ABSTRACT Nitrogen is an essential element for plant growth and, consequently, crop production. However, the cycling of nitrogen in the environment can have negative effects. Here, we review the historical development of scientific and public awareness of these effects and the influence this has had on political action to control them. Focusing on Germany as an example, we explore past nitrogen myths and how scientific progress has dispelled them, contextualizing our current position as a society seeking sufficient food, a clean environment, and an end to climate change. Given the continuous heavy burden placed on farmers to solve all these issues, we argue that from the state that we have reached today, further reducing nitrogen inputs for crop production may not necessarily lead to a further reduction in nitrogen cycling in the environment but rather to reductions in yields and product quality. Nevertheless, there is still potential to improve the efficiency of nitrogen use for stabilizing crop yields and to increase resilience against potential harm to the environment and human health. We make a couple of suggestions about what can be done.
ABSTRACT Background Soil salinity and sodicity are major constraints to crop production in the irrigated agro‐pastoral systems of northeastern Ethiopia, particularly in the Asaita district of the Afar region. Aim This study evaluated the effectiveness of integrated organic and inorganic soil amendments for improving maize and sorghum production under saline–sodic soil conditions. Methods Field experiments were conducted during 2024–2025 using a randomized complete block design (RCBD) with treatments consisting of different combinations of filter cake compost, gypsum, and salt‐tolerant forage species. Crop yield, yield components, biomass production, and economic returns were assessed to determine agronomic and economic performance. Results The results showed that the integrated application of compost and gypsum significantly improved crop productivity compared with the untreated control. In the biological reclamation trial, Panicum antidotale + 10 t ha −1 filter cake compost produced the highest maize grain yield (5.47 t ha −1 ) and sorghum grain yield (3.70 t ha −1 ), representing increases of 78% and 311%, respectively, over the control. Similarly, the combined application of 10 t ha −1 gypsum + 10 t ha −1 filter cake compost resulted in the highest grain yields of maize (5.00 t ha −1 ) and sorghum (3.70 t ha −1 ). Maximum above‐ground biomass yields were recorded under P. antidotale + compost treatments, reaching 11.50 t ha −1 for maize and 11.96 t ha −1 for sorghum. The highest net economic benefits were obtained from P. antidotale + 10 t ha −1 compost, yielding 35,230 Ethiopian Birr (ETB) ha −1 for maize and 39,720 ETB ha −1 for sorghum. Among the forage species evaluated, treatment effectiveness ranked as P. antidotale > Sesbania > Crotalaria > Alfalfa > Control. Sorghum consistently outperformed maize under saline–sodic conditions, confirming its greater salinity tolerance. Conclusion These findings demonstrate that integrating halophytic forage species with compost and gypsum provides an agronomically effective, economically viable, and sustainable strategy for reclaiming saline–sodic soils and enhancing cereal production in northeastern Ethiopia.
ABSTRACT The widely used physical model for wind erosion faces challenges in defining parameters with clear mechanical meaning that can be readily constrained by direct measurements. To address this issue, the impact crater scaling law is combined with the saltation transport model to derive a formula with undetermined constants, which are subsequently constrained using three wind tunnel datasets. The resulting expression for dry, loose soil under saltation bombardment closely resembles Owen's sand transport rate in form, with the effective size of saltating particles appearing as an additional parameter. This work proposes a conceptually interpretable scaling framework for estimating wind erosion on loose soils, while acknowledging that further experimental validation is needed to reduce predictive uncertainty.
