Environmental and Earth Sciences

Abstract: The formation and development of gullies is a pervasive driver of hillslope degradation, yet forecasting where and at what elevation gullies begin remains challenging. This study proposes a morphometric–energetic framework to anticipate gully initiation zones in catchments developed on low-permeability lithologies and limited tectonic control, across contrasting climatic and geomorphic settings. Using GIS analyses and morphometric parameters, some of these derived from hypsometric curves, our objective is to link basin-scale morphology and energy distribution to the propensity for linear incision, thereby defining an altitudinal belt and stream network positions most susceptible to gully initiation. The framework is designed to be quantitative, transferable among landscapes, and parsimonious in data requirements. By prioritizing diagnostics that can be computed from standard topographic datasets, the approach aims to support land-use planning and sediment-risk mitigation, offering a practical pathway for early identification and management of areas vulnerable to gullying.

Abstract: Water erosion is a critical degradation process that reduces fertility and agricultural sustainability, especially in semi-arid regions. The Universal Soil Loss Equation (USLE) allows for the quantification of this phenomenon using factors such as rainfall erosivity (R) and topography (length-slope, LS). In this study, both factors were estimated and analyzed in the Cañitas sub-basin, located in the semi-desert area of the state of Zaca-tecas, Mexico, characterized by irregular precipitation and limited data availability. The objective of this study is to estimate and analyze the R factor and LS factor to evaluate their influence on soil water erosion processes. Records from five meteorological stations (1986–2022) were used, along with the Modified Fournier Index (MFI) and Geographic Information Systems (GIS) tools, generating spatial maps of rainfall erosivity and to-pography. An average R factor of 240.608 MJ∙mm/ha∙h∙year was estimated, consistent with the values obtained using the MFI. The LS factor shows that the northwestern area of the study zone has the most extensive and steepest slopes (up to 20.78). This study provides useful information for understanding soil erosion processes, which can serve as a reference for planning conservation actions and managing watersheds in semi-arid areas with high climatic variability.

Abstract: The long-term relationship between climate change, vegetation change and soil development, is a highly complex process. Findings of multiproxy (sedimentological, MS, geochemical (AAS, XRD), micromorphological, anthracological, phytolith and malacological) studies from a loess/paleosol sequence in northeastern Hungary highlighted the transformation of a reddish-brown fossil soil layer (cambisol) to a podzolic soil with signs of iterative wildfires during the terminal part of MIS3. According to our findings, a Scots pine (Pinus sylvestris) dominated open parkland emerged on the northern slopes during the second phase of MIS3 hosted by a special reddish-brown soil. Then the last phase of MIS3 was marked by the development of spruce (Picea) dominated open parkland. Results further suggest that vegetation change passed a critical threshold leading to an unusually rapid expansion of spruce (within ca. 100 yr). This rapid expansion of spruce, changing the geochemistry of the litter to a more acidic state likely caused the initiation of podzolization and the transformation of the original soil. The opening of MIS2 marked not only intensive dust accumulation but a steady decline of arboreal elements as well leading to the emergence of a cold tundra on top of the podosol with charcoal remains.

Abstract: The dynamics of organic matter, nitrogen status, and biological activity in soils in southern Kazakhstan under various land-use systems were studied. A key feature of the research is the comprehensive comparison of humus status, nitrogen state, and biological activity of virgin and arable dark Kastanozem, Gleyic Calcisol, and Haplic Calcisol, as well as identification of their correlation with signs of functional depletion of organic component. The assessment was conducted using set of agrochemical and biological methods, including determination of humus content, available nitrogen forms, C/N ratio, microbial population, and enzymatic activity. It has been determined that the highest humus content is typical for dark chestnut soils under natural vegetation, while plowing of them is accompanied by decrease in humus content due to increased mineralization processes. Gleyic Calcisol - are characterized by more stable humus state, in some cases with increased organic matter content under arable conditions. Minimum humus values were found in Haplic Calcisol, due to arid conditions and limited supply of organic residues. It is shown that arable soils are characterized by a decreased C/N ratio and increased rates of organic matter transformation. Soil biological activity is linked to mineralization processes, as confirmed by microbial population dynamics and enzymatic activity. Additional assessment using digital tools reveals signs of functional depletion of organic component in agrocenoses. The obtained results indicate the need to consider biological indicators when assessing soil conditions and developing sustainable land management systems in arid climates.

