On the Potential of Biochar Soil Amendments as a Sustainable Water Management Strategy

Round 1

Reviewer 1 Report

This study assess the potential impacts of biochar as a soil amendment impacting water storage and plant water usage associated with tropical agriculture. Such study will help to understand how biochar amendments can ultimately contribute to sustainability in agriculture. Please consider the following comments to improve the manuscript.

Comments:

1. Please modify the abstract with more significant data. The significance of the study should be mentioned clearly in abstract section.
2. Provide significant words which are more relevant to the work in logical sequence as ‘keywords’. Also use keywords which are not present in title.
3. What is the current level of understanding in relation to potential of biochar as soil amendment? What are the knowledge gaps?. These should be included in the introduction section. The introduction is insufficient to provide the state of the art in the topic. Hypothesis should be given. How this work is different from the available data?
4. Improve the introduction part by adding more supporting data from the literature.
5. Line no 131-133; need to be more specific with coordinates.
6. It would be necessary to develop more bioinformatic/statistical analyses in the present study. 
7. The discussion and interpretation of results does not clearly explain its impact on the literature and the field. It is also recommended to discuss and explain what should be the appropriate policies based on the findings of this study. Also, the literature should be further elaborated to show how they could be used for real applications.
8. Add a paragraph 'practical implications of this study,' outlining the challenges in the current research, future work, and recommendations, before the conclusion.
9. Please note that the conclusion section should give a firm conclusion and should not include discussion. Please reorganize the conclusion.

Author Response

In the following letter, we have listed each individual review comment with our direct response and how our manuscript has been updated following in italics.

This study assess the potential impacts of biochar as a soil amendment impacting water storage and plant water usage associated with tropical agriculture. Such study will help to understand how biochar amendments can ultimately contribute to sustainability in agriculture. Please consider the following comments to improve the manuscript.

We thank the reviewer for the efforts assessing our work and appreciate the valuable comments provided. We are glad that the reviewer feels the study will help increase understanding of how biochar can help support sustainability in agriculture.

Comments:

1. Please modify the abstract with more significant data. The significance of the study should be mentioned clearly in abstract section.

Excellent suggestion. We have brought forward the significance of our study with the following addition to the abstract around L28:

“Biochar has been put forward as a potential technology that could help achieve sustainable water management in agriculture through its ability to increase water holding capacity in soils. Despite this opportunity, there are still a limited number of studies, especially in vulnerable regions like the tropics, quantifying the impacts of biochar on soil water storage and characterizing the impacts of biochar additions on plant water composition. To address this critical gap, we present a case study using stable water isotopes and hydrometric data from melon production in tropical agriculture to explore hydrological impacts of biochar as a soil amendment.”

Further, we have expanded the data presented in the abstract with the following quantifications around L35:

“Results from our 10-week growing season experiment in Costa Rica under drip irrigation demonstrated an average increase in volumetric soil moisture content of about 10% with an average moisture content of 25.4 cm³ cm^-3 versus 23.1 cm³ cm^-3, respectively, for biochar amended plots compared with control plots. Further, there was reduction in the variability in soil matric potential for biochar amended plots compared with control plots. Our isotopic investigation demonstrated that for both biochar and control plots, there was a consistent increase (or enrichment) in isotopic composition for plant materials moving from the roots, where the average δ18O was -8.1‰ and the average δ2H was -58.5‰ across all plots and samples, up through the leaves, where the average δ18O was 4.3‰ and the average δ2H was 0.1‰ across all plots and samples. However, as there was no discernible difference in isotopic composition for plant water samples when comparing across biochar and control plots, we find that biochar did not alter the composition of water found in the melon plant material, indicating that biochar and plants are not competing for the same water sources.”

1. Provide significant words which are more relevant to the work in logical sequence as ‘keywords’. Also use keywords which are not present in title.

