Hydrochar as an effective amendment for enhancing soil aggregation and carbon sequestration: evidence from comparative microcosm experiments

Abstract

Enhancing soil organic carbon (SOC) and aggregate stability is pivotal for maintaining soil health and ensuring agricultural sustainability. However, conventional organic amendments often exhibit suboptimal efficiency in achieving these goals. Hydrochar, synthesized via hydrothermal carbonization (HTC), offers a promising solution by integrating labile and recalcitrant carbon fractions to synergistically address these challenges. However, its mechanisms of action remain not fully understood. In the present study, a microcosmic incubation experiment was conducted to evaluate the short-term impacts of hydrochar on SOC sequestration and soil aggregation in comparison with biochar and straw in a purple soil (Entisol). Hydrochars derived from maize straw (SH), pig manure (PH), and Zanthoxylum stalks (HH) were also compared to assess feedstock-driven variability. The results demonstrated the superior performance of hydrochars, particularly those derived from Zanthoxylum stalks, which significantly increased the mean weight diameter (MWD) by 70–100% and SOC content by 143–149%, outperforming biochar and straw. Specifically, hydrochar-originated carbon persisted primarily as particulate organic matter (POM) and accumulated in macro-aggregate, while shifts in microbial communities contributed to SOC stabilization. In comparison, soil aggregation was driven by labile carbon fractions (e.g., dissolved organic carbon, DOC) and soil microorganisms, specifically Actinobacteria and Ascomycota. Feedstock properties, such as the C/N ratio and lignin content, modulated the effectiveness of hydrochar as a soil amendment. Notably, stalk-derived hydrochar exhibited superior carbon retention (12% total carbon loss vs. 30–44% for other amendments) and aggregate stability due to its recalcitrant lignin structure. Nutrient content and ratio further influenced these outcomes, with manure-derived hydrochar promoting microbial biomass carbon (845 mg kg⁻¹ vs. 350 mg kg⁻¹ in control), while stalk-derived hydrochar was more effective at optimizing carbon sequestration. These findings highlighted the dual role of hydrochar in enhancing soil structure and SOC sequestration, with feedstock selection critically determining functional priorities. Such insights could provide valuable guidance for tailoring hydrochar production and application to improve agricultural sustainability through soil quality improvement.

Graphic Abstract

Keywords

Soil quality / Organic input / Hydrochar / Carbon-deficient cropland / Carbon fraction / Soil aggregates

Highlight

•	Hydrochars best enhanced soil aggregation and C sequestration in organic amendment trials.
•	Hydrochars outperformed stalk and biochar in boosting soil structure and C storage.
•	Mechanisms of hydrochar-induced soil aggregation and C sequestration were proposed.
•	Stalk-derived hydrochar maximized soil aggregation and C sequestration over other feedstocks.
•	DOC and TC in hydrochars are key mediators of soil structural and C storage changes.

References

[1] Al-Nuaimy MNM, Azizi N, Nural Y, Yabalak E. Recent advances in environmental and agricultural applications of hydrochars: a review. Environ Res. 2024, 250. 117923

[2] Amelung W, Meyer N, Rodionov A, Knief C, Aehnelt M, Bauke SL, Biesgen D, Dultz S, Guggenberger G, Jaber M, Klumpp E, Kögel-Knabner I, Nischwitz V, Schweizer SA, Wu B, Totsche KU, Lehndorf E. Process sequence of soil aggregate formation disentangled through multi-isotope labelling. Geoderma. 2023, 429. 116226

[3] Andert J, Mumme J. Impact of pyrolysis and hydrothermal biochar on gas-emitting activity of soil microorganisms and bacterial and archaeal community composition. Appl Soil Ecol. 2015, 96: 225-239.

