Quality and Yield of Lettuce in an Open-Air Rooftop Hydroponic System
David Sanjuan-Delmás
Round 1
Reviewer 1 Report
I do believe that this article should be considered for publication, as it addresses an interesting topic that can represent a nice contribution for literature. Moreover, the article is well-written and well-structure.
However, I would like to highlight some relevant points that should be addressed before proceeding. Se below some comments, I hope these are useful to improve the article.
MAIN COMMENTS
- First of all, it is necessary to further describe the system for the rooftop system. Which type of building is it? Is it a 2nd flor, 3rd 4th? It is difficult to imagine right now, actually, including some pictures of the system would help have a better understanding of it.
- Regarding the reduction of the produce due to the wind speed (lines 161-163), it would be nice to compare (either in figure 4 or just mentioning it) the yield of the marketable produce.
- What I miss in the conclusions is a proper discussion of the trade-offs observed in the results. Apparently, rooftop systems have more light and nutrients, but the main drawback is the wing that reduces the marketable produce.
- Why not showing as well the nutrient consumption of the indoor in Table 2? Now you mention the percentages of one and another in lines 270 to 274, but why not including them in the table and then referring tot the table?
- Regarding Figure 6, I would either put the two figures side by side horizontally, so that the reader can easily compare them or do 6 smaller graphs for the different nutrients including both systems (resulting in a large figure). As it is now it is difficult to compare (you have to go up and down to see).
- Another point that should be discussed is the environmental/economic performance of the system, as it is addressed in many articles in the references assess (e.g., Sanjuan-Delmás et al., 2018). Of course, I understand that properly assess it is beyond the scope of the article, but you can elaborate in the discussion and/or the conclusions on how the findings of the article might affect the environmental/economic performance. For instance, an advantage of rooftop over indoor is that no artificial lighting is necessary, and therefore less energy is required, but then I understand it is less efficient in terms of nutrients use.
MINOR COMMENTS
- Potentially, figure 2 and 3 might be merged into one single figure (with 2 y axis).
- Typo in line 206 (reported)
- Figure 5: It is better if you use upper case letters for the subfigures, “(A)” and “(B)”, to avoid confusion with the letters for statistic differences
- Table 3 does not exist (line 272)
Author Response
Thank you for your valuable comments. Our responses to the points of the reviewer’s comments are underlined, and page number and line numbers are given with reference to the revised manuscript.
Point 1. It is necessary to further describe the system for the rooftop system. Which type of building is it? Is it a 2nd floor, 3rd 4th? It is difficult to imagine right now, actually, including some pictures of the system would help have a better understanding of it.
Response 1. The rooftop system is better described, and a picture of the system is included. We hope it is clearer now. (page 3 lines 108-140).
Point 2. Regarding the reduction of the produce due to the wind speed (lines 161-163), it would be nice to compare (either in figure 4 or just mentioning it) the yield of the marketable produce.
Response 2. The marketable fresh weight of commercial lettuce was given (page 5 line 206).
Point 3. What I miss in the conclusions is a proper discussion of the trade-offs observed in the results. Apparently, rooftop systems have more light and nutrients, but the main drawback is the wing that reduces the marketable produce.
Response 3. Please note that 75% of lettuce heads were equal or above the marked size of commercial lettuce. We mentioned in the conclusion that only some lettuce heads (25%) were below the marked size due to strong winds. The winds should not be a drawback if special consideration were taken for open-air rooftop hydroponic installation such as wind shields and we mentioned that in the conclusion.
Point 4. Why not showing as well the nutrient consumption of the indoor in Table 2? Now you mention the percentages of one and another in lines 270 to 274, but why not including them in the table and then referring tot the table?
Response 4. The value of the dry matter of the indoor lettuce leaves provided by Eurofins Laboratory was not precise so we could not calculate the nutrient consumption (g/kgdry matter) with precision as we did with rooftop lettuce. The percentages provided in lines 270 and 274 of the old manuscrpit were calculated by dividing nutrient content in leaves (we have this value) by total grams of nutrient consumption (g) (we have this value). To avoid ambiguity, I removed the percentages provided in lines 270 and 274 of the old manuscrpit.
