Soil Systems

Biochar is a stabilised, carbon-rich material created when biomass is heated to temperatures usually between 450 and 550 °C, under low-oxygen concentrations. This study evaluated the effectiveness of sawdust, cocoa pod ash and rice husk biochars in remediating metal-contaminated paddy soil in Nobewam, Ghana. Biochar was applied 21 days before cultivating the rice for 120 days, followed by soil sampling and rice harvesting for metals and physicochemical analyses. Compared to the untreated soils, biochar treatments exhibited an enhancement in soil quality, characterised by an increase in pH of 1.01–1.20 units, an increase in available phosphorus (P) concentration of 6.76–13.05 mg/kg soil and an increase in soil total nitrogen (N), and organic carbon (OC) concentration, ranging from 0.02% to 0.12%. Variabilities in electrical conductivity and effective cation exchange capacity were observed among the treated soils. Concentrations of potentially toxic metals (arsenic, cadmium, copper, mercury, lead and zinc) in paddy soils and rice analysed by atomic absorption spectroscopy showed significant differences (p < 0.05) among the sampled soils. The concentrations of arsenic and lead in all soil samples exceeded the Canadian Council of Ministers of the Environment soil quality guideline for agricultural soils, with untreated soils having the highest levels among all the soils. Cadmium had a potential ecological risk index > 2000 and a geoaccumulation index above 5, indicating pollution in all samples. In contrast, arsenic and mercury contamination were only found in the untreated soils. Among the tested treatments, rice husk and its combinations, particularly with cocoa pod ash, showed significant efficacy in reducing metal concentrations in the soils. The potential non-carcinogenic human health risks associated with the consumption of rice grown in biochar-treated soils were lower for all the metals compared to the control samples. Future research should focus on long-term field studies to validate these findings and explore the underlying mechanisms governing metal immobilization in paddy fields. Full article

Pyrite-bearing waste rock from legacy gold mines is a source of elevated arsenic, sulfate, and iron in the surrounding environments due to leaching. Waste rock in environments that experience cold winters is of particular concern because freeze–thaw cycling may mobilize elements through degradation and release of organic matter and accelerated mineral weathering. In boreal zones, wetlands are common recipients of mine-waste run-off, and microbial processes in wetland soil may promote the retention of mobilized elements, such as arsenic. We investigated the impacts of freeze–thaw cycling and ethanol amendment on soil from an arsenic-contaminated wetland in anoxic microcosms. Ethanol-amended microcosms exhibited enhanced microbial sulfate reduction, leading to sulfide precipitation and increased retention of arsenic in the soil. Sequential extraction studies indicated a shift of arsenic into more stable sulfide-bound fractions. The addition of ethanol significantly increased the growth of Geobacter spp. and other select sulfate-reducing bacteria. Freeze–thaw cycling increased dissolved arsenic over short time periods only and had no detectable impacts on microbial activity. These findings suggest that the use of ethanol as an amendment to wetlands during spring thaw may enhance arsenic sequestration in mining-impacted soils and may provide a viable remediation strategy for cold-climate environments, where seasonal freeze–thaw cycling could otherwise contribute to arsenic mobilization. Full article

Soil salinity affects crop growth and production, especially in arid and semi-arid regions of the world. The interactions between salt ions and soil particles vary depending on soil texture, mineralogy, and ion composition. The relationship between soil ions and particles and the effects of this interaction on crop plants remains underexplored. This study evaluated the plant water relations, growth, and yield of cowpea (Vigna unguiculata) as affected by the salinity of the irrigation water in two different soil types with varying weathering levels and contrasting mineralogies. The treatments consisted of six salinity levels based on the electrical conductivity (EC) of the irrigation water (0, 1.5, 3, 4, 5, 6.0, or 9 dS m⁻¹) and were tested in Ultisol (well-weathered soil) and Alfisol (less-weathered soil). The experiment was conducted over 80 days with 4 repetitions. The results showed that the plant salinity tolerance, growth, and yield in response to salinity varied depending on the soil type. Irrigation with saline water exceeding an EC of 3 dS m⁻¹ completely halted cowpea production in Ultisol, whereas in Alfisol, production ceased at an EC above 6 dS m⁻¹. Although it accumulates more salts under saline irrigation, Alfisol promotes better cowpea growth and yield than Ultisol. Full article