[4] Angulo V, Bleichrodt RJ, Dijksterhuis J, Erktan A, Hefting MM, Kraak B, Kowalchuk GA. Enhancement of soil aggregation and physical properties through fungal amendments under varying moisture conditions. Environ Microbiol. 2024, 26(5. e16627

[5] Beillouin D, Corbeels M, Demenois J, Berre D, Boyer A, Fallot A, Feder F, Cardinael R. A global meta-analysis of soil organic carbon in the Anthropocene. Nat Commun. 2023, 141. 3700

[6] Bento LR, Melo CA, Ferreira OP, Moreira AB, Mounier S, Piccolo A, Spaccini R, Bisinoti MC. Humic extracts of hydrochar and Amazonian Dark Earth: molecular characteristics and effects on maize seed germination. Sci Total Environ. 2020, 708. 135000

[7] Bever CG, Coronella CJ. Carbon sequestration potential of manure-derived hydrochar aided by secondary stabilization. ACS Sustainable Chem Eng. 2024, 1214): 5705-5715.

[8] Bi WY, Wang JJ, Dodla SK, Gaston LA, DeLaune RD. Lignin chemistry of wetland soil profiles in two contrasting basins of the Louisiana Gulf coast. Org Geochem. 2019, 137. 103902

[9] Bian Q, Zhao LX, Cheng K, Jiang YJ, Li DM, Xie ZB, Sun B, Wang XY. Divergent accumulation of microbe- and plant-derived carbon in different soil organic matter fractions in paddy soils under long-term organic amendments. Agric Ecosyst Environ. 2024, 366. 108934

[10] Burgess MS, Mehuys GR, Madramootoo CA. Decomposition of grain-corn residues (Zea mays L.): a litterbag study under three tillage systems. Can J Soil Sci. 2002, 82(2): 127-138.

[11] Chen XM, Liu JX, Deng Q, Yan JH, Zhang DQ. Effects of elevated CO₂ and nitrogen addition on soil organic carbon fractions in a subtropical forest. Plant Soil. 2012, 357(1-2): 25-34.

[12] Chen XB, Hu YJ, Xia YH, Zheng SM, Ma C, Rui YC, He HB, Huang DY, Zhang ZH, Ge TD, Wu JS, Guggenberger G, Kuzyakov Y, Su YR. Contrasting pathways of carbon sequestration in paddy and upland soils. Glob Change Biol. 2021, 27(11): 2478-2490.

[13] Chen Y, Zwieten LV, Xiao K, Liang C, Ren J, Zhang A, Li Y, Dong H, Sun K. Biochar as a green solution to drive the soil carbon pump. Carbon Res. 2024, 3(1. 44

[14] Chen ZM, He LL, Ma JC, Ma JW, Ye J, Yu QG, Zou P, Sun WC, Lin H, Wang F, Zhao X, Wang Q. Long-term successive biochar application increases plant lignin and microbial necromass accumulation but decreases their contributions to soil organic carbon in rice-wheat cropping system. GCB Bioenergy. 2024, 166. e13137

[15] Cheng Y, Luo M, Zhang TG, Yan SH, Wang C, Deng QG, Feng H, Zhang TB, Kisekka I. Organic substitution improves soil structure and water and nitrogen status to promote sunflower (Helianthus annuus L.) growth in an arid saline area. Agric Water Manag. 2023, 283. 108320

[16] Cotrufo MF, Ranalli MG, Haddix ML, Six J, Lugato E. Soil carbon storage informed by particulate and mineral-associated organic matter. Nat Geosci. 2019, 1212): 989-994.

[17] Cotrufo MF, Haddix ML, Kroeger ME, Stewart CE. The role of plant input physical-chemical properties, and microbial and soil chemical diversity on the formation of particulate and mineral-associated organic matter. Soil Biol Biochem. 2022, 168. 108648

[18] Dong XF, Liu C, Wu XD, Man HR, Wu XW, Ma DL, Li M, Zang SY. Linking soil organic carbon mineralization with soil variables and bacterial communities in a permafrost-affected tussock wetland during laboratory incubation. CATENA. 2023, 221. 106783

[19] Edgar R. UPARSE: highly accurate OTU sequences from microbial amplicon reads. Nat Methods. 2013, 10: 996-998.