ABSTRACT Background and aim The natural abundance of nitrogen isotopes (δ 15 N) provides a powerful integrative tracer of nitrogen uptake and assimilation in plants, yet the internal partitioning of δ 15 N among plant tissues remains insufficiently understood. Methods Here, we quantified isotopic discrimination during ammonium (NH 4 + ) and nitrate (NO 3 – ) uptake in maize ( Zea mays L.) grown under axenic hydroponic conditions at 0.2 and 2 mM N, representing low and high affinity transport systems, respectively. Results Distinct and systematic isotopic offsets between roots and shoots revealed contrasting assimilation patterns for the two nitrogen forms. Under NH 4 + nutrition, shoot and root δ 15 N were nearly identical, consistent with predominant assimilation in roots and limited translocation of reduced nitrogen. In contrast, NO 3 – nutrition produced strong 15 N enrichment in shoots relative to roots, reflecting spatially partitioned NO 3 – reduction and assimilation between organs. The δ 15 N of tissue NO 3 – was inversely related with its concentration, supporting isotopic fractionation during nitrate reduction and dilution by vacuolar storage. These results demonstrate that intra‐plant δ 15 N partitioning primarily reflects the spatial localization of nitrogen assimilation. Conclusion By establishing mechanistic baselines for intrinsic nitrogen isotope fractionation under controlled conditions, this study refines the physiological interpretation of plants δ 15 N and enhances its application to ecological and biogeochemical investigations.
ABSTRACT Background : Nitrous oxide (N 2 O) is a major greenhouse gas, and its production is shaped by soil organic matter (SOM). Yet, how different SOM‐derived labile carbon fractions regulate N 2 O remains unclear, especially in tropical paddy soils where weak SOM stabilization leads to low fertility and high nitrogen loss. Results : By collecting and analyzing soil samples from 16 tropical paddy soil sites with varying SOM contents (6–10 g kg −1 , 10–20 g kg −1 , 20–30 g kg −1 , and 30–40 g kg −1 ), we found that N 2 O emissions were twice as high in soils with higher SOM content compared to those with lower SOM content and that N 2 O emissions increased significantly with increasing SOM content. This stimulation of N 2 O emissions was accompanied by increases in soil easily oxidizable organic carbon (EOC), particulate organic carbon (POC), total nitrogen, microbial biomass carbon (MBC), and the abundances of nitrification and denitrification genes as SOM content increased. Moreover, increasing SOM above 20 g kg −1 increased the proportion of small soil aggregates (<0.053 mm), creating more anaerobic microsites that favored denitrify gene proliferation and ultimately led to higher N 2 O emissions. Conclusion : Our results highlight the critical roles of organic carbon fractions and soil aggregates in controlling N 2 O emissions in tropical soils.
ABSTRACT Background The German Soil Systematics is a pedogenetic classification based on the morphological expressions of pedogenic processes and has been developed over several stages since 1952. The system has successfully been in use for soil classification and soil survey for almost 70 years. Pedogenic processes are identified in most cases with parameters recognizable in the field. Almost 20 years after the last edition, a revision of the soil systematics and its horizon definitions has been made.. Aims The revision was done in order to include (i) soil geneses which logically did not fit into the previous structure of the system, e.g. soils with accumulation from lateral influx (Rheosole), (ii) soils resulting from environmental change, e.g. former peat soils whose peat degradation has progressed so far that they are no longer organic soils (Abmoor Subtypes of several mineral soils), and (iii) the Andosole and Umbrisole (similarly defined as in the WRB). Besides, some logical inconsistencies should be addressed. Guiding ideas for the rearrangement and additions were to make the pedogenetic principles better visible, to have a more homogeneous, balanced structure, and to cover all soils relevant for soil survey and mapping. Results The pedogenic processes that formed the soil are identified in most cases with parameters recognizable in the field and encoded with an extensive system of horizon symbols. The presence and (to some extent: the absence) of certain horizons in a certain depth in the profile and some thickness criteria are used to class the soil in a seven‐level Soil Systematics with: Divisions (2, mineral and organic soils), Subdivisions (7, related to water and oxygen availability), Classes (23, main genetical pathways), Types (56, genesis and intensity of processes), Subtypes (ca. 300, including Norm, Deviating and Transitional Subtypes), Varieties (2000, qualitatively diverging from their subtypes) and Subvarieties (quantitative additions to the Variety information). The logical inconsistencies were resolved by dissolving some former Classes and Types into now Types or Subtypes. The number of Types did not increase. Conclusions A new, consistent structure with all required new entitities could be achieved that will serve current and future needs. To include more objective criteria in the delimitation of soil systematic units is a common endeavor of the development of many national systems. A closer proximity to WRB was not a primary goal here, in contrast to other national system updates of the last years. This was to keep the clear advantages of the German Soil Systematics, some of them setting it apart from WRB and/or US Soil Taxonomy, in particular a more consistent justification for its higher‐level classes.
