Subsoil Horizons Research Articles

Problems of Abandoning Deep Soil Loosening and Economic Efficiency of Technical Means for Loosening the Subsoil Horizon

The problems of refusal from deep soil loosening are analyzed, the parameters of effective chisel plows and subsoilers tested at machine-testing station are presented. The modes and functional indicators of their work as part of machine-tractor units are given; the comparative analysis of economic assessment indicators is performed.

Physical qualities of acid sulfate soil: its limitations and implications for oil palm production

ABSTRACT Global demand has pressured the extension of oil palm production areas in Thailand to acid sulfate soils. Besides their severe acidity and nutrient imbalance, the soil physical quality is expected to restrict production. This research defined the critical physical limitations of acid sulfate soils for oil palm production. The soil parameters of physical quality were assessed, covering 32 points in both the topsoil (Ap) and subsoil horizons. These parameters consisted of penetration resistance in the wet and dry seasons, saturated hydraulic conductivity (Ksat), bulk density (BD), the water characteristic curve, available water capacity (AWCA), available water content (AWCO), infiltration, and the S-index (a single indicator of soil physical quality derived from the parameters of the van Genuchten equation). The results showed critical physical quality constraints, particularly concerning the S-index and water shortage. The poor physical quality was more distributed in the Ap horizon (S-index = 0.024) than in the subsoil (S-index = 0.033). The penetration resistance was moderately restricted (3.26 Mpa) to the plant roots only in the dry season. Corresponding to the S-index data, the Ap horizon had a lower AWCA (0.21) than the subsoil (0.30). Most negative AWCO values in the subsoils (78%) during the wet season suggested a severe water shortage for oil palm production. Further research is needed to refine a specific partial drainage technique under oil palm canopies, focusing on the air-water balance system.

The impact of arable soil management on physical functions – The ratio of air capacity and air permeability or hydraulic conductivity as a document of harmful soil compaction

Soil health or soil degradation criteria are until now not well documented for a greater number of soil profiles under conventional and conservation tillage management in the literature. In order to evaluate the compaction status of more than 700 arable sites analyzed within the last 40 years, the Compaction Verification Tool (CVT) was applied according to Zink et al. (2011). Besides the ratio of air capacity (AC, at a matric potential of −6 kPa) and saturated hydraulic conductivity (Ks), the ratio of AC and air conductivity (Ka, at a matric potential of −6 kPa) was considered for evaluating the compaction status with respect to potentially harmful soil alterations. The compaction status was classified into the CVT classes I–IV, where a harmful subsoil compaction was assumed, if both values of AC and Ks or AC and Ka simultaneously exceeded (are smaller than) their defined critical value indicating limited conditions for plant growth (CVT class IV). We analyzed the compaction status of soil profiles with respect to clay content, soil type, structural stage (aggregate forms) and time span of sampling (1980–1999, 2000–2020) under conventional and conservation tillage for top- and subsoil horizons. While also some of the annually plowed topsoils under conventional tillage showed critical values of AC, Ks and Ka, the occurrence of harmful soil compaction is most dominant in the subsoil horizons (> 30 cm depth) because of a higher proportion of class IV which increased with the clay content (from < 12 % to > 12 % clay), irrespective of the applied ratio used for verification (AC/Ks or AC/Ka). Especially the highly productive Luvisols showed a high percentage of harmful compaction in the subsoil (30–41 % in CVT class IV). Soil profiles under conservation tillage management are less affected by harmful compaction. The more aggregated subsoils showed smaller proportions of class IV, which was further influenced by the clay content.

Влияние гумата калия и гуминового препарата «BIO-Дон» на азотный режим чернозема обыкновенного под горохом

The article presents the results of short-term field experience for 2021-2023. Experience is laid down in the hospital of agricultural chemistry and plant protection FSBSI “FRARC”. The effect of the use of potassium humate and the humic preparation “Bio-Don” on the content of mobile nitrogen forms in the Calcic Chernozem in the cultivation of the pea Alliance (Pisum sativum L.) was studied. The experience scheme included options using mineral fertilizer (Azofoska 40:40:40) and without its use. Humic preparations were used in the phase of forming beans foliric, both together with insecticide and without it. It was established that the use of potassium humate shows a positive tendency to accumulate nitrate nitrogen in the Calcic Chernozem. The use of the “BIO-Don” humic preparation per year with an increased amount of precipitation has led to a decrease in the N-NO3 content, which may be associated with the migration of this form of nitrogen down into the subsoil horizon. The use of humic stimulants affected by the forms of ammonium nitrogen, which is available to plants, practically did not affect.

