Saturated Hydraulic Conductivity of Nine Soils According to Water Quality, Soil Texture, and Clay Mineralogy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1、The study lacks innovation.

It explores the impact of different water qualities on the saturated hydraulic conductivity of nine soils in northeastern Brazil, incorporating soil texture and clay mineralogy. This offers a new perspective for soil hydrology and irrigation management. The specific impacts of diverse mineral components on saturated hydraulic conductivity could be explored more deeply. For instance, the differences in reactions of various clay minerals under different water qualities can be compared, or new analytical techniques can be introduced to more precisely measure the impact of minerals on water movement.

2、Is the number of experimental repetitions (4) sufficient for statistical significance? More repetitions are recommended to enhance data robustness.（Lines 171）

3、Data analysis could be enhanced.

In the statistical analysis section, interactions between soil types and water quality factors should be explored beyond individual soil regression analyses. For instance, a multifactorial ANOVA can assess main and interaction effects of soil types and water quality parameters more comprehensively.

4、Validation of multicollinearity between variables (e.g., whether ECw and SAR are independent) is needed, as well as an explanation of the basis for model selection (e.g., why quadratic or interaction terms were used).

5. The abnormal trend of CTH of Fluvisol (Figure 6) may be related to high organic matter  (TOC = 16.23 g kg-¹), but its mechanism has not been explored in depth. It is recommended to add the analysis of the effect of organic matter on the balance of charge.

6. In practice, how to balance nutrient supply (e.g., Ca2+) and hydraulic conductivity in high saline water? It is recommended to provide some specific management strategies (e.g., ratio of calcium source).

7. To improve the manuscript's quality, the authors are encouraged to revise the manuscript according to this reviewer's comments, trying to improve data analysis and provide a more in-depth discussion. 

 

Author Response

Comments 1: The study lacks innovation. It explores the impact of different water qualities on the saturated hydraulic conductivity of nine soils in northeastern Brazil, incorporating soil texture and clay mineralogy. This offers a new perspective for soil hydrology and irrigation management. The specific impacts of diverse mineral components on saturated hydraulic conductivity could be explored more deeply. For instance, the differences in reactions of various clay minerals under different water qualities can be compared, or new analytical techniques can be introduced to more precisely measure the impact of minerals on water movement.

Response 1: We took your comment carefully and we are happy that we did approach some of your suggestions for future studies in our current one. Also, thanks for stating that our study offers a new perspective of soil hydrology and irrigation management. We also understand that the reviewer would like to see the impacts of diverse mineral components on K_sat.  In this regard, aspects of soil mineral assemblage, diverse mineral components (smectites, kaolinites, illites, etc.), physical characteristics (clayey vs. sandy), and the ionic composition (water quality comparison) of saline water vs. low-salinity water on the K_sat of nine diverse soils.  Thus, our study approached most of the aspects the reviewer suggested for a more complete study, except new analytical techniques. However, this could be the subject of another study as no study is 100% complete on the view of all reviewers. Thanks for your insights and positive comments on our manuscript.

Comments 2: Is the number of experimental repetitions (4) sufficient for statistical significance? More repetitions are recommended to enhance data robustness.（Lines 171)

Response 2: We would like the reviewer to know that robustness was our first concern when designing our study. We planned the statistical analysis of the data as a factorial (5 x 5), with four replicates for each of the 9 soils. This ensures that the degree of freedom of the residual of the analysis of variance was 75, allowing a robust statistical analysis of the main effects of the independent variables (SAR and EC_w), and their interaction.

Comments 3: Data analysis could be enhanced. In the statistical analysis section, interactions between soil types and water quality factors should be explored beyond individual soil regression analyses. For instance, a multifactorial ANOVA can assess main and interaction effects of soil types and water quality parameters more comprehensively.

Response 3: Yes, we analyzed the data in a multifactorial ANOVA and found that there were double interactions between the soil factor and the EC_w and SAR factors. However, because the EC_w and SAR factors are quantitative and it was necessary to make estimates when K_sat was zero, we chose to use multiple regressions. In addition, after discussing with the other co-authors, we decided that it would be more useful to study the trend of EC_w at different SAR levels and vice-versa, for each soil. With our experimental set-up and data enhanced analyses, we found that 1) soil drainage can be more easily interrupted in clayey soil rich in smectites than in sandy soils, proving that waters with SAR lower than 25 can completely degrade the hydraulic properties of soils from tropical sub-humid and semiarid climates; 2) Water ionic composition affected primarily tropical sub-humid and semiarid soils, such as Pellic Vertisol, Albic Planosol, Chromic Luvisol, and Fluvic Cambisol; 3) the water percolation in tropical humid soils, such as Umbric Ferralsol, Ferralic Nitisol, and Haplic Lixisol was not affected by the ionic composition of the waters evaluated in this study, and 4) It is important of know the interaction between soil type and irrigation water composition to implement management practices aimed at preventing the chemical and physical degradation of agricultural soils. We provide the farmers and farmer advisor lots of technical information on different soils and water compositions that can help mitigate the effects of salinity and sodicity, such as: when faced with waters that are high in Na⁺ and/or poor in Ca²⁺, farmers can delay or mitigate soil sodification by adding calcium amendments directly to the soil or through the fertigation water.