ABSTRACT Background : Grass–clover and silage maize are key for dairy feed production and frequently occur within the same crop rotations. Fertilizer management in grass–clover may leave residual effects that influence both environmental outcomes and the performance of subsequent maize crops. Aims : The study aimed to quantify how increasing cattle slurry nitrogen (N) application rates in grass–clover affect (1) nitrate leaching during the following maize phase and (2) maize growth and N status. The central research question was whether higher slurry N inputs in grass–clover elevate leaching losses and improve the productivity of subsequent maize. Methods : A long‐term crop rotation experiment was used to assess legacy effects of graded slurry N fertilization in grass–clover. Nitrate leaching, maize dry matter yield, and plant N content were measured, along with N uptake by an intermediate cover crop. Results : Higher slurry N rates in grass–clover significantly increased nitrate leaching during the maize phase, with 0.16–0.18 kg NO 3 ‐N leached per additional kg N previously applied. In contrast, maize dry matter yield showed little response to slurry N history. Although maize N content varied among treatments, overall concentrations remained above critical thresholds for N limitation. Cover crop N uptake (0.4–9.6 kg N ha −1 ) was too low to account for observed leaching patterns, emphasizing the predominant influence of crop sequence and soil mineralization. Conclusions : Slurry N fertilization in grass–clover can elevate nitrate leaching risks without reliably enhancing maize yield, highlighting the need for integrated N management to balance productivity and environmental protection.
ABSTRACT Background and aim Rice paddies are major agricultural sources of greenhouse gases (GHG), yet it remains unclear whether regulating carbon (C) and nitrogen (N) distribution among soil aggregate fractions can mitigate emission intensity. Methods Based on a long‐term paddy‐field experiment established in 1981 in Jiangxi, China, we examined four fertilization regimes: CK (unfertilized control), NPK (mineral nitrogen, phosphorus, and potassium), DNPK (double‐rate NPK), and NPKM (NPK combined with seasonal organic amendments). Soil‐surface fluxes of methane (CH 4 ), nitrous oxide (N 2 O), and carbon dioxide (CO 2 ) were measured using static chambers, and 0–20 cm soil was fractionated into >2 mm, 0.25–2 mm, 0.053–0.25 mm, and <0.053 mm aggregates to quantify soil organic carbon (OC) and total nitrogen (TN). Global warming potential (GWP), greenhouse gas intensity (GHGI), and C/N ratio were then calculated. Results Fertilization significantly increased grain yield, with NPKM producing the highest yield (16,777.68 kg ha −1 ), followed by DNPK. DNPK generated the greatest CO 2 emissions and the highest GWP (≈6524 kg CO 2 ‐eq ha −1 ). Although DNPK and NPKM increased absolute CH 4 and N 2 O fluxes, NPKM maintained a comparatively low GHGI because of its larger yield response. NPKM increased the proportion of >2 mm macroaggregates and enhanced OC (29.19%–167.15%) and TN (42.24%–137.57%) across multiple fractions, whereas DNPK primarily increased OC in the 0.053–0.25 mm fraction. Redundancy analysis revealed that GWP was mainly driven by C/N in 0.25–2 mm aggregates, TN in >2 mm aggregates, and OC in <0.053 mm aggregates. GHGI was more sensitive to TN and OC in the 0.053–0.25 mm fraction and OC in the 0.25–2 mm fraction. Conclusion These findings suggest that long‐term integrated organic–inorganic fertilization enhances macroaggregate structure while strengthening meso‐microaggregate buffering capacity and C with N coordination. This dual mechanism sustains higher rice yields while reducing GHGI.
