The Mechanism of the Influence of Different Irrigation Methods on Groundwater Recharge

Round 1

Reviewer 1 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

Although some modifications have been done to the original manuscript, but there are some more to do. Some cases have been mentioned on the new text.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English language is fine.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

This is a very nice and concise piece of work exploring the difference between flood irrigation and “smart” irrigation on a floodplain in arid-temperate northern China. The design and construction of the experiment is nicely done and provides an efficient and precise experimental environment to convincingly explore the differences in the two irrigation methods. The results are well presented and make logical sense, namely that the smart (or “intelligent”, as used by the authors) irrigation wets to a shallower depth than the flood irrigation and contributes less to groundwater recharge. The study thus provides some useful data to substantiate a commonly assumed dynamic.

I do have a few comments that I would appreciate consideration of, and these are included as comments in the attached and edited pdf. Critically:

1.     I do not see where intelligent irrigation is described in the document. That is, what are the thresholds used and how does the system operate in practice?

2.     The experimental system is impressive. I would like to see more information. Particularly, when was the experiment built? Are these chambers used just for this study? How is water applied to the soil? Is it possible to exclude rainfall? Importantly, what were the antecedent conditions for the soil chambers immediately prior to the start of the study? What was the base-line moisture profile? How long were the chambers allowed to equilibrate before being used for this study? These questions are important to validate the comparison between the 2 chambers and the 2 irrigation types.

3.     There is no discussion on the optimisation process for the modelling. Nor on any sensitivity analysis of the parameters prior to scenario runs. What is the uncertainty in the parameters listed in Table 1?

4.     A general comment is that I found it difficult to tell when the paper was considering the observational data and when the modelling results. Sometimes this was stated but often only became apparent after repeated reading and cross-checking. This needs to be clearer.

5.     The discussion should be used to explore the results presented in the conclusion and not merely list the limitations of the study. These can be part of the discussion and should be included in the experiment design description (Section 2.2).  

Other comments are not critical and are provided for consideration only.

I feel that this makes a useful contribution to field and modelling studies of irrigation practices and should be published following responses to my comments.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

English is generally good. There are a couple of new sections (in red) that appear to have been written by a different person to the rest of the document and the English is not so good.

There are a few instances of "curious" terminology. This is particularly the case in the introduction, where the examples of pervious work are quite dis-jointed and lacks flow or specific relevance. The sense is understandable, however, hence is not a significant issue. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Paper Review: Irrigation Methods and Groundwater Recharge.

Line 38: Normally, we would say that irrigation is dependent on water supply, not the other way around. I think the authors need to define the context in which they are using the terms irrigation and water supply. Also in this line, they are referring to the groundwater recharge, I think.

Line 39: Does the number 10mm/day include water losses during irrigation or it is crop ET alone? In the latter case, it seems to be quite high.

Line 49-68: I am not used to considering the practice of irrigation as a source of groundwater recharge. Because, when we do that then the more inefficient the way irrigation water is applied the greater the groundwater recharge. That is , the gravity flow surface water application (flooding, furrow, border methods) would result in greater groundwater recharge compared to the sprinkler and drip irrigation methods. Seems like reverse logic.

“Intelligent” irrigation is not a universal term. Please define. Do you mean drip or sprinkler irrigation with better water control?

Figure 4 shows the amount of water applied over a 40 day period of crop growth. Was the study conducted for the first 40 days of crop growth? If it was conducted for the whole crop growth period, then why not show for the whole crop season?

Also, 1000 mm of irrigation water was applied over a period of about 40 days. If my observation is correct, this much water application is well above the crop ET and would result in high percolation to the  groundwater.

Figure 6: The two groundwater models shown are exactly the same. So, why not just show one? And, the figure shows just a typical soil profile. What do you want to reader to take from this figure?

Equation 2: Water uptake by the crop is the crop transpiration, which can be determined by using the Penman-Monteith Equation. I am not familiar with the Feddes Equation.

Line 196: rootzone depth of 0-30 cms is true for the first month or so of the corn crop growth. But it can then increase to 60 cms as the maize crop achieves full vegetative cover. Are you considering the first 30-40 days of crop growth? That is surely not enough time frame for the study.

Figure 7 (b) title: what do you mean by “diffuse” irrigation?  Gravity flow flood irrigation?

Line 278-279: The data in figure 7-8 does not support the statement in case of flood irrigation.

Table 2: The results for R² and relative error etc are based on very few data points, and hence not reliable.

Figure 10: Is very hard to read and understand. The numbers and titles fonts are very small. Also, are these groundwater contour maps drawn using actual measured data or are these based on model simulations? 

Figure 11, 12 and related text: Are these data from actual field water applications and observations of its movement through the soil? Or, these are from computer simulations based on mathematical models? My understanding is that these are simulations rather than actual field experiments.

From my review, I understand that the authors performed very limited field experiments. The data from these experiments were then used to generate computer simulations. And most results presented in this paper are from computer simulations of mathematical models of the soil-water movement. This would limit how much faith I would have in the findings reported in this research. 