Comments 4: Validation of multicollinearity between variables (e.g., whether ECw and SAR are independent) is needed, as well as an explanation of the basis for model selection (e.g., why quadratic or interaction terms were used).

Response 4: Thank you for your comment. Before the regressions, we run the ANOVA for each soil. For soils with significant (p<0.05) interaction between ECw x SAR, the next step was regression. Then, we run 10 types of equation (pre-defined models) to analyze which one had all factors significant at t-test (p<0.10). The models were selected based on the significance of all parameters [excluding models with low R² (R²< 0.70) and with no significance in at least one of the parameters (p>0.10)]. Overall, for all the parameters in each equation (e.g. EC, SAR, EC x SAR, SAR², EC²…) there were significances with the t-test, which exclude the possibility of multicollinearity (the multicollinearity exists when there is no significance with the t-test). In all the equation that we chose, there were no problems related to significance in any parameter analyzed, which can be checked in Table 7 (please, see the asterisk next to each parameter in the models). So, in all models, R² was higher than 0.70, F (ANOVA) was significant (p<0.05), and t-test was significant (p<0.10). Furthermore, for the nature of the independent variables (e.g, ECw and SAR), there were no correlation between them; i.e., a high ECw does not mean that the SAR is higher or lower and vice-versa, as ECw is related to salt concentration in the soil solution and SAR is related to the ratio between Na⁺ and Ca²⁺ (or Ca²⁺ + Mg²⁺) in soil solution. However, we appreciate the suggestion and improved the "Statistical analysis" section of the article (Page 8). Here are some articles that, like ours, utilized ECw and SAR (in combination) to predict soil K_sat and C_TH. None of them used collinearity to evaluate the influence of ECw and SAR on Ksat.

https://doi.org/10.1590/1807-1929/agriambi.v18nsuppS53-S58

https://doi.org/10.1016/j.geoderma.2018.08.030

https://doi.org/10.2136/sssaj2013.03.0097

https://doi.org/10.1016/j.geoderma.2022.115772

https://doi.org/10.1016/j.geoderma.2022.115765

Comments 5: The abnormal trend of CTH of Fluvisol (Figure 6) may be related to high organic matter (TOC = 16.23 g kg-¹), but its mechanism has not been explored in depth. It is recommended to add the analysis of the effect of organic matter on the balance of charge.

Response 5: We partially agree with the reviewer on this topic. We agree that organic matter (O.M.) is relevant to understanding soil-charge balance. However, the focus of our research was to evaluate the dynamic of clay mineral charges and soil texture under different water qualities for nine soils. So, investigations into the dynamics of electrical charges at O.M. go beyond the objective of our study and this type of analysis could be carried out in another study that addresses the influence of the quality of organic matter on the soil K_sat. Thus, the result of Fluvisol in this research opens a new field of investigation related to the importance of the electrical charges of the O.M. in soils with high TOC content and its influence on Ksat. We will certainly consider the effect of organic matter on the soil-charge balance for a future study.

Comments 6: In practice, how to balance nutrient supply (e.g., Ca2+) and hydraulic conductivity in high saline water? It is recommended to provide some specific management strategies (e.g., ratio of calcium source).

Response 6: We appreciate your comment to increase the clarity and applicability of our results. We added two paragraphs on Page 20 on strategies to avoid soil degradation during irrigation. The Paragraphs are highlighted in the manuscript with changes marked (Lines 631 to 657).

Comments 7: To improve the manuscript's quality, the authors are encouraged to revise the manuscript according to this reviewer's comments, trying to improve data analysis and provide a more in-depth discussion.

Response 7: We thank the reviewer for all the time spent evaluating our work and for the comments and suggestions. We followed most of your recommendations to improve the clarity and highlight the new information provided by our experimental set up and data analysis. We are confident that our work is now presented in the best way possible.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present an analysis of the influence of water, soil texture and clay mineralogy on the saturated hydraulic conductivity (Ksat) of nine soils in north-eastern Brazil.

Methodologically, an experiment with vertical columns and constant-load permeameters was carried out to evaluate the behaviour of Ksat under the effect of water with different electrical conductivities (ECw) and sodium adsorption rates (SAR).

The authors have addressed a relevant issue in sustainable irrigation management, using a solid and well-structured methodological approach.

I found the experimental data to be comprehensive and the statistical analyses to be carried out consistently and reliably.