ABSTRACT Background : Enhanced rock weathering (ERW) using silicate rock dust is a promising strategy for soil remineralization and carbon dioxide removal. However, its agronomic efficacy is highly dependent on soil properties. Aim : This study provides a comprehensive comparative analysis of the influence of soil type on the performance of rock dust, focusing on a semiarid Ultisol from a previous experiment and comparing it with data from 19 other recent (2020–2025) global studies. Methods : A dataset of soil properties (pH, cation exchange capacity [CEC], texture, soil organic matter [SOM]) and crop responses from diverse soil orders, including Oxisols, Mollisols, Alfisols, Entisols, and Aridisols, was analyzed. Statistical analyses, including ANOVA, correlation, and principal component analysis (PCA), were performed. Results : The results reveal significant differences in initial soil properties across soil orders, with CEC showing the highest variability ( F = 104.6, p < 0.0001). A significant positive correlation was found between clay content and crop yield increase ( r = 0.510, p = 0.0304), indicating that finer‐textured soils enhance the benefits of rock dust. Comparative analysis showed that Ultisols have a significantly higher CEC than Oxisols (72.5% higher, p < 0.001), yet Oxisols demonstrated a greater (though not statistically significant) yield response. PCA explained 85.9% of the total variance, with PC1 (62.0%) being primarily driven by CEC and pH, and PC2 (23.9%) by SOM. Conclusion : These findings highlight that while high CEC is beneficial, the initial nutrient status and weathering intensity of soils like Oxisols may be drivers of the immediate agronomic benefits of rock dust. This research underscores the need for site‐specific recommendations for rock dust application, considering the complex interplay between soil properties and rock mineralogy.
ABSTRACT With this commemorative article in the centennial issue of the Journal of Plant Nutrition and Soil Science , we trace the evolution of microscopic soil characterization over the past 100 years, with a particular focus on German soil science. We acknowledge the groundbreaking work of Walter Kubiëna as the founding father of soil micromorphology and follow a timeline shaped by two soil structure‐related priority programs funded by the German Research Foundation, established in 1957 and 1989. Each program marked a pivotal transition: The former coincided with technical revolutions in the automation of soil thin section production for high‐throughput analyses, the latter with the transition from the analog to the digital era. Today, we are facing another technical revolution brought about by the potential of artificial intelligence. We highlight seminal advancements in techniques, terminology, and research focus—from early soil micromorphology to modern x‐ray computed tomography (x‐ray CT) and correlative microscopy. This retrospective is not just a look back—It is a call forward. By combining past insights with cutting‐edge tools, soil micromorphology is now poised to address modern challenges in soil science, tackling Kubiëna's original vision of soil as a living and dynamic system that can be observed with unprecedented precision and resolution.