Simulated soil erosion predominantly affects fungal abundance in the rapeseed rhizosphere

Eroded agricultural soils have reduced soil organic carbon (SOC) levels that may affect the plant-microbiome interactions in the rhizosphere. We explored the impact of simulated erosion on major microbial groups in a pot experiment with rapeseed (Brassica napus L.) grown on arable soil with the potential to capture SOC. An erosion gradient was simulated by admixture (0%, 12%, 24%) of subsoil horizon (Bt) to topsoil (Ap) material. Rapeseed plants were pulse-labeled with 14CO2 at three growth stages and two soil compartments (bulk and rhizosphere soil) were sampled. Fungal ITS copy numbers were consistently higher in the rhizosphere and decreased with progressing plant growth stages. A significant increase of bacterial 16S rRNA gene copies in the rhizosphere only occurred at flowering. A response of fungal abundance to subsoil admixture was found detectable based on fungi:Bacteria and fungi:Archaea ratio at flowering. Archaea were neither affected by soil compartment nor subsoil admixture. 14C activity of microbial biomass, an indicator for relative input of freshly assimilated C into soil microbiome, was impacted by growth stage and compartment and decreased with ongoing growth stage. During the rosette growth stage, the 14C activity of the microbial biomass was elevated in the rhizosphere of the eroded soil indicating a plant response to the erosion factor. Our experiment revealed a compositional separation of the fungal community along the simulated erosion gradient and a selection of fungi for the two different soil compartments at flowering. Olpidimycetes, Fusarium and Rhizopus and putative pathogens were enriched in the rhizosphere at flowering. Fungi may have a competitive advantage in the rhizosphere of strongly eroded and nutrient diluted soils due to ecological adaptation and morphological traits i.e. hyphae that can bypass soil areas with low nutrient availability.

Impact of Climate on Soil Organic Matter Composition in Soils of Tropical Volcanic Regions Revealed by EGA-MS and Py-GC/MS.

Soil organic matter (SOM) crucially influences the global carbon cycle, yet its molecular composition and determinants are understudied, especially for tropical volcanic regions. We investigated how SOM compounds change in response to climate, vegetation, soil horizon, and soil properties and the relationship between SOM composition and microbial decomposability in Tanzanian and Indonesian volcanic regions. We collected topsoil (0-15 cm) and subsoil (20-40 cm) horizons (n = 22; pH: 4.6-7.6; SOC: 10-152 g kg-1) with undisturbed vegetation and wide mean annual temperature and moisture ranges (14-26 °C; 800-3300 mm) across four elevational transects (340-2210 m asl.). Evolved gas analysis-mass spectrometry (EGA-MS) documented a simultaneous release of SOM compounds and clay mineral dehydroxylation. Subsequently applying double-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) at 200 and 550 °C, we detailed the molecular composition of topsoil and subsoil SOM. A minor portion (2.7 ± 1.9%) of compounds desorbed at 200 °C, limiting its efficacy for investigating overall SOM characteristics. Pyrolyzed SOM closely aligns with the intermediate decomposable SOM pool, with most pyrolysates (550 °C) originating from this pool. Pyrolysates composition suggests tropical SOM is mainly microbial-derived and subsoil contains more degraded compounds. Higher litter inputs and attenuated SOM decomposition due to cooler temperatures and lower soil pH (<5.5) produce less-degraded SOM at higher elevations. Redundancy analyses revealed the crucial role of active Al/Fe (oxalate-extractable Al/Fe), abundant in low-temperature/high-moisture conditions, in stabilizing these less-degraded components. Our findings provide new insights into SOM molecular composition and its determinants, critical for understanding the carbon cycle in tropical ecosystems.

