Agronomic and Physiological Performances of High-Quality Indica Rice under Moderate and High-Nitrogen Conditions in Southern China
Round 1
Reviewer 1 Report
The authors presented results of a 2-year field trial to explore yield performance of two types of rice varieties with contrasting quality under moderate and high N conditions. The manuscript is of interest to the journal; however, it requires some improvements. There are points that, in my opinion, must be addressed and lead me to suggest major revision for the paper in its actual form. The current version of the manuscript needs a revision to make sentences clearer and more concise.
In the introduction the authors comment that there are few studies with the hypothesis that is proposed. However, it is not clear if there are similar studies in other areas of other parts of the world with similar climate and growing conditions. In my opinion, this should be indicated in the manuscript. Most of the references cited both in the introduction and in the discussion are from authors from China. It would be important to add other references from other agricultural areas with similar climate and agricultural systems.
Regarding the material and methods part, it is where, from my point of view, I consider that important changes must be made so that this article can be published in this journal.
Line 104: the climatic classification, adding date average year rainfall and temperature, where the experiment was carried out should be referenced in this section. Under my point of view, I consider that presenting results of only 2 years is very scarce. In field experiments, it would be necessary to be at least 3 years old to be able to express conclusive results.
Line 107: Considering that the rice root can reach up to 40 centimeters, putting soil data on the first 20 cm seems insufficient. Was the electrical conductivity, nitrogen-nitric and carbon-nitrogen ratio analyzed? The soil parameters analyzed would be better expressed in a table.
Line 110: temperature and solar radiation are important and variable within each year. For this reason, Figure 1 should be presented at the beginning in the results part to be able to address it in this section and in the discussion. Figure 1 shows the temperature and solar radiation data for each of the two rice growing seasons analyzed in this study. However, no historical year date is shown by the authors), therefore it is difficult to compare whether each of the years of the study was very or low different than the historical data for the region. Therefore, it would be better to detail the historical temperature and solar radiation included in these months (growing seasons) to be able to make a more correct comparison of the variability there is in the climate of the area.
Line 121: Why have these doses been chosen? It would be important to put a sentence detailing and justifying the choice of those levels. Was the fertilizer incorporated o just broadcasted on surface? It is no clear. Did you account N losses by volatilization during and after urea application? The elevated NH4-N content of the urea could have decreased the nitrogen applied due to volatilization losses. It should have considered that less than the denoted N amount was available to the crops to carry out the NUE calculations. In addition, no information on N leaching was given. Although N leaching was not measured directly, it would be helpful to have an idea of the amount of N leaching, e.g. by using leaching models. In addition, the estimation of the monthly amount of percolation water may help to identify and quantify possible pathways. In addition, it would have been interesting to calculate a nitrogen balance estimating these possible nitrogen losses.
Line 124. Was the fertilizer incorporated o just broadcasted on surface? It is no clear. Did you account N losses by volatilization during and after urea application? The elevated NH4-N content of the urea could have decreased the nitrogen applied due to volatilization losses. It should have considered that less than the denoted N amount was available to the crops to carry out the NUE calculations (line 172-176). In addition, no information on N leaching was given. Although N leaching was not measured directly, it would be helpful to have an idea of the amount of N leaching, e.g. by using leaching models. In addition, the estimation of the monthly amount of percolation water may help to identify and quantify possible pathways. In addition, it would have been interesting to calculate a nitrogen balance estimating these possible nitrogen losses.
Line 182- 185. These paragraphs should be rewritten specifying in more detail how the comparison of means has been made. The analysis of variance and mean comparisons were not conducted with appropriate tests. Assuming that (not detailed anywhere in the text) the authors applied treatments on the same plots for 2 years, thus ANOVA model should consider repeated measurements in the design. Moreover, the authors forgot interactions year*treatment. In this way, if interactions occur, the post-hoc test must consider for that to get the right error term (find significant differences for one factor within levels of another). In any case the ANOVA model should be better described (fixed factor, repeated measurements). Most of the assumptions are based on few statistically different means (even if comparison should be done with appropriate tests). Treatments comparisons (within year) are also interesting, but from an agronomic point of view. For example, I think that improving urea application would also be a possibility to increase N efficiency, and thus should be discussed.
