Nutrient Dynamics and Resource-Use Efficiency in Greenhouse Strawberries: Effects of Control Variables in Closed-Loop Hydroponics
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this paper, the authors conducted two very interesting experiments which focused on increasing the knowledge on closed-loop hydroponic systems in strawberries and how effective are nutrient corrections at increasing nutrient use efficiency. The experiments are well designed and carried out. However, as there are some missing information, authors should consider some revisions in order for the manuscript to be completely reviewed. Below are the major points to be addressed:
L10: “Larger cultivation”? Do you mean simply “large cultivation”?
L16-18: Please re-write the sentence because it is not clear.
L35: What do you mean with the “shorter-use cycles”?
L120-122: When a correction treatment is applied, it is applied because uptake concentrations of plants have changed and the new NS prescription should be applied. The new uptake concentrations have occurred due to the different weather conditions or the growing stage of the plants. So, there is no need to apply the standard NS after one week. If so, please provide literature where this practice was applied.
Figure 1. Can you please explain something to me in Exp 2? Was the drain tank mixed firstly with raw water similarly with Exp 1? Did you pre-set an EC mixing level for this experiment?
Function (1), L132: Please state what IAdj means.
Table 1. What is “Raw water 1” and “Row water 2”? You haven’t mentioned anything in the text before. I propose you to transfer L239-243 to Material and Methods.
Table 1. How was Na and Cl removed from the final solution in Exp 1?
Figure 4. In Exp 2. Gray dotted lines which indicate the target concentration should vary regarding the corrections you applied at 2-week and 4-week correction treatments.
L349: was the 3% greater NUEyield statistically significant or not. Please note it there and in the abstract as well.
L398: Please correct the sentence.
Figure 6. please add the statistical analysis.
L431: the word ‘however’ should start with capital letter.
L453-454. This information is crucial and should be somehow transferred to Material and Methods section. You can leave the result “15 higher water consumption at discussion, but drainage discharge should be mentioned before.
L455 and Figure 6. It is interesting that EC 0.6 form Exp1 and Open System in Exp 2 had similar Water Use at the end of both experiments. How were these treatments so close? Do you have a comment?
L465-468: A mention in literature about similar experiments where open and closed system are compared by other researchers would strengthen your paper. Consider mentioning and comparing results from other scientific papers.
L471-475: It would be interesting to state that frequent correction is not so effective in strawberries but they would be effective on other crops (like tomato, cucumber etc) if literature is available with this information.
References: In general, references are few. Please consider increasing references. You should provide information at experiments on strawberries and compare your results based on the other studies.
Comments on the Quality of English LanguageQuality of English is adequate. Please consider only my comments about some sentenses that could be improved.
Author Response
C1: L10: “Larger cultivation”? Do you mean simply “large cultivation”?
R1: The sentence has been changed to "the large area of cultivation" for clarity. (L10)
C2: L16-18: Please re-write the sentence because it is not clear.
R2: Thanks for pointing that out. We have simply changed the sentence to “In Exp 1, a prolonged increase in drainage EC resulted in an imbalance of NS ion composition and reduced fruit yield.” (L16-17)
C3: L35: What do you mean with the “shorter-use cycles”?
R3: "Short use cycle" used to refer to the shorter use cycle of the substrate in hydroponics compared to soil cultivation. Thus, we changed the sentence for clarity to “The introduction of soilless media in greenhouse cultivation provided an opportunity to transition to a closed-loop hydroponic system, as it allows for precise nutrient control and mitigates microbial risks by reducing the use cycle to one year” (L32-34)
C4: L120-122: When a correction treatment is applied, it is applied because uptake concentrations of plants have changed and the new NS prescription should be applied. The new uptake concentrations have occurred due to the different weather conditions or the growing stage of the plants. So, there is no need to apply the standard NS after one week. If so, please provide literature where this practice was applied.
R4: As you know, nutrient uptake concentration determined from the accumulation of nutrients in plant tissues, this is what we call the standard solution. In fact, in countries like the Netherlands, nutrient calibration is done on a weekly basis, so we are constantly calculating and calibrating the plant ion uptake and nutrient solution, but in Korea, we have little practice in closed-loop hydroponics, so the calibration interval is relatively longer, or farmers use closed-loop solution empirically such as watching plant conditions… (e.g. leaf color). After visiting several farms, listening to the practices of consultants and growers, and hearing about relatively long ion calibration cycles in Korea. Thus, we followed farming practices and split the period, using standard and corrective nutrient solutions for half the time. And I tried to find ref and I've seen same content in PTC+(One of Netherlands consulting group) before, but I haven't checked the online references.
