Impact of Biochar Interlayer on Surface Soil Salt Content, Salt Migration, and Photosynthetic Activity and Yield of Sunflowers: Laboratory and Field Studies

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript focuses on the regulatory effects of a biochar interlayer on salt migration in saline soils and sunflower growth. By combining laboratory soil column experiments with field trials, the study systematically evaluates the impact of varying biochar dosages on soil physicochemical properties and plant physiological responses. The topic holds clear practical relevance, particularly for mitigating agricultural soil salinization and enhancing the resource utilization of biochar, thus contributing both theoretically and technically. The manuscript is well-structured and logically developed. The experimental data are generally sufficient, and the conclusions are largely supported by the findings. However, several methodological descriptions lack necessary detail, some interpretations remain superficial, and the discussion and literature review require further depth. A major revision is recommended. The following issues should be addressed to improve the scientific rigor and overall quality of the manuscript:

1. The method section lacks detail on the implementation of the biochar interlayer. The placement technique—whether layered compaction, uniform mixing, or single-layer application—is unclear. Additionally, the basis for determining layer thickness and the conversion formula from t/ha to cm are missing.
2. A clear and reproducible description of the biochar application method, including thickness calculation (e.g., based on bulk density), should be provided.
3. Field experiments do not adequately account for potential confounding factors. There is no mention of soil salinity heterogeneity assessments (e.g., baseline mapping or randomized block design), nor are environmental parameters such as rainfall, evaporation, and groundwater levels reported.
4. Inclusion of a spatial distribution map of the plots, GPS coordinates of sampling points, or an explanation of how environmental variability was controlled would enhance transparency.
5. The manuscript fails to report the number of replicates used in laboratory and field experiments. Statistical power justification is also lacking and should be addressed to support the validity of the experimental design.
6. Assumptions underlying statistical analyses are not addressed. ANOVA and LSD tests are used without confirming whether data met normality and homoscedasticity assumptions (e.g., via Shapiro-Wilk or Levene’s tests).
7. The methods section should include assumption testing procedures, or alternatively, non-parametric tests should be employed when assumptions are not satisfied.
8. Figure 3 presents inconsistent units for ion concentrations (“mg/g” and “cmol/kg”), which should be standardized for clarity.
9. In Tables 3 and 4, some units (e.g., for “K⁺”) are omitted. Additionally, superscript letters used to indicate statistical significance (a/b/c) are not defined in the figure captions.
10. Figure 2 appears to contain a typographical error in the unit “dBm⁻¹”, which should likely be corrected to “dS m⁻¹”.
11. The color contrast in Figure 3’s legend is insufficient, particularly for “Stage 1–3.” Improved contrast or alternative fill patterns would aid visual interpretation.
12. Several critical limitations remain unaddressed, including:
    The long-term structural degradation of biochar and its effects on sustained performance;
    b. Applicability across different soil types (e.g., sandy vs. clayey soils);
    c. Potential negative impacts such as waterlogging or salt accumulation at high biochar dosages.
13. Interpretation of results is overly descriptive, often stating outcomes as “increased” or “decreased” without elaborating on underlying mechanisms such as ion exchange, micropore adsorption, or rhizosphere modification.

14. Integrating the recent studies on the role of biochar in altering the rhizosphere microenvironment and regulating salt transport will significantly enhance the discussion.

15. The spelling of the term "Achene yield" is inconsistent between the abstract and the main text.

16. A comprehensive proofreading is necessary to ensure consistency in units (such as "t/ha" and "Mg/ha"), symbols (±), and abbreviations (such as the first mention of "EC")' definitions.

Author Response

Response to reviewer comments

This manuscript focuses on the regulatory effects of a biochar interlayer on salt migration in saline soils and sunflower growth. By combining laboratory soil column experiments with field trials, the study systematically evaluates the impact of varying biochar dosages on soil physicochemical properties and plant physiological responses. The topic holds clear practical relevance, particularly for mitigating agricultural soil salinization and enhancing the resource utilization of biochar, thus contributing both theoretically and technically. The manuscript is well-structured and logically developed. The experimental data are generally sufficient, and the conclusions are largely supported by the findings. However, several methodological descriptions lack necessary detail, some interpretations remain superficial, and the discussion and literature review require further depth. A major revision is recommended. The following issues should be addressed to improve the scientific rigor and overall quality of the manuscript:

1. The method section lacks detail on the implementation of the biochar interlayer. The placement technique—whether layered compaction, uniform mixing, or single-layer application—is unclear. Additionally, the basis for determining layer thickness and the conversion formula from t/ha to cm are missing.

Reply:

It is mentioned in the manuscript as “The implementation of biochar resulted in distinct layer thicknesses for each treatment”. For more clarification, biochar was not mixed with soil. It was placed as a distinct interlayer.

2. A clear and reproducible description of the biochar application method, including thickness calculation (e.g., based on bulk density), should be provided.

Reply:

A clear and reproducible description of the biochar application method, including the calculation of thickness based on bulk density, has been provided in the revised manuscript to ensure transparency and replicability.

3. Field experiments do not adequately account for potential confounding factors. There is no mention of soil salinity heterogeneity assessments (e.g., baseline mapping or randomized block design), nor are environmental parameters such as rainfall, evaporation, and groundwater levels reported.

Reply:

 

We have revised the manuscript to include additional details on the field layout, soil uniformity assessments, and available environmental parameters during the experimental periods.

