Struvite-loaded biochar beads fertilizer for different soils: nutrient slow release, soil properties improvement and heavy metal remediation

Abstract

This study investigates the use of struviterient-loaded magnesium-modified biochar beads (Ca/MgBC + NP) as a slow-release fertilizer and soil amendment, comparing its performance with commercially available slow-release fertilizers (SRF) in different soils and crop types. The results demonstrate that Ca/MgBC + NP exhibited satisfying swelling, water retention, and slow-release properties in all tested soils. In sandy soil, which showed the most significant differences (p < 0.05), Ca/MgBC + NP enhanced the growth of Brassica chinensis L. and Spinacia oleracea L. after 90 d, with shoot and root lengths, as well as fresh and dry weights, 1.25–2.84 times higher than those treated with SRF. The cation exchange capacity and organic carbon content of sandy soil were significantly improved (by 38.55% and 265.38%), overcoming its natural limitations in water and fertilizer retention. Principal Component Analysis (PCA) confirmed that soil properties played a crucial role in crop growth (52.67% variance explained). Spectroscopic analysis indicated that magnesium-related compounds, including struvite and Mg(PO₄)₃, contributed to the observed growth promotion. Furthermore, Ca/MgBC + NP effectively immobilized heavy metals, particularly Cr and Hg, with immobilization rates exceeding 80%. This study highlights the potential of Ca/MgBC + NP as a sustainable, low-cost fertilizer that not only enhances crop growth but also improves soil health and remediates heavy metal contamination, providing a promising alternative for green agriculture.

Graphical abstract

Keywords

Sustainable development / Slow-release fertilizer / Release behavior / Pot experiment / Soil property improvement / Heavy metal remediation

Highlight

	● Ca/MgBC + NP showed satisfactory slow-release properties in various soils.
	● Ca/MgBC + NP effectively promoted crop growth in various soil types and pH levels.
	● Ca/MgBC + NP improved soil properties in a variety of soil types and pH levels.
	● Ca/MgBC + NP effectively immobilized heavy metals, particularly Cr and Hg (over 80%).

References

[1] An X, Wu Z, Shi W, Qi H, Zhang L, Xu X, Yu B. (2021). Biochar for simultaneously enhancing the slow-release performance of fertilizers and minimizing the pollution of pesticides. Journal of Hazardous Materials, 407: 124865

[2] An X, Wu Z, Yu J, Cravotto G, Liu X, Li Q, Yu B. (2020). Copyrolysis of biomass, bentonite, and nutrients as a new strategy for the synthesis of improved biochar-based slow-release fertilizers. ACS Sustainable Chemistry & Engineering, 8(8): 3181–3190

[3] Antor N H, Mia S, Hasan M M, Lipi N J, Jindo K, Sanchez-Monedero M A, Rashid M H. (2023). Chemically and biologically activated biochars slow down urea hydrolysis and improve nitrogen use efficiency. Pedosphere, 33(4): 659–669

[4] Carneiro J S D S, Lustosa Filho J F, Nardis B O, Ribeiro-Soares J, Zinn Y L, Melo L C A. (2018). Carbon stability of engineered biochar-based phosphate fertilizers. ACS Sustainable Chemistry & Engineering, 6(11): 14203–14212

[5] Chen L, Chen X L, Zhou C H, Yang H M, Ji S F, Tong D S, Zhong Z K, Yu W H, Chu M Q. (2017). Environmental-friendly montmorillonite-biochar composites: facile production and tunable adsorption-release of ammonium and phosphate. Journal of Cleaner Production, 156: 648–659

[6] Chen M, Chen X, Xu X, Xu Z, Zhang Y, Song B, Tsang D C W, Xu N, Cao X. (2022). Biochar colloids facilitate transport and transformation of Cr(VI) in soil: active site competition coupling with reduction reaction. Journal of Hazardous Materials, 440: 129691

[7] Chen Q, Qin J, Sun P, Cheng Z, Shen G. (2018). Cow dung-derived engineered biochar for reclaiming phosphate from aqueous solution and its validation as slow-release fertilizer in soil-crop system. Journal of Cleaner Production, 172: 2009–2018