We have modified the keywords (L52) to reflect sequencing in scales and avoided redundancy with the title. The keywords are now “tropical agriculture; melons; biochar; hydrometric observations; stable water isotopes”

1. What is the current level of understanding in relation to potential of biochar as soil amendment? What are the knowledge gaps?. These should be included in the introduction section. The introduction is insufficient to provide the state of the art in the topic. Hypothesis should be given. How this work is different from the available data?

We have expanded the introduction (around L113) to better report on the current level of understanding of biochar as a soil amendment and highlighting current gaps with the following text:

“For example, biochar can be applied on the soil surface or incorporated into the soil changing the infiltration capacity across the soil profile [15,16]. Working biochar into deeper soil layers alters soil physical properties as a function of biochar type (e.g. particle size, shape and material) [16]. Since biochar disrupts the soil matrix by generally increasing porosity, aggregate stability and saturated hydraulic conductivity, pore size distributions, the altered soil physical characteristics thus tend to increase the soil water holding capacity and the amount of soil water available at a given soil matric potential, but this depends on soil texture type and application rates [2,17]. Mixing biochar into deeper soil layers also influences the matric potential and modifies the soil water retention curve [2]. In turn, this affects the binding of water to the soil, the soil water content and plant water availability. A meta-analysis by Omondi et al. [17] found that, on average, soil bulk density significantly decreased by 8% after biochar amendment. Soil porosity significantly and aggregate stability increased both by 8%, available water-holding capacity by 15%, and saturated hydraulic conductivity by 25%. However, the effects are highest with biochar application amounts above 80 t ha⁻¹ and low to insignificant at less than 20 t ha⁻¹.Despite the growing knowledge base around the impacts of biochar on soils gained through lab and pot experiments, there is need for more work leveraging multiple lines of data and evidence allowing for exploration of the variety of processes occurring in agroecosystems at field scale [15,18,19]. Specifically, there is a knowledge gap of how biochar affects water stores and fluxes and eventually plant water availability as we look to biochar as a sustainable water management strategy.”

Further, our hypothesis is clarified (around L137) and identify the difference between our work and previous efforts with the addition of the following text:

“We anticipated an increased ability of soil amended with biochar to store water would be evidenced at the plot scale through increases in soil moisture contents; however, we hypothesized that any shift in terms of the composition of water being stored in the soil or being found in the plants would be minimal given the complexity of plant-water interactions occurring at the plot scale.

1. Improve the introduction part by adding more supporting data from the literature.

We have improved the introduction per the reviewers comment specifically around better structure highlighting the current state of the science regarding understanding of how biochar impacts soils. We have achieved this improvement by providing better references from the current leading studies presented in the literature. Given that we are at 37 references and have covered several major publications and synthesis efforts, we feel this suffices as a relevant literature review to support our study.

1. Line no 131-133; need to be more specific with coordinates.

Yes. We have added the coordinates for the experiment plots (10^o 20’ 42.86”, 85^o 8’ 5.12”) to the caption for Figure 1 highlighting the location.

1. It would be necessary to develop more bioinformatic/statistical analyses in the present study. 

We have developed the methodology reporting out on our statistical analysis in our revision. This helps make clearer how data were compared to assess for significant differences and strengthens the bioinformatic/statistical analyses. The following lines were added around L212:

“For all comparisons, variance tests (F-tests two-sample for variances) were used to assess the variability of the data in multiple groups, namely control versus biochar plots, defined for identified time periods and to determine whether the data were different.”

1. The discussion and interpretation of results does not clearly explain its impact on the literature and the field. It is also recommended to discuss and explain what should be the appropriate policies based on the findings of this study. Also, the literature should be further elaborated to show how they could be used for real applications.

We have addressed this comment through our responses to the following two comments. Specifically, we have expanded literature and connected with possible policy work to be done to increase biochar adoption. All in all, we feel this strengthens the presentation of our work and helps connect with the current science.

1. Add a paragraph 'practical implications of this study,' outlining the challenges in the current research, future work, and recommendations, before the conclusion.