 

4. Inclusion of a spatial distribution map of the plots, GPS coordinates of sampling points, or an explanation of how environmental variability was controlled would enhance transparency.

Reply:

The map of the study area has been incorporated.

5. The manuscript fails to report the number of replicates used in laboratory and field experiments. Statistical power justification is also lacking and should be addressed to support the validity of the experimental design.

Reply:

The number of replicates used in both the laboratory and field experiments has been clearly stated in the revised manuscript. Additionally, justification for the number of replicates based on statistical power considerations has been provided to strengthen the validity and reliability of the experimental design.

 

6. The methods section should include assumption testing procedures, or alternatively, non-parametric tests should be employed when assumptions are not satisfied.

Reply:

Thank you for your observation. We agree that verifying statistical assumptions is essential before conducting ANOVA. In our analysis, assumption testing procedures were performed before ANOVA, including checks for normality and homogeneity of variances. All datasets met the required assumptions for parametric analysis. Therefore, ANOVA followed by LSD post-hoc testing was deemed appropriate.

7. Figure 3 presents inconsistent units for ion concentrations (“mg/g” and “cmol/kg”), which should be standardized for clarity.

Reply:

Corrected

 

8. In Tables 3 and 4, some units (e.g., for “K⁺”) are omitted. Additionally, superscript letters used to indicate statistical significance (a/b/c) are not defined in the figure captions.

Reply:

We have revised Tables 3 and 4 to include all missing units (e.g., for “K⁺”) and updated the figure captions to clearly define the superscript letters used to indicate statistically significant differences among treatments.

9. Figure 2 appears to contain a typographical error in the unit “dBm⁻¹”, which should likely be corrected to “dS m⁻¹”.

Reply:

It has been corrected.

10. The color contrast in Figure 3’s legend is insufficient, particularly for “Stage 1–3.” Improved contrast or alternative fill patterns would aid visual interpretation.

Reply:

The color contrast in Figure 3’s legend, particularly for 'Stage 1–3', has been improved in the revised manuscript.

11. Several critical limitations remain unaddressed, including:
    The long-term structural degradation of biochar and its effects on sustained performance;
    Applicability across different soil types (e.g., sandy vs. clayey soils);
    c. Potential negative impacts such as waterlogging or salt accumulation at high biochar dosages.

Reply:

More details have been incorporated in the manuscript, such as although the present study was conducted on a specific soil type, the applicability of biochar across diverse soil textures, such as sandy and clayey soils, remains an important area for further research. Variability in soil properties may influence the physicochemical interactions between biochar and the soil matrix, thereby affecting outcomes related to salinity reduction and soil fertility. Furthermore, the possibility of adverse effects, including waterlogging or salt accumulation under high biochar application rates, warrants attention. These limitations underscore the need for extended field trials under different edaphic and climatic conditions to ensure the robustness and scalability of biochar-based interventions.

 

12. Interpretation of results is overly descriptive, often stating outcomes as “increased” or “decreased” without elaborating on underlying mechanisms such as ion exchange, micropore adsorption, or rhizosphere modification.

Reply:

A relevant reference has been incorporated to support the proposed mechanisms, enhancing the scientific depth of interpretation [19].

13. Integrating the recent studies on the role of biochar in altering the rhizosphere microenvironment and regulating salt transport will significantly enhance the discussion.

Reply:

We have revised the discussion section to incorporate recent findings on the role of biochar in modifying the rhizosphere microenvironment and regulating salt transport. A supporting reference has been added [36] to strengthen the explanation of how biochar facilitates ion exchange and improves root-zone conditions under salt stress.

14. The spelling of the term "Achene yield" is inconsistent between the abstract and the main text.

Reply:

Corrected.

15. Comprehensive proofreading is necessary to ensure consistency in units (such as "t/ha" and "Mg/ha"), symbols (±), and abbreviations (such as the first mention of "EC")' definitions.

Reply:

corrected.

 

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript addresses an important agricultural challenge and provides valuable insights into biochar’s role in saline soil remediation. However, revisions are required. The introduction section should elaborate on the innovative aspects of this paper. In the Materials and Methods section, the narrative should be concise and avoid redundancy and excessive use of adjectives. It should clarify the logical relationship between the soil column experiment and the field experiment. For example, the soil column experiment should be able to provide appropriate irrigation water volumes. Currently, the two experiments appear to be independent of each other. In the Results section, the soil column experiment lacks relevant soil indicators, and the field experiment lacks stratified soil data. The Discussion section is not in-depth enough. The specific details are as follows:

• Lines 140-141, “soil samples were collected from two distinct depths: 0-20 cm and 20-40 cm.” Soil samples were collected from both 0-20 cm and 20-40 cm layers. However, Table 1 presents physicochemical data without stratification by depth. Please clarify the rationale for not providing layer-specific data and provide justification (e.g., statistical homogeneity between layers, analytical methodology constraints, or reference to standardized protocols). In addition, are the data in Table 1 labeled as "ion exchange capacity"? while water-soluble ions is used in subsequent sections. To avoid ambiguity, please clarify whether these terms refer to the same analytical parameter. The units is /, such as K, Ca Mg, what does this mean?
• Materials and Methods section: Integrate the data/content from Table 1 into the corresponding descriptive text; Ensure concise and technical writing throughout this section, avoiding excessive embellishments. Present methods and results in a straightforward manner.
• Soil column experiment: In the soil column experiment, there is a lack of measurement for key soil indicators such as salinity, ion concentrations, and nutrient content, particularly their distribution across different soil layers and in the leachate. This limits the mechanistic understanding of how biochar interlayers influence salt migration and nutrient redistribution. In addition, the soil columns were packed to a bulk density of 1.4 g cm⁻³. However, in actual field conditions, bulk density typically varies across different soil layers. The study also fails to provide bulk density data for distinct soil layers in the field experiment.
• lines161-164, bulk density of 0.52 cm^-3, 0.52 g cm^-3? “the biochar treatments were designated as BL20, BL40, BL60, and BL80, corresponding to the addition of 20, 40, 60 and 80 tons per hectare”, how many is the addition of biochar in each column?
• 2 field experiment section: The biochar application rates (up to 80 tons ha⁻¹) may exceed practical feasibility for large-scale farming. In the results, BL60 and BL80 were optimal results, but their economic and logistical viability is not discussed. In addition, which irrigation technology was applied, how much irrigation amount was used, and so on. What is the buried depth of the groundwater? Are there any drainage facilities? Where are soil salt and ions?
• Lines218-219, “20 plots?” five treatments with three replications, why 20 plots?
• Lines 236-237, “plant height, the number of leaves, stem diameter, and head diameter.” These indexes are not presented in the Results section.
• 2.2 section, present the analytical parameters and methods concisely, avoiding extended discussion. Those contents can be moved into discussion section.
• Lines 265, 2.2.1 should be 2.2.3
• Lines 267-269, Why was a soil-to-water ratio of 1:10 selected? Please clarify the theoretical or experimental basis (e.g., relevant standards, literature references, or preliminary tests) for this specific ratio.
• Lines 274-281, Please supplement the model numbers, manufacturers, and relevant technical specifications of all instruments and equipment used.
• Line 318, 3.1 should be 3.1.1
• Lines 341-343, which exhibits substantial overlap/redundancy with preceding sections of lines 192-200.
• Figures 1 and 2, Please supplement error bars. Please add superscript letters denoting statistical significance (e.g., a, b, c) to the bars in Figure 3 to clearly indicate significant differences between groups. In addition, suggest that adding the nutrient concentrations in the leachate.
• Section 3.1, Please add the total and stage volume of leachate. In addition, soil ions and nutrient concentrations should be added in the manuscript.
• Table 4 presents the data, 0-20 or 20-40 cm? The data are presented as the means ± SEs. However, no SEs in the table 4. In addition, the units of N,P,K are missed. Since the addition of biochar is conducive to the leaching of salts, it is also possible that soil nutrients will be leached. So, why does the addition of biochar increase the content of soil nutrients (nitrogen, phosphorus, potassium, and organic matter)? What is the mechanism behind this increase? Moreover, the biochar layer has a certain thickness. When measuring the electrical conductivity (EC) and ion content of the soil layers at 0-20 cm and 20-40 cm, is the biochar layer included? In addition, why is the determination of soil nutrients not conducted layer by layer?
• Lines 427-429, “The study examined various biochar treatments, including control (CK), and (BL20), (BL40), BL60), and (BL20), each of which led to substantial enhancements in the gaseous exchange characteristics of sunflowers cultivated under saline soil conditions.” Compared with whom did they show significant enhancement?
• In Section 2.4, the LSD test was introduced as the method to be used. However, it seems that this method was not applied in the result analysis section, such as in Table 5 and Table 6. Moreover, the labeling of significance letters in Table 5 and Table 6 is incorrect. Please verify.
• Discussion section. The discussion section is relatively simple, lacking comparative analysis with existing research results, and consists mostly of descriptive phrases. The discussion attributes reduced EC and salt migration to biochar’s porosity and cation exchange capacity but lacks direct evidence (e.g., soil hydraulic conductivity data, biochar-salt adsorption assays).

Author Response

Review-2

This manuscript addresses an important agricultural challenge and provides valuable insights into biochar’s role in saline soil remediation. However, revisions are required. The introduction section should elaborate on the innovative aspects of this paper. In the Materials and Methods section, the narrative should be concise and avoid redundancy and excessive use of adjectives. It should clarify the logical relationship between the soil column experiment and the field experiment. For example, the soil column experiment should be able to provide appropriate irrigation water volumes. Currently, the two experiments appear to be independent of each other. In the Results section, the soil column experiment lacks relevant soil indicators, and the field experiment lacks stratified soil data. The Discussion section is not in-depth enough. The specific details are as follows:

• Lines 140-141, “soil samples were collected from two distinct depths: 0-20 cm and 20-40 cm.” Soil samples were collected from both 0-20 cm and 20-40 cm layers. However, Table 1 presents physicochemical data without stratification by depth. Please clarify the rationale for not providing layer-specific data and provide justification (e.g., statistical homogeneity between layers, analytical methodology constraints, or reference to standardized protocols). In addition, are the data in Table 1 labeled as "ion exchange capacity"? while water-soluble ions is used in subsequent sections. To avoid ambiguity, please clarify whether these terms refer to the same analytical parameter. The units is /, such as K, Ca Mg, what does this mean?

Reply:

The analysis of 20-40 cm soil depth has been incorporated in Table 1. Also, more details are provided in a descriptive form.

• Materials and Methods section: Integrate the data/content from Table 1 into the corresponding descriptive text; Ensure concise and technical writing throughout this section, avoiding excessive embellishments. Present methods and results in a straightforward manner.