ABSTRACT On its 100th anniversary in 2026, the German Soil Science Society (DBG) is looking back not only on an eventful history with traditions and impressive achievements but also with painful interruptions and ruptures. One curious fact is that the DBG was initially founded as the national section of the International Soil Science Society (ISSS). German soil scientists, that is, F. Schucht, E.A. Mitscherlich, H. Stremme, and G.A. Krauß, played a decisive role in shaping the early development of the ISSS. Emil Ramann can undoubtedly be regarded as a nestor and pioneer of ISSS, which was founded in Rome in 1924. F. Schucht served as editor‐in‐chief of ISSS publications and ISSS President from 1935 to 1940. O. Lemmermann was the first DBG President. He founded the Zeitschrift für Pflanzenernährung , Düngung und Bodenkunde (now known as Journal of Plant Nutrition and Soil Science ), serving as the society's official publication. During the Nazi regime, soil science increasingly placed itself at the service of the political system. As Managing Director of DBG and in several other roles, F. Giesecke was the driving force behind the process of bringing institutions relevant to the self‐sufficiency initiative into line ( Gleichschaltung ). The reconstruction of the DBG in war‐torn Germany in 1949 was overshadowed by the looming division of Germany. Nevertheless, the DBG managed to operate as a pan‐German scientific society until 1961, the year the Berlin Wall was built. Although a separate soil science society existed in parallel in the former German Democratic Republic between 1967 and the reunification in 1990, for political reasons, ties were indirectly maintained. This helped foster the process of integration following reunification. The outstanding personality in the 1950s and 1960s was undoubtedly F. Scheffer, who was the first Managing Director and then served as President of the DBG (1955–1969). The commission structure and the major conferences, with their field excursions, remained a key constant. A highlight was the successful organization of the 13th World Soil Congress in Hamburg in 1986 by K.H. Hartge (ISSS President 1982–1986). Over the years, the DBG has combined basic research and methodology with a strong focus on practical application. The dynamics of its membership reflect the transformation from a small, originally rather elitist circle of soil‐related experts to an open, pluralistic community. Initially, DBG topics were typically related to agricultural and horticultural questions (soil and plant nutrition), pedogenesis (geology, mineralogy), amelioration, and forestry. Within the last 50 years, this character changed to a much broader environment‐related discipline. While soil science has long been male‐dominated at the management level, the proportion of women—including at the executive level—has grown steadily in recent decades. Together with strategic partners, DBG also seeks dialogue with politics and society. The stable high number of members and the remarkable proportion of younger members, a pronounced diversity of topics, and strong networking from the local to the international level testify to the DBG's continuing attractiveness, performance, and unbroken innovative strength.
ABSTRACT Soil organic carbon (SOC) is an important component influencing soil fertility, ecosystem functioning, and climate change mitigation. This study presents a comprehensive bibliometric analysis of global research on SOC under long‐term fertilization from 2005 to the first quarter of 2025. A total of 3171 peer‐reviewed articles indexed in Scopus were analyzed using VOSviewer and Biblioshiny to evaluate publication trends, collaboration networks, funding patterns, and thematic evolution. The annual growth rate of publications was 5.03%, with China, the United States, and India emerging as the leading contributors. Institutional and co‐authorship analyses revealed strong international collaboration, although research output was geographically concentrated. Keyword co‐occurrence and clustering analyses identified dominant themes including “soil organic carbon,” “carbon sequestration,” and “long‐term fertilization,” with increasing attention to microbial processes, carbon fractions, and climate‐smart management strategies in recent years. The mapped literature indicates a consistent research emphasis on integrated nutrient management practices, particularly combined organic and inorganic fertilization, in relation to SOC enhancement and stabilization. Emerging research frontiers include microbial necromass, isotopic tracing, metagenomics, and modeling approaches for carbon‐use efficiency. Despite substantial growth in the field, knowledge gaps remain regarding microbial‐mediated carbon dynamics and long‐term system resilience. This bibliometric synthesis provides a structured overview of global research trajectories and identifies priority directions for advancing sustainable soil management.
ABSTRACT Plant development and production are severely hampered by abiotic stresses such as salinity, temperature changes, heavy metals, nutrient inadequacies, and drought. Root exudates are a complex mixture of organic substances that are exuded by plants and are essential for regulating rhizosphere interactions and improving plant resilience to these stresses. This review summarizes current studies on how root exudates contribute to abiotic stress tolerance, with a particular emphasis on their interaction with the rhizospheric microbiome. The mechanisms by which root exudates enhance plant tolerance to diverse abiotic stresses are also explored. Under stressful conditions, root exudates modify microbial communities, foster favorable symbiotic relationships, and facilitate nutrient acquisition by plants. Despite the progress in comprehending these mechanisms, the specific chemical cues that stimulate these mutualistic relationships remain to be elucidated. Addressing these knowledge gaps is crucial to enhancing plant resilience in the face of escalating environmental challenges, and the development of sustainable solutions is imperative.