[8] Cheng S, Zeng W, Liu X, Zhao J, Qiu X, Lei Z. (2020). Anti-evaporation performance of water in soil of superabsorbent resin with fast water absorption rate. Water, Air, and Soil Pollution, 231(6): 291

[9] Costa P, Sousa Lobo J M. (2001). Modeling and comparison of dissolution profiles. European Journal of Pharmaceutical Sciences, 13(2): 123–133

[10] Ding Y, Liu Y, Liu S, Li Z, Tan X, Huang X. (2016). Biochar to improve soil fertility: a review. Agronomy for sustainable development, 36: 1–8

[11] Dou Z, Bini Farias M V, Chen W, He D, Hu Y, Xie X. (2023). Highly degradable chitosan-montmorillonite (MMT) nano-composite hydrogel for controlled fertilizer release. Frontiers of Environmental Science & Engineering, 17(5): 53

[12] Du Z, Sun X, Zheng S, Wang S, Wu L, An Y, Luo Y. (2024). Optimal biochar selection for cadmium pollution remediation in Chinese agricultural soils via optimized machine learning. Journal of Hazardous Materials, 476: 135065

[13] Duan Q, Jiang S, Chen F, Li Z, Ma L, Song Y, Yu X, Chen Y, Liu H, Yu L. (2023). Fabrication, evaluation methodologies and models of slow-release fertilizers: a review. Industrial Crops and Products, 192: 116075

[14] Fachini J, Figueiredo C C D, Vale A T D. (2022). Assessing potassium release in natural silica sand from novel K-enriched sewage sludge biochar fertilizers. Journal of Environmental Management, 314: 115080

[15] Gao D, Wu X, Huang Y, Zhou S, Wang G, Li B. (2024). Deciphering the interplay between wastewater compositions and oxytetracycline in recovered struvite: unveiling mechanisms and introducing control strategies. Journal of Hazardous Materials, 477: 135259

[16] Gao L Y, Deng J H, Huang G F, Li K, Cai K Z, Liu Y, Huang F. (2019). Relative distribution of Cd²⁺ adsorption mechanisms on biochars derived from rice straw and sewage sludge. Bioresource Technology, 272: 114–122

[17] Gong H, Yin Y, Chen Z, Zhang Q, Tian X, Wang Z, Wang Y, Cui Z. (2025). A dynamic optimization of soil phosphorus status approach could reduce phosphorus fertilizer use by half in China. Nature Communications, 16(1): 976

[18] Guo J H, Liu X J, Zhang Y, Shen J L, Han W X, Zhang W F, Christie P, Goulding K W T, Vitousek P M, Zhang F S. (2010). Significant acidification in major Chinese croplands. Science, 327(5968): 1008–1010

[19] GuoS, HuK, QiuR, HuangC, WuJ, ZhouC (2017). Research progress of biochar on acid soil improvement. Inner Mongolia Forestry Investigation and Design, 40(04): 92–94 (in Chinese)

[20] Hagemann N, Joseph S, Schmidt H P, Kammann C I, Harter J, Borch T, Young R B, Varga K, Taherymoosavi S, Elliott K W. . (2017). Organic coating on biochar explains its nutrient retention and stimulation of soil fertility. Nature Communications, 8(1): 1089

[21] Herath I, Kumarathilaka P, Navaratne A, Rajakaruna N, Vithanage M. (2015). Immobilization and phytotoxicity reduction of heavy metals in serpentine soil using biochar. Journal of Soils and Sediments, 15(1): 126–138

[22] Hossain M Z, Bahar M M, Sarkar B, Donne S W, Ok Y S, Palansooriya K N, Kirkham M B, Chowdhury S, Bolan N. (2020). Biochar and its importance on nutrient dynamics in soil and plant. Biochar, 2(4): 379–420

[23] HuaL, JinS, LuoJ (2012). Effect of bio-char on the microenvironment characteristics and humus in soil. Ecology and Environmental Sciences,21(11): 1795–1799 (in Chinese)

[24] Jin J, Sun K, Yang Y, Wang Z, Han L, Wang X, Wu F, Xing B. (2018). Comparison between soil- and biochar-derived humic acids: composition, conformation, and phenanthrene sorption. Environmental Science & Technology, 52(4): 1880–1888