C5: Figure 1. Can you please explain something to me in Exp 2? Was the drain tank mixed firstly with raw water similarly with Exp 1? Did you pre-set an EC mixing level for this experiment?
R5. In Experiment 2, no preset EC mixing values were used, and the discharge was simply determined by the EC level of the NS. Therefore, in Exp 2, all treatments were immediately matched to the NS EC value using drainage if the drain basin had drainage, and otherwise matched to EC using pure A and B tank’s fluids if there was no drainage in drain basin. This is the same as the 'All use' treatment in Exp 1.
C6: Function (1), L132: Please state what IAdj means.
R6: We added the state and changed IAdj to ICor in L135
C7: Table 1. What is “Raw water 1” and “Row water 2”? You haven’t mentioned anything in the text before. I propose you to transfer L239-243 to Material and Methods.
R7: We transfer L239-243 Material and Methods “L147-151”
C8: Table 1. How was Na and Cl removed from the final solution in Exp 1?
R8: In Exp 1, it was not removed as mentioned in the Table 1. In Exp 2, the occurrence of nutrient imbalance in Exp1 was confirmed and removed through a membrane filter, which showed almost ions being undetectable in the raw water composition of Exp 2. (L143-146, Table 1)
C9: Figure 4. In Exp 2. Gray dotted lines which indicate the target concentration should vary regarding the corrections you applied at 2-week and 4-week correction treatments.
R9: Thanks for pointing this out. As mentioned in the caption, the grey dashed line represents the target composition of the NS, not the drain. This will change over the course of the 2- and 4-week correction, but we want to see a trend based on the initial composition, so ions above the grey dotted line tend to accumulate and ions below tend to be more consumed. Therefore, we changed the fig. 4 caption to initial composition.
C10: L349: was the 3% greater NUEyield statistically significant or not. Please note it there and in the abstract as well.
R10: We did perform repeats at different sampling locations for ion analysis, but separately from this, the nutrient usage was calculated based on actual 'used' nutrients (used solution volume x each nutrient composition), so we were unable to perform statistical validation as the nutrient supply system is not divided enough to allow for replication (we only have 4 NS supply tanks for individual treatment).
We tried to calculate the nutrient usage with NS and drainage ion concentration, it may not be accurate due to other variables (analysis time, transpiration, remain ions in the plant residue…). Therefore, in this experiment, the total use amount of nutrient is inevitably the actual usage in the system, which has the limitation that it is difficult to analyze statistical significance. And the NUE calculation method (direct recording making record of NS) is mentioned in M&M 2.6.
C11:L398: Please correct the sentence.
R11: Revised sentence for clarity (L404-407)
C12: Figure 6. please add the statistical analysis.
R12: Same with R 10.
C13: L431: the word ‘however’ should start with capital letter.
R13: Corrected.
C14: L453-454. This information is crucial and should be somehow transferred to Material and Methods section. You can leave the result “15 higher water consumption at discussion, but drainage discharge should be mentioned before.
R14: Added discharge conditions for drainage solution in EC-based control (Exp 1) to Material & Method (L106-107). In 3.6 (result) mentions discharge ratio in each treatment in Exp 1.
C15: L455 and Figure 6. It is interesting that EC 0.6 form Exp1 and Open System in Exp 2 had similar Water Use at the end of both experiments. How were these treatments so close? Do you have a comment?
R15: The experiment took place over two seasons, but there is a gap of about two weeks between the experimental periods. As shown in Figure 5, the first year's experiment ended on 15 April, while the second year's experiment ended on 29 March, which explains the difference in the results. We added the end of date in materials & methods (L166-167).
C16: L465-468: A mention in literature about similar experiments where open and closed system are compared by other researchers would strengthen your paper. Consider mentioning and comparing results from other scientific papers.
R16: We added a reference that specifically mentions the effect of nutrient savings from introducing closed-loop hydroponics compared to open-loop (L469-471).