РАЗРАБОТКА РЕСУРСОСБЕРЕГАЮЩЕЙ ТЕХНОЛОГИИ И ТЕХНИЧЕСКИХ СРЕДСТВ ДЛЯ ВОЗДЕЛЫВАНИЯ КАРТОФЕЛЯ

A significant proportion of potatoes are cultivated in difficult soil and climatic conditions, which negatively affects the quality of harvested potatoes due to the consequences of contact of tubers with soil lumps. The technology for cultivating potatoes with alternating beds is proposed to increase the efficiency of potato cultivation to stabilize the accumulation of organic matter, decompact the soil and the subsoil horizon. The method includes basic tillage, pre-planting tillage with cutting ridges, planting potatoes in ridges, inter-row cultivation, maintenance soil moisture and density, digging up tubers and marking rows. The method differs in that during subsequent planting next year, the soil is cultivated so that the bottom of the ridges alternates with potato tubers. The research results showed that the greatest influence on the destruction of soil lumps is their moisture content and the speed at which the lumps collide with the beater drum. It has been shown that destruction of up to 80% of soil lumps occurs when falling from a height of 1 - 1.5 m and the destructive force of clay with a moisture content of 17 - 22% under static compression is 0.1-0.2 kN. Ultimately, the technology of growing potatoes with alternating ridges helps control weeds and minimizes the incidence of diseases and pests.

Successional development of the phototrophic community in biological soil crusts, along with soil formation on Holocene deposits at the Baltic Sea coast

Harsh environmental conditions form habitats colonized by specialized primary microbial colonizers, e.g., biological soil crusts (biocrusts). These cryptogamic communities are well studied in drylands but much less in temperate coastal dunes, where they play a crucial role in ecological functions. Following two dune chronosequences, this study highlights the successional development of the biocrust’s community composition on the Baltic Sea coast. A vegetation survey, followed by morphological species determination, was conducted. Sediment/soil cores of the different dune types were analyzed to uncover the potential impacts of the biocrust community on initial soil formation processes, with special emphasis on biogeochemical phosphorous (P) transformations. Biocrust succession was characterized by a dune type-specific community composition, shifting from thinner algae-dominated biocrusts in dynamic dunes to more stable moss-dominated biocrusts in mature dunes. The change in the biocrust community structure was accompanied by an increase in Chl a, water, and organic matter content. In total, 25 algal and cyanobacterial species, 16 mosses, and 26 lichens across all sampling sites were determined. The pedological characterization of these cores elucidated initial processes of soil genesis, such as decalcification, acidification, and the accumulation of organic matter with dune and biocrust development. Furthermore, the chemistry of iron (Fe)-containing compounds such as the Fedithionite/Fetotal ratios confirmed mineral weathering and the beginning of soil profile development. The biocrusts accumulated P over time, while the P content in the underlying sediment did not change. That implies that biocrusts take up P from the geological parent material in the dunes, thereby accumulating available P in the ecosystem, which gets transferred into subsoil horizons through leaching or redeposition. The relative proportion of the bioavailable P pool (56% to 74% of Pt) increased with dune succession. That happened at the expense of more stable bound P, which was transformed into labile P. Thus, the level of plant available P along the dune chronosequences increased due to the microbial activity of the biocrust organisms. It can be concluded that biocrusts of temperate coastal dunes play a crucial role in maintaining their habitat by accumulating nutrients and organic matter, supporting soil development and subsequent vegetation.

Accumulation of century-old biochar contributes to carbon storage and stabilization in the subsoil