Excellent suggestion. We have done this (along with restructuring the Concluding Remarks section) which has really improved the presentation of work. The follow section is now added (around L395):

“3.3 Practical Implications

Innovations that comprehensively address the food-water-energy nexus across a local-to-global axis are required to meet human demands for food while maintaining water and energy security - a trilemma entailing some of society’s greatest challenges. Given that most of the expansion and intensification of global agricultural production over the next several decades is projected to take place in tropical regions [32], innovations in tropical agricultural water management are particularly crucial. This need becomes more urgent when considering that the variability of tropical rainfall patterns is expected to increase due to climate change, particularly in terms of the arrival, duration and intensities of seasonal rainfall [33]. As such, there is an urgent need to develop methodologies to increase water use efficiencies in both rainfed and irrigated agriculture locally in order to improve food and water security globally. Based on this current study and several others, biochar seems to offer such a methodology with regards to sustainable water management.

It should of course be noted that while other studies have demonstrated generally in-creasing crop yields [34], our single-season experiment with drip irrigation did not see significant impact of biochar on melon production (Table 2). Considering the biochar in a broader sustainability context (Table 1), we find encouragement here as there is no negative influence of the biochar additions on production and, as such, biochar has not jeopardized production. Further, and again thinking beyond the water impacts, biochar additions to the soil represent a global negative emission potential of 0.7 Pg C yr^-1 [34]. Our study is consistent with these global projections in the sense that we have utilized a local waste feedstock material and low-technology biochar production method to produce the biochar which is directly sequestered into the soil on our experiment.

There is still clear need to explore the value of biochar across various conditions and settings in the tropics. Biochar may not be always a win-win technology for sustainable water resource management if not well synchronized with agro-ecological conditions of the application location and socio-economic status of the end-users [36]. Specifical, since there are several variables at play around how biochar is made and implemented in agricultural and water management practices, we see a need align social and environmental benefits of biochar technology with policy decision (e.g. [36]). Through such alignment, with appropriate understanding of long-term impacts and designing of biochar for conditions, biochar can begin to fulfill its potential to achieve sustainable water management.”

1. Please note that the conclusion section should give a firm conclusion and should not include discussion. Please reorganize the conclusion.

We have extended our Concluding Remarks to elaborate more on the impact of our findings relative to the current literature. We have also trimmed out the more discussion-oriented text to allow for a more concise presentation of conclusion. We have added the following text (around L445):

“Further, biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils [35]. There is need for reduction of costs of biochar production and application to increase the material's use efficiency need future development. A recent review by Basak et al. [35] highlight the need to link economic benefits with social and environmental issues for successful implementation of biochar technology in weathered tropical soils. Further, they recommend identification of biochar properties suitable for tropical soils are important to get the maximum benefit of biochar application. Basak et al. [35] point out that suitable application strategies and co-deployment of biochar with other suitable additives pro-vides a promising area for improving efficiency of biochar for agricultural application. Our work adds value here as we assess the impacts of a locally sourced biochar on water storage in addition to the potential impacts on yield. As such, when trying to motivate the adoption and application of biochar in tropic climates, we may look to consider the multiple (or stacked) benefits from the sustainability perspective. Strategies whereby additional benefits like increased water storage that can bring about reduced irrigation needs and longer periods of drought resistance for crops could help motivate farmer adoption of biochar as a management practice.”

 

 

Reviewer 2 Report

Comments:

1. In Introduction, the content is rather complicated and the emphasis is not prominent. It is suggested to combine the previous research content on soil improvement by biochar with in-depth excavation and integration, and highlight the importance and necessity of this research, that is, to express the lack of further research on soil and crop water use allocation based on biochar.
2. The contents of Table 1 are of limited argumentation for this academic research paper, and it is suggested to simplify the modification.
3. In section 2.1 Site Description, there is a lack of necessary physical and chemical properties such as geographical latitude, longitude and soil particle size composition of the test Site. And the test layout of Figure1 lacks necessary dimensioning.
4. In 2.2.1. Biochar and Melon Plants, whether artificial spacer belts are set between test plots to avoid mutual influence between test plots, and relevant contents are supplemented. The crop yield indicators are analyzed, while the planting patterns closely related to yield are not described in detail. The average yield of muskmelon in each experimental plot in Table 2 lacks units.
5. In 2.2.3 Isotopic Sampling and Analysis, it is suggested to simplify the description of unnecessary test procedures, highlight the determination and data processing methods applied in this paper, and supplement necessary references.
6. In Results and Discussion, the author often chooses week as the time unit to analyze the change of the measurement index. Therefore, it is suggested that the figure and text should be consistent, and the time interval should be divided by week in the figure. And it is suggested to enrich the types of graphs (Figure 2 and Figure 3) to distinguish the measurement indexes and analysis bias.
7. For Table 3, it is recommended that anything other than the table name be listed as a table comment. The sample number of rainfall isotope analysis is too thin, and the analysis of isotope changes between the experimental group and the control group in Table 3 is insufficient. For example, if there is a large difference in real isotopes, it is suggested to conduct in-depth analysis of the consistent rules and inconsistent parts.
8. In Concluding Remarks, the analysis content lacks in-depth elaboration on the principle of experimental phenomenon, and the thesis lacks relevant contents in the conclusion summary part, so it is suggested to supplement.
9. In References, some of the references are old, and a large number of new discoveries have been made in related fields. It is suggested to update the references and descriptions based on the contents of this paper.

Author Response

In the following letter, we have listed each individual review comment with our direct response and how our manuscript has been updated following in italics.

1. In Introduction, the content is rather complicated and the emphasis is not prominent. It is suggested to combine the previous research content on soil improvement by biochar with in-depth excavation and integration, and highlight the importance and necessity of this research, that is, to express the lack of further research on soil and crop water use allocation based on biochar.

This is an excellent suggestion. We have modified the introduction in this regard and specifically expanded the presentation of the current state of knowledge allowing us to also highlight the importance and necessity of this research. We have thus expanded the introduction (around L113) to better report on the current level of understanding of biochar as a soil amendment and highlighting current gaps with the following text:

“For example, biochar can be applied on the soil surface or incorporated into the soil changing the infiltration capacity across the soil profile [15,16]. Working biochar into deeper soil layers alters soil physical properties as a function of biochar type (e.g. particle size, shape and material) [16]. Since biochar disrupts the soil matrix by generally increasing porosity, aggregate stability and saturated hydraulic conductivity, pore size distributions, the altered soil physical characteristics thus tend to increase the soil water holding capacity and the amount of soil water available at a given soil matric potential, but this depends on soil texture type and application rates [2,17]. Mixing biochar into deeper soil layers also influences the matric potential and modifies the soil water retention curve [2]. In turn, this affects the binding of water to the soil, the soil water content and plant water availability. A meta-analysis by Omondi et al. [17] found that, on average, soil bulk density significantly decreased by 8% after biochar amendment. Soil porosity significantly and aggregate stability increased both by 8%, available water-holding capacity by 15%, and saturated hydraulic conductivity by 25%. However, the effects are highest with biochar application amounts above 80 t ha⁻¹ and low to insignificant at less than 20 t ha⁻¹.Despite the growing knowledge base around the impacts of biochar on soils gained through lab and pot experiments, there is need for more work leveraging multiple lines of data and evidence allowing for exploration of the variety of processes occurring in agroecosystems at field scale [15,18,19]. Specifically, there is a knowledge gap of how biochar affects water stores and fluxes and eventually plant water availability as we look to biochar as a sustainable water management strategy.”

1. The contents of Table 1 are of limited argumentation for this academic research paper, and it is suggested to simplify the modification.

This is a good recommendation. We have simplified the table down to the main considerations under each pillar of sustainability. This adequately reduces the complexity of the paper while still helping connect to the theme of the special issue.

