamics in the maritime Antarctic

Abstract. Repeated electrical resistivity tomography (ERT) surveys can substantially advance the understanding of spatial and temporal freeze–thaw dynamics in remote regions, such as Antarctica, where the evolution of permafrost has been poorly investigated. To enable time-lapse ERT surveys in Antarctica, an automated ERT (A-ERT) system is required, as regular site visits are not feasible. In this context, we developed a robust A-ERT prototype and installed it at the Crater Lake CALM-S site on Deception Island, Antarctica, to collect quasi-continuous ERT measurements. We developed an automated data processing workflow to efficiently filter and invert the A-ERT datasets and extract the key information required for a detailed investigation of permafrost and active-layer dynamics. In this paper, we report on the results of two complete year-round A-ERT datasets collected in 2010 and 2019 at the Crater Lake CALM-S site and compare them with available climate and borehole data. The A-ERT profile has a length of 9.5 m with an electrode spacing of 0.5 m, enabling a maximum investigation depth of approximately 2 m. Our detailed investigation of the A-ERT data and inverted results shows that the A-ERT system can detect the active-layer freezing and thawing events with high temporal resolution. The resistivity of the permafrost zone in 2019 is very similar to the values found in 2010, suggesting the stability of the permafrost over almost 1 decade at this site. The evolution of thaw depth exhibits a similar pattern in both years, with the active-layer thickness fluctuating between 0.20–0.35 m. However, a slight thinning of the active layer is evident in early 2019, compared to the equivalent period in 2010. These findings show that A-ERT datasets, combined with the new processing workflow that we developed, are an effective tool for studying permafrost and active-layer dynamics with very high resolution and minimal environmental disturbance. The ability of the A-ERT setup to monitor the spatiotemporal progression of thaw depth in two dimensions, and potentially in three dimensions, and to detect brief surficial refreezing and thawing of the active layer reveals the significance of the automatic ERT monitoring system to record continuous resistivity changes. An A-ERT monitoring setup with a longer profile length can investigate greater depths, offering effective monitoring at sites where boreholes are costly and invasive techniques are unsuitable. This shows that the A-ERT setup described in this paper can be a significant addition to the Global Terrestrial Network for Permafrost (GTN-P) and the Circumpolar Active Layer Monitoring (CALM) networks to further investigate the impact of fast-changing climate and extreme meteorological events on the upper soil horizons and to work towards establishing an early warning system for the consequences of climate change.

Influence of the clay fractions from various horizons on the radiation shielding parameters of an Arenosol

Abstract This study examines the effects of the chemical composition of the clay fraction of various soil horizons on radiation shielding parameters. X-ray fluorescence (XRF) analysis did not reveal significant differences in the concentration of the most abundant oxides (Al2O3, SiO2, Fe2O3) among the various horizons. Consequently, the mass attenuation coefficient did not vary among the horizons in terms of the photon energies studied (15 keV–10 MeV). The mean free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) did not differ for energies up to 100 keV. However, at higher energies, these parameters were mainly influenced by the differences in the densities of the soil horizons. The effective atomic number did not differ across the horizons for the various photon energies, nor did the mass attenuation coefficient. It is shown that slight differences in the chemical composition of the clay fraction of soil horizons do not affect radiation shielding parameters (MFL, HVL, TVL) for low photon energies (<500 keV). Density is more important for radiation shielding than the chemical composition of the various horizons of the same soil type for higher energies (>100 keV); hence, compacting the clay fraction might be more efficient for radiation shielding purposes at higher energies.