Abstract: This study characterized standard biochars produced at 300, 400, and 500 °C alongside a locally made biochar (LBC, drum kiln method with newly devised method of Bababe) to assess fertilizer value and toxicity against IBI thresholds. Pyrolysis temperature strongly influenced properties: electrical conductivity and salt content increased with tempera-ture (BC300 and BC500 highest; LBC lowest). All standard biochars were highly alkaline (pH 10.26–10.57), while LBC was near-neutral (7.84). Maximum carbon content occurred at 300–400 °C (56.8–56.9 %). At 10 kg ha⁻¹, standard biochars supplied 308–331 kg ha⁻¹ K, with BC400 providing the highest Ca and Mg. LBC had the highest volatile micronu-trients (B, Cu, Fe, Mn), which decreased with rising temperature. It can be particularly well suited to fertilizer coating or blending systems, especially for salt-sensitive soils where application rates are kept low (< 10 t ha⁻¹), thereby limiting agronomic risks such as Mo contaminant loading. Nevertheless, molybdenum levels in all biochars were 5–8 times above IBI safe limits (5–75 mg kg⁻¹), posing toxicity risk at 10 t ha⁻¹ application. Cd was undetectable, reduced Pb by 90 % at 400–500 °C, and kept Ni and Pd within limits. SEM revealed BC400 had optimal honeycomb porosity and homogeneous mineral dis-tribution. BC400 is most suitable for agricultural fertilizer value, BC500 for carbon se-questration, BC300 for potassium supply, and LBC as a low-cost, low-salinity material. However, excessive molybdenum across all biochars relates feedstock composition as the paramount safety factor. The weakness and limitation of this studies lies in the resource constraints from use of one feedstock, absence of direct measurement of surface area and phosphorus, and absence of measurement of biochar stability.

Abstract: Soil health and irrigation water quality are fundamental to sustainable agricultural productivity, particularly in semi-arid environments. This study evaluated the influence of irrigation water quality on soil physical and chemical properties within the Kagitumba Irrigation Scheme in Eastern Rwanda. An observational analytical design integrated field sampling, laboratory analysis, and statistical evaluation. Soil samples (n = 20) were col-lected at depths of 0–30 cm and 30–60 cm, alongside irrigation water samples (n = 5) from intake and distribution points. Soil parameters analyzed included texture, bulk density, pH, electrical conductivity (EC), organic matter, and nutrient content, while water quality assessment focused on pH, EC, turbidity, dissolved oxygen (DO), and oxidation–reduction potential (ORP). Data were subjected to descriptive statistics, Pearson correlation, and ANOVA at a 95% confidence level. Findings revealed predominantly sandy loam soils with low bulk density, moderate water-holding capacity, and near-neutral pH. Soil salin-ity remained low, indicating limited risk of degradation. Irrigation water was generally suitable for agricultural use in terms of pH and salinity; however, elevated turbidity showed a strong negative correlation with infiltration rate (r = −0.73). Additionally, low soil nitrogen levels were significantly associated with water quality, suggesting nutrient leaching. These results underscore the critical role of irrigation water quality in shaping soil health and emphasize the need for improved water filtration and integrated nutrient management to enhance long-term sustainability.