Soil organic carbon (C) is a key component of the global C budget. As soil organic C turnover rates decrease with depth, agricultural practices favoring deep organic C storage will gain importance as long-term climate change mitigation strategies. In addition, amendment of pyrogenic organic matter (biochar) is considered a promising practice for sequestering C in croplands. However, so far the >30 cm depth soil organic C pool, and subsoil biochar dynamics in particular, has been understudied.To address this, we focused on leftovers from pre-industrial charcoal kilns as a proxy to study the accrual of century-old biochar in the subsoil (30–100 cm) in comparison to adjacent control soil. Using thermal and elemental analyses as well as size and density fractionations (i.e., separating particulate and mineral-associated organic matter), we determined the distribution of pyrogenic organic C within the soil profile and investigated its stabilization in depth. We measured the dissolved organic carbon (DOC) concentrations as well as absorbance and fluorescence properties of dissolved organic matter (DOM) at different depths to characterize the effects of century-old biochar accumulation on the current leaching of DOM.Our results showed that the presence of century-old biochar resulted in an increase of 53.8 ± 25.1 t C ha−1 in 0–100 cm, and 12 % of the pyrogenic organic C was stored in 30–60 cm. No difference in C stocks was observed in 60–100 cm between kiln sites and reference soils. Most of the pyrogenic organic C has been translocated as particulate organic matter, either free or occluded, to subsoils. This led to a change in the dominant fraction of organic matter in the E horizon; in reference soils 64.7 % of the total C was associated with mineral phases as opposed to only 42.3 % in soils enriched with biochar. The thermal analysis of the mineral-associated organic matter revealed that pyrogenic organic C was associated with mineral phases. With depth, DOC concentrations decreased and the relative contribution of microbial byproducts to fluorescent DOM increased. The soils enriched with century-old biochar displayed lower DOC concentrations and more aromatic DOM in the Ap horizon, which suggests biochar dissolution is still an on-going process. Our results suggest that the vertical transfers of century-old biochar mainly occurred as particle leaching in macroporosity and bioturbation but continuous dissolution has also contributed in these fine-textured cropland soils. In conclusion, the association of pyrogenic organic C with mineral phases as well as its migration in subsoil horizons promoted its physical disconnection from abiotic and biotic degrading agents, which likely contribute to the long-term stability of biochar.

The results and perspectives for breeding of the green manure narrow-leafed lupine varieties for the productivity and morph-and-biological characters

The narrow-leafed lupine (Lupinus angustifolius L.) has long been used as a green manure crop. Alkaloid content which is incompatible with forage varieties is a desirable trait for green manure ones. Alkaloids presented in plowed biomass of the green manure lupine have disinfected action for soil resulted in the lower infection of the next crops. The undemanding nature of green manure lupine to growing conditions consists of several features: it is an active nitrogen accumulator and provides 70 % of nitrogen for own needs, and its deeply penetrated root system allows make up the deficit of nutritional substances in arable layer with use of sub-soil horizons. The aim of the study was to reveal perspective narrow-leafed lupine’s green manure varieties and breeding lines for grain and green mass yield, for length of the vegetation season, alkaloid content and other morphological and biological characters. The tests have been done under Bryansk region’s conditions (the South-West zone of the Central region of Russia) on soddy-podzolic loamy cultivated soils with the moderate fertility level. The objects of the research were seven green manure varieties and breeding lines of the narrow-leafed lupine which have been tested in competition tests of 2021-2022. The breeding line Siderat 265-19 stand out for grain (2.62 t/ha), green mass (31.9 t/ha) yield and for early maturing (84 days). Alkaloid content in its seeds made 1.003 %, the standard level. The article presents the results of structural analyses for morphological peculiarities and productivity elements of new green manure hybrid lines (the standard variety – Tshutchinskiy).). The No. 1764 (Siderat 46 x Kormovoy 344) had the best index for plant height. The No. 1749 (Siderat 46 x Bryanskiy siderat) picked out for grain productivity. The seed weight per a plant was 14.3 g and the pod’s seedingwas 5.2 seeds.

Rapid Determination of Soil Horizons and Suborders Based on VIS-NIR-SWIR Spectroscopy and Machine Learning Models