Reply:

The table has been improved for clarity and completeness; however, integrating its contents into the descriptive text is not feasible without compromising the conciseness and technical focus of the Methods section. Therefore, we have retained the table format to present the data efficiently and avoid unnecessary repetition.

 

• Soil column experiment: In the soil column experiment, there is a lack of measurement for key soil indicators such as salinity, ion concentrations, and nutrient content, particularly their distribution across different soil layers and in the leachate. This limits the mechanistic understanding of how biochar interlayers influence salt migration and nutrient redistribution. In addition, the soil columns were packed to a bulk density of 1.4 g cm⁻³. However, in actual field conditions, bulk density typically varies across different soil layers. The study also fails to provide bulk density data for distinct soil layers in the field experiment.

Reply:

These laboratory and field experiments were pilot study. We acknowledge that the lack of measurements for nutrient distribution in different soil layers and leachate limits a more mechanistic interpretation of biochar’s role in influencing salt migration and nutrient dynamics. Due to resource and instrumentation constraints, we focused primarily on overall soil improvement indicators and did not include detailed ionic or leachate analyses. We agree that including such data would strengthen the understanding of biochar interlayer effects, and we plan to address this in future studies by incorporating layer-wise and leachate analysis. This cylinder was filled with air-dried saline soil, which was carefully packed in layers measuring 0-20 and 20-40 cm each, adhering to the natural horizons of the soil to ensure realistic stratification. The bulk density of the packed soil (0-20 and 20-40 cm) was maintained at 1.40 and 1.34 g cm⁻³ to replicate natural soil conditions accurately.

• lines161-164, bulk density of 0.52 cm^-3, 0.52 g cm^-3? “The biochar treatments were designated as BL20, BL40, BL60, and BL80, corresponding to the addition of 20, 40, 60 and 80 tons per hectare”, how many is the addition of biochar in each column?

Reply:

Corrected as Bulk density of 0.52 g cm^-3. Biochar was strategically applied as interlayers within the column based on a bulk density of 0.52 cm⁻³. Five different amounts of biochar were applied: 0 tons per hectare (CK), 20 tons (BL20), 40 tons (BL40), 60 tons (BL60), and 80 tons (BL80), correlating to biochar thicknesses of 0 cm, 0.4 cm, 0.8 cm, 1.2 cm, and 1.6 cm, respectively. Thus, each Column received approximately 0, 16, 32, 48, and 64 g.

• 2 field experiment section: The biochar application rates (up to 80 tons ha⁻¹) may exceed practical feasibility for large-scale farming. In the results, BL60 and BL80 were optimal results, but their economic and logistical viability is not discussed. In addition, which irrigation technology was applied, how much irrigation was used, and so on. What is the buried depth of the groundwater? Are there any drainage facilities? Where are soil salt and ions?

Reply:

We have now justified in the discussion regarding the use of high biochar application rates, acknowledging their limitations in large-scale farming and emphasizing their relevance for experimental insight and mechanistic understanding. The below part is included in the discussion section.

Although biochar application rates up to 80 t ha⁻¹ may appear high for large-scale field use, it is important to note that in this study, biochar was applied as a one-time surface interlayer, rather than being mixed into the soil. This approach was intended to improve salt leaching and reduce capillary salt rise, particularly in saline-affected soils. Biochar possesses a high degree of structural stability and is known to degrade slowly over time, potentially maintaining its functional properties in the soil for several years. Therefore, even at higher rates, such application may be justified in the reclamation of salt-affected soils, where long-term mitigation outweighs the initial investment. Moreover, the porous structure and high surface area of biochar can significantly enhance water infiltration and act as a physical barrier to salt accumulation in the root zone [35; 36], thereby offering a sustainable, low-maintenance solution over time.

Flood irrigation, which is the conventional method commonly practiced in the region, was used before sowing and during the experiment. This method involves uniformly distributing water over the soil surface using gravity flow. Irrigation volumes were applied based on local agronomic practices, ensuring that water reached field capacity.

• Lines218-219, “20 plots?” five treatments with three replications, why 20 plots?

Reply:

Corrected.

• Lines 236-237, “plant height, the number of leaves, stem diameter, and head diameter.” These indexes are not presented in the Results section.

Reply:

Thank you for your observation. We focused on presenting only the most relevant and statistically significant agronomic indicators in the Results section to maintain clarity and focus.

• 2 section, present the analytical parameters and methods concisely, avoiding extended discussion. Those contents can be moved into discussion section.

Reply:

Consider where it is possible.

• Lines 265, 2.2.1 should be 2.2.3

Reply:

Corrected.

• Lines 267-269, Why was a soil-to-water ratio of 1:10 selected? Please clarify the theoretical or experimental basis (e.g., relevant standards, literature references, or preliminary tests) for this specific ratio.

Reply:

Thank you for your thoughtful comment. The 1:10 soil-to-water ratio was selected based on widely accepted standard procedures for salinity assessment in saturated paste extracts and leachate analysis, as recommended in several soil science protocols (e.g., U.S. Salinity Laboratory Staff, 1954; Rhoades, 1996). This ratio facilitates adequate solubilization of soluble salts from the soil matrix and provides reliable readings for electrical conductivity (EC) and ion concentrations in saline and sodic soils.

