Evaluating Growth, Yield, and Water Use Efficiency of African and Commercial Ginger Species in South Africa

Round  1

Reviewer 1 Report

Dear authors,

My comments can be found in the attached file. Hope these can help improve the paper towards a good publication. Good luck!

Review comments

Manuscript ID: water-406801

Title: Growth, yield and water use efficiency of African and commercial ginger species

Thanks for inviting me to review this paper. The study investigates the growth indices, yield, and water use efficiency of two ginger species in some country of Africa (?). Under four irrigation treatments, the research found as water stress decreased, plant height and number of stems were positively affected. Higher yield was found for commercial ginger at all water treatments. WUE was higher for commercial ginger.

This research is very interesting and relevant to the journal. Methods are clearly presented. Presentation of the results is well done. However, some work is needed to improve the paper before it can be published, especially, improvements to introduction (related to literature), discussion, and conclusion sections. Some of my major concerns can be found below. Note these are aimed to help authors efficiently improve the paper. An evaluation is needed for the revised version of the manuscript.

1.      The title needs to be rephrased. It is too general, and cannot reflect experimental nature and specific study area. You may consider: Evaluating growth, yield and water use efficiency of African and commercial ginger species in County Name.

2.      Introduction. This is a major concern. The linkage between previous research on GINGER and current research is not clear. You mentioned research on other plants in general, but not on ginger, or even plants belonging to the same species, genus, or family. Similar research has been done in different study areas. Well… you also mentioned some of the research in lines 188-192, with citations 15-18. Without a clear presentation of the research gap, though you mentioned the information limitation of ginger, the aim of the study seems to rush.

3.      Though there is no separate section for relevant literature, and the authors have included this review to intro section. This is fine, but limited information is provided in the intro section regarding previous literature. This is also the reason why the intro is my major concern.

4.      2.1 Experimental site, you need to introduce a bit about the study area. Since you are publishing in an international journal, introduction of the study location, regions (why choose this region, for example, because of large production of the crop?), and county (as well as market share of the ginger from this country. This market issues can also be presented in the intro section) can help readers better understand your research.

5.      Equations 3 and 4 need citations. If possible, you also need support for eqs 1 and 2. For example, the following study used similar definitions for water use and water use efficiency, and they evaluated WUE of different crops:

Fan, Y., Wang, C., & Nan, Z. (2014). Comparative evaluation of crop water use efficiency, economic analysis and net household profit simulation in arid Northwest China. Agricultural Water Management, 146, 335-345.

6.      The discussion section is combined with the results. This is fine, however, the discussion information is very limited, you need to add more to make an adequate argument, in particular for the results related to yield and water use efficiency.

7.      This research does not incorporate economics. This is fine, but an economic analysis will show more incentives for farmers to plant either ginger species. See the research recommended above. Why the economic analysis is not conducted? Valid reasons here are good, even you decide not to include any economics.

8.      The research limitation can be mentioned, if any. Alternatively, future research or research directions can provide more insights of this research.

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewers. We are grateful to the Reviewers  for the constructive comments and suggestions, which have greatly improved the quality of our manuscript. 

Author Response File: Author Response.docx

Reviewer 2 Report

Review of “growth, yield and water use efficiency of African and commercial ginger species”

The paper begins well, with a generally sound Introduction and Materials and Methods. There are a couple of places where the latter needs some enhancement. We get to line 139 before the critical information that the experiment was conducted under a rain shelter is revealed. As well, some verification that the fixation process described in Secn 2.9 did not affect the stomatal opening is necessary. That is, is there other evidence that the fixation method preserves in vivo stomatal aperture?

I have more serious concerns once we move to the Results and Discussion.

Line 164 et seq: I believe that there should be demonstration that the nominal water regimes were actually experienced. For instance, time series data of actual observed soil water showing that it remained within 100 and 75% of ASW for the 20-25% MAD treatment should be shown, and the same for other treatments. This would also show the rate of soil water depletion of the various treatments. As well, the authors should discuss whether the observed data bore out their guess (line 108) that water withdrawal would occur mainly in the 0-1000px soil stratum. We are not told if the data in Table 5 is based on 0-40 or 0-80 cm observations.

Table 5: It is obvious that the crops are responding differently to greater allowable soil water deficits in the two years, with water use generally being less responsive to treatment for 40% water depletion or greater in 2016/17. The weather records, which contain the drivers for water use (Table 4) don’t seem to me to offer much explanation for this. I suspect that the answer lies in either the treatments having some systemic difference between the years or the shapes of the drying cycle trends being different from one year to the next.

Lines 166-174: The statistical analyses have not been well interpreted. Take lines 166-8 as an example, which indicate that, for water use in 2015/16, CG20/25>AG20/25 and CG40/45>AG40/45. However, the multiple range indicators show that CG20/25 is not significantly different from AG20/25 and CG40/45 is not significantly different from AG 40/45. As well, the next sentence is equally poorly interpreted. 381mm may look bigger than 362mm, but the analysis does not offer any evidence to show that they are actually different. The apparent differences are probably due to sampling (experimental) error.