Soil carbon stocks and nutrient stratification in a volcanically active coffee-dominated landscape in south-central Guatemala

The volcanoclastic mountains of Central America offer elevations ideal for coffee production. Both vulcanism and land use can have significant impacts on soil formation and properties. We evaluated how the interactive impacts of soil formation and coffee-dominated land use modulate soil storage and vertical distribution of organic carbon and nutrient elements in a volcanically active landscape dominated by coffee agriculture in south-central Guatemala. Thirty-seven pedons under coffee production (n = 29), forest cover (n = 5) and pasture (n = 3) were characterized and classified, and concentrations and stocks of organic carbon and macronutrient and micronutrient elements were quantified across genetic horizons. Additionally, soil organic carbon (SOC) stock values calculated using the fixed depth (FD) and equivalent soil mass (ESM) methodologies were compared. The active stratovolcano in the region had a strong effect on the development of andic properties and soil horizon burial, with thirty-one pedons classified as Andisols, three as Inceptisols and three as Entisols. Land use management practices and soil horizon burial by deposition of volcanic material were partly reflected in the vertical distribution of SOC concentrations and stocks. The vertical distribution of macronutrients was generally more sensitive to land use than the vertical distribution micronutrients, which could potentially reflect differences in inputs via fertilizers and vegetation cover and in outputs with biomass harvest. Soil organic carbon stocks were similar when calculated by FD and ESM, reflecting relatively consistent depth-wise bulk density. These results demonstrate that in volcanically active landscapes, land use should be considered in concert with soil-forming factors to comprehensively understand organic carbon and nutrient element storage in soils.

Divergent responses of aggregate breakdown by slaking to nitrogen forms in solution for contrasting soil types

Aggregate stability strongly affects many soil processes and is critical to maintain sustainable agriculture. Aggregate breakdown is controlled by the interaction between soil intrinsic properties and solution characteristics. Nitrogen fertilization including different forms is well known to influence aggregate stability; however, relative to their long-term effects, there is little recognition on the rapid response of aggregate breakdown to nitrogen solutions. This study aimed to examine the effects of nitrogen form and concentration on aggregate stability for different types of soils. Aggregate breakdown against slaking of three soil types (Phaeozem, Luvisol, and Acrisol) and three horizons (organo-mineral (A), illuvium (B), and parent material horizons (C)) was determined subjected to nitrogen solutions of three forms (CO(NH2)2, NH4+, NO3–) and five concentrations (0.05 ∼ 1.0 mol/L). Among nitrogen forms, urea solution almost had non-significant effect irrespective of soil type and horizon (p > 0.05); for NH4+ and NO3– solutions, aggregate stability showed little variations (MWD of 0.19 ∼ 0.26 mm) with electrolyte concentration for Phaeozem in B and C horizons, overall increased for Luvisol and Phaeozem in A horizon, and decreased first and then reached a steady state for Acrisol. The effects of nitrogen forms on aggregate breakdown were dependent on soil aggregation status or cementing agents (mainly organic matter, clay mineralogy). Electrolyte nitrogen solutions (NH4+ and NO3–) inhibited aggregate breakdown mainly through reducing electrostatic repulsive forces for moderately developed soils rich in swelling clays, and promoted aggregate breakdown by both weakening particle cohesion and enhancing compression pressure of entrapped air for highly developed soils rich in non-swelling clays and Fe/Al oxides. These results facilitate an improvement of fertilizer management and irrigation to improve soil quality on different soil types.

Ecological Status Assessment of Permafrost-Affected Soils in the Nadym Region, Yamalo-Nenets Autonomous District, Russian Arctic

Permafrost-affected regions in the Russian Arctic are a critical study area for studying the sources of metal elements (MEs) in soils originating from geological/pedogenic processes or from anthropogenic sources via atmospheric transport. In the Nadym region of the Yamalo-Nenets Autonomous District, we investigated the contents of soil organic carbon (SOC), total nitrogen (TN), and MEs across different soil types and horizons, explored the source apportionment of MEs, and assessed local ecological risks of potentially toxic elements (PTEs). The results showed that (1) the contents of SOC and TN in Histic Cryosols (8.59% and 0.27%) were significantly higher than in Plaggic Podzols (Arenic, Gelic, and Turbic) (2.28% and 0.15%) and in Ekranic Technosols (Umbric) (1.32% and 0.09%); (2) the concentrations of MEs in the Nadym region were lower than in other Arctic regions; (3) the primary sources of MEs were identified as geological processes (36%), atmospheric transport (23%), agricultural activities (21%), and transportation (20%); and (4) the permafrost-affected soils in the Nadym region exhibited low ecological risks from PTEs. These results underscore the critical role of geological and anthropogenic factors in shaping soil conditions and highlight the relatively low ecological risk from PTEs, providing a valuable benchmark for future environmental assessments and policy development in Yamal permafrost regions.