Currently, increasing anthropogenic pressure and overexploitation expose soils to various forms of degradation, including contamination, erosion, and sealing. Soil contamination, primarily caused by industrial processes, agricultural practices (such as the use of pesticides and fertilizers), and improper waste disposal, poses significant risks to human health, biodiversity, and the environment. Common contaminants include heavy metals, mineral oils, petroleum-based hydrocarbons, aromatic hydrocarbons, chlorinated hydrocarbons, and polycyclic aromatic hydrocarbons. Remediation methods for contaminated soils include physical, physicochemical, chemical or biological approaches. This review aims to specify these methods while comparing their effectiveness and applicability in different contamination scenarios. Biochemical methods, particularly phytoremediation, are emphasized for their sustainability, effectiveness, and suitability in arid and semiarid regions. These methods preserve soil quality and promote resource efficiency, waste reduction, and bioenergy production, aligning with sustainability principles and contributing to a circular economy. The integrated phytoremediation–bioenergy approaches reviewed provide sustainable and cost-efficient strategies for environmental decontamination and green development. Special attention is given to the use of lignin in bioremediation. This work contributes to the existing knowledge by outlining priorities for the selection of the most appropriate remediation techniques under diverse environmental conditions, providing a comprehensive overview for future developments. Full article

Microplastics (MP) are widespread pollutants that pose a risk to soil ecosystems globally, especially in agricultural soils. This study introduces a method to extract and identify MP in Brazilian tropical soils, targeting debris of low-density polyethylene (LDPE) and polyvinyl chloride (PVC) polymers, commonly present in agricultural settings. The method involves removing organic matter and extracting MP using density separation with three flotation solutions: distilled water, NaCl, and ZnCl₂. Extracted MP are then analyzed through optical microscopy and Fourier transform infrared spectroscopy. The organic matter removal efficiency ranged from 46% to 89%, depending on the initial organic matter content in the soil. Recovery rates for LDPE ranged from 81.0% to 98.8%, while PVC samples showed a range of 59.7% to 75.2%. Finally, this methodology was tested in four agricultural raw soil samples (i.e., without any polymer enrichment) The values found in the soil samples were 2517.5, 2245.0, 3867.5, and 1725.0 items kg⁻¹, for ferralsol, nitisol, gleysol, and cambisol samples, respectively, with MP having diverse shapes including fragments, granules, films, and fibers. This approach lays the groundwork for future studies on MP behavior in Brazilian tropical agricultural soils. Full article

Water stress and nutrient stress are major limiting factors affecting crop productivity. Biochar-based organic fertilizers improve soil nutrient availability, water use efficiency (WUE), and crop yields under these adverse conditions. This study investigated the mechanistic effects of biochar–bokashi mixtures under a controlled glasshouse pot experiment on soil fertility, available nutrients, soil moisture, plant water use efficiency (PWUE), and wheat yield parameters under three moisture levels. Four treatments were included, (1) a control, (2) bokashi only, (3) 1% biochar + bokashi, and (4) 2% biochar + bokashi, under 30% (IR₃₀), 50% (IR₅₀), and 60% (IR₆₀) field capacity, totaling twelve treatments in a completely randomized design with three replications. The combined bokashi–biochar application significantly (p < 0.05) improved growth parameters and yields, including plant height, number of fertile tillers (NFT), number of spikes (NS), spike length (SL), 1000-grain weight, biological yield (BY), root biomass, and grain yield (GY), compared to the control and bokashi-only treatments. Bokashi with 1% biochar exhibited superior agronomic performance over the other treatments, including 2% biochar. Biochar addition enhanced soil moisture and PWUE across irrigation levels. Bokashi–biochar treatments under IR₃₀ outperformed the control and bokashi-only treatments under IR₆₀, highlighting biochar’s effectiveness in alleviating water stress and increasing yields. Moreover, co-application significantly increased soil pH while enhancing the organic carbon, total nitrogen, available phosphorous and exchangeable potassium nutrient levels, which positively correlated with yield. Bokashi–biochar mixtures have been proven to be an effective strategy to enhance soil fertility, increase soil moisture to alleviate water stress and support sustainable wheat production under water- and nutrient-limited conditions. Full article