In the presentation of the results there is an excess of tables that makes it very difficult to read and observe the results obtained in this investigation. In this sense, the significant differences derived from the ANOVA analyzes performed are not clearly observed in the different tables. There should be more graphs instead of some tables and perhaps separate the statistical significance derived from the analysis of the graphs where the different variables of the study are exposed.
Line 188: The authors showed significant effects between treatments. However, it is not clear if these values ​​correspond to the year 2020 or the year 2021 or the average between the two. It would be important to detail it both for performance and for the other variables analyzed.
Line 237. Does the error bar indicate standard deviation from the mean?
Finally, in the conclusions., it would be interesting if the authors addressed the importance of the experiment with the results obtained. In this sense, a section should be included with the applicability on a real scale (farmers) of the results obtained and argued throughout the discussion. In other words, it should be noted, why is this type of study important from the agronomic, economic and environmental point of view? Where will future research go?.
is this type of study important from the agronomic, economic and environmental point of view? Where will future research go?
Author Response
Dear Editors and Reviewers:
We highly appreciate your comments on our manuscript entitled “Agronomic and physiological performance of high-quality indica rice under moderate and high nitrogen conditions in southern China”. These comments are very valuable and helpful for revising and improving our manuscript, as well as for further guiding our research in future. We have studied these comments carefully and have made correction which we hope meet with your approval. Revised parts were marked up using the “Track Changes” function in manuscript. And the responds to the reviewer’s comments are as following:
Response to Reviewer 1
Point 1: In the introduction the authors comment that there are few studies with the hypothesis that is proposed. However, it is not clear if there are similar studies in other areas of other parts of the world with similar climate and growing conditions. In my opinion, this should be indicated in the manuscript. Most of the references cited both in the introduction and in the discussion are from authors from China. It would be important to add other references from other agricultural areas with similar climate and agricultural systems.
Response: We have added some key results in the introduction section from similar studies in India, Pakistan, the United States, and Senegal, which refer to 7 references.
Point 2: L 104, the climatic classification, adding date average year rainfall and temperature, where the experiment was carried out should be referenced in this section. Under my point of view, I consider that presenting results of only 2 years is very scarce. In field experiments, it would be necessary to be at least 3 years old to be able to express conclusive results.
Response: We already added the average year rainfall and temperature of the experimental site in the corresponding section. Usually, it would be necessary to present the conclusive results of at least 3 years for field experiments. In fact, we had carried out a similar experiment with twenty high-quality varieties (including Yexiangyoulisi, Wanxiangyou-982) and three N application rates (105, 165, and 225 kg N ha−1) in the same experimental site in 2019. The results indicated that grain yield of all high-quality rice varieties significantly increased from 105 kg N ha−1 to 165 kg N ha−1, while most varieties show no increase or even decrease in grain yield from 165 kg N ha−1 to 225 kg N ha−1. These results have been published on this journal on 2nd November 2022 with the title of “Varietal variances of grain nitrogen content and its relations to nitrogen accumulation and yield of high-quality rice under different nitrogen rates”. However, the agronomic and physiological responses of high-quality rice varieties to different N application rates are little known. Therefore, we continued to carry out a two-year experiment to verify the agronomic and physiological performances of high-quality rice varieties under moderate (165 kg N ha−1) and high (225 kg N ha−1) nitrogen application rates.
Point 3: L107, Considering that the rice root can reach up to 40 centimeters, putting soil data on the first 20 cm seems insufficient. Was the electrical conductivity, nitrogen-nitric and carbon-nitrogen ratio analyzed? The soil parameters analyzed would be better expressed in a table.
Response: Most rice fields are lowland and well-irrigated, and the plough layer is usually about 20 cm in southern China. Therefore, we usually analyze the basic physicochemical properties (including pH, organic C, total N content, available N, available P, and available K) for the upper 20 cm of the soil when the studies focus on crops but not on soils. Please reference to Xue et al. (2015) and Huang et al. (2020)
Xue, J. F.; Pu, C., ; Liu, S. L.; Chen, Z. D.; Chen, F.; Xiao, X. P.; Lal, R.; Zhang, H. L. Effects of tillage systems on soil organic carbon and total nitrogen in a double paddy cropping system in Southern China. Soil Till. Res. 2015, 153, 161-168.