1. In section 2.1 Site Description, there is a lack of necessary physical and chemical properties such as geographical latitude, longitude and soil particle size composition of the test Site. And the test layout of Figure1 lacks necessary dimensioning.

We have added appropriate latitude and longitude data and scale information to Figure 1. Further, we have added the following text in Section 2.1 regarding the physical properties of the study plots (around L154):

“The soil texture in the top 20 cm at the experimental site was characterized as 34% sand, 30% silt, and 36% clay and contained about 2% Organic Carbon.”

1. In 2.2.1. Biochar and Melon Plants, whether artificial spacer belts are set between test plots to avoid mutual influence between test plots, and relevant contents are supplemented. The crop yield indicators are analyzed, while the planting patterns closely related to yield are not described in detail. The average yield of muskmelon in each experimental plot in Table 2 lacks units.

We did not use whether artificial spacer belts are set between test plots however distance was left between planted mounds. We have clarified this and configuration of melon planting in the revision by including the following text (L189):

“Melons were planted every 0.3 m along the mounds. Space (about 0.8 m) was left between the mounds to reduce any potential mutual influence of treatments; however, artificial spacer belts were not utilized.”

In addition, we have added the correct units for Table 2.

1. In 2.2.3 Isotopic Sampling and Analysis, it is suggested to simplify the description of unnecessary test procedures, highlight the determination and data processing methods applied in this paper, and supplement necessary references.

We struggle with how to reduce this rather concise section. We have attempted to streamline where possible. Our fear is that removing perceived unnecessary descriptions will leave readers looking for that detailed confused. We have thus added details pertaining to the statistical analysis (at L257):

“Again, variance tests (F-tests two-sample for variances) were used to assess the variability of the various isotopic composition data between control and biochar plots confirming whether the data were different.”

1. In Results and Discussion, the author often chooses week as the time unit to analyze the change of the measurement index. Therefore, it is suggested that the figure and text should be consistent, and the time interval should be divided by week in the figure. And it is suggested to enrich the types of graphs (Figure 2 and Figure 3) to distinguish the measurement indexes and analysis bias.

We have updated all timeseries figures to have weekly tick marks on the horizontal time unit. This allows body text to align more clearly with figures. Further, to enrich Figures 2 and 3, we have added in the continuous line demarking the patterns observed with time.

1. For Table 3, it is recommended that anything other the table name be listed as a table comment. The sample number of rainfall isotope analysis is too thin, and the analysis of isotope changes between the experimental group and the control group in Table 3 is insufficient. For example, if there is a large difference in real isotopes, it is suggested to conduct in-depth analysis of the consistent rules and inconsistent parts.

We have changed the table caption to the following: Observed isotopic composition data based on samples collected in this study with values presented as averages both in time and across plots with standard deviations given in parenthesis.

Yes, we acknowledge that the low number of rain samples available limits our analysis. We highlight this limitation in the text at L364. Further, with regards to in-depth analysis of the main differences observed across the isotopic compositions, we have expanded our methodological overview of the statistical tests with the following text (L257):

“Again, variance tests (F-tests two-sample for variances) were used to assess the variability of the various isotopic composition data between control and biochar plots confirming whether the data were different.”

1. In Concluding Remarks, the analysis content lacks in-depth elaboration on the principle of experimental phenomenon, and the thesis lacks relevant contents in the conclusion summary part, so it is suggested to supplement.

We have extended our Concluding Remarks to elaborate more on the impact of our findings relative to the current literature. We have added the following text (around L445):

“Further biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils [35]. There is need for reduction of costs of biochar production and application to increase the material's use efficiency need future development. A recent review by Basak et al. [35] highlight the need to link economic benefits with social and environmental issues for successful implementation of biochar technology in weathered tropical soils. Further, they recommend identification of biochar properties suitable for tropical soils are important to get the maximum benefit of biochar application. Basak et al. [35] point out that suitable ap-plication strategies and co-deployment of biochar with other suitable additives pro-vides a promising area for improving efficiency of biochar for agricultural application. Our work adds value here as we assess the impacts of a locally sourced biochar on water storage in addition to the potential impacts on yield. As such, when trying to motivate the adoption and application of biochar in tropic climates, we may look to con-sider the multiple (or stacked) benefits from the sustainability perspective. Strategies whereby additional benefits like increased water storage that can bring about reduced irrigation needs and longer periods of drought resistance for crops could help motivate farmer adoption of biochar as a management practice.”

