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Cover crops are one of the climate-smart agricultural practices used to increase soil organic carbon (SOC) sequestration. However, the SOC sequestration potential and underlying mechanisms under different cover crops, especially in orchard agroecosystems, have not been fully elucidated. Here, we investigated three orchards in China using SOC fractionation methods, high-throughput sequencing, and biomarker analysis. Our objectives were to determine the effect of cover crops on the physical fractions and chemical compositions of SOC, as well as on microbial properties, and to clarify why legume and non-legume cover crops sequester SOC differently. The results showed different increases in SOC between legume and non-legume cover crops (+38% vs. +16%) compared with those in the control plots without cover crops. Legume cover crops increased mineral-associated and particulate organic carbon, whereas non-legume cover crops increased mineral-associated organic carbon only. These differences were attributed to their distinct effects on microbial SOC transformation pathways. Legume cover crops positively impacted microbial pathways by increasing the availability of soil substrates and nitrogen, such as dissolved organic carbon (+84%), O-alkyl carbon (+18%), and ammonium nitrogen (+42%). These results were supported by the increases in carbon and nitrogen enzyme activities, microbial community diversity indices, the abundance of dominant fungal taxa (Sordariomycetes), microbial biomass carbon (+105%), and microbial necromass carbon (+47%). Non-legume cover crops might have induced microbial nitrogen starvation, decreasing the efficiency of microbial pathways, as evidenced by the low β-glucosidase to β-N-acetylglucosaminidase ratios (−7%) and the lack of significant changes in the bacterial Shannon index or microbial necromass carbon. In addition, redundancy analysis revealed that enzyme activity, the microbial community, and microbial necromass carbon collectively dominated the changes in the SOC physical fraction. Site-specific soil properties such as soil texture and nitrogen availability were important factors influencing SOC sequestration under cover crops. Our study provides essential insights for optimizing cover crop management to increase SOC sequestration in orchard agroecosystems.

Wildfires are natural phenomena for most ecosystems on Earth. Many soil properties are impacted by fire, including soil hydraulic properties. We used a laboratory experiment to replicate the temperatures reached by a natural wildfire and documented the effects on soil hydraulic properties. This study hypothesizes that the impact of heating on soil hydrological properties can be explained by the interaction of a number of variables especially organic matter content (OM), cation exchange capacity (CEC), texture, pH, and electrical conductivity (EC). The main objective of this study is to explore the interconnections between soil hydraulic, chemical, and physical properties, focusing on understanding how these relationships change across different ecoregions and temperatures. Sixteen soils were collected across 16 sites susceptible to forest fires in the Central Zone of Chile and heated to 100 °C and 300 °C for two hours. These sites were representative of two distinct ecoregions: the Chilean Matorral (CM) and the Valdivian Temperate Forests (VTF). Chemical, physical, and hydraulic soil properties were measured before and after heating. At 100 °C, there were no significant changes in chemical, physical, or hydraulic soil properties. At 300 °C, significant changes were observed in most soil properties in soils from both ecoregions. The OM content and CEC decreased, whereas pH and electrical conductivity increased. In addition, clay content and water aggregate stability (WSA) decreased, while all hydraulic properties increased their values. The aforementioned results demonstrate that infiltration increased after the soil was heated. This can be attributed primarily to decreases in clay content. At the same time, the water repellency (R) index decreased, allowing water to more easily wet the soil particles. Correlations revealed that CEC and clay are the main factors ruling soil hydraulic properties at all temperatures. Clay mineralogy also contributes to the soil hydraulic behavior observed. Nonlinear models were developed to estimate hydraulic properties at 100 °C and 300 °C, using the main soil properties. The models illustrated that the soils of the CM ecoregion, which are characterized by lower OM and influence of clay/CEC ratio, would be less affected by fire compared to the soils of VTF. The water holding capacity would decrease in both ecoregions. However, due to the greater changes in OM and clay in VTF, the impact would be greater than in CM.¹

