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  • Nasreddine Makni*,
  • Riccardo Collu and
  • Massimo Barbaro*

Reviewer 1: Anonymous Reviewer 2: Anonymous Reviewer 3: Anonymous Reviewer 4: Anonymous

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have the following concerns that must be addressed before the final verdict. 

1) The study uses only six plants (three per treatment). How do the authors justify the statistical robustness of their findings with such a small sample size?

2) Why was Hydrangea macrophylla chosen, and how representative is it of crops commonly targeted in precision agriculture?

3) The experiment was done under uncontrolled terrace conditions. Can the authors provide detailed weather data (temperature, humidity, sunlight) and explain how these may have influenced the measurements?

4) What was the rationale for including a 10-day interruption period, and could this have confounded the interpretation of water stress and recovery?

5) Measurements were done in the evening while irrigation happened earlier in the day. Could circadian variation in leaf physiology have affected results independently of hydration status?

6) The impedance results rely on reapplying electrodes daily. How reproducible were the impedance measurements, and how was electrode–leaf variability controlled?

7) How was ambient sunlight interference in IR measurements quantified or corrected, and could shielding/filtering significantly change the outcomes?

8) The equivalent circuit model is assumed to represent leaf physiology. Can the authors validate this with independent physiological evidence or supporting references?

9) Were the IR and EIS devices calibrated over the course of the 20-day experiment to check for drift?

10) Why was a quadratic regression model selected for IR vs. RWC correlation instead of testing multiple model types?

11) Welch’s t-tests pooled data across timepoints. Could this approach mask time-dependent effects, and would a mixed-effects model be more appropriate?

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,
I have received from Digital Journal you manuscript proposal entitled "Development of Optical and Electrical Sensors for Non-Invasive Monitoring of Plant Water Status". The topic is interesting, but some improvements should be taken into consideration, according to the below list of recommendations.

1. Within the Introduction chapter, at lines 73 - 77, you describe the research goal. After this, I recommend you also define and describe the research questions, so that the readers understand what your article is answering to.

2. Before chapter "2. Materials and Methods", I recommend you include a new "Hypotheses Development" chapter. Here you should clearly define and describe the research hypotheses. Each modern scientific article should define at least one research hypothesis to be tested and validated by the research results.

3. At lines 90 - 92 you say that "The experiment involved six plants of Hydrangea macrophylla, selected for their large leaf surface area, numerous leaves, and significant water requirements, making them suitable for research on monitoring plant water status." Please provide additional information so that you prove and justify that the sample size is relevant for the generalization of the obtained results.

4. In the Discussion chapter, you should insist more on your own original results, which are different from previous results from the literature. This way, you will highlight your contribution to the field of knowledge.

5. In the Conclusions section, I recommend you also present some "managerial" implications. How your research results can be useful for the companies and for the economic actors from agriculture?
A few relevant aspects regarding costs, savings, production improvements, and efficient plant monitoring could add value to your work. This way, readers will better perceive the results of your research efforts and contributions to the field of knowledge. Please consider all these recommendations as constructive remarks.

Best Wishes!

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

With great interest I've got acquainted with the manuscript on the development and evaluation of two non-invasive sensor systems, namely, infrared spectroscopy and electrical impedance spectroscopy (EIS), for Hydrangea macrophylla water irrigation plans in not completely controlled external environment. The proposed technical means, as well as measurements processing, are simple and easily reproducible, unlike methods such as infrared monitoring with drones. This could provide practical plant health forecasts in economically underdeveloped regions and indoor environments (e.g., greenhouses). The relative water content (RWC) method confirmed the impact of irrigation frequency on plants health, as well as the accuracy of the proposed methods.

The work is written at a notable scientific level, is properly designed and illustrated. A literature review is fine. However, a number of questions and remarks arise while reading the manuscript.