[20] Even RJ, Cotrufo MF. The ability of soils to aggregate, more than the state of aggregation, promotes protected soil organic matter formation. Geoderma. 2024, 442. 116760

[21] Fan JP, Li FF, Fang DX, Chen QZ, Chen QK, Wang H, Pan B. Effects of hydrophobic coating on properties of hydrochar produced at different temperatures: specific surface area and oxygen-containing functional groups. Bioresour Technol. 2022, 363. 127971

[22] George C, Wagner M, Kücke M, Rillig MC. Divergent consequences of hydrochar in the plant-soil system: arbuscular mycorrhiza, nodulation, plant growth and soil aggregation effects. Appl Soil Ecol. 2012, 59: 68-72.

[23] Heikkinen J, Keskinen R, Soinne H, Hyväluoma J, Nikama J, Wikberg H, Källi A, Siipola V, Melkior T, Dupont C, Campargue M, Larsson SH, Hannula M, Rasa K. Possibilities to improve soil aggregate stability using biochar derived from various biomasses through slow pyrolysis, hydrothermal carbonization, or torrefaction. Geoderma. 2019, 344: 40-49.

[24] Hu YC, Su MR, Wang YF, Cui SH, Meng FX, Yue WC, Liu YF, Xu C, Yang ZF. Food production in China requires intensified measures to be consistent with national and provincial environmental boundaries. Nat Food. 2020, 1(9): 572-582.

[25] Huang X, Wang WL, Gong T, Wickell D, Kuo LY, Zhang XT, Wen JL, Kim H, Lu FC, Zhao HS, Chen S, Li H, Wu WQ, Yu CJ, Chen S, Fan W, Chen S, Bao XQ, Li L, Zhang D, Jiang LY, Khadka D, Yan XJ, Liao ZY, Zhou GK, Guo YL, Ralph J, Sederoff RR, Wei HR, Zhu P, Li FW, Ming RY, Li QZ. The flying spider-monkey tree fern genome provides insights into fern evolution and arborescence. Nat Plants. 2024, 10(2): 344-344.

[26] Huo CF, Liang JY, Zhang WD, Wang P, Cheng WX. Priming effect and its regulating factors for fast and slow soil organic carbon pools: a meta-analysis. Pedosphere. 2022, 32(1): 140-148.

[27] Islam MA, Limon MSHM, Romić M. Hydrochar-based soil amendments for agriculture: a review of recent progress. Arab J Geosci. 2021, 102. 14

[28] Jilling A, Kane D, Williams A, Yannarell AC, Davis A, Jordan NR, Koide RT, Mortensen DA, Smith RG, Snapp SS, Spokas KA, Grandy AS. Rapid and distinct responses of particulate and mineral-associated organic nitrogen to conservation tillage and cover crops. Geoderma. 2020, 359. 114001

[29] Khan TA, Saud AS, Jamari SS, Ab Rahim MH, Park JW, Kim HJ. Hydrothermal carbonization of lignocellulosic biomass for carbon rich material preparation: a review. Biomass Bioenergy. 2019, 130. 105384

[30] Khosravi A, Zheng H, Liu Q, Hashemi M, Tang YZ, Xing BS. Production and characterization of hydrochars and their application in soil improvement and environmental remediation. Chem Eng J. 2022, 430(4. 133142

[31] Krause L, Biesgen D, Treder A, Schweizer SA, Klumpp E, Knief C, Siebers N. Initial microaggregate formation: association of microorganisms to montmorillonite-goethite aggregates under wetting and drying cycles. Geoderma. 2019, 351: 250-260.

[32] Kumar A, Saini K, Bhaskar T. Hydochar and biochar: production, physicochemical properties and techno-economic analysis. Bioresour Technol. 2020, 310. 123442

[33] Lal R, Monger C, Nave L, Smith P. The role of soil in regulation of climate. Philos Trans R Soc B Biol Sci. 2021, 376. 1838

[34] Lavallee JM, Soong JL, Cotrufo MF. Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century. Glob Change Biol. 2020, 261): 261-273.

[35] Lehmann J, Kleber M. The contentious nature of soil organic matter. Nature. 2015, 528(7580): 60-68.