Freeze-thaw cycles (FTCs) extensively and intensely occur in cold regions, significantly affecting soil properties. However, quantifying the impacts of FTCs at different initial conditions on soil properties is challenging due to the complex interactive responses. In this study, porosity, bulk density, field capacity and saturated hydraulic conductivity (K_s) were measured to evaluate the responses of soil to FTCs. Eight FTCs (0, 1, 3, 5, 7, 10, 15 and 20 cycles), five initial soil mass water contents (10, 20, 30, 40 and 45 %), four eroded soils (original, degraded, deposited and parent), two initial bulk densities (1.2 and 1.3 g cm⁻³) and two freezing temperatures (−10 and −15 ℃) were employed to quantify the impacts of FTCs on physical properties. Results showed that repeated FTCs had a cumulative effect on soil physical properties, which generally entered a steady state after 10–15 FTCs. Changes in soil physical properties were highlighted after the initial 1–3 FTCs, and the effects of FTCs on physical properties diminished when the soil water content was below 20 %. Soil physical properties with different initial conditions responded differently to FTCs. Porosity increased with FTCs in increments ranging from about 0.2 to 8.7 %; however, the opposite result was observed when the initial soil water content exceeded 30 %. The bulk density decreased by 1.1–3.7 % with increasing FTCs, whereas the bulk density of the soils with high water content and severe soil erosion increased by 0.2–7.5 %. Compared to the initial state, the field capacity decreased by 0.1–15.3 % after 20 FTCs; however, the field capacity increased by 10.4 % under high bulk density. The K_s increased by 21.8–249.5 % with the increase of FTCs, whereas the K_s of the soils with 40 % and 45 % water content decreased by 28.7 % and 90.4 %, respectively. Overall, soil physical properties responded more strongly to FTCs at high water content, severe soil erosion, moderate bulk density and low freezing temperature. In comparison, the degree of soil erosion was the most critical factor influencing soil physical properties. These findings can help to improve the understanding of soil dynamic processes and provide new insight into mechanisms of erosion caused by seasonal FTCs.

Agro-development of northern territories results in radical transformation of soils of these ecosystems. On the example of Nadym district (N 65.5; E 72.6) of Yamal-Nenets Autonomous Okrug (Russia) it is shown that the process of agrogenic transformation of reference podzols is similar to the process of formation of Plaggen soils, which were repeatedly found in Northern Europe and other regions (Plaggen Anthrosols – result of Plaggen Management). As a result of the application of large amounts of organic substrate (Plaggen Material), the thickness of the surface horizons increases considerably (from 3 cm to more than 30 cm in some cases). These soils occupy an intermediate position from reference soils to highly transformed − Hortic/Plaggic Podzols. Hortic and Plaggic horizons are characterized by reduced acidity (pH H₂O 5–6, pH CaCl₂ 4–5), increased content and stock of organic carbon (5.4–14.5 %). Soils of agrogenic and postagrogenic ecosystems are characterized by relatively high content of basic nutrients (P-P₂O₅ up to 386 mg kg⁻¹, K-K₂O up to 239.0 mg kg⁻¹) and clay (up to 20.9 %), also the degree of their microstructure increases in comparison with reference Podzols of Nadym district. The taxonomic composition of soil microbiome also changes greatly in the process of agricultural development of soils. In reference Podzols Proteobacteria, Actinobacteria and Bacteroidetes dominate. In general the microbiological profile in the of agrogenic and postagrogenic soils shifts towards the increase of the phyla Proteobacteria, Acidobacteria, Planctomycetes, Nitrospirae, Verrucomicrobia (for abandoned lands) and Actinobacteria, Bacteroides, Firmicutes, Euryarchaeota (for soil in use).

Despite the crucial importance of technogenic materials in the urban environment, the influence of construction and demolition waste (CDW) on soil diversity still needs to be recognized. To address this knowledge gap, our study aimed to analyze how CDW can shape urban soil diversity. We propose a comprehensive approach based on a statistical analysis of over 100 profiles from Zielona Góra (western Poland) assigned to four groups distinguished using criteria of the WRB classification (2022). Physicochemical and chemical parameters differentiated the groups, and similarities between groups were determined. High heterogeneity of soil properties of the soils was found, mainly shaped by parameters associated with CDW such as artifact content, pH-H₂O, coarse fragments (ø >2 mm), and total Fe and Co content. However, a completely different picture of the diversity of urban soils was obtained, presenting their internal variation within specific WRB classification units. Moderately and strongly human-transformed soils (Technosols, Regosols, Anthrosols) were characterized by greater similarity than natural soils (Podzols, Arenosols, Gleysols). This increased similarity is likely due to the homogenizing effect of human activities, particularly the significant impact of construction and demolition waste (CDW) on soil characteristics. It also indicates the rationality of WRB classification criteria for soils with different degrees of technogenic transformation and CDW contribution to soil material. This study also demonstrated the usefulness of the Bray-Curtis distance and ANOSIM comparison in the analysis of soil diversity.

A recent assessment states that 60–70% of soils in Europe are considered degraded. Protecting such valuable resource require knowledge on soil status through monitoring systems. In Europe, different types of monitoring networks currently exist in parallel. Many EU Member states (MS) developed their own national soil information monitoring system (N-SIMS), some being in place for decades. In parallel in 2009, the European Commission extended the periodic Land Use/Land Cover Area Frame Survey (LUCAS) led by EUROSTAT to sample and analyse the main properties of topsoil in EU in order to develop a homogeneous dataset for EU.

Both sources of information are needed to support European policies on soil health evaluation. However, a question remains whether the assessment obtained by using soil properties from both monitoring programs (N-SIMS and LUCAS Soil) are comparable, and what could be the limitations of using either one dataset or the other.