This is a trend that permeates the paper. In Figs 1-3, one can find similar poor interpretation of the analysed date, which renders the description of the data invalid. This is a fatal flaw.

Line 194 (and for other figures): It is difficult to compare numeric lsd values with graphical trends. The convention is to show the lsd’s as a graphical element (a bar, for instance) so that its size can be visually compared to the distance between trend lines. Also, the labels (day numbers) should be opposite the relevant tick marks on the axis, not between them.

Sec’n 3.5 and 3.6: Given that the treatments are defined by a range, I find regressions based on a single nominal value of the treatment unsound. The authors have not demonstrated that the treatments actually achieved those deficit levels. However, water use was measured and would be a more compelling driving variable.  

Given the metrics in Table 6, I wonder if Fig 7 adds value to the paper. In Table 6, I would have included information about the size of the stomatal pores.

Table 7. I find this table difficult to believe. Typically, water use efficiency is a conservative parameter, with little effect of water stress upon it. Variation from this is mostly due to poor accounting of water, but that cannot be the case here as the growing conditions, with no incident rainfall due to the rain shelter and astute management of irrigation, constitute a closed system, with, simply, measured irrigation volume in and an accounting for soil moisture changes over each season. The dry WUE values are probably the best to examine, as the possibly variable water content of tissues has been accounted for. For AG, in both seasons, the value hovers around 9-10, with no significant differences within season, and, visually, none between seasons. The values for CG are, in comparison, almost random. What is going on?

Unfortunately, the authors do not discuss these results, ie, interpret them. This, too, is a feature throughout the paper, with results poorly described and with very little interpretation or discussion. Equally, the Conclusions is largely a summary of the results, which is inadequate.

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewer. We are grateful to the Reviewers and the Editor for their constructive comments and suggestions, which have greatly improved the quality of our manuscript. P

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper compares commercial and African ginger in terms of response to water stress condition. In particular, the parameters relating to water use, growth, yield and water use efficiency of the plants are been evaluated by the authors.

The paper cover an interesting topic, is scientifically sound and clearly written.

I suggest the pubblication of the paper in the present form

Comments for author File: Comments.docx

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewers. We are grateful to the Reviewers and the Editor for their constructive comments and suggestions, which have greatly improved the quality of our manuscript.

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper describe the important problems relating the two gingers species growth and yield in situaltion of gradual increase of water stress.

The experiment is correctly prepared and the methods of keeping MAD levels are fully professional. The measurement are very complex and tuched all effects od water stress of plant growth. Several different parameters (morphological and physiological)  are deeply measured and presented in the manuscript body.

The correction are made in the text of paper. In my opinion the conculsion can be changed in relation to the obtained results. The commercial ginger seems to be more resistant to water stress than African ginger. Please distinguish to use  the suggested corrections of the paper submitted to publication 

Comments for author File: Comments.pdf

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewer. We are grateful to the Reviewers and the Editor for their constructive comments and suggestions, which have greatly improved the quality of our manuscript. 

Author Response File: Author Response.pdf

Round  2

Reviewer 1 Report

One more comment: for the equations 1-4, the citations should be added to the sentences before the equations rather than at the end of the equations. This is also consistent with the  general format of publications.

Other than that, the paper has been improved and the authors have addressed my concerns well. The paper can be accepted for publication after some format edits. 

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewer. We are grateful to the Reviewers and the Editor for their constructive comments and suggestions, which have greatly improved the quality of our manuscript. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of “ Evaluating growth, yield and water use efficiency of ginger”

Secn 2.9. The description of the procedure raises a number of concerns.

a.       Was 30% or 3% glutaraldehyde used?

b.       The description in ref 22 suggests the dehydration sequence as 30, 50, 70, 90, 100, 100% ethanol. There is no mention of “the procedure was repeated three times” in ref 22. What does this mean? Surely not that the dehydration sequence was repeated three times.

c.       The bulk of the text in this section is essentially the same as in ref 22. The authors should rephrase, restricting their text to the key differences from the procedure in ref 22.

d.       Ref 22 provides no information regarding my initial query, whether the sample preparation procedure, including dehydration, would have affected stomatal opening.

Secn 3.1.

a.       Line 218. I think the well-watered treatment was 20-25% MAD.

b.       Lines 220-222. I agree with the first sentence. However, the statistical evidence presented, that water use by treatment 2-4 and 6-8 were not significantly different in season 2, does not support the assertion of a general trend. In fact, the second season produced quite different patterns of water use from the first season.

c.       My initial concerns regarding the exact nature of the water conditions under which the crops grew have not been assuaged by the authors’ pointing to this table. The cumulative ETo was similar for both seasons (1270 mm for the first, 1280 for the second). Average FI was lower in the second season (Fig 5) and, assuming that this average represented a common pattern of development of light interception through the season, then the crop coefficient should follow this trend. In the absence of rain input, drainage and runoff, as explained in lines 186-188, water use can be roughly calculated as ETo x crop coefficient. For the well-watered treatments, the data in Table 5 are not consistent with this calculation.