• Lines 274-281, Please supplement the model numbers, manufacturers, and relevant technical specifications of all instruments and equipment used.

Reply:

Model numbers, manufacturers, and relevant technical specifications have been added where possible. For equipment where such details were unavailable, standard descriptions (References) have been retained based on the original experimental documentation.

• Line 318, 3.1 should be 3.1.1

Reply: Corrected.

• Lines 341-343, which exhibits substantial overlap/redundancy with preceding sections of lines 192-200.

Reply. Corrected

• Figures 1 and 2, Please supplement error bars. Please add superscript letters denoting statistical significance (e.g., a, b, c) to the bars in Figure 3 to clearly indicate significant differences between groups. In addition, suggest that adding the nutrient concentrations in the leachate.

Reply: Thank you for your suggestion regarding the inclusion of nutrient concentrations in the leachate. While Figures 1 and 2 have been updated with error bars, and statistical significance letters have been added to Figure 3, we would like to note that the analysis of nutrient concentrations in the leachate is still ongoing as part of a separate, complementary investigation. Once this analysis is complete, we plan to integrate the findings into future work or a follow-up publication.

• Section 3.1, Please add the total and stage volume of leachate. In addition, soil ions and nutrient concentrations should be added in the manuscript.

Reply:

We would like to note that the analysis of soil ion and nutrient concentrations and total and stage volume of leachate is part of an extended investigation. These results will be incorporated into a future publication focused specifically on nutrient leaching behavior and soil chemical changes under biochar treatment. We appreciate your understanding.

• Table 4 presents the data, 0-20 or 20-40 cm? The data are presented as the means ± SEs. However, no SEs in the table 4. In addition, the units of N, P, K are missed. Since the addition of biochar is conducive to the leaching of salts, it is also possible that soil nutrients will be leached. So, why does the addition of biochar increase the content of soil nutrients (nitrogen, phosphorus, potassium, and organic matter)? What is the mechanism behind this increase? Moreover, the biochar layer has a certain thickness. When measuring the electrical conductivity (EC) and ion content of the soil layers at 0-20 cm and 20-40 cm, is the biochar layer included? In addition, why is the determination of soil nutrients not conducted layer by layer?

Reply:

Table 4 presents the data of 0-20 cm. SEs have been incorporated. The units have been corrected. While it is true that biochar can enhance salt leaching due to its influence on soil structure and water movement, it does not necessarily lead to nutrient loss. By enhancing soil aggregation and porosity, biochar can promote microbial activity and nutrient cycling, leading to better nutrient availability. Biochar layer was not included. Soil nutrients have parts of separate investigation.  

• Lines 427-429, “The study examined various biochar treatments, including control (CK), and (BL2.0), (BL40), BL60), and (BL20), each of which led to substantial enhancements in the gaseous exchange characteristics of sunflowers cultivated under saline soil conditions.” Compared with whom did they show significant enhancement?

Reply: The table data have been reviewed and corrected to ensure consistency with the text and accuracy in representing the experimental results. All values and significance indicators have been updated accordingly.

• In Section 2.4, the LSD test was introduced as the method to be used. However, it seems that this method was not applied in the result analysis section, such as in Table 5 and Table 6. Moreover, the labeling of significance letters in Table 5 and Table 6 is incorrect. Please verify.

Reply:

The reanalysis has been carried out, and the LSD test was correctly applied to the data. The significance letters in Table 5 and Table 6 have been verified and corrected accordingly.

• Discussion section. The discussion section is relatively simple, lacking comparative analysis with existing research results, and consists mostly of descriptive phrases. The discussion attributes reduced EC and salt migration to biochar’s porosity and cation exchange capacity but lacks direct evidence (e.g., soil hydraulic conductivity data, biochar-salt adsorption assays).

Reply:

In response, the Discussion section has been revised and expanded to include comparative analysis with relevant existing studies.

 

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript “Impact of Biochar Interlayer on Surface Soil Salt Content, Salt Migration, and Photosynthetic Activity and Yield of Sunflowers: Laboratory and Field Studies” is an interesting study. Some details are recommended for the authors:

1. In the abstract, it is unclear which are the field methodology and results, and which are from the laboratory, it is recommended to review this. The phrase "with the time required for the effluent EC to decrease to 2 dS m–1 26 markedly reduced" is also unclear and should be revised. Furthermore, despite the title mentioning work with sunflower, its importance is not specified in the abstract.
2. In the introduction an all the manuscript, the authors do not mention why they worked with sunflower cultivation.
3. In the Materials and Methods section, the authors include information that belongs to the Results or Discussion sections. For example, lines 144-146, 192-209, , it is recommended to review this
4. Table 1, mentioned in line 152, page 4, is included on page 7. It is recommended to include it earlier in the manuscript.
5. In section 2.1.1, the authors do not describe how the soil columns were packed, nor what was added to the controls instead of biochar. Furthermore, it is unclear how the volume in the columns was maintained if a different amount of biochar was added in the different treatments. In such a case, was less soil used? It is recommended to describe and clarify these points.
6. The information in lines 351-353 and in section 3.2.3 belongs to the Discussion section. It is recommended to include this information in the corresponding section.
7. The conclusion section is repetitive with the discussion. It is recommended to generate a conclusion consistent with the main objective of the research conducted.
8. Please ensure that all scientific names are in italics.
9. It is recommended to standardize the references and follow the journal's format.