In an effort to improve the efficiency of soil classification, traditional methods are being combined with analytical and computational techniques. This integration has strengthened the connection between conventional classification and the application of machine-learning (ML) models to interpret soil spectral reflectance data. Due to the time and computational cost, several studies are limited to testing the classification performance of a few algorithms and do not always explore the best parameters for model optimization. The study aims to assess the efficiency of combining soil spectral reflectance with prevalent ML models for classifying pedogenetic horizons and soil suborders, enhancing traditional classification methods. We collected seven soil monoliths, previously classified according to the Brazilian Soil Classification System (SiBCS) and soil taxonomy. Using the ASD Fieldspec spectroradiometer, we obtained spectral reflectance samples along each monolith (n = 800 per monolith) to classify horizons and n = 5600 for suborder classification. Spectral fingerprints were obtained and explored by Principal Component Analysis (PCA). The spectral data were subdivided into training (70%) and test (30%) sets and submitted to the Logistic Regression (LR), Artificial Neural Network (NN), Support Vector Machine (SVM), Random Forest (RF), and Gradient Boosting (GB) models for the classification of horizons and suborders, considering the model’s adjustment parameters. Accuracy and F-Score were used to verify the performance of the models. There was a significant influence of particle size and soil organic carbon on the spectral fingerprint of the soils. The PCA indicated that topsoil horizons clustered in most of the monoliths analyzed, while most of the subsoil horizons showed data overlap. The NN model showed the highest accuracy in the classification of horizons (97%), while the SVM showed the lowest performance (52% accuracy). The classification of soil suborders presented accuracies between 95% and 98%. Therefore, our study concludes that spectral data combined with ML models can enhance the discrimination and classification of soil horizons and suborders, improving upon traditional methods.

Decomposition decreases molecular diversity and ecosystem similarity of soil organic matter

Soil organic matter (SOM) is comprised of a diverse array of reactive carbon molecules, including hydrophilic and hydrophobic compounds, that impact rates of SOM formation and persistence. Despite clear importance to ecosystem science, little is known about broad-scale controls on SOM diversity and variability in soil. Here, we show that microbial decomposition drives significant variability in the molecular richness and diversity of SOM between soil horizons and across a continental-scale gradient in climate and ecosystem type (arid shrubs, coniferous, deciduous, and mixed forests, grasslands, and tundra sedges). The molecular dissimilarity of SOM was strongly influenced by ecosystem type (hydrophilic compounds: 17%, P < 0.001; hydrophobic compounds: 10% P < 0.001) and soil horizon (hydrophilic compounds: 17%, P < 0.001; hydrophobic compounds: 21%, P < 0.001), as assessed using metabolomic analysis of hydrophilic and hydrophobic metabolites. While the proportion of shared molecular features was significantly higher in the litter layer than subsoil C horizons across ecosystems (12 times and 4 times higher for hydrophilic and hydrophobic compounds, respectively), the proportion of site-specific molecular features nearly doubled from the litter layer to the subsoil horizon, suggesting greater differentiation of compounds after microbial decomposition within each ecosystem. Together, these results suggest that microbial decomposition of plant litter leads to a decrease in SOM α-molecular diversity, yet an increase in β-molecular diversity across ecosystems. The degree of microbial degradation, determined by the position in the soil profile, exerts a greater control on SOM molecular diversity than environmental factors, such as soil texture, moisture, and ecosystem type.

Predicting soil organic carbon stocks in different layers of forest soils in the Czech Republic

Carbon dioxide, the most produced anthropogenic greenhouse gas, could be moderated by sequestering carbon in forest soils. Forest soils store more carbon than there is in the atmosphere. Thus, the smallest variation in soil carbon levels could trigger a significant change in atmospheric carbon. This study focused on predicting the spatial distribution of carbon stocks within surface organic and mineral topsoil and subsoil layers of the forty-one natural forest areas of the Czech Republic. Cubist and Random Forests machine learning algorithms were employed with a grid search hyper tuning to improve prediction accuracy. We used the five-fold cross-validation to verify the model accuracy using Root Mean Square Error (RMSE), coefficient of determination (R2), and Mean Absolute Error (MAE). Random Forests yielded lower RMSE of 1.10 kg/m2, 3.85 kg/m2, and 4.77 kg/m2 in the surface organic horizon (F + H layer), mineral topsoil (0–30 cm layers) and subsoil horizons (30–80 cm layers), respectively, compared to the RMSE values of Cubist, which were 1.14 kg/m2, 3.90 kg/m2, and 4.91 kg/m2 in the surface organic, mineral topsoil and subsoil horizons, respectively. R2 values of both models were low for all three horizons considered. Random Forests were the preferred algorithm for SOC stock prediction in all layers of the forest soils. Cubist predicted the spatial distribution of SOC stocks with more covariates than Random Forests. Altitude was the most important covariate for the spatial distribution of SOC stocks for both Random Forests and Cubist in all soil horizons considered. High SOC stocks for all soil horizons are spatially concentrated in soil horizons along the country borders in the mountaineous natural forest areas.