1. In References, some of the references are old, and a large number of new discoveries have been made in related fields. It is suggested to update the references and descriptions based on the contents of this paper.

By our count, 72% of the references come from the last 10 years with 14% coming from the past 2 years. The other older papers are seminal in the field. Still, we have added the following recent reference which provides an excellent review of biochar in the tropics and helped us elaborate our conclusion:

Basak, B.B.; Sarkar, B.; Saha, A.; Sarkar, A.; Mandal, S.; Kumar Biswas, J.; Wang, H.; Bolan, N.S. Revamping highly weathered soils in the tropics with biochar application: What we know and what is needed. Science of the Total Environment 2022, 822, 153462.

 

 

 

Reviewer 3 Report

This study examines the effects of biochar application on soil moisture and its potential for soil water management. The research topic is novel and of great significance. However, there are some issues with the manuscript that deserve attention.

1. Results and discussion section is more about results description than discussion. For example, L234-235, why was soil moisture content of biochar treatment higher than that of control treatment? The entire 3.1 and the first half of 3.2 sections, there arefew references, what are the reasons and basis for these results.
2. Concluding remarks section should highly summarize the research findings rather than introducing the research significance and discussing the results with references. L362-374 and L385-397 were better for the introduction section, and L375-384 was better for the Results and discussion section.

Author Response

In the following letter, we have listed each individual review comment with our direct response and how our manuscript has been updated following in italics.

Reviewer #3

This study examines the effects of biochar application on soil moisture and its potential for soil water management. The research topic is novel and of great significance. However, there are some issues with the manuscript that deserve attention.

We appreciate the reviewer’s time and effort spent evaluating our manuscript. We are glad they find the work novel and the topic of great significance.

1. Results and discussion section is more about results description than discussion. For example, L234-235, why was soil moisture content of biochar treatment higher than that of control treatment? The entire 3.1 and the first half of 3.2 sections, there are few references, what are the reasons and basis for these results.

We have expanded our Results and Discussion section now (per another reviewer comment) to include discussion of the practical implications of our findings. The follow section is now added (around L395):

“3.3 Practical Implications

Innovations that comprehensively address the food-water-energy nexus across a local-to-global axis are required to meet human demands for food while maintaining water and energy security - a trilemma entailing some of society’s greatest challenges. Given that most of the expansion and intensification of global agricultural production over the next several decades is projected to take place in tropical regions [32], innovations in tropical agricultural water management are particularly crucial. This need becomes more urgent when considering that the variability of tropical rainfall patterns is expected to increase due to climate change, particularly in terms of the arrival, duration and intensities of seasonal rainfall [33]. As such, there is an urgent need to develop methodologies to increase water use efficiencies in both rainfed and irrigated agriculture locally in order to improve food and water security globally. Based on this current study and several others, biochar seems to offer such a methodology with regards to sustainable water management.

It should of course be noted that while other studies have demonstrated generally in-creasing crop yields [34], our single-season experiment with drip irrigation did not see significant impact of biochar on melon production (Table 2). Considering the biochar in a broader sustainability context (Table 1), we find encouragement here as there is no negative influence of the biochar additions on production and, as such, biochar has not jeopardized production. Further, and again thinking beyond the water impacts, biochar additions to the soil represent a global negative emission potential of 0.7 Pg C yr^-1 [34]. Our study is consistent with these global projections in the sense that we have utilized a local waste feedstock material and low-technology biochar production method to produce the biochar which is directly sequestered into the soil on our experiment.