d.       Given the influence of FI on actual crop water use, the relatively flat trend in Fig 5A stands in contrast to the steep decline in water use in the first season (Table 5) in the progression from treatments 1-4 and 5-8. Equally, the somewhat steeper decline in FI with water stress in Fig 5B is inconsistent with the trends on Table 5 for the second season.

e.       ASW was regularly calculated for irrigation management (Secn 2.5) and these data might resolver my uncertainties, but they have not been presented. In this, I disagree wit the authors’ response that Table 5 provides sufficient illumination on what was happening to the water status of the crops.

f.        ASW was calculated on the 0-1000px depth (lines 158-9), but lines 228-230 contain the allusion to a greater water contribution by “deeper layers”. What depths are being referred to? If >1000px, then the basis of irrigation management is questionable.

g.       Looking at the paper as a complete work, with different parameters contributing to a single coherent description of the environments to which the plants were subjected and their responses to these, I am not convinced that the irrigation treatments provided the neat range of expected environments and certainly appear to be different between seasons. On that basis, the use of nominal MAD as a quantitative treatment descriptor, in my opinion, has not been adequately validated.

Line 243: Fig 1B is difficult to quantitatively interpret, but my imprr3ession is that there were few statistically significant differences between water treatments for AG, particularly towards the end of the crop cycle.

Line 261: I think that 160 could be 130.

Lines 265-268: In the first season, the number of stems appears to have been much more reduced by MAD80 in CG than in AG. This suggests to me that AG is in fact less sensitive to water stress than CG. In the second season, the pattern is more complicated with all water stress treatments showing effects on stem number in both species. Certainly, I see little evidence that CG is more resistant to stress than AG.

Lines 280-284: The statistical evidence provided does not support these statements. The well-watered (MAD20) treatments were not better than MAD40 or MAD60 for CG in season one and all four treatments had no significant influence in AG in this season. In season two, MAD20 was better than other treatments for AG, but not better than MAD40 or MAD60 for CG. The general trend emerging here is that the two species behaved differently across most parameters in each season and no explanation of that is forthcoming.

Secn 3.5. It would be more informative to have the time series data for LAI presented as for Figs 2 and 3. When did the peak occur, how long was it sustained, and so on are physiologically interesting questions. As well, given my scepticism regarding the actual stress levels achieved, I find no basis exists for disposing the nominal water treatments quantitatively on the x-axis in this and following diagrams. The comments on leaf number in line 300 are not consistent with data in Fig 3, eg, any water stress had no significant effect on leaf number in AG, season two.

Secn 3.6: I have assumed that these data (FI) represent seasonal averages, but, as above, seasonal trends in FI would be more informative, given the fundamental importance of light interception in driving both crop growth and water use. There is no indication of when these measurements were made. Further, there is generally a good relationship between LAI and FI. My attempt to generate that for the two species using the data in Figs 4 and 5 shows only a very poor possible relationship. Why would this be so?

Secn 3.7: There is not a single piece of statistical data presented in this section, hence any attempt to assign treatment effects is futile. I had assumed that the data in Table 6 was based on several replicates from each treatment unit and hence could be quantitatively interpreted. The only allusion to Figs 6 and 7 is a casual one, duplicating information in Table 6, so they could be eliminated without detriment.

Secn 3.8: The authors do not differentiate between fresh and dry rhizome yield in terms of practical importance. For example, on what basis is ginger sold, fresh or dry yield? If the latter, then effects of water stress on carbon accumulation will be important. If the former, additionally the effects on water content will need to be included in any interpretation of results. Dry yield for  AG seems to be consistent across seasons, somewhat less so for CG. When one considers the fresh yield, CG appears to have retained water in its rhizomes better in season two.

Secn 3.9. As I noted in my previous review, WUE based on dry weight is a more fundamental and more generally reported derivation of this parameter than that based on wet weight. On that basis, a general trend is obvious. The statistics provided show that WUE for AG is invariant across treatments and years, somewhere in the region of about 9. This is consistent with a broad literature showing WUE is a conservative parameter. For CG in season one, there is a trend of WUE increasing with stress, which is inconsistent with a lot of crop literature. In season two, for CG, there is no trend. Two categories of explanation come to mind. First, there may have been agronomic processes not measured in the experiments that imposed an unplanned stress on the crops, such as a pest invasion. Two, the basis of calculating water use has not been completely explained in this paper. It could be either the total of the water supplied, or the sum of time-to-time changes in measured soil water content, preferably measured over 0-2000px to ensure no influence of occasional overwatering, or, under-reporting of water actually used from the 40-2000px strata. My concerns noted in my comments about Secn 3.1 are relevant here: basically, something seems inconsistent in the crop water balance, but the authors have not provided the information which they measured and which could resolve this.

Author Response

Thank you for the opportunity to make corrections to the manuscript according to the comments of the reviewer. We are grateful to the Reviewers and the Editor for their constructive comments and suggestions, which have greatly improved the quality of our manuscript. 

Author Response File: Author Response.pdf