Afforestation Promotes Soil Organic Carbon and Soil Microbial Residual Carbon Accrual in a Seasonally Flooded Marshland

This study aimed to delve deeper into the alterations in the microbial residual carbon (MRC) accumulation in the Yangtze River’s wetland ecosystems as a consequence of afforestation and to evaluate their impact on soil organic carbon (SOC). The hypothesis posited that afforestation could foster soil aggregation by augmenting arbuscular mycorrhizal fungi (AMF) hyphae and glomalin-related soil protein (GRSP) in deep soil, thereby suppressing the proliferation of genes pivotal to microbial residue decomposition and enhancing MRC accumulation. We collected soil samples at 0–20, 20–40, 40–60, 60–80 and 80–100 cm respectively. Metagenomic sequencing, the quantification of soil amino sugars and MRC, soil aggregate distribution profiling and the measurement of AMF mycelium length density alongside GRSP levels were analyzed. Our findings showed that afforestation notably elevated the concentration of soil amino sugars and the levels of total and fungal MRC, with increases ranging from 53%–80% and 82%–135%, respectively, across the five soil depths examined, in stark contrast to the eroded, non-afforested control. The role of MRC in the SOC was observed to escalate with increasing soil depth, with afforestation markedly amplifying this contribution within the 40–60 cm, 60–80 cm and 80–100 cm soil layers. The study concludes that the SOC content in the deeper soil horizons post-afforestation witnessed a significant rise, paralleled by a substantial increase in both total and fungal MRC, which exhibited a robust positive correlation with the SOC levels. This underscores the pivotal role that amino sugar accumulation from microbial residues plays in the retention of SOC in the deeper soil layers of afforested regions, challenging the conventional wisdom that plant residues are recalcitrant to decomposition within forested SOC matrices.

Deep regolith weathering controls δ30Si composition of groundwater under contrasting landuse in tropical watersheds