Application of municipal reclaimed water to forests for water reclamation is a pragmatic approach that provides water and nutrients to soil and lowers the liability of reclaimed water disposal, yet little is known about the long-term impacts of reclaimed water amendment on forest soil chemical properties. We hypothesized that reclaimed water constituents will increase plant nutrient availability in soil with the magnitude of response depending on the facility establishment date. We collected samples from three mineral soil depths to 75 cm from treated and control plots at five water reuse facilities that represent a four-decade time series. Depth explained most of the observed variation. Several plant nutrients increased in soil at the different sites in response to reclaimed water treatments, including N, Ca, Fe, S, and B concentration as well as B content, while P was not significantly affected. Increases in cation concentrations positively correlated with pH and salinity. The treatment response was significantly greater at all facilities for total N, B and Na. However, the treatment response only occurred at long-established facilities for NO₃-N and Ca concentrations and for Fe and S content. The outcomes of this study are useful for guiding future management of soil at forest water reclamation facilities and for limiting the risk of downstream environmental impacts. Full article

Urban green spaces are important components of city spaces that are vulnerable to degradation in soil–water–climate processes. This vulnerability is exacerbated by current climate change and park usage density. This study examines the dynamics of soil water repellency in the topsoils of selected urban parks in Berlin, aiming to assess the relationships between weather conditions, soil water content, and soil water repellency. This study is based on monthly sampled soils from spots originating from three selected parks—Fischtal Park, Stadtpark Steglitz, and Rudolph-Wilde Park—between September 2022 and October 2023; two of the parks are exclusively rainwater fed, and one is irrigated during summer months. For each sample soil, water repellency persistence and severity were analyzed. Time series analysis was conducted including soil water content. In addition, the total organic carbon content (TOC) and sample texture were analyzed. The results show that the rainfall amount, number of dry days, and maximum temperature during different time intervals prior to the sampling date predominantly control the variation in the soil water repellency via the soil water content. Soil water repellency variations observed appear more event-related than monthly or seasonal, as rainfall is evenly distributed through the years without a distinct dry or wet season in Berlin. The non-repellency of the soil samples was usually observed when the associated water content was increased, which is linked to high cumulative rainfall and short dry periods. Low rainfall amounts and long dry periods in summer result in the re-establishment of the soil water repellency, possibly affecting increased runoff generation and soil erosion risk. Spatially, the repellency properties were observed at locations under healthy vegetation cover, while soils located on the upper slope locations and on the pathways lacked repellency characteristics. Full article

Heavy metal(loid) (HM) contamination in soils from smelting activities poses significant environmental and public health risks, as well as disruptions in microbial community dynamics and HM resistance gene profiles. This study investigates the microbial diversity, resistome, and physicochemical properties of soils from the abandoned Avalos smelter in Chihuahua, Mexico. Through soil analyses, we identified elevated concentrations of certain HMs, which pose serious environmental and health hazards. The metagenomic analysis of the microbial community, composed of bacteria, archaea, and fungi, was dominated by genera such as Streptomyces, Bradyrhizobium, Halobaculum, Nitrosocosmicus, Fusarium, and Aspergillus in rhizospheric soil. Furthermore, a diverse array of metal resistance genes (MRGs) were detected, associated with copper, arsenic, iron, lead, cadmium, zinc, and other HMs. Additionally, metagenome-assembled genomes (MAGs) revealed the presence of functional genes linked to HM resistance, providing deeper insights into the ecological roles and metabolic capabilities of microbial taxa. These findings highlight the significant impact of smelting-derived contamination on microbial diversity and functional potential, offering valuable insights for the development of bioremediation strategies in HM-contaminated environments. Full article