Take‐home message Our study (Xu et al. 2025) evaluated the field‐scale soil health effects of incorporating bagasse—an industrial byproduct—into sugarcane soils and did not involve or imply redistribution of organic matter across the landscape. The Comment's landscape‐scale concerns do not apply to this closed‐loop system. Bagasse incorporation remains a practical field‐level soil improvement strategy, while broader sustainability questions require additional, multi‐scale research.
ABSTRACT Cadmium (Cd 2 + ) contamination in agricultural soils has been reported to pose risks to crop productivity, food safety, and human health. This review synthesizes current knowledge on the mechanisms by which essential (S, Zn, Fe, Mg, K, Ca) and beneficial (Si, Se, rare earth elements) elements mitigate Cd 2 + toxicity in plants. We examine their roles in the competitive inhibition of Cd 2+ uptake through the modulation of metal transporters, including NRAMP5, IRT1, and members of the HMA and ZIP families. They also enhance vacuolar sequestration via ABCC and HMA3 transporters, activate antioxidant defense systems and phytochelatins, and reinforce apoplastic barriers through the deposition of suberin and lignin. Recent advances in synergistic nutrient applications, particularly Zn–Si–Se combinations, reduce grain Cd 2+ by limiting root uptake, strengthening endodermal barriers, and enhancing internal detoxification. Furthermore, combining nutrient‐based interventions with rhizosphere microbiome management, modern plant breeding, and gene‐editing technologies targeting Cd 2+ transporters may provide additional synergistic benefits. This review highlights the importance of optimizing application strategies, preventing nutrient imbalances, and validating these approaches through long‐term field studies. Future perspectives include exploration of multi‐element interactions, and the development of nano‐enabled formulations to achieve effective and scalable Cd 2+ risk mitigation in agricultural production systems.
Background Nitrogen (N) losses in low-fertility alkaline soils substantially reduce nitrogen use efficiency and limit wheat productivity. Although biochar has been widely studied as a nutrient-retentive soil amendment; however, its potential to assist fertilizer reduction under alkaline soil conditions remains insufficiently understood.Aim This study evaluated the effectiveness of integrating biochar with urea to regulate soil N transformations and enhance wheat productivity in alkaline soil.Method A 1-month laboratory incubation study was conducted in soil amended with biochar at 1%, 2%, and 3% (w/w) and urea at the recommended rate of 150 kg N ha-1 (0.0144 g urea jar-1). In a complementary pot experiment, wheat was grown in alkaline soil amended with 1% biochar combined with urea applied at 100%, 85%, and 70% of the recommended rate (0.87, 0.74, and 0.60 g urea pot-1), respectively.Results Results showed that 3% biochar was the most effective rate in the laboratory incubation, significantly lowering NH4+-N concentration and delaying its nitrification to NO3--N; however, on the basis of the practical applicability, 1% biochar was selected for the pot experiment. Results for pot experiment revealed that wheat plants receiving 85% of the recommended urea with 1% biochar displayed improved agronomic attributes and produced higher grain yield (15.5 g pot-1) and total N in roots, shoots, and grain than plants supplied with 100% urea alone.Conclusion Overall, the results demonstrate that low biochar application rate (1%) can partially substitute for mineral N fertilizer by regulating urea-derived N dynamics and improving wheat performance in alkaline soil.
ABSTRACT Background Plant tissue analysis has been used for the diagnosis of both deficiencies and excess in plant nutrition. The nutrient concentrations in crops are compared with critical values (CVs in the sense of target values or ranges) reported in the literature, which were determined on the basis of extensive nutrient enrichment and survey studies. Due to changing framework conditions—such as climate change, emission reductions, and new crop varieties—regular monitoring of these values appears advisable. Aim This work aimed to set up an open‐source datasheet as well as open‐source evaluation tools to facilitate the calculation of target ranges in the future. The datasheet is meant to be expanded and kept up to date regularly by additional data from experts. Methods A total of 1.212 datasets were compiled on samples from field and trial sites in three growing seasons from eight arable crops. Using the programmed formula, we exemplarily compared target ranges currently used with target ranges calculated from mean nutrient concentrations of high‐yielding subsets or derived from a boundary line fitted to scatter plots of nutrient concentration versus yield, using the CV as maximum. Results The boundary‐line approach proved applicable to deduce target (critical) values from the datasets where sample numbers were sufficient. Conclusion On the basis of the datasets of this work, the majority of values currently used in Central Europe could be confirmed. For sulfur, we suggest lower target ranges, especially in cereals and corn. Further, we recommend reducing the target range width for magnesium, manganese, and zinc in corn and for boron in sugar beets and potatoes. Data and formulas are published open access under https://github.com/ANAPLANT‐Project/ANAPLANT . Interested experts in plant tissue analysis are invited to make use of it.
