Adequate Irrigation Amount per Application Is Required to Secure Uniform Water Management in Drip Irrigation Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article investigated the effects of different irrigation amounts on the uniformity of substrate VWC and the uniformity of sweet basil growth in the drip irrigation system, aiming to find out the optimal irrigation amount that can both ensure the water utilization efficiency and realize the uniformity of VWC, which is of certain practical significance and application value. However, the article has the following problems that need to be improved.
(1) The introduction should be supplemented with the gaps in the existing research in drip irrigation to explain the necessity of the research.
(2) The description of the innovativeness of the article in the introduction needs to be emphasized.
(3) There is no detailed description of how environmental factors affect the stability and accuracy of the sensor in Materials and Methods.
(4) The results are not analyzed in depth, and the results and discussion only describe the results, but do not discuss the mechanisms and reasons for the results in detail.
(5) It is recommended to add a comprehensive analysis of multiple variables to fully and comprehensively evaluate the effect of irrigation amount on sweet basil.
(6) Whether the monitoring period of 14 days for the experiment can adequately assess the combined effects of long-term irrigation practices on plant growth and VWC.
Author Response
Comments 1: The article investigated the effects of different irrigation amounts on the uniformity of substrate VWC and the uniformity of sweet basil growth in the drip irrigation system, aiming to find out the optimal irrigation amount that can both ensure the water utilization efficiency and realize the uniformity of VWC, which is of certain practical significance and application value. However, the article has the following problems that need to be improved.
The introduction should be supplemented with the gaps in the existing research in drip irrigation to explain the necessity of the research.
Response 1: Although most drip irrigation studies focused on water use efficiency along with plant growth responses, this study emphasizes uniform production under drip irrigation. Regarding drip irrigation uniformity, previous research has mainly investigated the uniform application of water within drip irrigation systems, targeting consistent delivery across a given plot. However, our study extends this perspective by investigating the actual substrate water content uniformity within individual pots across the irrigated plot. To clarify this distinction, we have revised the introduction section and added relevant references (lines 63–67).
Comments 2: The description of the innovativeness of the article in the introduction needs to be emphasized.
Response 2: The main innovation of our study is that it addresses not only water use efficiency but also the uniformity of crop production within a drip irrigation system by rigorously quantifying the uniformity of substrate moisture content among replicate pots and its impact on plant growth uniformity — an aspect that has received limited attention in previous research. To demonstrate this, the substrate moisture content of each and every pot was continuously monitored under different irrigation amount treatments using soil moisture sensors. In response to the reviewer’s suggestion, this contribution has been more clearly emphasized in the introduction (lines 69–72).
Comments 3: There is no detailed description of how environmental factors affect the stability and accuracy of the sensor in Materials and Methods.
Response 3: According to the sensor manufacturer’s manual, when a medium-specific calibration is applied (lines 103–106), the measurement accuracy of the sensor is ±0.02 m3 m-3. As you noted, environmental factors, especially temperature, can influence electrical conductivity, which in turn affects volumetric water content measurements. Parsons and Bandaranayake (2009) reported that the EC-5 sensor readings increased by approximately 1% when the temperature rose from 3 °C to 38 °C. In our study, however, the mean daily temperature was relatively stable at 22.8 °C with a standard deviation of 0.5 °C (lines 92–95). Therefore, while we acknowledge that temperature may introduce minor measurement errors, this effect is considered negligible within our experimental conditions. This information will be included in the manuscript if necessary.
Parsons, L.R., and Bandaranayake, W.M., 2009. Performance of a new capacitance soil moisture probe in a sandy soil. Soil Sci. Soc. Am. J. 73, 1378–1385. http://doi.org/10.2136/sssaj2008.0264.
Comments 4: The results are not analyzed in depth, and the results and discussion only describe the results, but do not discuss the mechanisms and reasons for the results in detail.
Response 4: We acknowledge that various factors, including plant biological variability, spatial heterogeneity and hydrophobicity of the substrate, and microclimatic conditions, can contribute to volumetric water content (VWC) variation and may interact in complex ways. However, the primary objective of this study was to evaluate the main effect of irrigation amount on uniformity of VWC and plant growth, rather than to examine each contributing mechanism in depth. We believe that the current level of analysis provides sufficient context for growers and researchers to understand the practical implications of the findings. To address this point, we have added a clarifying statement in the conclusion to highlight the need for further research into the underlying mechanisms (lines 306–310).
Comments 5: It is recommended to add a comprehensive analysis of multiple variables to fully and comprehensively evaluate the effect of irrigation amount on sweet basil.