Land use changes are known to alter terrestrial silicon cycling and the export of dissolved silicon from soil to fluvial systems, but the impact of such changes on groundwater systems remain unclear. In order to identify the processes responsible for groundwater geochemistry and to assess the impact of agricultural processes, we examined multiple isotopic tracers (δ30Si, oxygen (δ18O) and hydrogen (δ2H) isotopes) in groundwater, soil porewater and surface water from two contrasted watersheds having the same gneissic lithology, one forested (Mule Hole) and one intensely cultivated (Berambadi) in the Kabini basin in South India. In the cultivated watershed, groundwater exhibits high Cl− and NO3− concentrations indicative of fertilizer inputs and solute enrichment from evapotranspiration due to multiple groundwater pumping/recharge cycles. The DSi concentration in groundwater is significantly higher in the cultivated watershed (980 ± 313 μM) than in the forested one (711 ± 154 μM), indicating more intense evapotranspiration due to irrigation cycles. The groundwater δ30Si values ranged from 0.6 ‰ to 3.4 ‰ and exhibit no significant differences between cultivated (1.2 ± 0.5 ‰) and forested (1.0 ± 0.2 ‰) watersheds, indicating limited impact of land use and land cover. Groundwater also shows no significant seasonal differences in DSi and δ30Si within watersheds, indicating a buffer to seasonal recharge during wet season. The δ30Si of a majority of groundwater samples fits a steady-state open flow through system, with an isotopic fractionation factor (30ε) between precipitating phase and groundwater ranging from −1.0 ‰ and − 2.0 ‰, consistent with precipitation of kaolinite-type clays, dominant in the study area. The steady-state flow through system in groundwater can be interpreted as a continuous DSi input from mineral weathering reactions with a dynamic equilibrium between Si supply and precipitation of secondary phases. We also observe, in both watersheds, similar DSi and δ30Si values in local surface water that includes small streams and a river (406 ± 194 μM, 1.6 ± 0.3 ‰) and in soil porewater (514 ± 119 μM, 1.6 ± 0.2 ‰). Compared to soil porewater, groundwater exhibits significantly lower δ30Si signatures and higher DSi, reflecting the contribution of an isotopically light silicon source, resulting from water-rock interaction during percolation through the unsaturated zone. We assign this steady input of DSi to the weathering of primary silicate minerals in the regolith, such as Na-plagioclase, biotite and chlorite, with formation of kaolinite and smectites type clays. A simple isotopic mass balance suggests that deep regolith weathering can contribute to almost half of the DSi in groundwater. We conclude that silicon cycling in soil porewaters, and surface waters are directly impacted by land use, while the isotopic composition of groundwater remains unaffected. Our results indicate that Si isotopic signatures of weathering, adsorption, and plant uptake occurring in the shallow soil and saprolite horizons are partly overprinted and homogenized by the regolith weathering in the deep critical zone, irrespective of land use and seasonality.

Nitrogen addition reduces soil phosphorus leaching in a subtropical forest of eastern Tibetan Plateau

Globally, increased atmospheric nitrogen (N) deposition has comprehensively altered phosphorus (P) biogeochemical cycling in terrestrial ecosystems. Phosphorus is the second most common nutrient limiting for ecosystem productivity. Even though, ultimately under enhanced atmospheric N deposition it is likely to be the primary one. However, the response of soil P leaching to the elevated atmospheric N deposition in subalpine forests are still elusive. Here, we examined the effects of >7-year N additions on soil P leaching in a subalpine forest of eastern Tibetan Plateau. We found that independent of soil horizon (organic versus mineral horizons) and N addition rate (control 0, low 8 and high 40 kg N/ha yr−1), dissolved inorganic P (DIP), rather than dissolved organic P (DOP), dominated soil P leaching. The N addition treatments reduced the leaching of total P and DIP throughout the soil profile by 13 % and 14 %, respectively. The enhanced biological immobilization and P adsorption capacity (increased by 15–33 % in organic horizon and 9–35 % in mineral horizon) under the N addition contributed to the decrease in soil P leaching. We conclude that the reduction in soil P leaching under the elevated atmospheric N deposition should boost the enhanced N driven forest productivity and ecosystem carbon sequestration in the subalpine forests.

Do soil horizons and land-uses screen different sets of soil quality indicators in the hilly region of northeast India?

Do soil horizons and land-uses screen different sets of soil quality indicators in the hilly region of northeast India?

The added value of CoreVESS score and penetration resistance in predicting the soil–water retention curve