ABSTRACT Background : Renewable peat‐reducing components are needed for horticultural substrates; however, the combined effects of biochar activation state, particle size, and dose on substrate function remain unresolved. Aim : This study evaluated the effects of pine nut shell biochar on peat substrate properties and arugula microgreen performance and identified screening‐level criteria for peat‐reduced substrate design. Methods : Peat was partially replaced by nonactivated or steam‐activated biochar at 10% or 20% (v/v) using fine (<30 µm) or large (2–10 mm) fractions. After 28 days, the substrate hydrophysical and chemical properties, extractable nutrients, mobile trace elements, germination, morphometric traits, and biomass were determined. Results : Steam activation significantly increased the biochar pH; electrical conductivity; surface area; and extractable K, Mg, Ca, and P contents. In the substrate, fine fractions improved the water‐holding capacity and total porosity, whereas activated large fractions reduced these properties. Nonactivated biochar lowered the substrate electrical conductivity relative to the peat control, whereas activated biochar markedly increased it. Potassium increased in all amended substrates, but phosphorus usually declined, except for a slight increase in the 10% fine activated treatment. The best plant response was obtained with 10% fine biochar. Fresh biomass was approximately 2.0–2.8‐fold higher than that in the peat control, whereas the 20% rate provided no additional benefit, and some activated‐biochar treatments reduced germination and growth. Mobile heavy metal concentrations remained low across all treatments. Conclusions : Under the tested conditions, 10% fine nonactivated pine nut shell biochar provided the best overall compromise between peat replacement, substrate performance, and manageable electrical conductivity.
ABSTRACT Biochar and hydrochar have emerged as promising carbon‐based amendments for enhancing soil carbon sequestration and mitigating greenhouse gas emissions. This review synthesizes and critically compares current knowledge on the production technologies, physicochemical properties, stabilization mechanisms, carbon persistence, and life‐cycle climate performance of biochar and hydrochar, emphasizing their comparative roles as negative emission technologies. Biochar, produced via pyrolysis, is characterized by highly aromatic and condensed carbon structures that confer long‐term stability in soils, frequently yielding mean residence times from centuries to millennia. Hydrochar, generated through hydrothermal carbonization, offers a more efficient path for processing wet feedstocks and waste valorization, yet generally exhibits lower intrinsic stability and greater variability in mineralization rates. The review demonstrates that carbon persistence is governed not only by molecular recalcitrance but also by soil‐mediated mechanisms, including organo‐mineral interactions, aggregate occlusion, and microbial feedbacks. Impacts on CO 2 , N 2 O, and CH 4 fluxes are strongly context‐dependent, reflecting interactions among char properties, soil texture, climate, and management practices. Life‐cycle assessments indicate that biochar systems more consistently deliver net climate benefits, whereas hydrochar performance depends on energy sources and process integration. Beyond climate mitigation, both materials provide agronomic and environmental co‐benefits, including improved soil fertility, water retention, and waste recycling. However, large‐scale deployment remains constrained by methodological heterogeneity, regulatory uncertainty, and economic barriers. The review concludes that biochar and hydrochar are complementary components of climate‐smart land management systems. Future progress depends on standardized methodologies, long‐term field experiment validation, and harmonized carbon accounting frameworks enabling reliable contributions to global net‐zero pathways. Policy alignment will be decisive for responsible and equitable global deployment.