  1. Infrared spectroscopy results are compared directly with RWC, appropriate plots and formulae are given. With that, EIS lacks of this comparison. Also, both methods were not numerically compared with each other side by side.
  2. Another issue is that in a Second Phase, infrared sensor provided non-injective curve vs RWC, and thus the use of IR values could not provide full information about plant status. The simultaneous use of impedance sensor could potentially solve the problem by simple aggregation of data. I encourage authors to perform it.
  3. More detailed schematics, providing e.g. exact op amp and IR LED part names, as well as signal generation and measurement schematics would be beneficial, enhancing technical contribution of the work and its reproducibility. Also, I believe that such  measurements may be performed using low cost prototyping platforms, e.g. Arduino or IoT-friendly ESP32, and discussing this issue is also of interest.
  4. Minor textual issues may be found. Some abbreviations, e.g. (RWC), are placed between unnessesery brackets.

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript proposes two non-invasive sensor systems for monitoring the hydration status of plant tissue. The first system employs infrared spectroscopy, and the second one electrochemical impedance spectroscopy. The experiments are performed on the Hydrangea macrophylla plants using the relative water content method for data validation. The results confirm that both proposed sensor systems recognize differences in the watering status of the well and poorly irrigated plant groups.

The manuscript is well written and technically correct. The topic it addresses is actual, and the suggested non-invasive, low-cost methods are interesting. Several key limitations of the study are outlined in the manuscript, along with the proposal for its further improvement. However, there are some issues regarding the manuscript content that should be addressed. Please make comments on the following remarks:

  1. Experimental setup:
  1. Did all the plants have approximately the same number of healthy mature leaves? In Fig. 1(b), a healthy mature plant is presented, while in Fig. 2(b), the plant has a massive loss of mature leaves. Please comment on this.
  2. Hydrangea macrophylla is very sensitive to direct sun exposure. Where were the plants placed, considering the shading conditions?
  3. How was the amount of water provided daily to the plants determined? Since the RWC values of well-irrigated plants exhibited a constant decrease during the experiment, it can be concluded that they needed more water to maintain the steady hydration status. Another issue is the watering method. I believe that the water was poured from the top of the pot. Better rehydration of the plant can be achieved by immersing the pot in a container filled with water for a specified time period.
  4. It would be interesting to have data on the temperature values during the measurement to get better insight into the experimental conditions.
  1. Infrared Spectroscopy:
  1. It is stated that the IR LED was driven by a ramp-up voltage, from 0 to 5V, to improve signal resolution and data accuracy. If the results were acquired for several voltage values, it would be good to list the exact data.
  2. Fig. 5: Values of the normalized absorption coefficient at 16-20th day for the poorly irrigated plants diverge from the expected ones. They are higher than for the well-irrigated plants in the 16th-18th day period. Also, after watering on the 18th day, there is a sharp decrease in the normalized absorption value, while for the well-irrigated plants, there is an increase. Please comment on this.
  3. Fig. 6: Data from this figure does not contribute to the manuscript content since Fig. 5 is more informative.
  4. What is the reason to separate the two phases of the experiment when evaluating a relationship between (RWC) and the normalized absorption coefficient? Since the normalized values are considered, there should be one consistent relationship.
  1. Electrical Impedance Spectroscopy:
  1. The frequency sweep was used for the fitting of the impedance spectra. What was the frequency of the measurement signal during the experiment?
  2. Fig. 10: It is evident that data for normalized CPE0 and C0 have large standard deviations (up to 6 orders of magnitude). What caused such results?
  1. Discussion:
  1. It is stated that “the irregular irrigation applied during the interruption period caused significant water stress, and that even after one week of rehydration, the plants had not yet fully recovered at the beginning of the second phase“. That may explain several data inconsistencies during the first and second phases of the experiment. However, it again raises the question of the amount of water provided daily to the plants (already mentioned in question 1.c).
  2. In my opinion, determination coefficients R²=0.57 and R²=0.51 can not be declared as a strong correlation, especially in the case when they are calculated in two different experimental phases.

Minor remarks are:

  1. Lines 49-68, 212: The reference numbers do not follow the proper order.
  2. Line 395: I believe it should be reference [34] instead of [33].
  3. Line 281: It should be Figure 6 instead of Figure 5.

Author Response

Please, see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Accept.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

I consider that you addressed all my recommendations from the previous round of review.

Kind Regards!

Reviewer 4 Report

Comments and Suggestions for Authors

The authors updated the manuscript according to the reviewers' remarks. Therefore, I believe it is suitable for publication.