[36] Li J, Chen XH, Yu SG, Cui M. Removal of pristine and aged microplastics from water by magnetic biochar: adsorption and magnetization. Sci Total Environ. 2023, 875. 162647

[37] Li JY, Chen P, Li ZG, Li LY, Zhang RQ, Hu W, Liu Y. Soil aggregate-associated organic carbon mineralization and its driving factors in rhizosphere soil. Soil Biol Biochem. 2023, 186. 109182

[38] Li YH, Feng XJ, Huai YB, Hassan MU, Cui ZL, Ning P. Enhancing crop productivity and resilience by promoting soil organic carbon and moisture in wheat and maize rotation. Agric Ecosyst Environ. 2024, 368. 109021

[39] Liang C, Amelung W, Lehmann J, Kästner M. Quantitative assessment of microbial necromass contribution to soil organic matter. Glob Change Biol. 2019, 25(11): 3578-3590.

[40] Liao QH, Yuan F, Fan QY, Chen HY, Wang YM, Zhang CC, Lu C, Qiu PH, Wang CL, Zou XQ. Plant- and microbial-mediated soil organic carbon accumulation in Spartina alterniflora salt marshes. CATENA. 2024, 237. 107777

[41] Liu MY, Chang QR, Qi YB, Liu J, Chen T. Aggregation and soil organic carbon fractions under different land uses on the tableland of the Loess Plateau of China. CATENA. 2014, 115: 19-28.

[42] Ma T, Zhu SS, Wang ZH, Chen DM, Dai GH, Feng BW, Su XY, Hu HF, Li KH, Han WX, Liang C, Bai YF, Feng XJ. Divergent accumulation of microbial necromass and plant lignin components in grassland soils. Nat Commun. 2018, 9(1. 3480

[43] Ma T, Yang ZY, Shi BW, Gao WJ, Li YF, Zhu JX, He J. Phosphorus supply suppressed microbial necromass but stimulated plant lignin phenols accumulation in soils of alpine grassland on the Tibetan Plateau. Geoderma. 2023, 431. 116376

[44] Ma YQ, Woolf D, Fan MS, Qiao L, Li R, Lehmann J. Global crop production increase by soil organic carbon. Nat Geosci. 2023, 16. 12

[45] Ma HH, Peng M, Yang Z, Yang K, Zhao CD, Li K, Guo F, Yang ZF, Cheng HX. Spatial distribution and driving factors of soil organic carbon in the Northeast China Plain: insights from latest monitoring data. Sci Total Environ. 2024, 911. 168602

[46] Ma SH, Cao YD, Lu JW, Ren T, Cong RH, Lu ZF, Zhu J, Li XK. Response of soil aggregation and associated organic carbon to organic amendment and its controls: a global meta-analysis. CATENA. 2024, 237. 107774

[47] Mustafa A, Xu MG, Shah SAA, Abrar MM, Sun N, Wang BR, Cai ZJ, Saeed Q, Naveed M, Mehmood K, Núñez-Delgado A. Soil aggregation and soil aggregate stability regulate organic carbon and nitrogen storage in a red soil of southern China. J Environ Manag. 2020, 270. 110894

[48] Naisse C, Girardin C, Lefevre R, Pozzi A, Maas R, Stark A, Rumpel C. Effect of physical weathering on the carbon sequestration potential of biochars and hydrochars in soil. GCB Bioenergy. 2015, 73): 488-496.

[49] Oldfield EE, Bradford MA, Wood SA. Global meta-analysis of the relationship between soil organic matter and crop yields. Soil. 2019, 5(1): 15-32.

[50] Qiao L, Wang XH, Smith P, Fan JL, Lu YL, Emmett B, Li R, Dorling S, Chen HQ, Liu SG, Benton TG, Wang YJ, Ma YQ, Jiang RF, Zhang FS, Piao SL, Müller C, Yang HQ, Hao YN, Li WM, Fan MS. Soil quality both increases crop production and improves resilience to climate change. Nat Clim Change. 2022, 12(6): 574-280.

[51] Rashid MI, Mujawar LH, Shahzad T, Almeelbi T, Ismail IMI, Oves M. Bacteria and fungi can contribute to nutrients bioavailability and aggregate formation in degraded soils. Microbiol Res. 2016, 183: 26-41.