[25] Kang X, Geng N, Li Y, He W, Wang H, Pan H, Yang Q, Yang Z, Sun Y, Lou Y. . (2024). Biochar with KMnO₄-hematite modification promoted foxtail millet growth by alleviating soil Cd and Zn biotoxicity. Journal of Hazardous Materials, 477: 135377

[26] Karim A A, Kumar M, Mohapatra S, Singh S K. (2019). Nutrient rich biomass and effluent sludge wastes co-utilization for production of biochar fertilizer through different thermal treatments. Journal of Cleaner Production, 228: 570–579

[27] Kottegoda N, Sandaruwan C, Priyadarshana G, Siriwardhana A, Rathnayake U A, Berugoda Arachchige D M, Kumarasinghe A R, Dahanayake D, Karunaratne V, Amaratunga G A J. (2017). Urea-hydroxyapatite nanohybrids for slow release of nitrogen. ACS Nano, 11(2): 1214–1221

[28] Li H, Wang Y, Zhao Y, Wang L, Feng J, Sun F. (2023a). Efficient simultaneous phosphate and ammonia adsorption using magnesium-modified biochar beads and their recovery performance. Journal of Environmental Chemical Engineering, 11(5): 110875

[29] Li H, Wei Y, Wang Y, Zhao Y, Wang L, Feng J, Sun F. (2024a). Cooperative adsorption of Sb(V) in water by magnetic MgFe₂O₄-biochar composite beads. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 684: 133133

[30] Li J, Yang D, Zou W, Feng X, Wang R, Zheng R, Luo S, Chu Z, Chen H. (2024b). Mechanistic insights into the synergetic remediation and amendment effects of zeolite/biochar composite on heavy metal-polluted red soil. Frontiers of Environmental Science & Engineering, 18(9): 114

[31] Li P, Yu J, Huangfu Z, Chang J, Zhong C, Ding P. (2020). Applying modified biochar with nZVI/nFe₃O₄ to immobilize Pb in contaminated soil. Environmental Science and Pollution Research International, 27(19): 24495–24506

[32] Li S, Xie Y, Jiang S, Yang M, Lei H, Cui W, Wang F. (2023b). Biochar decreases Cr toxicity and accumulation in sunflower grown in Cr(VI)-polluted soil. Toxics, 11(1): 787

[33] Li Y, Abdo A I, Shi Z, Merwad A R M A, Zhang J. (2023c). Biochar derived from invasive plants improved the pH, macronutrient availability and biological properties better than liming for acid rain-affected soil. Biochar, 5(1): 59

[34] Li Y, Yin H, Guo Z, Zhu M, Yan C, Li X, Dang Z. (2023d). Effects of α-Fe₂O₃ modified chicken manure biochar on the availability of multiple heavy metals and soil biochemical properties. Journal of Environmental Chemical Engineering, 11(3): 109922

[35] Liu X, Chen L, Hua Z, Mei S, Wang P, Wang S. (2020). Comparing ammonia volatilization between conventional and slow-release nitrogen fertilizers in paddy fields in the Taihu Lake region. Environmental Science and Pollution Research International, 27(8): 8386–8394

[36] Liu Y, Rillig M C., Liu Q, Huang J J, Khan M A, Li X, Liu Q, Wang Q, Su X, Lin L. . (2023). Factors affecting the distribution of microplastics in soils of China. Frontiers of Environmental Science & Engineering, 17(9): 110

[37] Lu J, Cheng M, Zhao C, Li B, Peng H, Zhang Y, Shao Q, Hassan M. (2022). Application of lignin in preparation of slow-release fertilizer: current status and future perspectives. Industrial Crops and Products, 176: 114267

[38] Lu J, Li Y, Cai Y, Jiang P, Yu B. (2023). Co-incorporation of hydrotalcite and starch into biochar-based fertilizers for the synthesis of slow-release fertilizers with improved water retention. Biochar, 5(1): 44

[39] Luo W, Qian L, Liu W, Zhang X, Wang Q, Jiang H, Cheng B, Ma H, Wu Z. (2021). A potential Mg-enriched biochar fertilizer: Excellent slow-release performance and release mechanism of nutrients. Science of the Total Environment, 768: 144454