Phytoremediation has been reported as a more energy-efficient, and therefore cost-effective, method of environmental restoration compared to traditional remediation methods for heavy-metal-contaminated soils. Biochar has been shown to have variable effects on remediation potential in heavy-metal-contaminated soils. The objective of this study was to evaluate the effects of soil contamination level (i.e., low, medium, and high), industrial hemp (Cannabis sativa L.) cultivar (i.e., ‘Carmagnola’ and ‘Jinma’), biochar rate (i.e., 0, 2, 5, and 10% by volume), and their interactions on root tissue Cd, Pb, and Zn concentrations and uptakes; whole-plant Cd, Pb, and Zn uptakes; and translocation factors after 90 days of hemp growth in contaminated soil from the Tar Creek Superfund Site near Picher, Oklahoma. Hemp removal of Cd, Pb, and Zn differed between soil contamination levels (p < 0.01), but was unaffected (p > 0.05) by the hemp cultivar or biochar rate, except for total Zn uptake. Total Zn uptake was affected (p = 0.02) by the biochar rate in the medium- and high-contaminated soils, where total plant Zn uptake in the high-contaminated soil was numerically the largest with 10% biochar (0.28 mg cm⁻²) and in the medium-contaminated soil was numerically the largest with 2% biochar (0.07 mg cm⁻²), but was unaffected (p > 0.05) by the biochar rate in the low-contaminated soil. The translocation factor for Zn uptake in the low and medium soils was >1, indicating industrial hemp as a potential Zn hyper-accumulator up to a threshold soil contamination level. Results demonstrate that biochar amendment has the potential to enhance hemp’s remediation capability of heavy-metal-contaminated soils. Full article

Salinity and water scarcity are among the major environmental challenges requiring the use of non-conventional water sources and the adoption of salt-tolerant crops. We assessed the impact of irrigation with different concentrations of NaCl: 50 mM and 150 mM on the growth parameters and yield of triticale, soil salinity, distribution of active root density, and concentrations of Na⁺ and NO₃⁻ ions at harvest compared to freshwater under zero leaching conditions. Irrigation was applied on a daily basis based on weight measurements of micro-lysimeter pots. Growth parameters, including plant height, LAI, number of leaves, number of tillers, and soil salinity, were observed across the growing season. Spatial distributions of soil salinity, normalized root length density (NRLD), concentrations of Na⁺ and NO₃⁻ in soil profile were measured in two dimensions. The results indicate that irrigating with 150 mM of NaCl H₂O significantly affected the crop growth, causing salts, particularly Na⁺, to reside in the topsoil, reducing NRLD with soil depth, crop water demand, and NO₃⁻ uptake. The application of 150 mM and 50 mM of NaCl H₂O reduced crop water use by 4 and 2.6 times as well as grain yield by 97% and 42%, respectively, compared to freshwater. This shows that irrigation with concentration equal to or higher than 150 mM NaCl will result in very low production. To achieve higher yield and crop water productivity, irrigation with NaCl concentration of 50 mM or less is recommended to grow triticale in marginal regions with limited freshwater resources. Full article