[52] Ren FL, Zhang RQ, Sun N, Li YL, Xu MG, Zhang FS, Xu W. Patterns and driving factors of soil organic carbon sequestration efficiency under various manure regimes across Chinese croplands. Agric Ecosyst Environ. 2024, 359. 108723

[53] Rex D, Schimmelpfennig S, Jansen-Willems A, Moser G, Kammann C, Müller C. Microbial community shifts 2.6 years after top dressing of Miscanthus biochar, hydrochar and feedstock on a temperate grassland site. Plant Soil. 2015, 397(1-2): 261-271.

[54] Richter DD. A world without soil: the past, present, and precarious future of the Earth beneath our feet. Science. 2021, 374(6574): 1452-1452.

[55] Si HY, Wang R, Zhao YQ, Hao H, Zhao CK, Xing S, Yu HW, Liang XH, Lu JK, Chen XX, Wang B. Large-scale soil application of hydrochar: reducing its polycylic aromatic hydrocarbon content and toxicity by heating. J Hazard Mater. 2024, 471. 134467

[56] Six J, Elliott ET, Paustian K, Doran JW. Aggregation and soil organic matter accumulation in cultivated and native grassland soils. Soil Sci Soc Am J. 1998, 62(5): 1367-1377.

[57] Six J, Bossuyt H, Degryze S, Denef K. A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics. Soil till Res. 2004, 79(1): 7-31.

[58] Sokol NW, Sanderman J, Bradford MA. Pathways of mineral-associated soil organic matter formation: integrating the role of plant carbon source, chemistry, and point of entry. Glob Change Biol. 2019, 25(1): 12-24.

[59] Song CF, Shan SD, Yang C, Zhang C, Zhou XQ, Ma Q, Yrjälä K, Zheng HB, Cao YC. The comparison of dissolved organic matter in hydrochars and biochars from pig manure. Sci Total Environ. 2020, 720. 137423

[60] Song FB, Liu KL, Lou YL, Kuzyakov Y, Wang YD. Divergent responses of aggregate stability to long-term mineral and organic amendments between upland and paddy soils. J Soils Sediments. 2022, 22(12): 2969-2981.

[61] Sonsri K, Watanabe A. Insights into the formation and stability of soil aggregates in relation to the structural properties of dissolved organic matter from various organic amendments. Soil Tillage Res. 2023, 232. 105774

[62] Sun K, Han LF, Yang Y, Xia XH, Yang ZF, Wu FC, Li FB, Feng YF, Xing BS. Application of hydrochar altered soil microbial community composition and the molecular structure of native soil organic carbon in a paddy soil. Environ Sci Technol. 2020, 54(5): 2715-2725.

[63] Sun Q, Meng J, Lan Y, Shi GH, Yang X, Cao D, Chen WF, Han X. Long-term effects of biochar amendment on soil aggregate stability and biological binding agents in brown earth. CATENA. 2021, 205. 105460

[64] Tarf OJ, Akça MO, Donar YO, Bilge S, Turgay OC, Sinag A. The short-term effects of pyro-and hydrochars derived from different organic wastes on some soil properties. Biomass Convers Biorefin. 2022, 12(1): 129-139.

[65] Tian SY, Zhu BJ, Yin R, Wang MW, Jiang YJ, Zhang CZ, Li DM, Chen XY, Kardol P, Liu MQ. Organic fertilization promotes crop productivity through changes in soil aggregation. Soil Biol Biochem. 2022, 165. 108533

[66] Ul Islam M, Jiang FH, Guo ZC, Peng XH. Does biochar application improve soil aggregation? A meta-analysis. Soil Tillage Res. 2021, 209. 104926

[67] Verrone V, Gupta A, Laloo AE, Dubey RK, Hamid NAA, Swarup S. Organic matter stability and lability in terrestrial and aquatic ecosystems: a chemical and microbial perspective. Sci Total Environ. 2024, 906. 167757