Conducted in the context of European Joint Programme (EJP) SOIL, this study shows the results of a comparison between N-SIMS and LUCAS Soil programs among 12 different EU member states including BE, DE, DK, EE, ES, FR, DE, HU, IT, NL, PL, SE and SK. The comparison was done on: (i) the sampling strategies including site densities, land cover and soil type distribution; (ii) the statistical distribution of three soil properties (organic carbon, pH and clay content); (iii) two potential indicators of soil quality (i.e. OC/Clay ratio and pH classes). The results underlined substantial differences in soil properties statistical distributions between N-SIMS and LUCAS Soil in many member states, particularly for woodland and grassland soils, affecting the evaluation of soil health using indicators. Such differences might be explained by both the monitoring strategy and sampling or analytical protocols exposing the potential effect of data source on European and national policies. The results demonstrate the need to work towards data harmonization and in the light of the Soil Monitoring Law, to carefully design the future of soil monitoring in Europe taking into account both LUCAS Soil and N-SIMS considering the significant impact of the monitoring strategies and protocols on soil health indicators.

Desiccation cracking is a common and natural phenomenon under a drought climate. The geometric and morphologic characteristics of the crack pattern are critical to understanding the response of soil mechanical and hydraulic properties to drought climate. It is always a big challenge to obtain the refined geometric structure of the in-situ soil desiccation crack network. This study proposes an integrated method named ERT⁺ for determining the three-dimensional geometry of in-situ soil desiccation crack networks by integrating multi-source data from electrical resistivity tomography (ERT), surface image analysis, and depth investigation. The proposed method was applied to three in-situ expansive soil sites with different crack geometries and soil properties. The results showed that the joint application of ERT with other investigations reduced the ambiguity of interpreting each technique independently. The crack network model characterized the three-dimensional geometric structure of the desiccation crack accurately and quantitatively, verifying the effectiveness and feasibility of the ERT⁺ method. Field and laboratory experiments showed that heterogeneity in soil properties resulted in different cracking morphologies (width, depth, and width-depth ratio). The crack geometric data suggested that the width-depth ratio of the crack network was related to the cracking modes and the soil properties, indicating the non-homology of different crack networks. In addition, the correction gradients calculated from the ERT⁺ method also varied with the cracking modes and soil properties, further suggesting the reliability and prospect of the proposed method.

Pedogenic minerals reflect the environmental conditions that prevailed during soil formation. The present study investigates the clay mineral composition of the fine clay fraction separated from four soil profiles in the Tatra Mountains, Poland. All profiles were developed from granitoids or granitic moraines and were classified as Podzols. The clay fraction (<0.2 μm) was separated from each soil horizon by centrifugation after removing carbonates, organic matter, and poorly crystalline iron phases through reactions with sodium acetate-acetic acid buffer, sodium hypochlorite, and citrate-bicarbonate-dithionite, respectively. The obtained clay fraction was then characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy, thermogravimetry, chemical analysis, and cation exchange capacity measurements. The dominant mineral in the studied samples was illite–smectite, followed by dioctahedral mica and kaolinite. Hydroxy-interlayering was observed within the mixed-layer minerals. Chlorite and gibbsite were also detected in some horizons. Selected XRD patterns were modeled using Sybilla software. Layer charge measurements of the expandable component of the samples indicated values corresponding to low-charge vermiculite/high-charge smectite, with these values being uniform for all investigated samples. The uniformity of the layer charge values may reflect the uniformity of the parent material or the uniformity of processes controlling the chemistry of the weathered part of the mica structure. The general absence of discrete smectite, despite the presence of kaolinite (and gibbsite), suggests that smectite may not be stable under the acidic conditions prevailing in the alpine Podzols of the Tatra Mountains.

Biological soil crusts (BSCs) play an essential role in soil stabilization and nutrient cycling in arid environments, being a hotspot of microbial activity including soil enzyme production. However, the changes in microbial communities of the BSCs from different age are poorly understood. In over a 60-year dune revegetation chronosequence (2021, 2016, 1973, and 1962) in the southeastern Tengger Desert, China, we compared the development of BSCs and underlying sands using metagenome sequencing and enzyme assays. In both BSCs and the underlying sand substrate, enzyme activity increased along the time series but was always greater for BSCs than the substrate, emphasizing the potential for nutrient cycling activity. A clear trend in community composition and co-occurrence network complexity was observed in the BSCs: the family-level taxonomic network of BSCs became more connected in the older age BSCs, while in the substrate, there was no such trend. Unexpectedly, considering their low relative abundance and diversity, archaea emerged as major keystones in establishing community networks, being key to network stability. In the underlying substrate, by contrast, archaea did not play this key role. During the time series of BSCs, the dominant archaeal groups were Nitrososphaeria, Methanomicrobia, Halobacteria, and an unclassified Thaumarchaeota, mainly linked to functional genes related to carbon and nitrogen, such as CHB2, xylA, amyA, amoB, nxrA, nxrB, and nirB. This suggests that in BSCs, the key role of archaea relates to their role in nitrogen cycling. This perspective adds to the emerging view that archaea play an important role in community structure and function in dryland environments.

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.