Effect of Terracing on Soil Moisture of Slope Farmland in Northeast China’s Black Soil Region

Round 1

Reviewer 1 Report

The manuscript presents interesting research on the effect of terracing on soil water conditions in a Chinese black soil area and shows and quantifies the benefits of this management. The manuscript is written in a comprehensive language and contains all important information and parts. However, I found some imperfections which should be corrected. From the general point of view, I would point out these comments: The authors should use unified terminology throughout the manuscript (see specific comments). The authors should clearly separate results and discussions. In the current form, they are mixed (see specific comments). The authors analysed also the soil properties, but it is uncertain what was the source of these data. The authors showed how terracing improved soil moisture. The soil moisture increase ranged only a few percent (L528-529). Can the authors say if there is any threshold which would say that from this point it is beneficial for plants and soil?

 

Specific comments:

 

Generally, the authors should use the past tense to present their own results throughout the whole manuscript.

 

Please unify the terminology soil moisture content, soil water content, and soil moisture condition throughout the whole manuscript. In the graphs (figures 4 and 6), the authors use water content but in the text, they use moisture content,

 

Methods: Please add information about the slope and orientation of the sites.

 

In the Results section, the authors present the results of other studies to compare their results. These parts should be included in the Discussion. For example:

L135, L158-159, L162-264, L173-175, L181-185, L192-194, 265-266,

 

Figure 2: Please replace rainfall in the figure caption for „precipitation“ to correspond to the y-axis. It would be also better if you wrote the whole word „precipitation“ on the y-axis. If it is air temperature, please add „air“ in the caption, and (Tmean) should follow to explain the abbreviation in the graph.

 

Figures 4 and 6: Pease, state in the figure caption what the bar and line-scatter plots are. It will make it easier for the reader to understand. In the graphs, you used below, middle, upper. Is it the same as the lower/upper slope, which you use in the text? If so, it should be unified (actually, check all figures for this). It would probably make it more comprehensive if you label the x-axis (like Slope position, or something like that)

 

L 206: How did you do the field investigation of the roots? There is nothing in Methods about this

 

L305-306 and L347-324: These parts belong to the Methods section

 

L326: Replace controlling for control

 

Figure 7. It should be clear that SMt/SMs in the graph and “benefits” in the figure caption are the same. It should be also explained what SMt and SMs mean.

 

Chapter 3.4: The authors analysed the relationship between soil moisture and soil properties, which are also summarised in Figure 8. However, I did not find any information on how these values were obtained. Did the authors do the soil analyses by themselves (then they should be described in the Methods section) or were the values taken from another source? (Then the source should be presented)

 

L405: more sensitive compared to what? Please specify

 

L474-492 and 501 515: These parts describe the results, therefore, they should be shifted to the Results section

 

Table 6: Please try to rewrite the table caption, I had no clue what it meant without checking the text. Maybe “δ values of …”? But it should be explained what δ value is.

 

L530: Delete “but”

 

IL546: I believe that the sentence “In addition, terracing weakens the impact of slope position on soil moisture.” is a repetition of L538-540.

Author Response

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Reviewer 2 Report

Dear Authors,

 In order to make your article as high quality as possible, please find my comments bellow.

Comments for author File: Comments.pdf

Author Response

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Reviewer 3 Report

Scientific soundness is rated low only because the authors make a major claim that they have provided no evidence for. With revision if they are able to produce evidence supporting their claim then scientific soundness of the paper should be rated "average".

They are comparing the hydraulic properties of terraced sites vs. unterraced control sites, claiming that the two sites are similar except for the terracing. It is vital that they provide elevation information for the sites, indicate slope gradient for the sites, provide landscape context for the sites, so that the reviewers can evaluate the claim that the control sites are indeed equivalent to the terraced sites. Without this, the comparison of the hydraulic features of the control sites to that of the terraced sites is not very meaningful. 

The authors have omitted very important details about laboratory and field methodology as well. They need to include these details for a proper perspective on what was done and how.

 

 

English was mainly good, but with a few mistakes. It requires an English editor.

The term "hydrothermal" is used incorrectly several times. Other grammatical errors are mostly minor.

Detailed comments:

Line 31 - Can you provide a definition of what is meant by "slope farmland"? How is it distinguished from non-sloping farmland or other kinds of farmland?

