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Article

Contrasting Pre- and Post-Pyrolysis Incorporation of Bentonite into Manure Biochar: Impacts on Nutrient Availability, Carbon Stability, and Physicochemical Properties

by
Thidarat Rupngam
1,2,
Patchimaporn Udomkun
1,2,*,
Thirasant Boonupara
3 and
Puangrat Kaewlom
1,*
1
Department of Environmental Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai 50200, Thailand
2
Office of Research Administration, Chiang Mai University, Chiang Mai 50200, Thailand
3
Living Soil Co., Ltd., Chiang Mai 50100, Thailand
*
Authors to whom correspondence should be addressed.
Agronomy 2025, 15(8), 2015; https://doi.org/10.3390/agronomy15082015
Submission received: 25 June 2025 / Revised: 11 August 2025 / Accepted: 15 August 2025 / Published: 21 August 2025
(This article belongs to the Section Agricultural Biosystem and Biological Engineering)

Abstract

Manure-derived biochar is a promising soil amendment, though its effectiveness is often constrained by limited structural stability and inconsistent nutrient retention. This study evaluated how the pyrolysis method (pre- vs. post-pyrolysis) and rate (5%, 10%, 20%, and 30% w/w) of bentonite incorporation influence the physicochemical properties, nutrient availability, and carbon stability of manure-derived biochar. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses revealed that pre-pyrolysis addition enhanced mineral integration, with silicon and aluminum contents increasing by up to 500% and 600%, respectively, while carbon content decreased by up to 34%. Water holding capacity (WHC) improved by approximately 102% with 5–10% bentonite, and carbon stability more than doubled (≥100% increase) at moderate application rates under pre-pyrolysis treatment. However, nitrate (NO3) and potassium (K) availability declined by up to 89% and 47%, respectively, in pre-pyrolysis treatments due to strong nutrient immobilization. In contrast, post-pyrolysis bentonite addition increased NO3 by ~44% and K by ~29%, while phosphorus (P) availability rose by 133% at 30% bentonite. Principal component analysis (PCA) showed a clear distinction between pre- and post-pyrolysis bentonite-treated biochar. Pre-pyrolysis treatments were linked to higher pH, WHC, and carbon stability, while post-pyrolysis treatments were associated with greater nutrient availability (e.g., NO3, and K levels) and higher EC. These findings underscore the importance of the pyrolysis method, showing that pre-pyrolysis bentonite incorporation strengthens biochar’s structural integrity and long-term carbon sequestration potential, whereas post-pyrolysis addition enhances immediate nutrient availability. This duality enables the development of targeted biochar formulations tailored to specific agronomic needs—whether for sustained soil improvement or rapid fertility enhancement in climate-smart and sustainable land management systems.
Keywords: biochar–bentonite composite; pre- and post-pyrolysis modification; soil amendment; carbon stabilization; nutrient retention; sustainable agriculture; greenhouse gas mitigation biochar–bentonite composite; pre- and post-pyrolysis modification; soil amendment; carbon stabilization; nutrient retention; sustainable agriculture; greenhouse gas mitigation

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MDPI and ACS Style

Rupngam, T.; Udomkun, P.; Boonupara, T.; Kaewlom, P. Contrasting Pre- and Post-Pyrolysis Incorporation of Bentonite into Manure Biochar: Impacts on Nutrient Availability, Carbon Stability, and Physicochemical Properties. Agronomy 2025, 15, 2015. https://doi.org/10.3390/agronomy15082015

AMA Style

Rupngam T, Udomkun P, Boonupara T, Kaewlom P. Contrasting Pre- and Post-Pyrolysis Incorporation of Bentonite into Manure Biochar: Impacts on Nutrient Availability, Carbon Stability, and Physicochemical Properties. Agronomy. 2025; 15(8):2015. https://doi.org/10.3390/agronomy15082015

Chicago/Turabian Style

Rupngam, Thidarat, Patchimaporn Udomkun, Thirasant Boonupara, and Puangrat Kaewlom. 2025. "Contrasting Pre- and Post-Pyrolysis Incorporation of Bentonite into Manure Biochar: Impacts on Nutrient Availability, Carbon Stability, and Physicochemical Properties" Agronomy 15, no. 8: 2015. https://doi.org/10.3390/agronomy15082015

APA Style

Rupngam, T., Udomkun, P., Boonupara, T., & Kaewlom, P. (2025). Contrasting Pre- and Post-Pyrolysis Incorporation of Bentonite into Manure Biochar: Impacts on Nutrient Availability, Carbon Stability, and Physicochemical Properties. Agronomy, 15(8), 2015. https://doi.org/10.3390/agronomy15082015

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