Soil hydraulic properties, such as the soil–water retention curve (SWRC), play a crucial role in simulating water transport within the vadose zone. They can be directly measured in the laboratory or field, or indirectly predicted by using Pedotransfer Functions (PTFs). It has been advocated that accounting for soil structure could marginally improve the prediction accuracy of PTFs in its wet range. The aim of this study was to test whether the use of an easy-to-determine soil structure-related variable could effectively increase the prediction accuracy of water retention curve PTFs. Additionally, we explored whether including soil strength, another soil property that is easy and quickly to determine in the field in many replicates, could improve PTF performance. Our investigation involved extensive sampling of 252 soil horizons across 42 cropped fields, each exhibiting within-field variations in soil structural degradation. Soil structure was represented by a soil structural quality score (Sq) taken from a semi-quantitative visual soil assessment (CoreVESS), which was included in the PTFs as predictor variable or as discriminator (Sq) for data grouping in addition to or instead of ‘classical’ predictors such as soil organic carbon content, clay and sand content, bulk density and soil layer. Penetration resistance (PR) was taken as a variable for soil strength. Various regression methods from classical regression to machine learning were evaluated on Train and Test subdatasets. To evaluate the effect of data grouping, the dataset was split in two based on structure and on texture. Both point and parametric PTFs were developed, with the latter predicting the parameters of the Van Genuchten (VG) water retention equation. Overall, the k-nearest neighbors PTFs (KNN-PTFs) achieved the best performance showing the highest R2 and lowest RMSE values. Moreover, the point PTFs showed much better and more stable predictive ability than parametric PTFs. The inclusion of PR as an additional predictor variable slightly improved the prediction performance in the wet range of the SWRC. Interestingly, Sq proved beneficial when substituted for bulk density but not when used in addition to it. Grouping data based on texture and structure improved the prediction accuracy of the PTFs, particularly evident in textural grouping and MLR, but not in KNN.

Mulching drive changes in soil microbial community assembly processes and networks across aggregate fractions

Soil microbial community assembly processes and networks in croplands have been widely explored; however, their dynamics and how they regulate winter wheat yield across distinct soil aggregate fractions under the combined effects of mulching and soil horizons have not been comprehensively understood. Therefore, based on a 9-y field experiment, the responses of soil bacterial and fungal community assembly processes and interkingdom association networks to mulching were specifically investigated at the soil aggregation level. Soil properties and microbial biomass were separated into distinct mulching in the topsoil (0–10 cm), and soil water content was considered the most critical factor. The soil bacterial community was affected mainly by mulching and soil horizon compared with the fungal community in microaggregates (<0.25 mm). Notably, the bacterial community displayed more robust stochastic processes than the fungal one, and microbial interkingdom association networks were more complex and stable in micro-than macroaggregates. Soil potential carbon mineralization, pH, and total nitrogen were the dominant properties regulating winter wheat grain yield in combination with microbial community composition, assembly processes, and networks in each soil aggregate class. Wheat yield decreased under straw mulching and was mainly regulated by bacterial community composition and assembly processes. Thus, this study enhanced our understanding of the regulations for wheat yield, which could facilitate soil microbial community management at the aggregation level for sustainable crop production in mulching conservation agroecosystems.

Assessment of Soil Horizons and Their Matric Potential from Ground-Penetrating Radar Signal Attributes

Soil plays significant roles in different phases and in the continuous existence of human life. Its comprehensive knowledge, particularly as related to its physical characteristics, enhances its utilization, conservation, and management. The traditional methods of soil study are characterized with some pitfalls such as much time needed to perform such assessments. There are also issues of invasiveness that affect the soil structures and discrete sampling that may not reflect true spatial attributes in the outcome of such techniques. These problems are largely due to the concealing nature of soil layers that made its thorough evaluation difficult. In this study, an alternative geophysical approach has been adopted. The technique is the ground-penetrating method (GPR) that utilizes electromagnetic pulse energy via its equipment’s sensors, which can allow the investigation of soil properties, even in its concealing state. This study aimed at qualitatively evaluating the soil horizons and the matric potentials using the GPR signal attributes within the unsaturated zone with a view of having insight into the test field’s characterization. Field data measurements were obtained using MALA ProEX GPR equipment with its accessories manufactured by MALA Geosciences, Stockholm, Sweden. Evaluation of the processed field data results and computed attributes show soil characteristics variations with depth that was interpreted as the layers. This can be seen from the GPR data presentation as an image representing the subsurface of the zones of propagation of the pulse energy. Spectral analysis of the GPR signals allows for the delineation of two zones of contrasting features, which were tagged as high and low matric potentials. Although the conventional direct measurement of the matric potential was not made at the time of the study to complement and confirm the veracity of the approach, the results indicate the possibility of the approach towards a quick and in situ technique of soil investigations. Such evaluation may be valuable input in precision agriculture where accurate data are sought for implementation.