Line 75 - I don't think you mean "hydrothermal" in the normal sense of the word ("relating to or denoting the action of heated water in the earth's crust"). You are not talking about volcanic activity, are you? I'd change the sentence to say "hydric, temperature, and soil quality conditions".

Line 83 - again, I invite you define what is meant by "slope farmland" as the term is not clear. Is this the same term as "sloping farmland" used in the following article? https://doi.org/10.1016/j.agwat.2020.106564 Most farmland has some slope, but I don't know how much slope is needed to categorize the land as "slope farmland" or "sloping farmland". Are the two terms synonymous? What is the percentage slope beyond which a farm land is considered sloping? Since you have determined that 60% of the soils in the black soil region are slope farmland we should know what determines and delineates slope farmland from other classes of farm land.

Line 83 and following - please provide elevation information about each site. State the high elevation, low elevation, average change in elevation, field convexity vs. concavity, and other details about the land surface shape. This is crucial information the reader needs to know to understand what you have done and why.

Line 84 - again, unless you are talking about magma influence or volcanic conditions, change "hydrothermal" to a correct term.

Please add a description of all methods used to obtain soil texture, bulk density, porosity, capillary water capacity, field capacity, and pH measurements. How many samples were collected? What field and laboratory procedures were used? This discussion is entirely absent from the methods and the data presented in Figure 8 and onwards comes as a surprise. The reader does not have a context for this information if not told how it was collected and what procedures were used to obtain the values.

Figure 1 - please provide detailed elevation information for each site. This could be done by giving topographic elevation lines (topographic contour lines), a color-coded elevation model representation, or some other quantitative way for the reader to determine the shape, elevation gradient, change in elevation, slopes, etc. of each site. Please provide a scale bar for each county site. The reader needs to know how big the sites were, the scale of measurement, etc. Please indicate the meaning of the shape of the sites in the figure. They seem to be rendered in 3D representation, but we are not told if a vertical exaggeration was used. We are also not able to see the shapes of the terrace features in the figure. It would be better if we could see the elevation change with terracing in the figures. Is the line of sampling parallel to the terrace or perpendicular to the terrace? This should be indicated and made clear in the figure or the text.

Also, for each site please indicate the relative locations of the terraced area and the control area. We need to see something of the landscape context for each site. That is, we need to see the site boundaries at a landscape scale so we can see where these sites occur in a greater context. How far away from the terrace sites is each control site? What shape does the control site have? On what landscape position does each site occur? Please provide an elevation model for the context of each site with site boundaries indicating the site locations so readers can see where they occur on the landscape.

Line 96 - There are several different types of agricultural terrace. Please fully describe the terraces at each site. What kind of terraces were used? How were they constructed? What is the elevation difference between terrace and adjacent field? Are they broad-base terraces with crops grown on them, are they earthen embankment type terraces with no crops on them? Please fully describe them! If you can, please indicate any changes in soil properties due to the terracing? For example, was field material, such as A horizon, used to make the terraces or were they constructed from imported material. How did terrace construction change the soils in terms of A horizon thickness, soil texture changes, etc?

Line 113 - Briefly describe what the TRIME-PICO64TDR instrument is and how it works. Tell why it was chosen, its strengths and weaknesses, and defend why it is an acceptable instrument to use for this project.
Line 119 - while the term "thermal" is not incorrect, I would encourage you to use "temperature" instead, as it has a more focused meaning. "Water and temperature conditions" would be a better way of beginning this sentence. As explained above, "hydrothermal" does not mean what you think it does.

Line 127 - considering that you are using ArcMap for GIS, there are several ways to generate contour maps. Similar processes are available in QGIS (free software)

Figure 3 - like with figure 1 we need scale bars here, telling us the dimensions of the sites.

Table 2. At the very least we need a statistic of average slope value for the terraced fields and the control fields. The difference in average soil moisture could have more to do with landscape position, slope, concavity, distance to stream network, etc, than it does with terracing. Without taking landscape features into account it's unlikely that you will convince readers that the increase in soil moisture has anything to do with terracing.

Essentially you need to characterize the landscapes of your sites and show their context so we can know that the control and the terraced fields would be expected to have the same soil moisture conditions if terraces were absent. There is a lot of moisture differentiation from one site to another that can be attributed to topographic characteristics -- elevation, topographic wetness index, distance to channelization, etc. -- that you have not accounted for. Please do so.

