Why We Should Include Soil Structural Dynamics of Agricultural Soils in Hydrological Models

Round  1

Reviewer 1 Report

The manuscript of Chandrasekhar et al. addresses a very important, but so far less studied topic. The temporal variability of the soil pore space and associated soil hydraulic properties finally receives more attention and has to be adopted in hydrological modeling, but also into biogeochemical models in general. Chandrasekhar et al. compiled studies that deal with this issue and summarize the main important, as well as contradictory, outcomes. Furthermore, they apply a pore evolution model to literature data and evaluate the applicability of the model to predict the reported observations.

The manuscript is nicely written and has a clear structure in general. However, some questions arise when reading the text and some more explanations are needed at specific points. Moreover, the compilation of the studies in Table 1 is not clear and the reader can only assume that the table is supposed to be a continuation of the study presented by Strudley et al. (2008).

Generally, the two tables included in the manuscript are helpful, but appear to be a bit messy and it is hard to understand which rows belong together and at which point a new entry begins. This might need some improvement.

The title is easily understandable, but I am doubting a bit if the expression “management-induced” is appropriate. The authors certainly mention a number of agricultural management practices, but the main topic of the study is on the effects of tillage and the modeling study is limited to this practice. Furthermore, the authors list “Tillage effects” as a keyword, instead of “Management effects”. I myself consider this a very minor comment, but maybe the title could be a bit more informative in this perspective.

Throughout the text, there is a frequent change between “modelling” and “modeling”. Please decide for one of them.

I have some specific comments that might help to achieve a better understanding by even non-expert readers.

Abstract

l 22: I suggest to extent “factors” to “environmental factors” or “external factors”, which  basically captures all influences and stresses that act upon soil and pores structure

l. 26: I suggest to add “after disturbance” at the end of the sentence

l. 28: it might not be clear what is meant by “predicted values”

ll. 28 – 29: what is meant by “reasonably well”? Please give some examples for the evaluation criteria, i.e., r2 or RMSE.

ll. 29 – 31: This is a very understandable and conclusive statement

1. Introduction

l. 44: “affects”

l. 61: what is meant by “poor decision support systems”?

l. 64: “these dynamics”

Figure 1: This is a very illustrative figure, but I am not sure about the graphical contribution in the lower part, i.e., “Influenced soil depth”. Maybe it would be easier to just mention a classification, e.g., “deep”, “intermediate”, “shallow”

2. Impacts of anthropogenic and natural influences on SHP

l. 82: does “natural” mean “environmental”? I suppose the authors refer to the impact of weather, i.e., precipitation and temperature?

ll. 85 – 86: please give either a citation or an equation (or both) at this point

l. 88: “influence”

ll. 95 – 97: already here the authors could mention if the measurements were performed in the laboratory or in the field. This becomes an important issue in the further manuscript.

ll. 98 – 99: This second part of the sentence is a bit too vague. What is the reason for the high uncertainty?

l. 105: “help”

l. 119: the reference to [30] is a bit inconvenient for the reader and does not really help. I suggest to give the equation or some more explanations

ll. 135 – 136: please mention the main outcomes of the study published by Strudley et al. (2008)

l. 137: I suggest to add “published after 2008” to this sentence

ll. 142 – 219: this section needs a more distinct structure and some of the references should be shifted accordingly within the text. I suggest to include subtitles mentioning the respective management practices, i.e. tillage (ll. 142 – 179), cover crops (ll. 187 – 206) and land use change (ll. 179 – 186 + ll. 162 – 164)

l. 161: “lead”

ll. 162 – 164: this reference should be mentioned at another stage, as it deal with land use change, but the paragraph is about tillage effects

ll. 177 – 179: this reference should be mentioned at a later or earlier stage. It deals with the impacts of tillage on C storage, but the more important aspect for the present study might be that there were significant differences in bulk density between treatments

l. 178: please replace “RT” by “NT”

l. 187: please replace “was” by “were”

l. 188: what is the source of the binding agents? Root exudates?

l. 189: what is “it” referring to? Cover crops?

l. 190 – 192: Suggestion: “A review of Ball et al. on the role of crop-rotations indicated that the amount of organic matter incorporated into the soil was more important to preserve soil structure than the farming technique employed.”

ll. 198 – 199: how is “soil organic matter and biota” linked to SHP and pore structure?

Table 1: if available, please add information about the measurement technique to the studies and if the measurements were conducted in the laboratory or in the field

3. Time variable SHP in soil water simulations

l. 308: I suggest to replace “by” by “when”

l. 309: I suggest to replace “altered” by “varying”

l. 310: I suggest to add “, i.e., constant” after “time-invariable”

l. 319: what is meant by “water yield”

l. 325 – 327: this sentence is hard to understand . what is meant by “both the changes yield effects”?

l. 328: “these dynamics”

l. 329: what is meant by “they”?