Reducing the environmental risks of using mobile energy-saturated units during seed potatoes growing taking into account the patterns of heat and moisture transfer within the root spreading zone in the soil

Because potato is a crop, demanding moisture supply conditions its yield depends on the ability to use the moisture accumulated during the calendar year by the root system during the growing season. However, the intensification of technological methods of potato production using powerful energy-saturated mobile agricultural units leads to a significant deterioration of the soil condition due to over compaction of the arable and subsoil horizons which hinders the normal mode of movement of intrasoil moisture and the development of the root system of plants. Reducing the number of passes of agricultural units across the field is possible when using combined units that perform several technological processes in one pass. For this purpose, a multifunctional combined potato-planting unit has been developed at St. Petersburg State Agrarian University that combines preplant tillage, planting potato seeds, the use of agrochemicals, pesticides and water-retaining agents, as well as deep loosening of interrow spacing and the formation of full-volume ridges. The conducted studies have shown the effectiveness of the use of such a combined unit by providing favorable soil conditions for the growth and development of plants.

Structure dependent changes in pore water pressure due to stress application and consequences on the effective stress

Divergent processes in soils affect the pore systems and alter hydraulic, gaseous and thermal fluxes as soon as the internal soil strength (= the precompression stress) is exceeded. Especially the intense changes of the hydraulic flux properties during soil deformation result in retarded soil settlement due to their dependency on time and stress dependent changes in pore water pressure as well as the water saturation degree. These processes depend besides on texture and bulk density especially on aggregation level, but the linkage between changes in effective stress and soil structure in various soil horizons defined by the precompression stress is still not analyzed and is therefore subject of this investigation. In this study, stress strain and pore water pressure data from almost 900 (predrained to −60 hPa) samples from arable top- and subsoil horizons subjected to oedometer compaction tests are evaluated. Among others, hydraulic stress parameters like the effective stress and χ-factor are calculated and linked to the precompression stress values. Results are presented for 6 differently aggregated soil horizons. Ap horizons with a very weak soil structure document no defined soil rigidity due to a reduced functionality of the pore systems and a stress dependent weakening, while especially the soil deformation behavior of sandy Bw horizons is less controlled by the precompression stress and the calculated effective stresses. The E and Bg horizons indicate anthropogenic impacts on structure properties and the related stress-strain behavior. While it could be documented that the enhanced strain coincides with an increase in the calculated χ-factor, it does not coincide in correspondingly enhanced effective stresses due to the non- equilibrated pore water pressure even after 45 h of increasing stress application. We conclude that further investigations are needed to quantify the highly dynamic interactions between the stress dependent hydraulic conductivity / pore water pressure ratio and the impact on the stress affected pore water pressure reequilibration. Furthermore, the contribution of the sorptive potential in soils with more negative initial matric potential on these changes would elucidate also the physico chemical impacts on soil strength more clearly especially under drier soil conditions.

Phosphorus hotspots in pedogenic carbonate coatings determined by zoned microscale arrangement and organo-mineral interactions