Point 5. Regarding Figure 6, I would either put the two figures side by side horizontally, so that the reader can easily compare them or do 6 smaller graphs for the different nutrients including both systems (resulting in a large figure). As it is now it is difficult to compare (you have to go up and down to see).
Response 5. The two figures are now side by side horizontally and we hope it is easier to compare.
Point 6. Another point that should be discussed is the environmental/economic performance of the system, as it is addressed in many articles in the references assess (e.g., Sanjuan-Delmás et al., 2018). Of course, I understand that properly assess it is beyond the scope of the article, but you can elaborate in the discussion and/or the conclusions on how the findings of the article might affect the environmental/economic performance. For instance, an advantage of rooftop over indoor is that no artificial lighting is necessary, and therefore less energy is required, but then I understand it is less efficient in terms of nutrients use.
Response 6. We shortly discussed the environmental/economic performance of rooftop systems in the discussion (page 9 Lines 316-321).
Point 7. Potentially, figure 2 and 3 might be merged into one single figure (with 2 y axis).
Response 7. Figure 2 and 3 are now merged into one single figure.
Point 8. Typo in line 206 (reported)
Response 8. We rectified the typo
Point 9. Figure 5: It is better if you use upper case letters for the subfigures, “(A)” and “(B)”, to avoid confusion with the letters for statistic differences
Response 9. We changed the lower case letters to upper case letters.
Point 10. Table 3 does not exist (line 272)
Response 10. We removed lines 170-174 as we revised the paper.
Reviewer 2 Report
It is great to see the study of rooftop vegetable production. However, the manuscript should be improved before publication.
- The author should describe the experimental design in detail. How many replicates of the experiment? How to make the rooftop and indoor vegetable production system comparable? The sampling and analysis?...
- The experiment was not well controlled. The maximum and minimum shoot fresh weight of rooftop hydroponic lettuce were 781g and 36g, indicating the unacceptable experimental error.
Author Response
Point1. The author should describe the experimental design in detail.
Response 1. The experimental design is better described in the revised version (lines 84-93 page 2 and lines 108-140 page 3). Numbers of replicas is specified and we mentioned that results are means ± SD (lines 217 and 218 page 6 and line 251 page 7).
Point 2. The experiment was not well controlled. The maximum and minimum shoot fresh weight of rooftop hydroponic lettuce were 781g and 36g, indicating the unacceptable experimental error.
Point 2. Please note that 8% of lettuce heads weighed more than 500 g. These lettuce were close to the fence that surrounds one side of the hydroponic system so they are not affected by strong winds. 25% of lettuce heads are undersized because they are the most affected by strong winds. We mentioned that in the results and discussion section.
Reviewer 3 Report
Dear editor and authors,
in my opinion the manuscript “Quality and Yield of Lettuce in an Open-Air Rooftop Hydroponic System” can be acceptable for publication after major revisions. Please find below my specific comments and suggestions divided per section.
Abstract: the abstract is clear and concise. I do not fully agree with the manuscript “average fresh weight and yield” approach and I suggest to highlight also in the abstract that the open-air rooftop system led to the loss of a % of marketable heads. Please remove lines 10-12 (that description is sufficient in the material and methods section).
Introduction: the introduction can be improved. When hypothesizing why rooftop systems are not very spread please also mention that roofs are generally not designed to host cultivations nor people working on, so initial investments are to be considered. Please also report some literature results at least on leafy vegetables grown in similar conditions.
Materials and methods: this section is generally clear but lacks in certain important information.
Line 62: if the lettuce cycle is of about 4 weeks, plus the germination 2 weeks, why the experimental period is so long?
Lines 82-84: not clear, why and when 7 harvests?
Line 85-86: how many samples of the nutrient solution? Did you never replace it during the trial?
Line 88-89: here it is stated that lettuce was harvested after 4 weeks of growth in the NFT-system, not clear why and when you should have performed 7 harvests. The harvest was performed on how many replicas?
Line 89-91: on how many replicas the macro- and microelements analyses were performed?
Line 100: why did you choose to grow a summer crop in autumn season?