The concept of metal bioavailability in soils is increasingly becoming the key to addressing potential risks. Yet, space–time variations of heavy metal concentrations in salt-affected soils is still vague. The current work, therefore, is the first attempt to address spatial and seasonal analyses of heavy metals in a Mediterranean arid agroecosystem. This study was conducted in a coastal area in northeastern Egypt as an example. The DTPA-extractable concentrations of Cr, Co, Cu, Fe, Pb, Mn, Ni, and Zn in addition to the main properties of 70 georeferenced soil samples (0–30 cm) were determined during the wet (March) and dry (September) seasons. The results revealed that except for Cu, the concentrations of all the determined metals stood below the safe limits. On average, the concentrations of Cu were 4.1- and 5-fold the acceptable limit of 0.20 mg kg⁻¹, respectively. The statistical analysis indicated that seasonal variations greatly affect the concentrations of Mn, Ni, and Zn. Compared with the wet season, significant increases of 1.25, 1.50, and 1.28-fold in the concentrations of these metals occurred during the dry season, respectively. The principal component analysis affirmed that the presence of Cr, Co, Fe, and Ni was closely related to geogenic factors; meanwhile, agronomic practices were likely the main inputs of Cu, Pb, and Zn. The geostatistical analysis illustrated that the geographic variability of Cr, Fe, Mn, and Zn was due to interactions of natural and stochastic processes. Farming practices controlled the spatial variability of Ni, Pb (in the wet period), and Co (in the dry period). The effect of natural processes during the wet period was evident for Cu, which showed strong spatial variability. The kriged maps showed that the concentrations of Co, Fe, and Ni tended to increase seaward and were found to be affected by pH, salt ions, and exchangeable Na⁺. Moreover, both silt and organic matter content had profound impacts on the spatial distribution of Cr, while the distributions of Cu, Pb, and Zn were linked to that of CaCO₃ content. The suggested mechanisms governing metal bioavailability were sorption and complexation with ligands (for Co, Fe, and Ni), redox potential (for Cr), dissolution–precipitation (for Mn), and ion exchange (for Cu, Pb, and Zn). The results of this study affirm that drying–wetting cycles and spatial distribution affect the bioavailability of heavy metals in coastal salt-affected soils of arid regions. These findings imply that seasonality (wet and dry) and spatiality should be considered for monitoring and rehabilitation of degraded soils under similar ecological conditions. Full article

Carbon dioxide (CO₂) efflux from soil (or soil respiration, SR) is one of the most important yet variable characteristics of soil. When evaluating large areas, CO₂ efflux modeling serves as a viable alternative to direct measurements. This research aims to identify site-specific differences and their effects on empirical CO₂ efflux modeling. The experimental data from 25 years of field observations were utilized to identify the optimal site- and weather-specific models, parameterized for normal, wet, and dry years, for the forest and grassland ecosystems located on similar Entic Podzols (Arenic) in the same bioclimatic coniferous–deciduous forest zone. The following parameters were considered in the examined models: mean monthly soil or air temperatures (Tsoil and Tair), amount of precipitation during the current (P) and the previous (PP) months, and the storage of soil organic carbon (SOC) in the top 20 cm of soil. The weighted non-linear regression method was employed to estimate the model parameters for the normal, wet, and dry years. To increase the magnitude of the model resolutions, we controlled the slope and intercept of the linear model comparison between the measured and modeled data through the change in R₀—CO₂ efflux at Tsoil = 0 °C. The mean bias error (MBE), root-mean-square error (RMSE), and determination coefficient (R²) were employed to assess the quality of the model’s performance. The measured Tsoil, Tair, and P, as well as the litter (for forest) or sod (for grassland) horizon (modeled by the Soil SCLmate Statistical Simulator (SCLISS)), and soil temperatures (Tlit_m, Tsoil_m) and moistures (Mlit_m, Msoil_m), were used for SR simulation. For the CO₂ efflux in the forest ecosystem with the lower SOC availability for mineralization, the direct Tsoil and Tair measurements in combination with SOC storage provided better parameterization for the empirical TPPC model. For the CO₂ efflux in the grassland ecosystem with the high SOC availability for mineralization, the temperature became the governing factor, and the TPPrh model provided better performance over all the considered models. The model’s performance was the best for the wet years, and the worst for the dry years for both ecosystems. For forest ecosystems, the model performance for average precipitation years was equivalent to that in wet years. For grassland ecosystems, however, the model performance was equivalent to that in dry years due to differing exposure and hydrothermal regimes. The wet-year R₀ obtained for both forest and grassland ecosystems differed from the normal- and dry-year values. The measured SR values relevant for the R₀ estimations distribute along the precipitation range for the forest and along the temperature range for the grassland. The SCLISS-modeled Tlit_m and Mlit_m provide good alternatives to direct atmospheric measurements, and can be used as initial temperature and moisture data for CO₂ efflux modeling when direct soil and moisture observations are not available on site. Full article