Author Response

Review-3

The manuscript “Impact of Biochar Interlayer on Surface Soil Salt Content, Salt Migration, and Photosynthetic Activity and Yield of Sunflowers: Laboratory and Field Studies” is an interesting study. Some details are recommended for the authors:

1. In the abstract, it is unclear which are the field methodology and results, and which are from the laboratory, it is recommended to review this. The phrase "with the time required for the effluent EC to decrease to 2 dS m–1 26 markedly reduced" is also unclear and should be revised. Furthermore, despite the title mentioning work with sunflower, its importance is not specified in the abstract.

Reply:

In the abstract. All these comments have been incorporated.

1. In the introduction an all the manuscript, the authors do not mention why they worked with sunflower cultivation.

Reply:

The rationale for selecting sunflower cultivation has now been clearly incorporated into the introduction, highlighting its regional importance, salt tolerance, and potential for biochar production from straw residues.

1. In the Materials and Methods section, the authors include information that belongs to the Results or Discussion sections. For example, lines 144-146, 192-209, , it is recommended to review this.

Reply:

It has been reviewed and revised.

1. Table 1, mentioned in line 152, page 4, is included on page 7. It is recommended to include it earlier in the manuscript.

Reply:

It has been replaced according to the recommendation.

1. In section 2.1.1, the authors do not describe how the soil columns were packed, nor what was added to the controls instead of biochar. Furthermore, it is unclear how the volume in the columns was maintained if a different amount of biochar was added in the different treatments. In such a case, was less soil used? It is recommended to describe and clarify these points.

 

Reply:

It has been revised to clearly describe it.

1. The information in lines 351-353 and in section 3.2.3 belongs to the Discussion section. It is recommended to include this information in the corresponding section.

Reply:

Thank you for your suggestion. We appreciate the recommendation to move the content from lines 351–353 and Section 3.2.3 to the Discussion section. However, we respectfully believe that this mechanistic explanation is more appropriately placed within the Results section, as it directly interprets the findings presented in the preceding data and supports the observed trends. This placement ensures continuity between the results and their immediate interpretation, while broader implications and literature comparisons are addressed in the Discussion section.

1. The conclusion section is repetitive with the discussion. It is recommended to generate a conclusion consistent with the main objective of the research conducted.

Reply:

In response, the Conclusion section has been revised to eliminate redundancy with the Discussion and to more clearly reflect the core objectives and key findings of the research. The updated conclusion now provides a concise summary of the quantified leaching duration, ion sequence behavior, and the recommended biochar application strategy, aligning directly with the study’s goals.

1. Please ensure that all scientific names are in italics.

Reply:

Ensured.

1. It is recommended to standardize the references and follow the journal's format.

Reply:

Ensured.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Can be accepted in current form

Author Response

The conclusion section has now been condensed into key points, eliminating redundancy while clearly summarizing the major findings and implications of the study.

Reviewer 2 Report

Comments and Suggestions for Authors

Reviewer's Comments (for Author):

Overall, the author's response to the revision comments is constructive but could be further improved. The author has addressed each comment with specific actions, such as supplementing data, correcting errors, and providing explanations, demonstrating a strong commitment to refining the manuscript. However, some responses lack depth. For example, the mechanisms behind biochar's impact on soil nutrient content and the logical connection between the soil column and field experiments are not thoroughly discussed. Additionally, some issues, like the missing key soil indicators in the soil column experiment and the feasibility of biochar application rates, are acknowledged but not fully resolved. Strengthening the discussion section by comparing with existing research and elaborating on biochar's mechanisms with supporting data would also significantly improve the manuscript's quality and persuasiveness. The specific details are as follows:

• suggest that a tracked changes version be provided as well.
• Abstract: Lines 17-22 contain overlapping content. I suggest reorganizing the language. In my opinion, there is no need to introduce the hypothesis of this paper in the abstract. It is sufficient to focus on the background, objectives, methods, results, and conclusions. In this abstract, the content of the results section is a bit thin and lacks quantitative data.
• Lines 163-165, “15% sand, 80% silt, and 5% clay”, is for 0-20cm or 20-40 cm ?
• Figure 1 is not clear.
• In Section 2.2.2, why was the coefficient of variation (CV) of electrical conductivity (EC) only investigated for the 0-20 cm soil layer, but not for the 20-40 cm soil layer?
• The units is /, such as K, Ca Mg, what does this mean?
• 2 field experiment section: which irrigation technology was applied, how much irrigation amount was used, and so on. What is the buried depth of the groundwater? Are there any drainage facilities? How many is the irrigation amount for flood irrigation (lines 276)?
• Some content is overly redundant. In the section on indicators and their measurement methods, simply introduce the indicators to be measured and the methods used. The importance of the indicators can be reflected in the Results or Discussion sections.
• Line 341, Please supplement the model numbers, manufacturers, and relevant technical specifications for flame photometry.
• Figures 1 and 2, no error bars, and did the column experiment had no replication? Please add superscript letters denoting statistical significance (e.g., a, b, c) to the bars in Figure 3 to clearly indicate significant differences between groups.
• Lines 431-436, are 54.53%(0-20) and 56.05%(20-40) the mean for biochar treatments? Or in which treatment are they? In addition, how to present the soluble salt content? (line 432)
• Lines 437-442, Calculating the average reduction across different treatments may not be very meaningful. It might be more meaningful to provide the range and patterns of reduction in soil water-soluble ions for different biochar application rates (for example, whether the reduction decreases with increasing biochar application).
• In Section 3.2.3, the analyses are all qualitative, lacking quantitative analysis. In addition, the sub-stomatal conductance in BL80 is extremely high (1789.67), please verify the data (table 5). In table 6, for biomass yield, the labeling of significance letters is incorrect. Please verify
• Lines 541-545, “Additionally, these results are consistent with previous research, which highlighted the crucial role of biochar interlayers in enhancing soil water and salt dynamics. Specifically, they reduce infiltration rates, promote a more uniform distribution of moisture and salts throughout the soil profile, suppress excessive water evaporation, and support long-term water retention and salt adsorption [19,30].” First of all, no soil water moisture was measured. Furthermore, in this paper, biochar did not promote a more uniform distribution of moisture, but promote the leaching of salt.
• Discussion section. the comparison and analysis between the results of this study and existing research lack logical coherence.
• Conclusion section: the content is overly redundant; it would be sufficient to condense it into 2-3 key points.