Huang, M.; Lei, T.; Cao, F.; Chen, J.; Shan, S.; Zou, Y. Grain yield responses to nitrogen rate in two elite double-cropped inbred rice cultivars released 41 years apart. Field Crops Res. 2020, 259, 107970.
Point 4: L110: temperature and solar radiation are important and variable within each year. For this reason, Figure 1 should be presented at the beginning in the results part to be able to address it in this section and in the discussion. Figure 1 shows the temperature and solar radiation data for each of the two rice growing seasons analyzed in this study. However, no historical year date is shown by the authors), therefore it is difficult to compare whether each of the years of the study was very or low different than the historical data for the region. Therefore, it would be better to detail the historical temperature and solar radiation included in these months (growing seasons) to be able to make a more correct comparison of the variability there is in the climate of the area.
Response: We have presented the temperature and solar radiation data during rice growing seasons in the results section (Table 3.) and addressed them in this section and in the discussion.
Moreover, we found that the daily average temperature and solar radiation of September 2019 and 2021 were higher (3.7-4.2℃ and 3.3-3.8 MJ M-2) than those of 2020. Generally, the heading date of late-season rice is in September in double-season cropping system in southern China. The abnormal lower temperature and solar radiation in September will delay the heading date of late-season rice and lead to significantly decreased grain setting rate and grain weight.
Point 5: L121: Why have these doses been chosen? It would be important to put a sentence detailing and justifying the choice of those levels. Was the fertilizer incorporated or just broadcasted on surface? It is no clear. Did you account N losses by volatilization during and after urea application? The elevated NH4-N content of the urea could have decreased the nitrogen applied due to volatilization losses. It should have considered that less than the denoted N amount was available to the crops to carry out the NUE calculations. In addition, no information on N leaching was given. Although N leaching was not measured directly, it would be helpful to have an idea of the amount of N leaching, e.g. by using leaching models. In addition, the estimation of the monthly amount of percolation water may help to identify and quantify possible pathways. In addition, it would have been interesting to calculate a nitrogen balance estimating these possible nitrogen losses?
Response 4: In our former study, we have found that grain yield of all tested twenty high-quality rice varieties significantly increased from 105 kg N ha−1 to 165 kg N ha−1, while most varieties show no increase or even decrease in grain yield from 165 kg N ha−1 to 225 kg N ha−1. However, many studies showed that grain yield of ordinary-quality or high-yielding rice varieties still significantly increased from 165 kg N ha−1 to 225 kg N ha−1. Therefore, the objective of this study was to verify the different agronomic and physiological responses of high- and ordinary-quality rice varieties to moderate (165 kg N ha−1) and high (225 kg N ha−1) nitrogen application rates.
The basal fertilizers were incorporated to field with a rotary cultivator before transplanting, but the top-dressing fertilizers were broadcasted on the field surface by hand.
In this study, we did not focus on the nitrate leaching and nitrogen fate. However, we have published the relevant results (excluding nitrate leaching) on this journal on 2nd November 2022 with the title of “Varietal variances of grain nitrogen content and its relations to nitrogen accumulation and yield of high-quality rice under different nitrogen rates”. We highly appreciate your meaningful advice and will further study the nitrate leaching and nitrogen fate in the current scenarios in future.
Wu, J.; Que, R.; Qi, W.; Duan, G.; Wu, J.; Zeng, Y.; Pan, X.; Xie, X. Varietal variances of grain nitrogen content and its relations to nitrogen accumulation and yield of high-quality rice under different nitrogen rates. Agronomy 2022, 12, 2719.