The alpine peatlands in western Sichuan Province are currently experiencing aridification. To understand the effects of aridification on the characteristics of organic carbon release from alpine soils, the soil in the northwest Sichuan Plateau was investigated. Soil columns were incubated under different moisture conditions in situ and in the laboratory, and ultraviolet-visible absorption spectroscopy and three-dimensional fluorescence spectroscopy were used to assess the soil dissolved organic carbon (DOC) levels. The results revealed that (1) the cumulative release of DOC from alpine soil in the northwest Sichuan Plateau decreased with decreasing moisture content. The cumulative release of soil DOC in the laboratory (0–5 cm soil reached 1.93 ± 0.43 g/kg) was greater than that from soil incubated in situ (0–5 cm soil reached 1.40 ± 0.13 g/kg); (2) the cumulative release of DOC in 0–5 cm soil exhibited the greatest response to changes in water content, and the cumulative release of DOC from the 0–5 cm soil layer (1.40 ± 0.13 g/kg) was greater than that from the 5–15 cm soil layer (1.25 ± 0.03 g/kg); and (3) UV-visible absorption spectra and 3D fluorescence spectral characteristics indicated that aridification increases the content of chromophoric dissolved organic matter (CDOM) components with strong hydrophobicity, especially tyrosine components (surface soil increased 39.59~63.31%), in alpine soil DOC. This increase in hydrophobic CDOM components enhances the aromaticity and degree of humification of DOC. Our results revealed that drought inhibits the release of soil DOC, which is unfavorable for the sequestration of organic carbon in alpine soils, potentially resulting in the loss of soil carbon pools and further degradation of alpine ecosystem functions. Full article

Physical soil crust (PSC) is a dense structural layer formed on the surface of bare or very low-cover land due to raindrop splashes or runoff. The formation of crust changes the properties of the soil and strongly affects water infiltration and runoff and sediment production processes on slopes. The irrational use of soil and water resources and frequent human production activity under the influence of urbanization increase the possibility of inducing erosion. Studying the formation and structural characteristics of PSC to predict terrestrial hydrological processes and improve models for predicting erosion is very important. Many studies of PSC have been carried out in China and abroad, but they are mainly unilateral discussions of the basic properties and characteristics of crust and its effects on runoff and sediment yield on slopes. Studies systematically analyzing and synthesizing the progress of crust research, however, are lacking. By reading the literature and analyzing the developmental history of PSC, we provide a comprehensive review of the following: (1) the meaning, main types, and classification of PSC, (2) the mechanism of formation and the characteristics and dynamic development of crust, (3) the factors affecting the formation of crust, including natural and anthropogenic factors and comprehensive effects, and (4) the development and formation of crust in the soil environment, i.e., hydrological processes and erosion. We also summarize the potential directions for future research on PSC: (1) studying the dynamics of soil structure during the development of crust, (2) developing an objective and standardized quantitative method for studying crust formation, (3) using models of erosion influenced by crust development, (4) improving the scale of the degree of crust development and structural characteristics, and (5) rationalizing the management of crust to optimize land structure and increase crop yield. Full article