Abstract:

To investigate the effects of long-term biochar application on different forms of potassium (K) content in maize rhizosphere soil and maize growth, two biochar application rates (B0: 0 t ha⁻¹ yr⁻¹, B1: 2.625 t ha⁻¹ yr⁻¹) and two K fertilizer application rates (K0: 0 kg ha⁻¹ yr⁻¹, K1: 60 kg ha⁻¹ yr⁻¹) to create four treatments (B0K0, B0K1, B1K0, B1K1). In this long-term field trial, we investigated various forms of K in the maize rhizosphere soil, together with soil physicochemical properties and maize growth indicators. Results indicate that biochar significantly increased microbial biomass carbon (MBC), cation exchange capacity (CEC), and electrical conductivity (EC) in the rhizosphere soil, while also improving rhizosphere soil pH. Compared with the treatment without biochar, biochar application significantly increased the content of water-soluble potassium (WSK), exchangeable potassium (EK), and non-exchangeable potassium (NEK) in the rhizosphere soil by 18.57% (2021) and 11.18% (2022), 13.49% (2021), and 11.43% (2022), 14.65% (2021), and 17.06% (2022), respectively. Maize roots were more developed, and plant height, stem diameter, and leaf area index were significantly increased. With above-ground dry weight and K uptake significantly increasing by 13.87% (2021) and 12.04% (2022), and 41.84% (2021) and 43.87% (2022), respectively. Compared with B0K0, the B1K1 treatment—which combined biochar with K fertilizer—exhibited the highest K content in all forms within the rhizosphere soil, along with the greatest maize aboveground dry weight and K uptake. This study demonstrates biochar’s potential in meeting crop root K demands, laying the foundation for its application in enhancing soil K fertility.

Abstract: The aim of this study was to assess potential uplift in soil organic carbon (SOC) levels within different types of agricultural land. A total of 1,032 soil samples were collected from 43 fields across six farms during the same year. Fields were used for arable, temporary grass and permanent grass production. The study compared SOC levels (in g/kg, ratio to clay and ratio to nitrogen) between the field boundary and within field areas. The field boundary was classed as either open (boundary with fence and/or wall) or covered (with hedgerow and/or trees). From the fields sampled, 69% of within field samples and 88% of boundary samples were categorized as having ‘very good’ levels of SOC. On average, the SOC in g/kg and ratio to clay were higher for permanent grass and boundary field areas compared to temporary and within field areas, with no difference between open or covered boundary areas. Benchmarking fields against the field boundary area or based on SOC to clay ratio can be used by land managers to identify fields for potential SOC uplift.

Abstract: This study investigates the influence of various land use systems (LUSs) on soil physico-chemical properties, nutrient dynamics, and soil organic carbon (SOC) stocks in the Central Plain Zone of Uttar Pradesh, India. Soil samples were collected from six distinct LUSs, i.e., fallow, crop-based, horticulture-based, forest-based, vegetable-based, and barren land, and analyzed across three depth intervals (0–15 cm, 15–30 cm, and 30–60 cm). Soil pH increased steadily with depth, ranging from 7.43 to 8.58 at the surface layer to 7.55 to 10.32 in deeper layers. Horticulture-based LUSs recorded the lowest pH, while barren lands had the highest. Electrical conductivity (EC) also rose with depth, ranging from 0.12 to 3.63 Mgm-1, at the surface to subsoil layers, all below critical salinity thresholds. Soil organic carbon (SOC) content decreased with increasing soil depth across all land-use systems. Among the studied systems, horticulture-based land use recorded the highest SOC content (0.77%), whereas barren land showed the lowest SOC content (0.21%).”Due to greater organic matter inputs and reduced disturbances, horticultural systems also exhibited significantly higher levels of macronutrients (N: 17.98 kgha⁻¹, P: 330.45 kgha-1, K: 374.81 kgha⁻¹, S: 84.33 mgha⁻¹) and micronutrients (Fe: 164.12 mgha⁻¹, Mn: 60.89 mgha⁻¹, Cu: 2.85 mgha⁻¹, Zn: 1.80 mgha⁻¹). Bulk density increased slightly with depth (1.46–1.63 Mgm-³), while soil moisture content remained relatively stable (43.43% to 42.31%) with moderate variability (CV: 24–27%). The mean total SOC stock was 10.77 t C ha⁻¹, ranging from 5.44 to 14.46 tCha⁻¹. Microbial properties also varied among land uses: dehydrogenase activity (DEA), an indicator of microbial functionality, peaked in vegetable-based systems (30.54 µgTPF g⁻¹), whereas microbial biomass carbon (MBC) was highest in forest-based systems (184.83 µg g⁻¹). Correlation and regression analyses revealed a strong positive relationship between SOC and nutrient availability, with the highest correlation observed for Zn (R² = 0.99), followed by N (R² = 0.83) and K (R² = 0.75). Overall, barren lands showed the poorest soil quality indicators, while horticulture-based systems consistently demonstrated superior soil fertility and carbon sequestration potential. These findings emphasize the critical role of land use management in regulating soil fertility, SOC dynamics, and the long-term sustainability of agro-ecosystems in the region.