Rapid characterization of soil horizons for different soil series utilizing Vis-NIR spectral information

The visible-near infrared (Vis-NIR) reflectance technique is a powerful tool, particularly for obtaining faster information about soil texture, organic matter, and calcium carbonate content. However, there is limited research on the characterization of soil horizons using Vis-NIR data in profiles of different soil series. This study investigated the relationship between soil properties and spectral reflectance (Vis-NIR) in eight soil profiles with varying genetic properties from Harran Plain, Türkiye, focusing on variations within profiles (A, B, and C horizons) and across different soil series. A total of 36 soil samples were collected from the A, B, and C horizons, and spectral reflectance was measured along with calcium carbonate, organic matter, and particle size distribution. High variability was observed in calcium carbonate (11.58–52.50%) and organic matter content (0.60–3.71%), reflecting complex soil composition influenced by parent material and land management. Distinct reflectance patterns were observed within profiles, reflecting variations in soil composition. Ap horizons with higher organic matter content often exhibited lower reflectance (visible region). Clay content influenced NIR reflectance, with higher absorption in clay-rich profiles. The Kaynakli series (Fine-loamy, mixed, mesic Typic Calcixerepts) showed differentiation in reflectance between A and B horizons after 700 nm due to horizon formation and clay/carbonate accumulation. Increasing calcium carbonate content in Ck horizons led to higher reflectance compared to other layers. Confirmed that Vis-NIR reflectance could explain a significant portion of the variance in soil properties (A: 87.7%, B: 88.3%, and C: 90.6%). PCA results supported the notion that spectral signatures captured by Vis-NIR reflectance measurements are indicative of inherent differences between A, B, and C horizons. This study contributes to the growing body of knowledge on the application of Vis-NIR spectroscopy for soil assessment and monitoring. However, future research should focus on understanding spectral reflectance variations under diverse soil and environmental conditions.

The Effects of Soil Acidity and Aluminium on the Root Systems and Shoot Growth of Lotus pedunculatus and Lupinus polyphyllus.

Lotus pedunculatus (lotus) and Lupinus polyphyllus (Russell lupin) persist in the upland grasslands of New Zealand, where soil acidity and associated aluminium (Al) toxicity impede conventional pasture legumes. This experiment investigated the response of lotus and Russell lupin to soil acidity and Al. The species were sown in 20 cm tall 1.2 L pots of acidic upland soil. A mass of 4.5 or 6.7 g lime (CaCO3)/L was added to either the top or bottom or both soil horizons (0-9 cm and 9-18 cm), resulting in six treatments across six randomised blocks in a glasshouse. The soil pH was 4.4, 4.9, and 5.4; the exchangeable Al concentrations were 24, 2.5, and 1.5 mg/kg for 0, 4.5, and 6.7 g lime/L. At 16 weeks post-sowing, the plants were divided into shoots and roots at 0-9 cm and 9-18 cm. Root morphology, shoot and root dry matter (DM), shoot nitrogen (N), and nodulation were measured. The total plant DM and shoot-to-root DM ratio were higher, and the shoot %N was lower for the lotus plants than the Russell lupin plants for the various lime rates (13.2 vs. 2.9 g plant-1, 5.6 vs. 1.6, and 2.4 vs. 3.3%, p < 0.05). No response to lime in terms of total DM or total root morphology parameters was exhibited in either species (p > 0.05). Root morphology adjustments in response to acidity between soil horizons were not observed. The results indicated that lotus and Russell lupin are tolerant to high soil acidity (pH 4.4-5.4) and exchangeable Al (1.5-24 mg kg-1), highlighting their considerable adaptation to grasslands with acidic soils.