Author Response

Overall, the author's response to the revision comments is constructive but could be further improved. The author has addressed each comment with specific actions, such as supplementing data, correcting errors, and providing explanations, demonstrating a strong commitment to refining the manuscript. However, some responses lack depth. For example, the mechanisms behind biochar's impact on soil nutrient content and the logical connection between the soil column and field experiments are not thoroughly discussed. Additionally, some issues, like the missing key soil indicators in the soil column experiment and the feasibility of biochar application rates, are acknowledged but not fully resolved. Strengthening the discussion section by comparing with existing research and elaborating on biochar's mechanisms with supporting data would also significantly improve the manuscript's quality and persuasiveness. The specific details are as follows:

Abstract: Lines 17-22 contain overlapping content. I suggest reorganizing the language. In my opinion, there is no need to introduce the hypothesis of this paper in the abstract. It is sufficient to focus on the background, objectives, methods, results, and conclusions. In this abstract, the content of the results section is a bit thin and lacks quantitative data.

Response: We have revised the abstract by removing the hypothesis statement, as suggested, to maintain a concise and objective structure. The abstract has now been revised to include key quantitative data from the results section, providing a clearer and more informative summary of the experimental findings.

Lines 163-165, “15% sand, 80% silt, and 5% clay”, is for 0-20cm or 20-40 cm ?

Response: The soil texture composition of “15% sand, 80% silt, and 5% clay” was determined for the 20–40 cm depth. However, this texture was consistent across both the 0–20 cm and 20–40 cm layers in our study.

Figure 1 is not clear.

Response: Figure 1 has now been revised and improved for clarity to ensure that all elements are easily distinguishable and visually informative.

In Section 2.2.2, why was the coefficient of variation (CV) of electrical conductivity (EC) only investigated for the 0-20 cm soil layer, but not for the 20-40 cm soil layer?

Response: The coefficient of variation (CV) of electrical conductivity (EC) was presented for the 0–20 cm soil layer; however, the CV values for the 20–40 cm layer were also assessed and found to be similar.

The units is /, such as K, Ca Mg, what does this mean?

Response: The units for elements such as K, Ca, and Mg have now been correctly specified and clearly presented in the revised manuscript to avoid any confusion.

2 field experiment section: which irrigation technology was applied, how much irrigation amount was used, and so on. What is the buried depth of the groundwater? Are there any drainage facilities? How many is the irrigation amount for flood irrigation (lines 276)?

Response: The experimental field was irrigated using normal surface (flood) irrigation two weeks prior to sowing to ensure adequate soil moisture conditions. Each plot received water from a tube well, with uniform distribution across all treatments. Although the exact depth of the groundwater table was not measured, the irrigation was sufficient to leach the salts and meet pre-sowing moisture needs. No artificial drainage facilities were installed at the site.

Some content is overly redundant. In the section on indicators and their measurement methods, simply introduce the indicators to be measured and the methods used. The importance of the indicators can be reflected in the Results or Discussion sections.

Response: the content under Section 2.2.5 "Analysis of Gas Exchange Characteristics" has been moved to the Results and Discussion section to avoid redundancy and maintain a clear focus on methodology in the Materials and Methods section.

Line 341, Please supplement the model numbers, manufacturers, and relevant technical specifications for flame photometry.

Response: The revised manuscript now includes the model numbers, manufacturers, and relevant technical specifications as follows: potassium (K) concentration was determined using flame photometry (Jenway, PF-7, UK), and phosphorus (P) concentration was measured with an ultraviolet/visible (UV/Vis) spectrophotometer (UV-1600PC, VWR, Radnor, PA, USA). These additions provide greater clarity and reproducibility of the analytical methods used.

Figures 2, no error bars, and did the column experiment had no replication? Please add superscript letters denoting statistical significance (e.g., a, b, c) to the bars in Figure 3 to clearly indicate significant differences between groups.

Response: The updated Figure 2 now includes error bars, as the column experiment was conducted with replication. Additionally, superscript letters denoting statistical significance (e.g., a, b, c) have been incorporated into Figure 4 to clearly indicate significant differences between treatment groups.

Lines 431-436, are 54.53%(0-20) and 56.05%(20-40) the mean for biochar treatments? Or in which treatment are they? In addition, how to present the soluble salt content? (line 432)

Lines 437-442, Calculating the average reduction across different treatments may not be very meaningful. It might be more meaningful to provide the range and patterns of reduction in soil water-soluble ions for different biochar application rates (for example, whether the reduction decreases with increasing biochar application).