[40] Luo Z, Li Y, Pei X, Woon K S, Liu M, Lin X, Hu Z, Li Y, Zhang Z. (2024). A potential slow-release fertilizer based on biogas residue biochar: nutrient release patterns and synergistic mechanism for improving soil fertility. Environmental Research, 252: 119076

[41] Lyu P, Li L, Huang J, Ye J, Zhu C. (2024). Magnetic biochar-supported layered double hydroxide for simultaneous remediation of As and Cd in soil: effectiveness, retention durability, and insight into a new immobilization mechanism. Journal of Cleaner Production, 434: 140136

[42] Ma W, Han R, Zhang W, Zhang H, Chen L, Zhu L. (2024). Magnetic biochar enhanced copper immobilization in agricultural lands: insights from adsorption precipitation and redox. Journal of Environmental Management, 352: 120058

[43] Mao J, Zhang K, Chen B. (2019). Linking hydrophobicity of biochar to the water repellency and water holding capacity of biochar-amended soil. Environmental Pollution, 253: 779–789

[44] Palansooriya K N, Li J, Dissanayake P D, Suvarna M, Li L, Yuan X, Sarkar B, Tsang D C W, Rinklebe J, Wang X. . (2022). Prediction of soil heavy metal immobilization by biochar using machine learning. Environmental Science & Technology, 56(7): 4187–4198

[45] SenD, GaoZ X (2006). Technical Specifications for Soil Analysis. Beijing: China Agriculture Press (in Chinese)

[46] Shang A, Yang K, Lu Y, Jia Q, Li Z, Ma G, Mu J. (2022). A novel slow-release fertilizer derived from itaconic acid–modified biochar: synthesis, characteristics, and applications in cucumber seedlings. Journal of Soil Science and Plant Nutrition, 22(4): 4616–4626

[47] Shen Y, Wang H, Liu Z, Li W, Liu Y, Li J, Wei H, Han H. (2021). Fabrication of a water-retaining, slow-release fertilizer based on nanocomposite double-network hydrogels via ion-crosslinking and free radical polymerization. Journal of Industrial and Engineering Chemistry, 93: 375–382

[48] Siepmann J, Peppas N A. (2011). Higuchi equation: derivation, applications, use and misuse. International Journal of Pharmaceutics, 418(1): 6–12

[49] Singh P, Rawat S, Jain N, Bhatnagar A, Bhattacharya P, Maiti A. (2023). A review on biochar composites for soil remediation applications: comprehensive solution to contemporary challenges. Journal of Environmental Chemical Engineering, 11(5): 110635

[50] Sui X, Guo H, Cai C, Li Q, Wen C, Zhang X, Wang X, Yang J, Zhang L. (2021). Ionic conductive hydrogels with long-lasting antifreezing, water retention and self-regeneration abilities. Chemical Engineering Journal, 419: 129478

[51] Wang C, Zhong Y, Liao H. (2024a). Partnering crops with root-associated microbes for soil health and agricultural sustainability. Pedosphere, 34(1): 26–29

[52] Wang Y, Li H, Zhao Y, Qi M, Wang L, Feng J. (2024b). Phosphate recovery from wastewater via vivianite crystallization using separable ferrous modified biochar beads. Chemical Engineering Journal, 498: 155453

[53] Wu C, Shi L, Xue S, Li W, Jiang X, Rajendran M, Qian Z. (2019a). Effect of sulfur-iron modified biochar on the available cadmium and bacterial community structure in contaminated soils. Science of the Total Environment, 647: 1158–1168

[54] Wu L, Wei C, Zhang S, Wang Y, Kuzyakov Y, Ding X. (2019b). MgO-modified biochar increases phosphate retention and rice yields in saline-alkaline soil. Journal of Cleaner Production, 235: 901–909

[55] Xia Y, Tang Y, Shih K, Li B. (2020). Enhanced phosphorus availability and heavy metal removal by chlorination during sewage sludge pyrolysis. Journal of Hazardous Materials, 382: 121110

[56] Xiao L, Yuan G, Feng L, Shah G M, Wei J. (2022). Biochar to reduce fertilizer use and soil salinity for crop production in the Yellow River delta. Journal of Soil Science and Plant Nutrition, 22(2): 1478–1489