Line 104: please rephrase as follows: due to non-optimal weather conditions, the trial lasted 5 weeks instead of 4. This is also something that has to be considered when discussing your results: you might have reached similar biomass, but it took longer, which has a cost
Line 125: please specify how did you register PAR, temperature, CO2, and wind speed.
Line 144: please remove “analyzed in Microsoft Excel” and leave “data were subjected to analysis of variance…”
Line 148-149: please remove. Always add the error bars in figures: if symbols cover it then please reduce symbols size
Results and Discussion
Line 156-158: please remove, redundant
Line 165: if you are referring to rooftop grown plants please specify it
Line 169 and Figure 4: I suggest to remove your results on yield and use only the shoot fresh weight: you can’t compare the kg/m2 because you did use 2 different set up (with different length, different diameter mm, and so on). Plus, this data do not add anything new to the shoot fresh weight.
Figure 4 (and all next figures): please specify the number of replicas, say that results are means ± SD
Line 191: please remove content and use concentration
Line 216: please remove luxury and use higher
Line 224-232: I suggest to remove this paragraph. Here you are speculating on the possibility of achieving comparable yields by using less nutrients: I am afraid your data do not support enough this hypothesis. Moreover, you are not under controlled conditions and if you repeated the experiment you would not obtain the same results, as just 2 or 3 days at different temperatures and weather would lead to different yields, so suggesting to use less nutrients sounds too bold based on your results.
Table 2: why not adding 2 columns also for indoor grown lettuce? Please also provide an explanation below the table on how you calculated consumption and efficiency
Line 271-271: please remove the percentages (already reported in Table 2)
Conclusions
Line 306: please remove some and change it with the %
Line 308: you are mentioning that here in the conclusions for the first time, you should introduce this observation in the results and discussion section
Line 312: please mention the % of lettuce heads that was lost in the rooftop system
Author Response
Thank you for your valuable comments. Our responses to the points of the reviewer’s comments are underlined, and page number and line numbers are given with reference to the revised manuscript.
Abstract
Point 1. The abstract is clear and concise. I do not fully agree with the manuscript “average fresh weight and yield” approach.
Response 1. We removed lines 17 and 18 from the abstract.
Point 2. I suggest to highlight also in the abstract that the open-air rooftop system led to the loss of a % of marketable heads.
Response 2. We mentioned that 25% of the total lettuce heads were below the marketable weight (lines 13 and 14 page1)
Point 3. Please remove lines 10-12 (that description is sufficient in the material and methods section).
Response 3. We removed lines 10-12.
Introduction
Point 4. When hypothesizing why rooftop systems are not very spread please also mention that roofs are generally not designed to host cultivations nor people working on, so initial investments are to be considered.
Response 4. Some statements with reference have been included (Lines 45-48 page 2).
Point 5. Please also report some literature results at least on leafy vegetables grown in similar conditions.
Response 5. some literature results on leafy vegetables have been included (lines 52-55 page 2)
Materials and methods
Point 6. Line 62: If the lettuce cycle is of about 4 weeks, plus the germination 2 weeks, why the experimental period is so long?
Response 6. The indoor hydroponic system was smaller than rooftop hydroponic and we only used quarter of the pipe so we did 7 harvest to reach approximately the same number of plants (the number of cultivated plants in indoor and outdoor is the same). We better explained how the indoor hydroponic system was operated in lines 84-93 page 2.
Point 7. Not clear, why and when 7 harvests?
Response 7. We responded to this point in the previous response and we better explained this point in the revised version. We hope it is clearer now.
Point 8. how many samples of the nutrient solution? Did you never replace it during the trial?
Response 8. We never replaced the nutrient solution. We only added nutrient solution to compensate for transpiration loss. Number of samples of the nutrient solution were added (line 172 page 4).
Point 9. Line 88-89: here it is stated that lettuce was harvested after 4 weeks of growth in the NFT-system, not clear why and when you should have performed 7 harvests.
Response 9. We better explained this point in lines 84-93 page 2
Point 10. Line 89-91: on how many replicas the macro- and microelements analyses were performed?
Response 10. We did three replicas.