Comments on the Quality of English Language

The English language is largely of acceptable quality. 

Author Response

Line 38: Normally, we would say that irrigation is dependent on water supply, not the other way around. I think the authors need to define the context in which they are using the terms irrigation and water supply. Also in this line, they are referring to the groundwater recharge, I think.

Reply: thank the experts for their valuable advice. The background of the original text has been defined and marked in red.

Line 39: Does the number 10mm/day include water losses during irrigation or it is crop ET alone? In the latter case, it seems to be quite high.

Reply: thank the experts for their valuable advice. The references have been carefully read and the figure does not include water loss during irrigation.

Line 49-68: I am not used to considering the practice of irrigation as a source of groundwater recharge. Because, when we do that then the more inefficient the way irrigation water is applied the greater the groundwater recharge. That is , the gravity flow surface water application (flooding, furrow, border methods) would result in greater groundwater recharge compared to the sprinkler and drip irrigation methods. Seems like reverse logic.

Reply: thank the experts for their valuable advice. The relevant definitions of the article have been modified.

“Intelligent” irrigation is not a universal term. Please define. Do you mean drip or sprinkler irrigation with better water control?

Reply: thank the experts for their valuable advice. Intelligent irrigation has been defined.

Figure 4 shows the amount of water applied over a 40 day period of crop growth. Was the study conducted for the first 40 days of crop growth? If it was conducted for the whole crop growth period, then why not show for the whole crop season?

Reply: thank the experts for their valuable advice. The article has been supplemented, this study is aimed at the whole growth period, select some data for research.

Also, 1000 mm of irrigation water was applied over a period of about 40 days. If my observation is correct, this much water application is well above the crop ET and would result in high percolation to the  groundwater.

Reply: thank the experts for their valuable advice. Figure 4 shows the change of corn growth height, but the vertical coordinate in the figure is not clear and has been modified.

Figure 6: The two groundwater models shown are exactly the same. So, why not just show one? And, the figure shows just a typical soil profile. What do you want to reader to take from this figure?

Reply: thank the experts for their valuable advice. The diagram has been modified. It is hoped that readers can understand the components and depth of the sample section on the way.

Equation 2: Water uptake by the crop is the crop transpiration, which can be determined by using the Penman-Monteith Equation. I am not familiar with the Feddes Equation.

Reply: thank the experts for their valuable advice. The literature has been supplemented.

Line 196: rootzone depth of 0-30 cms is true for the first month or so of the corn crop growth. But it can then increase to 60 cms as the maize crop achieves full vegetative cover. Are you considering the first 30-40 days of crop growth? That is surely not enough time frame for the study.

Reply: thank the experts for their valuable advice. This study mainly focuses on the first 40 days of crop growth, which is not clearly described in figure 4 and has been modified.

Figure 7 (b) title: what do you mean by “diffuse” irrigation?  Gravity flow flood irrigation?

Reply: thank the experts for their valuable advice. The statement is incorrect and has been modified.

Line 278-279: The data in figure 7-8 does not support the statement in case of flood irrigation.

Reply: thank the experts for their valuable advice. Figure 7-8 has been revised.

Table 2: The results for R² and relative error etc are based on very few data points, and hence not reliable.

Reply: thank the experts for their valuable advice.

Figure 10: Is very hard to read and understand. The numbers and titles fonts are very small. Also, are these groundwater contour maps drawn using actual measured data or are these based on model simulations? 

Reply: Thank you for the expert's valuable suggestions. The graphic fonts have been adjusted and modified, and the graphs are drawn based on actual measurement data.

Figures 11, 12 and related text: Are these data from actual field water use and its movement in the soil observation? Or, are these from computer simulations based on mathematical models? My understanding is that these are simulations, not actual field experiments.

Reply: Thank you for the expert's valuable suggestions. The data are all from actual data monitored by sensors at the experimental station in the study area.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Verify that this plain is a favorable region for agricultural activities.

2. Instead of intelligent irrigation system write sprinkler system.

3. With so many factors that affect infiltration of water to deep soil layers, this method of research is very site specific and cannot be generalize even for a vast plain. This is the  worst limitation of this experiment.

4. Please mention the reference(s) for the given equations.

5. Type the references uniformly.

Comments for author File: Comments.pdf

Author Response

1. Verify that this plain is a favorable region for agricultural activities.

Reply: thank the experts for their valuable advice. The content of the article has been adjusted.

2. Instead of intelligent irrigation system write sprinkler system.

Reply: thank the experts for their valuable advice.

3. With so many factors that affect infiltration of water to deep soil layers, this method of research is very site specific and cannot be generalize even for a vast plain. This is the  worst limitation of this experiment.

Reply: thank the experts for their valuable advice.

4. Please mention the reference(s) for the given equations.

Reply: thank the experts for their valuable advice. It has been supplemented in this article.

5. Type the references uniformly.

Reply: thank the experts for their valuable advice. It has been supplemented in this article.

Author Response File: Author Response.pdf