Continuous biochar amendment to achieve long-term CH₄ mitigation in paddy fields under water-saving irrigation: a 5-year experiment

Abstract

Biochar amendment is an effective strategy for mitigating methane (CH₄) emissions in paddy fields. However, the long-term efficacy of different biochar amendment strategies for mitigating CH₄ emissions remains unclear, particularly under different water management regimes. To address this knowledge gap, a 5-year (2018–2022) field experiment was conducted to determine CH₄ production potential, CH₄ oxidation potential, and CH₄ emissions in paddy fields under six treatments: flooded irrigation (F) without biochar amendment (FB0), F with once biochar amendment (12.5 t ha⁻¹, FB1), F with continuous biochar amendment (2.5 t ha⁻¹ year⁻¹, FB5), controlled irrigation (C) without biochar amendment (CB0), C with once biochar amendment (12.5 t ha⁻¹, CB1), and C with continuous biochar amendment (2.5 t ha⁻¹ year⁻¹, CB5). Additionally, random forest analysis and structural equation modeling (SEM) were used to elucidate interaction pathways among biochar amendment, water management, CH₄ production and oxidation potentials, and key soil properties affecting CH₄ emissions. In the first year, once biochar amendment demonstrated optimal CH₄ mitigation efficacy under different water management regimes, reducing cumulative CH₄ emissions by 18.87–36.32% compared to other treatments. However, this mitigation effect diminished progressively over 5 years under different water management regimes, with the most rapid decline occurring under C. Consequently, there was no significant difference in the 5-year cumulative CH₄ emissions between FB1 and FB5, while CB5 achieved a significant 29.32% reduction in 5-year cumulative CH₄ emissions compared to CB1. Random forest analysis and SEM identified soil redox potential (Eh), dissolved organic carbon (DOC), and ammonium nitrogen (

{\text{NH}}_4^{+}\text{-N}

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) as key soil properties driving CH₄ emissions. CB5 maintained higher soil Eh and

{\text{NH}}_4^{+}\text{-N}

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levels with lower DOC, leading to the lowest CH₄ production potential and highest CH₄ oxidation potential over 5 years, ultimately achieving the greatest CH₄ mitigation. Furthermore, CB5 achieved the lowest CH₄-attributed greenhouse gas intensity and net greenhouse gas emissions over 5 years. These findings highlight the necessity of long-term monitoring to accurately assess the effects of biochar amendments on CH₄ mitigation and offer technical guidance for implementation of biochar strategies in paddy fields under different water management regimes.

Highlights

•	Water-saving irrigation rapidly diminished the CH4 mitigation effect of the once biochar amendment.
•	Continuous biochar amendment combined with water-saving irrigation was the most effective strategy for CH4 mitigation over 5 years.
•	Soil Eh, DOC, and {\text{NH}}_4^{+}\text{-N} \documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$$\text{NH}^{+}_{4}\text{-N}$$\end{document} were key drivers of CH4 emissions over 5 years.

Graphical Abstract

Keywords

Paddy fields / Biochar amendment / Water-saving irrigation / CH₄ mitigation

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Funding

National Key Research and Development Program of China(2022YFD2300303)

RIGHTS & PERMISSIONS

The Author(s)