Below I leave some suggestions for further improving this interesting manuscript.

1. Include in the abstract a mention of the main numerical values obtained in the statistical analyses
2. Cite more recent references on similar research in Brazilian soils (I found some in the literature) I suggest filtering a scopus search by geographical area
3. Detail and discuss the selection criteria for the nine soils used in the study
4. Implement and discuss an analysis of experimental errors (e.g. uncertainties in the measurement of Ksat and variations between replicates)
5. The references section must be adapted to the guidelines of the journal. Many references are incorrectly stated.
6. Keywords should be listed in the abstract with numerical references.

Author Response

Comments 1: The authors present an analysis of the influence of water, soil texture and clay mineralogy on the saturated hydraulic conductivity (Ksat) of nine soils in north-eastern Brazil. Methodologically, an experiment with vertical columns and constant-load permeameters was carried out to evaluate the behaviour of Ksat under the effect of water with different electrical conductivities (ECw) and sodium adsorption rates (SAR). The authors have addressed a relevant issue in sustainable irrigation management, using a solid and well-structured methodological approach. I found the experimental data to be comprehensive and the statistical analyses to be carried out consistently and reliably. Below I leave some suggestions for further improving this interesting manuscript.

Response 1: We appreciate your comment about the quality of our research, and we improved and clarified the manuscript based on all the comments and suggestions made by the reviewer. Your comments were very useful for improving our work.

Comments 2: Include in the abstract a mention of the main numerical values obtained in the statistical analyses

Response 2: Thank you for your suggestion to improve the quality of our manuscript. The changes in abstract are highlighted in the changes- marked version of the manuscript (Lines 30 to 37).

Comments 3: Cite more recent references on similar research in Brazilian soils (I found some in the literature) I suggest filtering a scopus search by geographical area

Response 3: We followed the suggestion made by the reviewer. Here, we listed all the references about Brazilian research that were previously included in the manuscript and the references that we included in this new version: References previously cited in the manuscript:

1. https://doi.org/10.1590/S1415-43662003000100008
2. https://doi.org/10.1590/1807-1929/agriambi.v18nsupps53-s58
3. https://doi.org/10.1016/j.geoderma.2019.05.043
4. https://doi.org/10.21475/ajcs.19.13.07.p1686

New articles cited in the new version of the manuscript:

https://doi.org/10.36783/18069657rbcs20240003 (Reference 49 - Lines 394 and 402 – Ottoni and collaborator, highlighted in yellow)

https://doi.org/10.1016/j.geoderma.2023.116413 (Reference 50 - Line 395 - highlighted in yellow)

https://doi.org/10.36783/18069657rbcs20240013 (Reference 51 - Line 415 – Pedrón and coworkers, highlighted in yellow)

https://doi.org/10.1016/j.catena.2020.104583 (Reference 67 - Line 537 - Centeno and coworkers, highlighted in yellow)

https://doi.org/10.1016/j.catena.2022.106751 (Reference 68 - Line 541 – highlighted in yellow)

Comments 4: Detail and discuss the selection criteria for the nine soils used in the study

Response 4: Good question. We added a detailed explanation about the criteria for selecting the nine soils: “The soils were selected based on climate zones (tropical humid/hot, tropical sub-humid, and semiarid climates), texture (the soils ranged from sandy to clayey), and mineralogy of the clay fraction (soils with the constitution 1:1 minerals such as kaolinite; soils with 2:1 minerals such as smectites and illites, and soils with low and high concentration of Fe (hydr)oxides) as described in Figure 1 and Tables 1 and 4.” Our objective was to analyze water percolation in distinct soils (varying mineralogy and texture) from three different climate zones. The modification can be checked in the manuscript with changes marked, in the section ‘Material and Methods’, subsection ‘2.1. Soil Sampling and Characterization’, lines 107 to 111.

Comments 5: Implement and discuss an analysis of experimental errors (e.g. uncertainties in the measurement of Ksat and variations between replicates)

Response 5: In Table 7, we included the values of the coefficients of variation (CV) of the K_sat for each soil to show uncertainties in the measurement of K_sat and variations between replicates. In addition, we represented in the K_sat regressions the symbol that shows that the models are estimates In Table 7, we included the values of the coefficients of variation (CV) of the K_sat for each soil to show uncertainties in the measurement of K_sat and variations between replicates. In addition, we represented in the K_sat regressions the symbol that shows that the models are estimates.

Comments 6: The references section must be adapted to the guidelines of the journal. Many references are incorrectly stated.

Response 6: Thank you for your comment. We have made new adjustments in the reference section according to https://www.mdpi.com/journal/agronomy/instructions

Comments 7: Keywords should be listed in the abstract with numerical references.