Point 11. Line 100: why did you choose to grow a summer crop in autumn season?
Response 11. We wanted to study also the feasibility of growing lettuce in late season in Norway ( it is outside the scope of this paper).
Point 12. Line 104: Please rephrase as follows: due to non-optimal weather conditions, the trial lasted 5 weeks instead of 4.
Response 12: the statement was rephrased (lines 142 and 143 page 4).
Point 13. Line 125: please specify how did you register PAR, temperature, CO2, and wind speed.
Response 13. We specified how we registered PAR, temperature, CO2, and wind speed in lines 152 and 153, line 169 and, line 172 page 4.
Point 14. Line 144: please remove “analyzed in Microsoft Excel” and leave “data were subjected to analysis of variance…”
response 14. “analyzed in Microsoft Excel” was removed.
Point 15. Line 148-149: please remove. Always add the error bars in figures: if symbols cover it then please reduce symbols size.
Response 15. Line 148-149 was removed
Results and Discussion
Point 16. Line 156-158: please remove, redundant
Response 16. Line 156-158 was removed.
Point 17. Line 165: if you are referring to rooftop grown plants please specify it
Response 17. We specified it (line 210 page 5)
Point 18. Line 169 and Figure 4: I suggest to remove your results on yield and use only the shoot fresh weight:
Response 18. We removed yield results.
Point 19: Figure 4 (and all next figures): please specify the number of replicas, say that results are means ± SD
Responses 19 : numbers of replicas is specified and we mentioned that results results are means ± SD (lines 217 and 218 page 6 and line 251 page 7).
Point 20: Line 191: please remove content and use concentration
Response 20: Content is removed and replaced by concentration (line 220 page 6)
Point 21. Line 216: please remove luxury and use higher
Response 21. Luxury was removed and replaced by higher (line 245 page 6). Please note that the term luxury consumption or absorption is a technical term often used to describe nutrient absorption by the plant that does not influence yield.
Point 22. Line 224-232: I suggest to remove this paragraph. Here you are speculating on the possibility of achieving comparable yields by using less nutrients: I am afraid your data do not support enough this hypothesis. Moreover, you are not under controlled conditions and if you repeated the experiment you would not obtain the same results, as just 2 or 3 days at different temperatures and weather would lead to different yields, so suggesting to use less nutrients sounds too bold based on your results.
Response 22: the possibility of achieving comparable yields by using less nutrients is removed and replaced by a suggestion to apply quantitative management of the NS which implies that refill solution should be made based on calculations of actual nutrient uptake rates by the plants (lines 252 -254 page 7) .
Point 23. Table 2: why not adding 2 columns also for indoor grown lettuce? Please also provide an explanation below the table on how you calculated consumption and efficiency.
Response 23. he value of the dry matter of the indoor lettuce leaves provided by Eurofins Laboratory was not precise so we could not calculate the nutrient consumption (g/kgdry matter) with precision as we did with rooftop lettuce. The percentages provided in lines 270 and 274 of the old manuscrpit were calculated by dividing nutrient content in leaves (we have this value) by total grams of nutrient consumption (g) (we have this value). To avoid ambiguity, I removed the percentages provided in lines 270 and 274 of the old manuscrpit.
Explanation below the table on how we calculated consumption and efficiency was provided (lines 280-282 Page 8)
Point 24. Line 271-271: please remove the percentages (already reported in Table 2)
Response 24. Percentages are removed.
Conclusions
Point 25. Line 306: please remove some and change it with the %
Response 25. some was removed and replaced by 25% (line 327 page 9).
Point 26. Line 308: you are mentioning that here in the conclusions for the first time, you should introduce this observation in the results and discussion section
Response 26. This observation was included in the results and discussion section (lines 211-212 page 5)
Point 27. Line 312: please mention the % of lettuce heads that was lost in the rooftop system.
Response 27. The % of lettuce heads that was lost in the rooftop system was mentioned (line 332 page 9).
Round 2
Reviewer 3 Report
Dear author,
thank you for carefully addressing every comment, the manuscript has improved in the present version and in my opinion it is now ready for publication in Agronomy journal.