Subsoils of calcareous soils are often characterized by pedogenic carbonate precipitates coating soil aggregate and rock surfaces. Numerous studies identified the key mechanisms of pedogenic carbonate formation in calcareous soils. Still, little is known about the ecosystem function of carbonate precipitates for nutrient supply, their microscale structure and the interaction of microscale structure with nutrient distribution such as P. We investigated the mineral composition and P speciation of lithogenic carbonate coated by pedogenic carbonate precipitates. Subsoil horizons of a Rendzic Leptosol (Tuttlingen, C horizon) and a Eutric Cambisol (Benediktenwand, BC horizon) in Central Europe were sampled. We combined wet-chemical methods with X-ray diffraction, synchrotron-based P XANES spectroscopy, and specific surface area analysis (N2-BET). To investigate the spatial arrangement and elemental distribution at the microscale, a complementary approach using light microscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) as well as XANES spectroscopy at the microscale (µXANES) was conducted. In both soils, the pedogenic carbonate coatings showed an intricate porous microstructure and large specific surface area. The δ13C values of the coatings were halfway between those of the primary bedrock and soil organic matter (SOM), proving their formation by re-precipitation of dissolved carbonate through organic and inorganic (H2CO3) acids. Compared to the primary rocks, the coatings were enriched in Al, Fe, Mn, and K and in organic C, N, and P; additionally, they contained silicate minerals (muscovite, illite) and quartz. Whereas the P in the rock interior was mainly present as apatite, the P in the coatings was mainly organic P bound to Ca and Al minerals. NanoSIMS and µXANES analyses at Tuttlingen revealed a zoned microstructure of the pedogenic coating: An inner zone with most P co-localized and bound to Al minerals and an outer zone enriched again in Ca and SOM. The formation of these zones indicates the infiltration and residual accumulation of Al minerals which may contribute to mitigate P losses by leaching. Intensive penetration by fine plant roots and observations of fungal hyphae within the coatings indicate the potential of pedogenically altered carbonates as microbial habitat and ecosystem nutrient source, thus contributing to the scarce ecosystem P nutrition of initial calcareous soils.

Does soil thinning change soil erodibility? An exploration of long-term erosion feedback systems

Abstract. Soil erosion rates on arable land frequently exceed the pace at which new soil is formed. This imbalance leads to soil thinning (i.e. truncation), whereby subsoil horizons and their underlying parent material become progressively closer to the land surface. As soil erosion is a selective process and subsurface horizons often have contrasting properties to the original topsoil, truncation-induced changes to soil properties might affect erosion rates and runoff formation through a soil erosion feedback system. However, the potential interactions between soil erosion and soil truncation are poorly understood due to a lack of empirical data and the neglection of long-term erodibility dynamics in erosion simulation models. Here, we present a novel model-based exploration of the soil erosion feedback system over a period of 500 years using measured soil properties from a diversified database of 265 agricultural soil profiles in the UK. For this, we adapted the Modified Morgan–Morgan–Finney model (MMMF) to perform a modelling experiment in which topography, climate, land cover, and crop management parameters were held constant throughout the simulation period. As selective soil erosion processes removed topsoil layers, the model gradually mixed subsurface soil horizons into a 0.2 m plough layer and updated soil properties using mass-balance mixing models. Further, we estimated the uncertainty in model simulations with a forward error assessment. We found that modelled erosion rates in 99 % of the soil profiles were sensitive to truncation-induced changes in soil properties. The soil losses in all except one of the truncation-sensitive profiles displayed a decelerating trend, which depicted an exponential decay in erosion rates over the simulation period. This was largely explained by decreasing silt contents in the soil surface due to selective removal of this more erodible particle size fraction and the presence of clayey or sandy substrata. Moreover, the soil profiles displayed an increased residual stone cover, which armoured the land surface and reduced soil detachment. Contrastingly, the soils with siltier subsurface horizons continuously replenished the plough layer with readily erodible material, which prevented the decline of soil loss rates over time. Although our results are limited by the edaphoclimatic conditions represented in our data, as by our modelling assumptions, we have demonstrated how modelled soil losses can be sensitive to erosion-induced changes in soil properties. These findings are likely to affect how we calculate soil lifespans and make long-term projections of land degradation.

Geoecology of a granite dome: Spatial interactions between gnammas, rills, soils, and plant cover, Enchanted Rock (Texas, USA)