4. Modeling techniques to capture evolution of PSD post-tillage

l. 351: “tend”

l. 361: does “(1)” refer to Equation (1) or “(1)” from l. 351?

l. 369: please add “-“ after “from Spain” and replace “it” by “they”

l. 379: please add “-“ after “CT and NT”

4.2. Results and model suitability

l. 409: what is meant by “independent models”?

l. 427: “suggest”

ll. 429 – 430: does “over-estimation of predicted values” mean that the model overestimates the observed frequency?

ll. 432 – 433: please refer to Table 2 at the end of the sentence

ll. 439 – 440: I suggest to add “so far” after “sufficient studies”

5. Summary and outlook

l. 472: please replace “is” by “was”

ll. 475 – 477: it would be helpful for the reader if “this approach” would be named again

l. 483: please remove “will the”

Author Response

Dear Reviewer,

Thank you very much for your detailed and valuable comments. We have implemented almost all the suggestions you have provided and you will find it in the latest version of the manuscript. And, we have changed the title of the manuscript because we also found that 'management - induced' is indeed a very broad term. As for the tables, we followed the template provided by MDPI. We are not sure if we can change the format. We have listed studies after 2008 in Table 1 following the review by Strudley et al. (2008). Finally, we have changed all instances of 'modelling' to 'modeling'.

Thank you again for all the feedback. The response to each of your comments can be found in the attached file.

Best regards,

Parvathy Chandrasekhar

Author Response File: Author Response.docx

Reviewer 2 Report

Dear coleagues! I cannot evaluate your work "perfectly", because it seems to me that you have mixed all the possible factors of the dynamics of the pore space structure, instead of classifying them and considering them separately. Also, in my opinion, it was necessary not only to assess the scope of variation of the pore space structure in the surface layers of the soil, but, what is much more important, to obtain data on the basis of distributed models such as HYDRUS on the contribution of these changes to the total mass transfer in the soil-plant-atmosphere system, in the redistribution of moisture within the soil, in the ratio of surface and intra-soil runoff deep into the soil and into groundwater. Meanwhile, from Your review it is not clear how natural and anthropogenic dynamics of the structure of the SOIL SURFACE AND ITS UPPER LAYER (namely, there is everything You described to change) important for soil hydrology as a distributed body in General. Also in the review, you for some reason completely ignored the fundamental achievements of Russian soil Hydrophysics in this field of research (for example, the effects of thermodynamics of dispersion, the influence of organic carbon dynamics, modeling of pore dynamics due to hysteresis of hydrophysical functions (DOI: 10.1007/s10891-008-0082-8; DOI: 10.1007/s10891-015-1194-6; DOI: 10.1007/s10891-006-0046-9; DOI: 10.1134 / S1028334X13100036; Eurasian Soil Sci., 2003.Vol. 36, № 3, p.3.301-312; Eurasian Soil Science, 2004, Vol. 37, №3, p. 267-275; DOI: 10.1134/S1064229311020128; DOI: 10.1134/S1064229318070098;DOI: 10.1155/2016/8176728; DOI: 10.1088/1755-1315/90/1/012105 and so on).However, this does not prevent me to appreciate your review and recommend it for publication in the journal Water. I hope my comments will be useful in future work on this topic. 

Best wishes, your Reviewer

Author Response

Dear Reviewer,

Thank you very much for your valuable feedback. I agree and understand the need to consider the factors that cause dynamics in the soil pore space separately. I have added some of the reference suggestions (DOI 10.1007/s10891-015-1194-6, Journal of Engineering Physics and Thermophysics, Vol. 78, No. 6, 2005, http://dx.doi.org/10.1155/2016/8176728) you provided in the updated manuscript.

1) In response to your comment on mixing all the factors that cause dynamics of soil pore space: since the aim of the paper was to highlight the importance of including the temporal dynamics of soil hydraulic properties in hydrological modelling studies, due to a combination of natural and anthropogenic factors, we believe that considering each of these factors separately may exceed the scope of the paper. However, we will keep in mind your suggestions for future research.

2) We fully agree with using models to estimate " the redistribution of moisture within the soil, in the ratio of surface and intra-soil runoff deep into the soil and into groundwater". We hope that the model we 'test' in this manuscript will help us in implementing derived soil water retention and hydraulic conductivity functions, that are able to capture temporal dynamics of soil hydraulic properties, into hydrological models.

We hope that we were able to respond to your comments. Thank you again for your suggestions.

Best regards,

Parvathy Chandrasekhar