Response: The presentation of soluble salt content has been refined by showing the actual measured concentrations (in mg/g or dS/m) rather than percentages, to maintain clarity and scientific precision. We agree that calculating an overall average reduction may not be as informative. Instead, we now present the reductions as a range and describe the trend across treatments.

In Section 3.2.3, the analyses are all qualitative, lacking quantitative analysis. In addition, the sub-stomatal conductance in BL80 is extremely high (1789.67), please verify the data (table 5). In table 6, for biomass yield, the labeling of significance letters is incorrect. Please verify

Response: The sub-stomatal conductance value of 1789.67 reported for BL80 was due to a typing error and has been corrected in the revised manuscript. We appreciate your attention to detail. The significance letters for biomass yield in Table 6 have been reanalyzed and corrected to accurately reflect the statistical differences among treatments based on the updated post-hoc comparisons.

Lines 541-545, “Additionally, these results are consistent with previous research, which highlighted the crucial role of biochar interlayers in enhancing soil water and salt dynamics. Specifically, they reduce infiltration rates, promote a more uniform distribution of moisture and salts throughout the soil profile, suppress excessive water evaporation, and support long-term water retention and salt adsorption [19,30].” First of all, no soil water moisture was measured. Furthermore, in this paper, biochar did not promote a more uniform distribution of moisture, but promote the leaching of salt.

Response: The statement is replaced by: Our results are in line with [27] that biochar-amended columns exhibited earlier efflux discharge, occurring 24 to 40 days sooner than the control treatment without biochar (CK). Additionally, biochar application shortened the time required for efflux EC levels to drop to 5 dS m⁻¹ by 56 to 62 days. Among the three biochars, sunflower straw biochar (SSB) resulted in significantly lower concentrations of the most harmful ions, sodium (Na⁺) and bicarbonate (HCO₃⁻), in the soil by the experiment’s end.

Discussion section. the comparison and analysis between the results of this study and existing research lack logical coherence.

Response: Our study presents unique results under specific experimental conditions, and the discussion intentionally draws attention to these novel insights and context-specific outcomes, which may not directly replicate previous studies but still contribute meaningfully to the broader scientific understanding.

Conclusion section: the content is overly redundant; it would be sufficient to condense it into 2-3 key points.

Response: The conclusion section has now been condensed into key points, eliminating redundancy while clearly summarizing the major findings and implications of the study.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

Overall, the author's response to the revision comments is constructive but could be further improved. The specific details are as follows:

• Abstract: the results section should contain quantitative data.
• Lines 131-132, “The interlayer placed at 30 cm was particularly effective in preventing reverse salt migration and minimizing evaporation”. However, 20cm was selected, why?
• Lines 195-196, “calculated using the formula: Thickness (cm) = Mass of biochar (g) /Bulk density (g.cm⁻³) × Cross-sectional area of the column (cm²)”. And the formula is not correct. Please check.
• Figures 4, add the meaning of letters (e.g., a, b, c). did they represent the difference between different treatments or between different stages?
• g.kg⁻¹ should be g·kg⁻¹. check all the text.
• Figure 4 represents the data of the 0-20 cm soil layer, which should be clearly stated. In addition, it would be better to supplement the data of other soil layers.
• In Table 6, the data for biomass yield in the three revised versions are inconsistent, and they have changed each time. why do you change the data for biomass yield? The labeling of significance letters still has issues. There is a discrepancy between the given values and the labeled letters. For example, for the biomass yield and achene yield between the BL60 and BL80 treatments, the data suggest that there may be no significant difference, but the labeled letters indicate significance. Please carefully and thoroughly check this again.
• Conclusion section: the content is still redundant; it would be sufficient to condense it into 2-3 key points.

Author Response

Thank you for your suggestion. The changes has been made with red highlighted.

1. Quantitative data have now been incorporated into the abstract to strengthen the results section and clearly reflect the observed trends.
2. Although the sentence highlights the effectiveness of the 30 cm depth, various studies in the literature have explored straw and biochar interlayer depths ranging from 10 to 40 cm. Based on these referenced studies, we selected a 20 cm depth as a representative and practical option, which is cited and supported in our article.
3. The incorrect formula previously mentioned in Lines 195–196 has been removed from the manuscript for simplicity.
4. The letters (e.g., a, b, c) in Figure 4 indicate statistically significant differences between different treatments within each stage, evaluated separately.
5. All instances of "g.kg⁻¹" have been carefully reviewed and corrected to the proper format "g·kg⁻¹"
6. We would like to clarify that Figure 4 represents the eluents' ion concentrations. Data from soil layers have been collected and analyzed but are not included in this manuscript, as we intend to present them in a separate publication currently in preparation.
7. The inconsistencies in biomass yield data across revised versions were due to an error during unit conversion and an oversight in data formatting. In the current version, we have corrected the units from tons per hectare to kilograms per hectare to maintain consistency. Additionally, a thorough statistical reanalysis was conducted, and the significance letters in Table 6 have been revised accordingly to accurately reflect statistical differences between treatments, particularly between BL60 and BL80. We appreciate your careful review, which helped us improve the accuracy of our results.
8. The conclusion section has been condensed and reorganized into three concise paragraphs, each highlighting a key finding of the study. This restructuring eliminates redundancy and clearly presents the main outcomes.