Abstract: Accurate soil organic carbon (SOC) estimation is vital for analyzing the global carbon cycle. Currently the bare soil compositing approaches for multi-temporal images are widely used, however the optimized length of compositing period and influence of different indicators on SOC estimaiton for both bare soil and crop cover conditions is unknown. In this study, a time series of Landsat 8 Operational Land Imager multitemporal images was obtained from 2013–2018, with the aim of generating datasets that represent SOC changes across single dates, single years, and multiple years. Soil properties (S), terrain attributes (T), vegetation conditions (V), and farm management practices (F) were employed to predict the spatial distribution of SOC by using the random forest model for both bare soil and crop cover conditions. The results revealed that multi-temporal images from three years and longer produced accurate SOC predictions, with coefficients of determination (R2) and root mean squared errors (RMSEs) of 0.94-0.95 and 1.75-1.77 g kg-1, respectively. The four types of indicator combinations (S+T+V+F) achieved the best model performance, followed by the T+V+F, S+V+F, and V+F combinations for the bare soil condition in 2016-2018 period. This study provides a possible way for obtaining farmland SOC sequestration under crop cover conditions.

Abstract: This study evaluates the impact of water washing on the suitability of biochars from tomato (TB) greens and vineyard (VB) prunings as peat replacement in gardening substrates. Therefore, a 31-day pot-experiment was performed to assess seed germination and growth of tomato plants on biochar/peat substrates (60:40 v/v) using fresh (TB 0 and VB 0) and washed biochar (TB 1, TB 2 and VB 1, VB 2). For both biochars, washing resulted in a notable decline of the pH = 10 to values around 9. The electrical conductivity (EC) of TB 0 was with 9147± 96 µS cm-1 higher than that of VB 0 (1539 ± 33 µS cm-1), indicating a high salt content of the first. Washing reduced those values to 272 ± 21 µS cm-1 and 75.4 ± 4 µS cm-1, respectively. Performance of tomato plants, grown on the substrate mixture increased with salt removal. Statistical analysis revealed a stronger impact of EC than of pH on plant performance. High salt concentrations affected in particular the germination most likely through osmotic stress. Biomass production was reduced by high Ca and K concentrations and showed no significant correlation with EC, Na or Cl contents. This work demonstrates that biochars with high pH and salt content previously considered unusable in plant substrates can be transformed into a suitable peat substitute by simply washing with water. This helps to reduce wasting the ecological important peat while promoting circular economy by recycling green waste-derived biochar as sustainable gardening substrate.

