Systematic Calibration and Validation of Discrete Element Model Parameters for Cotton Root Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview comments 1:
The introduction currently lacks a thorough review of the existing literature on discrete element method (DEM) calibration. It is recommended that the authors expand the literature review to better contextualize the current state of research in this area and clearly articulate the significance of their study. Additionally, the application of DEM technology to cotton stalk harvesting is not sufficiently emphasized. It is suggested that the authors incorporate more applied research examples relevant to DEM in agricultural harvesting processes, particularly in the context of cotton stalks.
Review comments 2:
Section 2.1.1 presents the measurement and statistical analysis of root system morphological parameters; however, the explanation would benefit from the inclusion of illustrative figures with clearly labeled positions to enhance reader comprehension. Moreover, Table 1 currently reports only the morphological data of the taproot. It is suggested that the authors supplement the table with data on other relevant root structures to provide a more comprehensive morphological overview.
Review comments 3:
Figures 8 and 9 depict two distinct modeling strategies: a single-chain rod-shaped model using non-tangential particle arrangements and a multi-layer particle model employing tangential particle arrangements to form a structured model. It is strongly recommended that the authors elaborate on the rationale for adopting these different modeling approaches, explaining the criteria for selecting each method and their respective implications for simulation accuracy and performance.
Review comments 4:
Chapter 2 identifies Xinluzao Cotton 66 as the selected experimental material. The authors are advised to provide a justification for choosing this particular variety—such as its regional representativeness, prevalence in cultivation, or unique morphological characteristics—to strengthen the scientific basis for the study. Additionally, it should be clarified whether existing DEM calibration studies on cotton stalk models have also used Xinluzao Cotton 66. If not, the authors should discuss the morphological and mechanical differences among varieties and analyze how such variability may affect model comparability and the generalizability of the study’s findings.
Review comments 5:
The manuscript utilizes the Plackett–Burman test, the steepest ascent method, and the Box–Behnken design to calibrate contact parameters, while bonding parameters are calibrated using the Central Composite Design. As the calibration of contact parameters is inherently more complex, the authors are encouraged to provide a clear justification for the selection of these specific experimental designs. This explanation should include the reasoning behind the chosen sequence and how each method addresses the particular challenges of parameter calibration in DEM simulations.
Review comments 6:
The root system is complex in shape, which makes structured meshing difficult. The paper proposes a method for dividing the root into structured grids. It is suggested to briefly explain how the structured mesh was created and how the model ensures a reasonable representation of the root shape. If curved or irregular parts were simplified, please mention how this was handled in general terms. Adding one or two representative illustrations of the grid and particle distribution would improve clarity.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe title is precise and reflects the study’s content, clearly indicating the method (DEM) and the application (cotton root systems).
Abstract: The abstract is structured and quantitative, reporting specific results and relative errors that strengthen credibility. It is clear and contains quantitative results, but it is overly long and dense. The novelty should be stated at the beginning, sentences should be shorter, and the sequence should follow a clear method–result–significance structure. Avoid listing all statistical test names and focus on the main findings and their practical relevance.
Keywords: The selected keywords are relevant and appropriate for the study. However, consider whether adding one or two broader or related terms (e.g., “root–soil interaction,” “bonding parameters”) might help capture a wider audience interested in related modeling approaches.
Introduction: The introduction provides solid context on cotton production, the importance of whole-stalk removal, and the role of DEM modeling in agricultural engineering. It effectively cites relevant work on other crops and related modeling approaches. However, the novelty statement could be more explicit and placed earlier, clearly identifying what has not been done for cotton root systems and why this study is needed. The gap between existing DEM work and this research should be summarized in one or two clear sentences before stating the study objectives. Consider tightening some literature descriptions to focus on the most relevant prior studies and avoid over-detailing methods from other crops in this section.
Materials and Methods: The section is comprehensive, logically structured, and describes the experimental, modeling, and calibration procedures in sufficient detail for reproducibility. The integration of physical tests with DEM parameter calibration is a strength, and the use of statistical designs (Plackett–Burman, steepest ascent, Box–Behnken, CCD) is appropriate. Minor refinements could include briefly justifying certain fixed modeling parameters (e.g., particle radius of 0.5 mm) and considering whether some procedural details (e.g., extended image-processing steps) could be moved to supplementary material for conciseness. Overall, the methodology is rigorous and well aligned with the study objectives.
Results and Discussion: The section clearly presents the results but functions more like a report than a discussion. While statistical findings and error values are well documented, there is limited interpretation of why these results occurred and little benchmarking against existing DEM root modeling studies. Expanding the discussion to interpret trends, compare with literature, and highlight implications for cotton harvester design would strengthen the section and align it with high-impact journal expectations.
Also the Results and Discussion would benefit from deeper interpretation and benchmarking. Please explain the physical meaning of influential factors, for example why X3 and X5 dominate stacking angle trends, and compare your optimal parameter ranges and error levels against the closest prior DEM root studies already cited in your paper.
Discuss generalizability, since soil inputs were selected for sandy loam with specific moisture and stiffness values, and clarify how parameters might transfer to other soils and moisture states.
Tensile verification error: You report measured 36.287 N and simulated 32.780 N, yet the relative error is stated as about 1.53 percent. Please recompute and confirm the correct percentage, and align text, table, and figure values.
Lateral-root shear modulus is inconsistent. The text gives 5.27 × 10^6 Pa, but Table 2 lists 5.27 × 10^7 Pa. Reconcile one order of magnitude difference.
ANOVA lack-of-fit P-value appears as 0.0852 in Table 12, but the narrative states 0.0874. Use one value consistently and ensure it matches the software output.
Table 13 has an impossible unit. “Bond stress 2.13 × 10^6 MPa” is physically implausible. Likely intended Pa or MPa, not 10^6 MPa. Correct the unit and magnitude. Also fix “Unite” to “Unit.” on Table 13.
DMS seconds exceed 59. Please provide valid DMS or decimal-degree coordinates.
Conclusion: Accurate quantitative recap, now add one line on practical impact for harvester design and DEM parameter libraries, one line on limits tied to the single sandy-loam field condition, and one line on transferability across soils and moisture with a brief sensitivity plan.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThank you for your detailed responses to my comments. I have carefully reviewed the revisions and clarifications provided, and I find them satisfactory. The manuscript has improved as a result of the changes, and I have no further concerns. I appreciate the authors’ efforts in addressing the issues raised.
Comments on the Quality of English LanguageThe quality of English is clear and acceptable for publication. While I am not a language expert, I find the manuscript understandable and well written. Minor improvements could be made through careful proofreading to further enhance readability.