[57] Xiao Q, Zhu J, Peng H, Yan J, Xionghui J. (2021). Effect of controlled release fertilizer combined with rice straw on ammonia volatilization from double-cropping rice fields. Journal of Agro-Environment Science, 40(12): 2788

[58] Xiao R, Wang J J, Gaston L A, Zhou B, Park J H, Li R, Dodla S K, Zhang Z. (2018). Biochar produced from mineral salt-impregnated chicken manure: fertility properties and potential for carbon sequestration. Waste Management, 78: 802–810

[59] Yadav S, Pipil H, Haritash A K, Reddy K R. (2024). Fe(III)-modified bamboo biochar for the removal of phosphate from synthetic and field stormwater runoff. Sustainable Water Resources Management, 10(4): 140

[60] Yang Q, Wang Y, Zhong H. (2021). Remediation of mercury-contaminated soils and sediments using biochar: a critical review. Biochar, 3(1): 23–35

[61] Yang S, Xiao Q, Li B, Zhou T, Cen Q, Liu Z, Zhou Y. (2024). Insights into remediation of cadmium and lead contaminated-soil by Fe-Mn modified biochar. Journal of Environmental Chemical Engineering, 12(3): 112771

[62] Yang Z, Zhang Z, Zuo Y, Zhang J, Zhang P. (2023). Comparison of exogenous degrader-enhanced bioremediation with low-dose persulfate oxidation for polycyclic aromatic hydrocarbon removal in alkaline soil: efficiency and influence on ecological health. Frontiers of Environmental Science & Engineering, 17(11): 133

[63] Yao Y, Gao B, Chen J, Yang L. (2013). Engineered biochar reclaiming phosphate from aqueous solutions: mechanisms and potential application as a slow-release fertilizer. Environmental Science & Technology, 47(15): 8700–8708

[64] Ye H M, Li H F, Wang C S, Yang J, Huang G, Meng X, Zhou Q. (2020). Degradable polyester/urea inclusion complex applied as a facile and environment-friendly strategy for slow-release fertilizer: Performance and mechanism. Chemical Engineering Journal, 381: 122704

[65] Ye X, Kang S, Wang H, Li H, Zhang Y, Wang G, Zhao H. (2015). Modified natural diatomite and its enhanced immobilization of lead, copper and cadmium in simulated contaminated soils. Journal of Hazardous Materials, 289: 210–218

[66] Yesigat A, Worku A, Mekonnen A, Bae W, Feyisa G L, Gatew S, Han J L, Liu W, Wang A, Guadie A. (2022). Phosphorus recovery as K-struvite from a waste stream: a review of influencing factors, advantages, disadvantages and challenges. Environmental Research, 214: 114086

[67] Yuan Y, Liu Q, Zheng H, Li M, Liu Y, Wang X, Peng Y, Luo X, Li F, Li X. . (2023). Biochar as a sustainable tool for improving the health of salt-affected soils. Soil & Environmental Health, 1(3): 100033

[68] Zhang B, Liu C, Li Q, Ye J, Lin Y, Wang Y, Burton D L. (2025a). Evaluating the effect of biochar rate and combination with fertilizer on the dynamics of soil nitrogen supply in tea plantation. Scientific Reports, 15(1): 3135

[69] Zhang L, Chang L, Liu H, De Jesús Puy Alquiza M, Li Y. (2025b). Biochar application to soils can regulate soil phosphorus availability: a review. Biochar, 7(1): 13

[70] Zhang Y, Cao L, Zhang J, Wang J, Tian G. (2024). Eco-friendly preparation of biochar nanomaterials from waste walnut shell and their adsorption application. Industrial Crops and Products, 213: 118462

[71] Zhong D, Jiang Y, Zhao Z, Wang L, Chen J, Ren S, Liu Z, Zhang Y, Tsang D C W, Crittenden J C. (2019). pH dependence of arsenic oxidation by rice-husk-derived biochar: roles of redox-active moieties. Environmental Science & Technology, 53(15): 9034–9044

[72] Zhuang Q L, Yuan H Y, Qi J Q, Sun Z R, Tao B X, Zhang B H. (2024). Phosphorus fertiliser application mitigates the negative effects of microplastic on soil microbes and rice growth. Journal of Hazardous Materials, 465: 133278

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