the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 09 Feb 2026
The pH and Phosphorus Availability as Primary Drivers of Compost-Induced CO2 Emissions from Malaysian Tropical Soil: Mechanistic Evidence
Abstract. Confronting the global need for climate-smart agriculture, this study investigated the mechanisms controlling CO2 emissions from a Malaysian tropical soil amended with four composts. Multiple regression analyses identified soil available phosphorus (AP) and pH as the key interactive drivers of CO2 emissions, which followed the order: chicken dung compost (CDCS) > sludge compost (SLS) > goat manure-leaf compost (GLCS) > food waste compost (FWCS).The significantly higher emissions from CDCS were primarily due to its pronounced elevation of soil pH, likely stimulating microbial activity. The positive correlation with AP indicated that enhanced phosphorus availability further promoted microbial carbon mineralization. The findings demonstrate that compost is not a carbon-neutral amendment; its net climate impact depends on the specific physic-chemical changes it induces in the soil. This provides a scientific basis for optimizing compost selection to reconcile soil fertility improvement with greenhouse gas mitigation in tropical agroecosystems
Competing interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Chiu Chuen, Onn reports financial support was provided by Malaysia Ministry of Higher Education. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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Status: open (until 06 May 2026)
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EC1: 'Comment on egusphere-2026-150', Rafael Clemente, 26 Feb 2026
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AC1: 'Reply on EC1', Chiu Chuen Onn, 09 Apr 2026
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We thank the reviewer for their careful reading of our manuscript and for identifying the issues in the reference list. We have thoroughly revised all citations and the reference list to ensure consistency and accuracy. The corrected version has been uploaded. We appreciate the reviewer’s valuable feedback, which has helped improve the quality of our paper.
Citation: https://doi.org/10.5194/egusphere-2026-150-AC1
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AC1: 'Reply on EC1', Chiu Chuen Onn, 09 Apr 2026
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RC1: 'Comment on egusphere-2026-150', Anonymous Referee #1, 01 Apr 2026
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1. the manuscript has some grammar and spelling errorsÂ
2. the type of composts selected needs to be clearly described on how it was produced, line 90Â Â3. Need to explain the justification of the 2 amendment ratio, line 95Â
4. References missing for back titration method, line 100Â
5. You cannot decide compaction effect based on figures, where is your numerical data, Line 120Â
6. Figure 2, standardize if you want to show figures/error bars for all, Line 145Â
7. Figure 4, spelling errors on axisÂ
8. Multiple linear regression analysis, where the values , 0.74, 0.73, in figure tested for significance?, Line 190Citation: https://doi.org/10.5194/egusphere-2026-150-RC1 -
CC1: 'Comment on egusphere-2026-150', Yurui Fan, 02 Apr 2026
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This is a high-quality, well-executed study that makes a valuable contribution to understanding soil carbon dynamics in tropical agroecosystems. The research addresses a critical gap in climate-smart agriculture by systematically quantifying CO2Â emissions from compost-amended Malaysian Ultisols and identifying pH and available phosphorus as the primary interactive drivers. The experimental design is rigorous, the statistical approach is robust (ridge regression effectively resolves multicollinearity), and the core findings are novel and mechanistically sound. The manuscript is clearly structured, well-written, and provides actionable insights for optimizing compost management to balance soil fertility and greenhouse gas mitigation. It merits publication with only minor revisions.
- Define all compost abbreviations (CDCS, SLS, GLCS, FWCS) upon their first appearance in the abstract, as abstracts should be self-contained and follow standard academic formatting.
- Add a brief statement in Section 2.1 indicating the maturation period of the tested composts, which will improve the transparency and reproducibility of the experimental protocol.
- Standardize "CO2" to "CO2" (with subscript) in the titles of Figures 3 and 4.
- Correct the misspelling "ART-soil" in Section 3.1 to "ARC-soil".
- Delete the redundant "Maisture" in the correlation matrix section (Section 3.3).
- Fix the spelling error "Analyss" in the title of Figure 5 to "Analysis".
- Add the initial pH and available phosphorus values of the original ARC-soil in Section 2.1 for direct comparison.
- Add "soil pH" to the keyword list, as it is one of the two primary drivers identified in this study and a central research variable.
- Briefly acknowledge the limitation of this being a laboratory incubation study (lack of long-term field validation) in the conclusion.
- Standardize the journal name abbreviations in the references per the target journal's guidelines.
Citation: https://doi.org/10.5194/egusphere-2026-150-CC1 -
RC2: 'Comment on egusphere-2026-150', Anonymous Referee #2, 04 Apr 2026
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- Introduction
In the introduction section, the authors do not include the hypothesis of the study.
- Material and methods
In materials and methods section, the text references Supporting information, but these files are not available for download. Please, ensure all supplementary information is properly uploaded. Further, please, include the main methods for nitrogen fraction, available phosphorus and pH assessment in the main manuscript. Further, please, include critical information such as incubation temperature of the soils.
Regarding the use of compost, it’d be interesting to include an initial characterization of the compost used, as the authors state later in the manuscript, the nature of compost used is essential in assessing its effects on soil parameters.
Please specify the exact days of the 14 gas sampling events in the text, rather than leaving the reader to infer them from the graphs.
Regarding the statistical analysis, the manuscript lacks information on how differences between treatments for the soil physicochemical parameters (Figure 2) were assessed. While Section 2.3 solely describes the Multiple Linear Regression model, Section 3.1 repeatedly claims "significant" increases in parameters like TN, AP, and AK without stating the specific mean comparison tests used (e.g., ANOVA, Tukey's HSD). Additionally, Figure 2 omits significance letters to statistical differences and fails to define the error bars in the caption.
- Discussion
Regarding the use of "mechanistic" in the title and abstract, this terminology is an overstatement. While the study successfully identifies strong statistical relationships through multiple linear regression (e.g., between pH, available phosphorus, and CO2 production), correlation does not equate to a biological mechanism. Since the experimental design does not include direct biological measurements such as microbial community shifts, specific enzymatic activities, or isotopic carbon tracing, it cannot claim to provide mechanistic evidence. I strongly recommend softening these claims throughout the manuscript and revising the title to reflect that the study investigates "empirical relationships" or "primary drivers" rather than mechanisms
Citation: https://doi.org/10.5194/egusphere-2026-150-RC2
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I have identified several errors in the references list, including incorrect author names/surnames, mismatched DOIs, and citations that cannot be verified by title or author. These inconsistencies must be thoroughly addressed and corrected if a revised version is later submitted.Â