Point 6: L182-185. These paragraphs should be rewritten specifying in more detail how the comparison of means has been made. The analysis of variance and mean comparisons were not conducted with appropriate tests. Assuming that (not detailed anywhere in the text) the authors applied treatments on the same plots for 2 years, thus ANOVA model should consider repeated measurements in the design. Moreover, the authors forgot interactions year*treatment. In this way, if interactions occur, the post-hoc test must consider for that to get the right error term (find significant differences for one factor within levels of another). In any case the ANOVA model should be better described (fixed factor, repeated measurements). Most of the assumptions are based on few statistically different means (even if comparison should be done with appropriate tests). Treatments comparisons (within year) are also interesting, but from an agronomic point of view. For example, I think that improving urea application would also be a possibility to increase N efficiency, and thus should be discussed.
Response: We have rewritten the paragraph of the “Statistical Analysis” section. All related data were separately analyzed within year using analysis of variance (ANOVA), because the two-year experiments were carried out in adjacent fields and the climate parameters (such as temperature and solar radiation) were comparable in September of 2020 and 2021. However, we directly compared and analyzed the means of repeated measurements between two years.
Point 7: L188, The authors showed significant effects between treatments. However, it is not clear if these values correspond to the year 2020 or the year 2021 or the average between the two. It would be important to detail it both for performance and for the other variables analyzed.
Response: In this study, significant effects between treatments and these values of all parameters corresponded to each year. We have detailed it in this manuscript.
Point 8: Line 237, Does the error bar indicate standard deviation from the mean?
Response: Yes, it does.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear authors,
Thanks for contacting me to review the manuscript “Agronomic and physiological performance of high-quality indica rice under moderate and high nitrogen conditions in southern China.” The manuscript's topic is interesting, and I believe the paper meets the Journal of Agronomy criteria for accepting a manuscript; however, I have some minor suggestions and comments, and here is a point-by-point.
Abstract; it is very long and exceeds 200 words according to journal instructions, so I recommend that the authors make it short and more precise and follow the style of structured abstracts.
Introduction; No comment; the introduction covered the research point from all sides, presented the topic, and provided background and details of the research problem.
Materials and methods; the description of analysis methods is well; however, the extraction of available nutrients and methodology should be written in the methodology section; more details are needed in this part, for example, which method was used to extract the available P? Mehlich 3 or Bray II, be more specific.
Results; the description of results is satisfactory; however, there are minor suggestions 1). In Table (6), the standard deviation should be added to see the differences between each observation and the mean. I have another concern I would like the authors to clarify their point. “they stated that the different yield responses of HQIR and OQIR to moderate 307 and high N application rates were mainly explained by the difference in spikelets m−2 308 and/or grain setting rate”. They are trying to figure out the optimum rate of nitrogen, so what about the genetic variation within varieties?
Discussion; the discussion should be supported and justified accordingly with some latest references and modern style, and it needs some formatting as the manuscript has been opened in different MS Office.
Conclusion; No comment; it is well-written and more focused on the practical results of the study.
References; all references are according to the journal style; however, some references should be updated with the latest.
Final decision; Based on the above-mentioned comments, the decision is to “accept” this work as the study has some novelty, so it should be improved and published.
I don't have any comments. I just noticed a few mistyping; make sure to double check
Author Response
Response to Reviewer 2
Point 1: Abstracts; it is very long and exceeds 200 words according to journal instructions, so I recommend that the authors make it short and more precise and follow the style of structured abstracts.
Response: We have made further correction follow the style of structured abstracts.
Point 2: Materials and methods; the description of analysis methods is well; however, the extraction of available nutrients and methodology should be written in the methodology section; more details are needed in this part, for example, which method was used to extract the available P? Mehlich 3 or Bray II, be more specific.
Response: We have made correction according to the reviewer’s comments and showed the methodologies of the extraction of available nutrients in Table 3.
Point 3: Results; the description of results is satisfactory; however, there are minor suggestions 1). In Table (6), the standard deviation should be added to see the differences between each observation and the mean. I have another concern I would like the authors to clarify their point. “they stated that the different yield responses of HQIR and OQIR to moderate and high N application rates were mainly explained by the difference in spikelets m−2 and/or grain setting rate”. They are trying to figure out the optimum rate of nitrogen, so what about the genetic variation within varieties?