[68] Wang GC, Wang MM, Guo XW, Yu YQ, Han PF, Luo ZK. Efficiency of additional organic inputs for carbon sequestration in agricultural soils modulated by the priming effect and physical accessibility. Geoderma. 2022, 406. 115498

[69] Wang X, Li Z, Cheng YD, Yao H, Li H, You XW, Zhang CS, Li YQ. Wheat straw hydrochar induced negative priming effect on carbon decomposition in a coastal soil. iMeta. 2023, 24. e134

[70] Wang YY, Li H, Li YW, Guo H, Zhou J, Wang TC. Metagenomic analysis revealed sources, transmission, and health risk of antibiotic resistance genes in confluence of Fenhe, Weihe, and Yellow Rivers. Sci Total Environ. 2023, 858. 159913

[71] Wang HG, Wang X, Zhang L, Zhang XY, Cao YB, Xiao R, Bai ZH, Ma L. Meta-analysis addressing the potential of antibiotic resistance gene elimination through aerobic composting. Waste Manag. 2024, 182: 197-206.

[72] Wang R, Zheng XY, Feng ZY, Feng YH, Ying Z, Wang B, Dou BL. Hydrothermal carbonization of Chinese medicine residues: formation of humic acids and combustion performance of extracted hydrochar. Sci Total Environ. 2024, 925. 171792

[73] Watson C, Schlösser C, Vögerl J, Wichern F. Hydrochar, digestate, and process water impacts on a soil’s microbial community, processes, and metal bioavailability. Soil Sci Soc Am J. 2021, 85: 717-731.

[74] Xiao R, Wang JJ, Gaston LA, Zhou BY, Park JH, Li RH, Dodla SK, Zhan ZQ. Biochar produced from mineral salt-impregnated chicken manure: fertility properties and potential for carbon sequestration. Waste Manag. 2018, 78: 802-810.

[75] Xiong WJ, Luo YP, Shangguan WG, Deng Y, Li RH, Song D, Zhang MY, Li ZY, Xiao R. Co-hydrothermal carbonization of lignocellulosic biomass and swine manure: optimal parameters for enhanced nutrient reclamation, carbon sequestration, and heavy metals passivation. Waste Manag. 2024, 190: 174-185.

[76] Xiong WJ, Zhang MY, Wei YY, Wei YY, Song D, Luo YP, Wang JT, Cheng S, Xiao R. Co-hydrothermal carbonization of lignocellulosic biomass and swine manure for humic substance abundant target products: impacts of hydrothermal temperature and feedstock composition. J Environ Chem Eng. 2025, 266: 242-248.

[77] Yan T, Zhang ZR, Zhang Z, Wang WZ, Li D, Zhang T, Zhu ZP. Applying hydrochar affects soil carbon dynamics by altering the characteristics of soil aggregates and microbes. Agronomy. 2024, 145. 1015

[78] Yu WJ, Huang WJ, Weintraub-Leff SR, Hall SJ. Where and why do particulate organic matter (POM) and mineral-associated organic matter (MAOM) differ among diverse soils?. Soil Biol Biochem. 2022, 172. 108756

[79] Zhang ZZ, Wang DM, Li MX. Soil respiration, aggregate stability and nutrient availability affected by drying duration and drying-rewetting frequency. Geoderma. 2022, 413. 115743

[80] Zhang J, Zhang FH, Yang L. Continuous straw returning enhances the carbon sequestration potential of soil aggregates by altering the quality and stability of organic carbon. J Environ Manag. 2024, 358. 120903

[81] Zhao RN, Kuzyakov Y, Zhang HY, Wang ZR, Li TP, Shao LY, Jiang LC, Wang RZ, Li MH, Sun JX, Jiang Y, Han XG. Labile carbon inputs offset nitrogen-induced soil aggregate destabilization via enhanced growth of saprophytic fungi in a meadow steppe. Geoderma. 2024, 443. 116841

Funding

Key Technologies Research and Development Program of China(2022YFD1901402)

Science and Technology Plan Projects of Tibet Autonomous Region(XZ202201ZY0003N)

Chongqing Municipal Environmental Protection Bureau(2023-003/002)

RIGHTS & PERMISSIONS

The Author(s)