Abstract: Soil health is fundamental for food security, climate regulation, and ecosystem resili-ence, yet global research and development efforts remain uneven and fragmented. To date, no study has comprehensively integrated development investments, scientific output, and technological innovation into a unified assessment of global soil health dynamics. Addressing this gap, this study provides a multi-scalar analysis of soil health research from 1990 to 2025 by combining international project data and scien-tific publications activity across six key thematic domains. This time frame captures the transition from conventional soil research to modern molecular and next-generation sequencing (NGS)-based approaches. Using a PRISMA-based methodology, we analyzed 1,402 World Bank projects, 190 mi-crobiome-related projects from CORDIS, and bibliometric data from Scopus, Web of Science, and PubMed. Results show sustained global growth in soil research, with nu-trient management and soil degradation remaining dominant, while soil microbiome research and carbon sequestration have expanded rapidly, particularly after 2015. Despite this growth, significant regional disparities persist, with research concentrated in Asia, Europe, and North America. To address the lack of a coherent microbiome-based soil health assessment system, we propose a structured microbial indicator framework based on twelve functional mi-crobial groups, evaluated through culturable abundance, functional gene abundance, and relative abundance. Additionally, we introduce a unified, database-driven micro-biome reference framework that interprets soils relative to known types and condi-tions. This approach enables more standardized, scalable, and context-aware diagnos-tics, supporting the identification of healthy, degraded, and transitional soil states.

Abstract: Agricultural waste accumulation offers potential for sustainable soil management in climate-resilient farming systems, but it also poses ongoing environmental challenges. This study examines the effects of vermicomposting, which turns agricultural waste into nutrient-rich organic fertilizer using Eisenia fetida, on crop productivity and soil fertility. Treatments were compared using a randomized experimental design that included many combinations of organic waste and a control. Crop growth and yield indices were examined in addition to soil physicochemical characteristics such as pH, organic carbon, total nitrogen, available phosphorus, and exchangeable potassium. Comparing vermicompost treatments to the control, the soil's nutritional content and structural quality significantly increased (p < 0.05). Mixed organic waste substrate trials outperformed single substrate trials, suggesting synergistic interactions that enhance microbial activity and nutrient cycling. Vermicompost application improved soil fertility indicators and increased crop growth and production. These findings show that vermicomposting is an effective waste valorization technique that supports the circular economy and sustainable agriculture. The study demonstrates how it can reduce environmental pollutants while enhancing soil health, agricultural yield, and fertilizer use efficiency. All factors considered, vermicomposting is a scalable and environmentally friendly way to increase the climate resilience of agricultural systems. More research should be done on long-term field performance, economic viability, and substrate combination optimization under different agroecological conditions.

Abstract: Organo-mineral complexes are intimately involved in protecting the stability of soil organic carbon (SOC), as they are influenced by environmental factors such as pH and redox conditions, as well as by the implementation of appropriate management practices. Nevertheless, the mechanism between environmental factors and the fractions of organo-mineral complexes, as well as their response to tillage practices, remain poorly understood. This study investigated the effects of rotary tillage (RT), plow tillage (PT), and no-tillage (NT) on organo-mineral complexes (water-dispersible G0 fraction, sodium-dispersible G1 fraction, grinding-dispersible G2 fraction) and their organic carbon (OC) in the black soil region of Northeast China in 2002 and 2022. Compared to 2002, the content of organo-mineral complexes and their OC in 2022 increased by 5.54% and 3.15%, respectively. Relative to PT, RT and NT increased the organo-mineral complex content by 0.39% and 8.40%, and increased the OC content by 9.41% and 20.56%, respectively. Between 2002 and 2022, tillage measures led to greater contributions of organo-mineral complexes to soil carbon sequestration. RT and PT primarily enhanced the contribution rate of the G0 fraction, whereas NT resulted in enhanced contribution rates for both the G0 and G1 fractions. This suggests NT is most conducive to transforming SOC into stable organo-mineral complexes. Redundancy and correlation analyses identified exchangeable Ca²⁺ in G1, pH, clay, TP, along with iron and aluminium oxides, as key environmental factors influencing the transformation pathways among the complexes fractions.