This research examines geoecological connections between geomorphic, pedological,hydrological, and vegetation components in gnammas—shallow pans and deeper basin pans—and in various microforms on Enchanted Rock (Texas), a large granite dome where an intricate rill drainage network connects microforms. Gnamma morphometric analysis (GMA) showed the association between mean basin length (418.8 cm) and width (258.2 cm) was more significant than in pans (150.9 × 84.0 cm); mean basin depth (44.0 cm) was correlated with length, but pan depth (7.8 cm) was independent. Debris depth was assessed by auger probing along transects on 8 basins and 20 pans; basin soils (11–98.5 cm) were deeper than those in pans (1–5 cm). Lens-shaped basins show Typic-Lithic Haplustolls or Typic-Lithic Dystrudepts with complex profiles; pans are shallow and flat-bottomed, and display simple Lithic Ustorthents with thin surficial gravel layers shielding finer subsoil horizons. Deeper basin profiles, along with greater SOM, nutrients, and fine-particle content, provided high water retention, facilitating dense plant growth. Rills showed discrete areas of debris deposition sequentially along channels; sediment patch size decreased downslope, while gravel content increased, and fine grains decreased, downhill.Plants on gnammas and microforms included 48 vascular species, mostly annual or perennial herbs and nanoshrubs, followed by ferns and cacti. Vegetation on gnammas showed distinctive patterns of sequential, concentric, plant rings, with outer bands of Sedum nuttallianum and Allium drummondii on shallow (0–10-cm) soils, followed by narrow strips of annual plants growing on 8–40-cm-deep soils, and a sizable central area of tall perennial grasses, mainly Andropogon glomeratus, on ≤ 98.5-cm-deep profiles. A conceptual developmental model of geoecological interactions between gnammas, rills, and other microforms, suggests these are interconnected via channeled runoff and/or sheetwash, which transports debris and SOM downhill; in this view, gnammas on Enchanted Rock and their sediments, are not static and permanent, but remain in a perpetual state of flux and development.

Retention of dissolved organic matter during podzolisation: Testing processes in laboratory experiments and at the submicron scale

Immobilisation of organic matter in illuvial subsoil horizons is a characteristic result of Podzol formation and development. We tested dissolved organic matter (DOM) immobilisation by mineral mixtures as models of initial illuvial horizons and conducted laboratory experiments by irrigating mineral mixtures with a DOM solution and analysing the eluate solutions. The mineral mixtures consisted of quartz with accessory H+-saturated illite, or Ca2+-saturated illite, or quartz with ferrihydrite. Furthermore, we studied the transport of colloidal proto-imogolite in the ferrihydrite-containing mixture and analysed the spatial distribution of elements by nanoscale secondary ion mass spectrometry (NanoSIMS). Retention of DOM in the presence of Ca2+-saturated illite did not exceed that in the presence of H+-saturated illite, as the promoting effect of the divalent cation was counterbalanced by the initially higher pH. The mineral mixture containing ferrihydrite retained most DOM. In all experiments, aromatic and oxidised DOM moieties were preferentially adsorbed. Colloidal proto-imogolite co-precipitated with DOM and reduced the pore space of the mineral mixture, which increased the residence time and DOM adsorption on ferrihydrite. NanoSIMS analyses showed proto-imogolite deposited on ferrihydrite, with ferrihydrite as the more important DOM adsorbent in ferrihydrite-proto-imogolite assemblages. Furthermore, NanoSIMS revealed less N in adsorbed DOM closer to the mineral surface. Thus, we differentiated between processes of DOM retention in simulated early podzolisation, detecting preferentially adsorbed species and compositional differences within adsorbed DOM layers.

Assessment of fallow grey forest soils fertility in sub-taiga zone of Omsk Priirtyshye

There is a need to obtain information on the current state of their properties when reintroducing fallow soils into arable land. The aim of the research was to study fertility indicators of grey forest soils (Luvic Greyzemic Phaeozems) The research area was located in the city of Tara, Omsk region (south of Western Siberia). A field survey of soils and vegetation cover was carried out in plots with different age of fallow land with the establishment of the value of the above ground mass. The results of the research showed that the fallow area with age of less than 10 years is represented by a thick grey forest soil, with age of 10-20 years - by a medium thick grey forest soil. The value of air-dry aboveground mass of plants varied from 1.01 to 1.01 2.58 t/ha. High density, low porosity, and aeration porosity were found in soils throughout the profile. The humus content and reserves in soils are low and average; its distribution in profiles is markedly decreasing. Reaction of soil medium is acidic (рН=4.4-4.8). The sum of exchangeable cations in humus horizons is elevated and high. In composition of cations calcium prevails (71.5-74.9 %) with magnesium share - 22.4-26.9 % and insignificant content of sodium (1.6-2.5 %). The surveyed soils can be reintroduced to arable land. However, it is necessary to provide measures to reduce acidity, improve organic matter balance, reduce density, and increase porosity of upper and subsoil horizons.