Line 163 and 167: consider replacing "turning point of soil moisture" with "soil moisture maxima", as "turning point" in this context is colloquial and imprecise.

Line 195: for this difference to be meaningful you need to account for average slope gradient percentage and slope length of the compared sites. What is the elevation difference between high and low parts of each field? How long is the slope? How concave or convex? Without addressing these questions the difference is not meaningful.

Line 197: I believe this is true from other studies, but you have not shown it because you've omitted slope and landscape information.

Figure 4: Please clarify whether the asterisks indicate significant differences among depths or among slope positions. Is the difference between shallow and deep soils the absolute difference, or is it (deep - shallow) or (shallow - deep)? Please indicate.

Figure 7: Please remove the line for SMt/SMs in the figure and replace it with a bar. The line implies a linear progression from Dongaliao to Keshan, which is not appropriate. You are not making a claim that the SMt/SMs increases steadily as you go from one site to the next, are you? Each site is considered separately as a separate geographic entity, correct? If you do think there is a geographic linear increase from one site to the others then you will have to examine a lot more data at many more sites to make that case!

Line 385: This is a good discussion of soil properties, but these need to be contextualized with respect to a discussion of terrace type and construction. Why did terrace construction cause any changes in soil properties? How did that work? Also, please discuss landscape context and why the soils may be different because of landscape position and occurrence.

I think this is a good paper, but there are too many missing gaps at the moment. You need to fill in key missing parts of the story. I think it could be published if you characterize the elevation and landscape context of the sites, tone down some of the claims you are making, show more about your methods, and be more forthcoming about some of the shortcomings of your efforts.

I wasn't convinced that your statistical analysis was valid because I didn't get enough information about how the data was collected and analyzed. More detail would be welcome here too.

Author Response

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Reviewer 4 Report

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Comments for author File: Comments.pdf

The English must be improved, and more proper terminology has to be used!

Author Response

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Round 2

Reviewer 1 Report

The manuscript has been sufficiently improved. I have no other comments

Author Response

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Reviewer 3 Report

Figure 1 should be improved to allow the reader to judge the physical relationships between terraced and untreated sites.

Thank you for adding the insets to figure 1 that show the locations of terraced sites relative to the control sites. Please make these images higher quality so they don't look blurry and illegible to the reader (more pixels per millimeter) and add labeled topographic contour lines to each one so the reader can discern the topographic character of each. (Remember, I asked you to do this in the first review.) The scientific integrity of the study hinges on whether the soil moisture differences you attribute to terracing can be explained by other factors such as landscape position and elevation differences. You have not given sufficient numerical evidence of topography or local elevation of the sites. You also need to discuss alternative explanations of moisture differences. As you know, soils may be moist in low convergent areas and drier in high sloping areas. Discuss the influence of landscape position on the control sites to allow us to judge the degree to which moisture differences are influenced terracing vs. landscape position and elevation.

I see that you have added a statement that each site has a slope of 10 degrees. This is a helpful start, but not an adequate description of the shape and topographic character of the sites. It is doubtful that all sites meet the strict criteria of having a 10 degree slope. What is the margin of error of this estimate? What topographic variation exists at the various sites? You need to address this. The simplest way would be for you to provide topographic contour lines on a high-resolution image.

Please make the border around China the same level of grey as the borders around other countries in the figure. As it is now it appears to show that Taiwan is within the dark black border of China. This is inappropriate and I cannot accept this. As a reviewer from a country that does not recognize certain political claims, I am not allowed to accept such geopolitical maneuvers. Try to keep politics out of scientific papers if you can!

English language should be checked by a separate reviewer, if possible. Some corrections were neglected, others were over-done. For example, the authors originally referred to "upper," "middle," and "lower" slope positions, but the reviewer arbitrarily changed these to "above", "middle", and "below" slope positions. As a native English speaker I have to say the "above slope" and "below slope" sounds a little odd. I like the original phrasing better! Also, there is no need that I can see to change "soil moisture" to "soil water". The former is preferred in the literature. Line 60 should be changed from "is poorly studied" to "is poorly understood" (unless you think the existing studies are bad!).

Author Response

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