Abstract: Abstract Ganzhou City in Jiangxi Province is a core production area for navel oranges in China and represents a typical selenium-rich specialty agricultural region. However, the selenium-rich red soils in southern Jiangxi are strongly acidic with high iron-manganese oxide content, which strongly immobilizes soil selenium, severely restricting the development of the local selenium-enriched navel orange industry. Low-molecular-weight organic acids (LMWOAs), as root exudates and microbial metabolites, can activate soil selenium and synergistically promote plant growth. However, the regulatory mechanisms of LMWOAs on soil selenium speciation remain unclear. This study investigated how low-molecular-weight organic acids (LMWOAs) affect selenium transformation and availability in selenium-enriched red soils. Six LMWOAs at concentrations of 0.1–100 mmol kg⁻¹ were tested to examine their influence on selenium speciation and dissolved organic matter (DOM) composition. Soil selenium speciation and DOM fluorescent components were analyzed following LMWOAs application to assess the relationship between DOM changes and selenium transformation. LMWOAs significantly increased soluble selenium (SOL-Se) content, especially under 100 mmol kg⁻¹ citric acid (CA). Low-concentration treatments (≤10 mmol kg⁻¹) promoted the release of exchangeable (EXC-Se) and Fe-Mn oxide-bound (FMO-Se) selenium, while high-concentration treatments (100 mmol kg⁻¹) of CA, acetic acid (AA), and n-butyric acid (N-BA) inhibited their release. Only oxalic acid (OA) increased organically bound selenium (OM-Se). DOM components were negatively correlated with bioavailable selenium under CA treatment, but positively correlated with bound selenium under 10 mmol kg⁻¹ OA. LMWOAs notably alter soil selenium speciation. Short-term application enhances selenium bioavailability, promoting plant uptake. Prolonged use may increase humification, immobilizing selenium and reducing its availability. In contaminated areas, long-term LMWOAs application can mitigate selenium toxicity through immobilization. As natural rhizosphere exudates, LMWOAs are biodegradable and environmentally safe, posing minimal risk to soil ecosystems.

Abstract: In southern Brazil, a large proportion of farmers maintain their fields under fallow conditions during the transition period between summer and winter crops. During this interval, mechanical practices such as chiseling or the introduction of cover crop spe-cies may contribute to improving soil management and conservation in no-tillage sys-tems. Therefore, this study aimed to investigate the effects of mechanical soil chiseling and production system intensification on soil physical–hydric properties and soybean performance. The experiment was conducted in São José do Ouro, Rio Grande do Sul, Brazil, from September 2023 to April 2025. The experimental design consisted of three factors: soil chiseling (spring 2023, autumn 2024, and no-till), post-maize cover (millet and fallow conditions), and winter cover crops (black oat, white oat, vetch, and radish) grown either as monocultures or in mixtures. A randomized block design with split plots and three replicates was used. The evaluated variables included dry biomass of winter cover crops, soil bulk density, total porosity, microporosity, macroporosity, soil water content at field capacity, soil penetration resistance, plant gas exchange, leaf area index, thousand-grain weight, and soybean grain yield. The results indicated that soil chiseling altered soil physical properties by reducing soil bulk density, penetration resistance, microporosity, and field capacity, while increasing total porosity and macroporosity. Soil chiseling promoted short-term increases in thousand-grain weight and soybean grain yield. Production system intensification, through the use of cover crops and millet, did not affect grain yield but increased stomatal conductance and soybean leaf area index.

Abstract: Soil salinization is a major global issue that inhibits plant growth, disrupts rhizosphere microbial ecology, and compromises plant health. Utilizing salt-tolerant, plant-growth-promoting microorganisms offers a promising strategy for mitigating salt stress and improving soil productivity. In this study, a salt-tolerant, phosphate-solubilizing fungal strain was isolated from coastal saline-alkaline soil and designated as Penicillium oxalicum PF1. Its salt tolerance and phosphorus mobilizing capacity were characterized, and pot experiments were conducted to elucidate its effects on plant salt tolerance and the underlying mechanisms. The results showed it could survive up to 17 % (w/v) NaCl in culture medium and solubilized different insoluble phosphorus sources in the order Ca-P > Mg-P > Fe-P, with a maximum solubilization of 980.09 mg/L when Ca-P was supplied. Pot experiments and metagenomic analysis revealed that PF1 significantly promoted alfalfa growth in saline soil, it triggered significant restructuring of the alfalfa rhizosphere microbiome, promoting the functional transformation of rhizosphere microbial communities, thereby alleviating salt stress imposed on alfalfa. In summary, P. oxalicum PF1 exhibits robust salt tolerance and high phosphate-solubilizing activity, restructures the alfalfa rhizosphere microbiome, enhances host stress resistance, mitigates salt-induced physiological damage, and ultimately promotes plant growth in saline soil.