There is still clear need to explore the value of biochar across various conditions and settings in the tropics. Biochar may not be always a win-win technology for sustainable water resource management if not well synchronized with agro-ecological conditions of the application location and socio-economic status of the end-users [36]. Specifical, since there are several variables at play around how biochar is made and implemented in agricultural and water management practices, we see a need align social and environmental benefits of biochar technology with policy decision (e.g. [36]). Through such alignment, with appropriate understanding of long-term impacts and designing of biochar for conditions, biochar can begin to fulfill its potential to achieve sustainable water management.”

In addition, through expansion of our Introduction section to include the impacts of biochar on soil properties, we have highlighted the mechanisms by which we see higher soil moisture in the biochar treatment. Collectively, we feel these text additions have help improve both this section and the quality of the manuscript.

1. Concluding remarks section should highly summarize the research findings rather than introducing the research significance and discussing the results with references. L362-374 and L385-397 were better for the introduction section, and L375-384 was better for the Results and discussion section.

Agreed. We have made the recommended edits to this section. Further, moving the text helps expand the results and discussion section and thus improves our overall presentation. We have edited and expanded the conclusions in this regard. As such, the following text are added (around L445):

“Further biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils [36]. There is need for reduction of costs of biochar production and application to increase the material's use efficiency need future development. A recent review by Basak et al. [36] highlight the need to link economic benefits with social and environmental issues for successful implementation of biochar technology in weathered tropical soils. Further, they recommend identification of biochar properties suitable for tropical soils are important to get the maximum benefit of biochar application. Basak et al. [36] point out that suitable application strategies and co-deployment of biochar with other suitable additives pro-vides a promising area for improving efficiency of biochar for agricultural application. Our work adds value here as we assess the impacts of a locally sourced biochar on water storage in addition to the potential impacts on yield. As such, when trying to motivate the adoption and application of biochar in tropic climates, we may look to consider the multiple (or stacked) benefits from the sustainability perspective. Strategies whereby additional benefits like increased water storage that can bring about reduced irrigation needs and longer periods of drought resistance for crops could help motivate farmer adoption of biochar as a management practice.”

 

 

Reviewer 4 Report

Paper "On the potential of biochar soil amendments as a sustainable water management strategy" presents research related to the hydrogeology and water management of agricultural land, in general. The paper also presents a real case study. The paper presents an interesting research, and in several items, several suggestions will be emphasized.

 

• Keywords cannot be words from the title of the paper. These are usually significant words from the abstract. A change is proposed.
• Figure 1 shows a map that contains only the border. A geological or pedological map is proposed.
• Figures 2 & 3 (Section Results and Discussion) is not representative. A change is proposed.
• Is it really necessary to cite references in the conclusion?
• It is proposed to edit the conclusion in the sense that it should contain facts related to stating specific details related to the academic and scientific contribution of the paper.

Author Response

In the following letter, we have listed each individual review comment with our direct response and how our manuscript has been updated following in italics.

Paper "On the potential of biochar soil amendments as a sustainable water management strategy" presents research related to the hydrogeology and water management of agricultural land, in general. The paper also presents a real case study. The paper presents an interesting research, and in several items, several suggestions will be emphasized.

• Keywords cannot be words from the title of the paper. These are usually significant words from the abstract. A change is proposed.

We have modified the keywords (L52) to reflect sequencing in scales and avoided redundancy with the title. The keywords are now “tropical agriculture; melons; biochar; hydrometric observations; stable water isotopes”

• Figure 1 shows a map that contains only the border. A geological or pedological map is proposed.

Given the size of the country map, there would be a considerable lack of detail in such a map. As such, we opt to retain the county boundary map. We have added the coordinates for the study site to help orient the reader better to the location.

• Figures 2 & 3 (Section Results and Discussion) is not representative. A change is proposed.

We have updated all timeseries figures to have weekly tick marks on the horizontal time unit. This allows body text to align more clearly with figures. Further, to enrich Figures 2 and 3, we have added in the continuous line demarking the patterns observed with time.