Response 5: We appreciate the reviewer’s thoughtful suggestion. We fully agree that a more comprehensive analysis involving multiple variables could provide a deeper understanding of the effects of irrigation amount on sweet basil. However, the primary objective of this study was to establish a focused baseline evaluation of substrate moisture and plant growth uniformity using controlled variables and a simple experimental design. Expanding the scope to include additional variables would require a more complex experimental framework, which is beyond the scope of this study. To acknowledge this limitation and to encourage future work, we have emphasized in the conclusion that further research should include a broader investigation of the underlying factors affecting uniformity and consider scaling up to build on these initial findings (lines 306-310).
Comments 6: Whether the monitoring period of 14 days for the experiment can adequately assess the combined effects of long-term irrigation practices on plant growth and VWC.
Response 6: The primary scope of this study was to establish a focused baseline evaluation of substrate moisture and plant growth uniformity in relation to irrigation scheduling, particularly the irrigation amount. To isolate the effect of irrigation amount on substrate water content and plant growth uniformity, we aimed to minimize biological variability and accumulated environmental influences. Accordingly, basil was selected as the test plant due to its rapid physiological response to moisture conditions (Driesen et al., 2021). Prior to initiating the experiment, the basil plants were acclimated and sorted to ensure similar initial growth status. The experiment was conducted during the vegetative stage, which is known to be the most water-sensitive phase for basil (Al-Huqail et al., 2020). Therefore, a two-week duration was deemed sufficient to clearly capture the effects of irrigation amount on substrate water content and plant growth uniformity, and this rationale has been added to the Materials and Methods section (lines 83-86, 131-133). Additionally, our results showed that volumetric water content (VWC) uniformity decreased significantly over time under frequent irrigation with small amounts. If irrigation were continued for a longer period, this accumulated variation in VWC among replicates could lead to increased variability in plant growth, especially for crops with a longer vegetative growth cycle. Therefore, we have added to the conclusion that future research should include longer experimental periods to further validate and expand upon these findings (lines 306-310).
Driesen, E., De Proft, M., Saeys, W., 2021. Soil moisture levels affect the anatomy and mechanical properties of basil stems (Ocimum basilicum L.). Plants 10, 1320. http://doi.org/10.3390/plants10071320.
Al-Huqail, A., El-Dakak, R.M., Sanad, M.N., Badr, R.H., Ibrahim, M.M., Soliman, D., Khan, F., 2020. Effects of climate temperature and water stress on plant growth and accumulation of antioxidant compounds in sweet basil (Ocimum basilicum L.) leafy vegetable. Scientifica 2020, 1-12. http://doi.org/10.1155/2020/3808909.
Reviewer 2 Report
Comments and Suggestions for AuthorsI think that you should also evaluated the application uniformity of the water outlets. Even though you used pressure-compensated emitters, it would be interesting to perform an audit to get sure that the uniformity is indeed close to 100%.
Author Response
Comments 1: I think that you should also evaluate the application uniformity of the water outlets. Even though you used pressure-compensated emitters, it would be interesting to perform an audit to get sure that the uniformity is indeed close to 100%.
Response 1: We acknowledge that the uniformity of the drip irrigation system should be clearly stated. The mean Christiansen uniformity coefficient, which is widely used to represent the uniformity of emitter discharge along the dripline, was 98.8% in our study (lines 113–115).
Reviewer 3 Report
Comments and Suggestions for AuthorsI have two main concerns with the research study: it's very short duration (12 days) and its very small scale (pot size 12 cm). Given these concerns, I am not sure how representative this study is compared to the real situation farmers face in the field. You can't do much about these concerns as you can't change these parameters now. However, you might want to acknowledge these concerns and provide your reasons for such experiment design and finally an analysis of how your experiment design relates to the real field conditions.
Normally, after stating the need for research and its objectives, the second section presents a good analysis of literature review so that your research can benefit from the previous knowledge. But I don't see that in this paper.
Some other comments:
Section 1, Introduction.
What is the need or purpose for this research, what objectives and how your research gets at those objectives are not clearly stated.
Section 2.1: The experimentation is very small scale as the pots are only 10cm round. As such, is it reasonable to assume it represents real field conditions? I think some analysis of this concern would be helpful and the authors need to acknowledge such shortcomings of such experiments.
Section 2.4: The two-week duration for the research is very short and raises a lot of concern whether its results have any value when compared to the real field conditions.
Author Response
Comments 1: I have two main concerns with the research study: it's very short duration (12 days) and its very small scale (pot size 12 cm). Given these concerns, I am not sure how representative this study is compared to the real situation farmers face in the field. You can't do much about these concerns as you can't change these parameters now. However, you might want to acknowledge these concerns and provide your reasons for such experiment design and finally an analysis of how your experiment design relates to the real field conditions.