Abstract: Identifying the main drivers of soil CO₂ emissions in tropical agroecosystems is essential for balancing productivity and climate mitigation. This study evaluated the effects of crop type, irrigation, phenological stage, and fertilization on soil respiration in a humid marshland system in Rwanda using a two-season field experiment. Five crops (maize, soybean, common bean, Irish potato, and Brachiaria) were grown under irrigated and rainfed conditions, and soil CO₂ emissions were measured across 19 sampling campaigns in both crop-covered and adjacent bare soil conditions in all plots. Crop type and growth stage were the dominant drivers of soil CO₂ emissions (p < 0.001), while irrigation had no significant direct effect despite increasing yields (p < 0.001). As a result, irrigation reduced yield-scaled CO₂ emissions for several crops (p < 0.05–0.01). Brachiaria showed higher emissions, particularly during the development stage, but its high bio-mass led to lower emissions per unit yield. Fertilization significantly increased soil respiration (p < 0.001), and emissions were higher under crop-covered soils than bare soils (p < 0.001). These findings indicate that crop traits and nutrient inputs primarily control soil respiration under moisture-sufficient tropical conditions.

Abstract: Hydrochar has emerged as a promising carbonaceous amendment to enhance soil quality, yet its short-term effects on soil carbon (C) and nitrogen (N) dynamics and microbial functioning remain poorly understood. Here, a 77-day greenhouse pot experiment was conducted using a Cambisol cultivated with sunflower (Helianthus annuus L.) under two irrigation regimes simulating well-irrigated (WI) and water-deficit (WD) scenarios. Two doses of chicken manure–derived hydrochar (3.25 and 6.5 t ha⁻¹) and mineral fertilizer (MF) treatments providing equivalent N inputs were evaluated. Hydrochar promoted microbial growth and enhanced enzymatic and respiratory activities despite its low apparent C and nutrient input. After 77 days under WI, the addition of 6.5 t ha-1 hydrochar enhanced the activity of phenol oxidase (POA) and acid phosphomonesterase (AcPA). Concomitantly, the availability of soluble C and N increased, whereas total organic C (TOC) and N decreased relative to the initial values. These responses indicate a hydrochar-induced priming effect. The increase in POA relative to β-glucosidase is in line with a functional shift from a predominant degradation of labile compounds towards an increased oxidation of more complex structures. This interpretation is supported by solid-state ¹³C NMR data, revealing a higher degradation index of the soil organic matter. Under WD, these hydrochar-induced effects were attenuated but not suppressed, emphasizing the interactive influence of moisture and amendment dose. Overall, our results show that hydrochar modulates soil biochemical processes primarily through microbially mediated mechanisms rather than through direct nutrient inputs.

Abstract: Soil is a fundamental resource for humankind’s sustenance; however, excessive or inadequate use contributes to its degradation and erosion, therefore limiting its health and capacity to sustain biological activity. An option for restoration is the use of biocrusts—formations of photosynthetic organisms that protect and stimulate soil. The present research aimed to determine whether changes in soil conditions occur when treated with cyanobacterial biocrusts, specifically examining differences in microbial counts. Our results show significant changes in soil humidity, indicating an improvement in water retention. We also found that all microbial counts increased in the treatment group, but this increase was not statistically significant; additionally, there were no changes in the total organic carbon content. These results could be linked to low production of exopolysaccharides by the used species, low photosynthetic activity, and the need for a longer evaluation period for biocrust treatment.