• Is it really necessary to cite references in the conclusion?

We feel this is appropriate. Further, we have reduced the number of references in the Conclusion section through our edits moving several to the Results and Discussion section.

• It is proposed to edit the conclusion in the sense that it should contain facts related to stating specific details related to the academic and scientific contribution of the paper.

Agreed. We have edited and expanded the conclusions in this regard. As such, the following text are added (around L445):

“Further biochar has been found to improve crop productivity and soil quality consistently through liming and fertilization effects in low pH and infertile soils under low-input conditions typical of weathered tropical soils [36]. There is need for reduction of costs of biochar production and application to increase the material's use efficiency need future development. A recent review by Basak et al. [36] highlight the need to link economic benefits with social and environmental issues for successful implementation of biochar technology in weathered tropical soils. Further, they recommend identification of biochar properties suitable for tropical soils are important to get the maximum benefit of biochar application. Basak et al. [36] point out that suitable application strategies and co-deployment of biochar with other suitable additives pro-vides a promising area for improving efficiency of biochar for agricultural application. Our work adds value here as we assess the impacts of a locally sourced biochar on water storage in addition to the potential impacts on yield. As such, when trying to motivate the adoption and application of biochar in tropic climates, we may look to con-sider the multiple (or stacked) benefits from the sustainability perspective. Strategies whereby additional benefits like increased water storage that can bring about reduced irrigation needs and longer periods of drought resistance for crops could help motivate farmer adoption of biochar as a management practice.”

Round 2

Reviewer 1 Report

The authors have addressed all of the queries in the revised manuscript.

Author Response

Thank you for your efforts as a reviewer.

Reviewer 2 Report

Some comments are presented as follows,

1. In line 190, it is suggested to mark the latitude and longitude range of the test site in Figure 1, and put the text description at line 170.

2. In line 208, the planting mode of crops, including row spacing and plant spacing, and planting one or two rows on a ridge, all need to be clearly described.

3. In Concluding Remarks, it’s suggested to focus on summarizing the research results and significance of the paper, without describing the relevant contents of the references.

Author Response

Thank you for your efforts reviewing

Some comments are presented as follows,

1. In line 190, it is suggested to mark the latitude and longitude range of the test site in Figure 1, and put the text description at line 170.

We have done this in the revision in figure and text. We do not list bounding box and the plots are very small.

2. In line 208, the planting mode of crops, including row spacing and plant spacing, and planting one or two rows on a ridge, all need to be clearly described.

We have clarified these details and changed to the following sentence:

“Melons were planted by hand every 0.3 m along the mounds in a single row.”

3. In Concluding Remarks, it’s suggested to focus on summarizing the research results and significance of the paper, without describing the relevant contents of the references.

We have separated out a clear and concise conclusion section based on this recommendation. That section is as follows:

“4. Conclusion

This study quantifies biochar as a potential approach to secure sustainable water management. Specifically, we assessed the impacts of a locally sourced biochar on water storage in addition to the potential impacts on yield – which both must be considered when we think about achieving sustainable water management. Our findings add value, for example, when trying to motivate the adoption and application of biochar in tropic climates where we may need to consider multiple (or stacked) benefits from the sustainability perspective. Our results demonstrate this potential with regards to biochar in the tropics. Strategies whereby additional benefits like increased water storage that can bring about reduced irrigation needs and longer periods of drought resistance for crops could help motivate farmer adoption of biochar as a management practice.”

Reviewer 3 Report

The manuscript has been revised as suggested. However, it is rare to include references in the conclusion section, please use your discretion accordingly.

Author Response

Thank you for your efforts reviewing.

We have made a clear and concise conclusion section without references in our revision.

 

Reviewer 4 Report

In the newly submitted version of the paper, the authors made an effort to improve the quality of the paper.

 

While I disagree with the fact that the conclusion contains readings, I think the paper is worth publishing.

Author Response

Thank you for your efforts reviewing.

We have made a clear and concise conclusion section without references in our revision.