Response 7: We appreciate your comment. The keywords are cited below the abstract, according to the section “instructions to authors” at the Agronomy website on how to organize the keywords (https://www.mdpi.com/journal/agronomy/instructions). However, We did not understand the comment about using numerical references for keywords.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript investigates the effects of water quality on the saturated hydraulic conductivity (Ksat) of nine different soil types, emphasizing the interactions among electrical conductivity (ECw), sodium adsorption ratio (SAR), soil texture, and mineral composition. The study is well-structured, with a clear experimental setup and thorough data analysis. Several aspects require further clarification and improvement.   1. The criteria for selecting the nine soil types should be clarified. Were these soils chosen based on prevalence in salt-affected regions? 2. The conclusion is rather mediocre and lacks quantitative values. 3. While regression models are applied, the manuscript does not clearly explain which independent variables have the strongest influence on Ksat. 4. The manuscript discusses Ksat variations but lacks practical recommendations for irrigation management. 5. The references are too outdated.

Author Response

Comments 1: This manuscript investigates the effects of water quality on the saturated hydraulic conductivity (Ksat) of nine different soil types, emphasizing the interactions among electrical conductivity (ECw), sodium adsorption ratio (SAR), soil texture, and mineral composition. The study is well-structured, with a clear experimental setup and thorough data analysis. Several aspects require further clarification and improvement.

Response 1: We appreciate your comments about the quality and soundness of our research and we improved and clarified the manuscript based on all the comments and suggestions made by the reviewer. Thanks for your time evaluating the manuscript and making comments to strengthen its clarity and value. 

Comments 2: The criteria for selecting the nine soil types should be clarified. Were these soils chosen based on prevalence in salt-affected regions?

Response 2: Good question. We added a detailed explanation about the criteria for selecting the nine soils: “The soils were selected based on climate zones (tropical humid/hot, tropical sub-humid, and semiarid climates), texture (the soils ranged from sandy to clayey), and mineralogy of the clay fraction (soils with the constitution 1:1 minerals such as kaolinite; soils with 2:1 minerals such as smectites and illites, and soils with low and high concentration of Fe (hydr)oxides) as described in Figure 1 and Tables 1 and 4.” Our objective was to analyze water percolation in distinct soils (varying mineralogy and texture) from three different climate zones. The modification can be checked in the manuscript with changes marked, in the section ‘Material and Methods’, subsection ‘2.1. Soil Sampling and Characterization’, lines 107 to 111.

Comments 3: The conclusion is rather mediocre and lacks quantitative values.

Response 3: We agree with your remarks on the conclusion. We have rewritten the conclusion using quantitative values where appropriate but, most importantly, highlighting the take-home messages of our work, based on our results. We hope that the revised conclusions are more to your liking than the original one. The changes are highlighted in the manuscript version with changes marked.

Comments 4: While regression models are applied, the manuscript does not clearly explain which independent variables have the strongest influence on Ksat.

Response 4: Thank you for your conmment. We used only two independent variables [sodium adsorption ratio (SAR) and water electrical conductivity (EC_w)] and discussed their influence on the saturated hydraulic conductivity (K_sat) of different soils. The influence of one compared to the other was dependent on the characteristics of each soil, mainly on the mineralogy (mineral assemblage) of these soils. The independent variable that most influenced Ksat depended on the soil’s chemical characteristics, texture, and on the water ionic composition. Thus, we cannot make a general statement of which independent variable was the one that had the most influence for all nine soils.

Comments 5: The manuscript discusses Ksat variations but lacks practical recommendations for irrigation management.

Response 5: We appreciate your comment, and we believe it was very useful to improve our work. We added two paragraphs on Page 20 about some strategies to avoid soil degradation during irrigation. The Paragraphs are highlighted in the manuscript with changes marked (Lines 631 to 657).

Comments 6: The references are too outdated.

Response 6: Thank you for your suggestion. Here are the new references added to the manuscript:

https://doi.org/10.36783/18069657rbcs20240003 (Reference 49 - Lines 394 and 402 – Highlighted in yellow)

https://doi.org/10.1016/j.geoderma.2023.116413 (Reference 50 - Line 395 – Highlighted in yellow)

https://doi.org/10.36783/18069657rbcs20240013 (Reference 51 - Line 415 – Highlighted in yellow)

https://doi.org/10.1007/s11368-025-03997-w (Reference 55 - Line 467– Highlighted in yellow)

https://doi.org/10.1016/j.jhydrol.2024.131619 (Reference 61 - Line 514 – Highlighted in yellow)

https://doi.org/10.1016/j.catena.2020.104583 (Reference 67 - Line 537 – Highlighted in yellow)

https://doi.org/10.1016/j.catena.2022.106751 (Reference 68 - Line 541 – Highlighted in yellow)

https://doi.org/10.3390/plants12112150 (Reference 74 - Line 656 – Highlighted in yellow)

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

OK