C17: L471-475: It would be interesting to state that frequent correction is not so effective in strawberries but they would be effective on other crops (like tomato, cucumber etc) if literature is available with this information.
R17: Thank you for your guide. While there is no research on the correction frequency in general, we have added it because there are references that a fortnightly cycle is generally adequate to maintain stable root-zone ion concentrations for greenhouse crops (L479-482).
C18: References: In general, references are few. Please consider increasing references. You should provide information at experiments on strawberries and compare your results based on the other studies.
R18: Overall, the things you mentioned were very helpful and we've added references based on them. Added several references related to root-zone ion concentrations and nutrient calibration (L468-470). We strengthened the discussion on the appropriate frequency of nutrient calibration based on prior research (L480-483) and the flow of the discussion on why strawberries are relatively sensitive to salt compared to other greenhouse crops (L493-497). New references added on L591-598
C19: Comments on the Quality of English Language
Quality of English is adequate. Please consider only my comments about some sentenses that could be improved.
R19: Thank you for kind comments, we've made improvements based on your suggestions.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe manuscript titled “Nutrient Dynamics and Resource-Use Efficiency in Greenhouse Strawberries: Effects of Control Variables in Closed-Loop Hydroponics” is conducted in well manner, and has scientific worth for the growth and water/nutrient use efficiency of greenhouse strawberry crops using closed-loop hydroponics.
Summary of this article:
This study analyzed the growth and water/nutrient use efficiency of greenhouse strawberry crops using closed-loop hydroponics in Korea. The research comprised two experiments: Exp 1 controlled the system based on drainage EC mixed with raw water, while Exp 2 corrected the nutrient solution based on ion concentrations in the drainage at different intervals. In Exp 1, an imbalance in nutrient solution composition led to decreased fruit yield over time due to increasing drainage EC. Exp 2, with periodic nutrient correction, stabilized the nutrient solution composition, maintaining fruit yield comparable to open-loop systems but significantly improving nutrient use efficiency (NUE). The closed-loop system with 2- and 4-week correction intervals showed 94% and 88% higher NUE, respectively, compared to open-loop systems, with the 2-week interval demonstrating the highest NUE improvement. Shorter ion correction intervals are crucial for optimal NUE and normal plant growth in recirculating hydroponic systems for strawberry cultivation.
My minor comments are as follows:
1- In all figures, first give a common title to the figure and then explain it different subsections of the figures.
2- In figure 4: the front size of figure is too small! The figure error bars and values are hard to examine, I suggest authors to provide a larger front size and visible figure captions. Secondly what does the bar means? is it error bars or st. deviation?. Have you used any statistical software to analysis the figure 4 data? If yes, than what will be the statistical level of significance in different ions. And if not, then why authors didn’t analyze the level of significance?
3- Where is figure of strawberry fruit? If you have the experimental figures of strawberry than add in the main manuscript.
Author Response
C1. In all figures, first give a common title to the figure and then explain it different subsections of the figures.
R1. We've fixed it as you suggested, thank you for comments (L296-299)
C2. In figure 4: the front size of figure is too small! The figure error bars and values are hard to examine, I suggest authors to provide a larger front size and visible figure captions. Secondly what does the bar means? is it error bars or st. deviation?. Have you used any statistical software to analysis the figure 4 data? If yes, than what will be the statistical level of significance in different ions. And if not, then why authors didn’t analyze the level of significance?
R2. Thank you for detail direction. The figure has been modified to be as large as possible(fig. 4). Bars represent standard deviations, and the number of samples was mentioned in the caption (L297-299, L338-339, L372, L397). Statistical analyses were performed, but only standard deviations were represented with vertical bars because the trend in drainage concentrations is most important information in this figure. I didn't add it because it's a visually small in each figure box, but if you need a statistical information in this figure, I'll add it.
C3: Where is figure of strawberry fruit? If you have the experimental figures of strawberry than add in the main manuscript.
R3: Strawberry yields and quality were recorded in Figure 5 and Table 2. If we need photos of the actual plants grown or the experimental set-up, we will add them in a supplementary figure. Thank you.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsDear Authors,
You have done a very respectfull work of correcting and adding importan information to the manuscript. Therefore, it is now acceptable for publication
Author Response
Thank you for your comments and suggestions
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors did sufficient revisions, the current version can be accepted for publication.
Author Response
Thank you for your comments and suggestions