Phosphate sorption data are often analyzed by least-squares fitting to the two- or three-parameter Freundlich model. The standard methods are flawed by (1) treating the measured pseudo-equilibrium concentration C as the independent (hence error-free) variable and (2) neglecting the weighting that should accommodate the varying precision of the data. Here, we address both of these shortfalls and use a global fit model to achieve optimal precision in fitting data for five acidic Australian soil types. Each individual dataset consists of measured C values for up to nine phosphate spiking levels C₀. For each soil type, there are three–five such datasets from varying levels of phosphate fertilizer pre-exposure (P_f) two years earlier. These datasets are fitted simultaneously by expressing the Freundlich capacity factor a and exponent b as theoretically predicted functions of the assay amounts of Fe, Al, and P measured for each P_f. The analysis allows for uncertainty in both C and C₀, with inverse-variance weighting from variance functions estimated by residuals analysis. The estimated presorbed P amounts Q depend linearly on P_f, with positive intercepts at P_f = 0, indicating residual phosphate in the soils prior to the laboratory phosphate treatments. The key takeaway points are as follows: (1) global analysis yields optimal estimates and improved precision for the fit parameters; (2) allowing for uncertainty in C is essential when the data include C values near 0; (3) varying data precision requires weighting to yield optimal parameter estimates and reliable uncertainties. Full article

(1) Background: This study aimed to evaluate the effects of organic fertilizer dose on soil nutrients, wolfberry fruit nutrient compositions, and fruit yields. (2) Methods: We conducted a two-year field trial in two typical fields with different fertility levels in the Qaidam area. Six treatments were applied to each field, including CK, M2 M4, M6, M8, and M10 (representing 0, 2, 4, 6, 8, and 10 kg organic fertilizer/plant, respectively) in the high-fertility field and CK, M3, M6, M9, M12, and M15 (representing 0, 3, 6, 9, 12, and 15 kg organic fertilizer/plant, respectively) in the low-fertility field. An ANOVA was used to determine the significant difference between treatments, and the LSD method was used for multiple comparisons of analysis of variance. (3) Results: In the high-fertility field, the application of organic fertilizer significantly affected the total nitrogen (N) content, mineral N storage, and soil organic matter content. The application of too much organic fertilizer significantly increased the soil’s EC value. In the low-fertility field, the effect of organic fertilizer application on soil nutrient enhancement differed significantly among soil layers but significantly increased the contents of total phenols, flavonoids, and amino acids in wolfberry fruit, and there was a significant trend of increasing wolfberry yield with increasing organic fertilizer application. (4) Conclusions: In the Qaidam area of the Tibetan Plateau, it is recommended to apply 2–4 kg commercial organic fertilizer/plant in the high-fertility wolfberry orchards while 9–12 kg in the low-fertility wolfberry orchards is recommended. Full article

The relationships between soil aggregates, aggregate-associated carbon (C), and soil compaction indices in pomegranate orchards of varying ages (0–30 years) in Assiut, Egypt, were investigated. Soil bulk density (Bd) and organic carbon (OC) content increased with orchard age in both the surface (0.00–0.20 m) and subsurface (0.20–0.40 m) layers 0.20–0.40 m). The percentage of macroaggregates (R_0.25) and their OC content in the aggregate fraction > 0.250 mm increased as the pomegranate orchard ages increased in the surface layer (0.00–0.20 m). Older pomegranate orchards show improved soil structure, indicated by higher mean weight diameter (MWD) and geometric mean diameter (GMD), alongside reduced fractal dimension (D) and erodibility (K). As orchard ages increased, maximum bulk density (B_Max) decreased due to an increase in OC, while the degree of compactness (DC) increased, reaching a maximum at both soil layers for the 30 Y orchards. Soil organic carbon and aggregate-associated C significantly influenced B_Max, which led to reducing the soil compaction risk. Multivariate analyses identified the >2 mm aggregate fraction as the most critical factor influencing the DC, soil compaction, and K indices in pomegranate orchards. The OC content in the >2 mm aggregates negatively correlated with B_Max, DC, and K but was positively associated with MWD and GMD. Moreover, DC and Bd decreased with higher proportions of >2 mm aggregates, whereas DC increased with a higher fraction of 2–0.250 mm aggregation. These findings highlight the role of aggregate size fractions and their associated C in enhancing soil structure stability, mitigating compaction, and reducing erosion risks in pomegranate orchards. Full article