Response 1: The primary scope of this study was to establish a focused baseline evaluation of substrate moisture and plant growth uniformity in relation to irrigation scheduling, particularly the irrigation amount. To isolate the effect of irrigation amount on substrate water content and plant growth uniformity, we aimed to minimize biological variability and accumulated environmental influences. Accordingly, basil was selected as the test plant due to its rapid physiological response to moisture conditions (Driesen et al., 2021). Prior to initiating the experiment, the basil plants were acclimated and sorted to ensure uniform initial growth status. The experiment was conducted during the vegetative stage, which is known to be the most water-sensitive phase for basil (Al-Huqail et al., 2020). Therefore, a two-week experimental period was considered sufficient to clearly capture the effects of irrigation amount on substrate water content and plant growth uniformity, and this rationale has been added to the Materials and Methods section (lines 83–86, 131–133). Additionally, our results showed that volumetric water content (VWC) uniformity decreased significantly over time under frequent irrigation with small amounts. If irrigation were continued for a longer period, this accumulated variation in VWC among replicates could lead to increased variability in plant growth, particularly for crops with a longer vegetative growth cycle. Accordingly, we have revised the conclusion to emphasize that future research should include longer experimental periods to further validate and expand upon these findings (lines 306–310). However, our findings should not be directly extrapolated to field conditions. Field conditions inherently involve highly heterogeneous soils and uncontrollable environmental factors, which limit the clarity of uniformity analyses and make it more challenging to isolate the effects of irrigation amount. Therefore, a soilless substrate with potted production was selected to capture the distinct effect of irrigation amount under controlled conditions. For practical field application, further studies will be required (lines 306-310).
Driesen, E., De Proft, M., Saeys, W., 2021. Soil moisture levels affect the anatomy and mechanical properties of basil stems (Ocimum basilicum L.). Plants 10, 1320. http://doi.org/10.3390/plants10071320.
Al-Huqail, A., El-Dakak, R.M., Sanad, M.N., Badr, R.H., Ibrahim, M.M., Soliman, D., Khan, F., 2020. Effects of climate temperature and water stress on plant growth and accumulation of antioxidant compounds in sweet basil (Ocimum basilicum L.) leafy vegetable. Scientifica 2020, 1-12. http://doi.org/10.1155/2020/3808909.
Comments 2: Normally, after stating the need for research and its objectives, the second section presents a good analysis of the literature review so that your research can benefit from the previous knowledge. But I don't see that in this paper.
Response 2: As we mentioned in lines 52–62, most previous studies have primarily focused on crop quality and water use efficiency. With respect to irrigation uniformity, most research has investigated the uniform application of water within drip irrigation systems, targeting consistent delivery across a given plot. However, our study extends this perspective by investigating the actual substrate water content uniformity within individual pots across the irrigated plot. To clarify this distinction, we have revised the introduction section and added relevant references (lines 63–67).
Comments 3: (Section 1, Introduction) What is the need or purpose for this research, what objectives and how your research gets at those objectives are not clearly stated.
Response 3: The need of this study is to address a critical yet often overlooked aspect of soil moisture sensor-based drip irrigation systems: although most previous studies have focused on maximizing water use efficiency and ensuring uniform water delivery, limited attention has been given to the actual uniformity of substrate moisture among replicates and its impact on crop growth uniformity. The main objective of our study is addressing not only water use efficiency but also the uniformity of crop production within a drip irrigation system by rigorously quantifying the uniformity of substrate moisture content among replicate pots and its impact on plant growth uniformity. To get our objectives, the substrate moisture content of each pot was continuously monitored under different irrigation amount treatments using soil moisture sensors. To better clarify the objectives, we have revised the introduction section (lines 69–72).
Comments 4: (Section 2.1) The experimentation is very small scale as the pots are only 10cm round. As such, is it reasonable to assume it represents real field conditions? I think some analysis of this concern would be helpful and the authors need to acknowledge such shortcomings of such experiments.
Response 4: To isolate the effect of irrigation amount on substrate water content and plant growth uniformity, a soilless substrate under potted production conditions was used to minimize biological variability and accumulated environmental influences, thereby ensuring clear and distinct treatment effects. We acknowledge that these findings should not be directly extrapolated to field conditions; therefore, we have noted the need for scaled-up experiments to validate the results under practical field conditions (lines 306–310).
Comments 4: (Section 2.4) The two-week duration for the research is very short and raises a lot of concern whether its results have any value when compared to the real field conditions.
Response 4: Our findings provide a baseline evaluation of substrate moisture content and plant growth uniformity, an aspect that has received limited attention despite its importance. As this study aimed to establish a baseline, the focus was placed solely on the effect of irrigation amount on uniformity, minimizing biological variation and accumulated environmental influences. Expanding the scope to include additional factors would require a more complex experimental design, which was beyond the intent of this study. To acknowledge this limitation and to encourage future research under practical field conditions, we have emphasized in the conclusion that further studies should be conducted (lines 306–310).
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThis version of the manuscript meets the requirements for publication.