Response: We have added the standard deviation to Table 6 (updated to Table 8) according to the reviewer’s comments. To keep the uniform style for all tables, we supplement Table 8 with standard deviation as additional files.
We agree with the reviewer that we should consider the genetic variation within varieties when figure out the optimum rate of nitrogen. Furthermore, we found that most HQIR varieties obtained the maximum grain yield in moderate N rates and had little degradation in quality in our and previous studies.
Table 8. Aboveground plant N uptake and NUEg of HQR and OQR varieties under moderate and high N rates.
|
Year |
N rate |
Variety |
N uptake at heading (kg ha−1) |
N uptake at maturity (kg ha−1) |
Post-anthesis N uptake (kg ha−1) |
Pre- anthesis N exportation (kg ha−1) |
NUEg (kg kg−1) |
|
2020 |
Moderate |
YXY |
123.5±0.21c |
149.9±6.14c |
26.4±5.93b |
44.5±0.33b |
50.2±2.99bc |
|
|
N |
WXY |
122.4±5.69c |
157.9±1.98b |
35.5±3.76a |
41.8±5.25b |
48.4±1.36c |
|
|
|
MeanHQR |
122.9±3.65C |
153.9±4.12D |
30.9±4.44AB |
43.2±3.66C |
49.3±2.13B |
|
|
|
KY |
129.8±2.06b |
164.6±1.36a |
34.8±0.94a |
55.3±1.75a |
52.4±0.39a |
|
|
|
JY |
134.7±3.76a |
162.7±4.43a |
28.0±3.54b |
59.4±3.60a |
51.2±0.76ab |
|
|
|
MeanOQR |
132.3±3.39B |
163.7±3.01C |
31.4±3.59A |
57.3±3.38B |
51.8±0.94A |
|
|
High N |
YXY |
156.2±3.77ab |
177.8±4.23b |
21.6±2.95b |
62.2±3.10b |
41.4±0.42b |
|
|
|
WXY |
152.0±2.14bc |
174.6±4.03b |
22.6±3.62b |
56.3±1.65c |
42.8±1.62b |
|
|
|
MeanHQR |
154.1±3.59A |
176.2±4.09B |
22.1±3.01C |
59.2±3.92B |
42.2±1.30C |
|
|
|
KY |
151.5±4.13c |
184.5±3.22a |
33.0±2.56a |
68.4±3.96a |
49.8±1.81a |
|
|
|
JY |
160.4±1.76a |
184.5±4.37a |
24.101±4.56b |
69.9±1.83a |
48.2±0.34a |
|
|
|
MeanOQR |
155.9±3.68A |
184.5±3.43A |
28.6±4.06B |
69.1±2.87A |
49.0±1.45B |
|
2021 |
Moderate |
YXY |
125.6±2.63bc |
142.6±1.29d |
17.0±1.42c |
50.9±2.96c |
59.4±0.15b |
|
|
N |
WXY |
124.4±4.05c |
146.9±1.76c |
22.5±2.36ab |
47.2±4.10d |
59.8±1.63ab |
|
|
|
MeanHQR |
125.2±3.13D |
144.8±1.66D |
19.7±2.35B |
49.1±3.78C |
59.6±1.33A |
|
|
|
KY |
128.9±3.85ab |
152.6±1.65b |
23.7±3.05a |
56.9±2.79b |
61.4±1.58a |
|
|
|
JY |
136.7±2.57a |
155.1±4.22a |
18.4±1.70bc |
61.2±2.85a |
60.2±2.49ab |
|
|
|
MeanOQR |
132.8±4.81C |
153.8±3.88C |
21.0±2.51B |
59.0±3.46B |
60.8±2.18A |
|
|
High N |
YXY |
159.6±6.52a |
172.1±3.25b |
12.5±4.76c |
64.7±6.31bc |
47.5±1.30c |
|
|
|
WXY |
153.9±3.04b |
167.8±2.48c |
13.9±1.70c |
59.8±2.87c |
50.3±0.52b |
|
|
|
MeanHQR |
156.7±5.18A |
170.0±3.51B |
13.2±3.20C |
62.2±5.13B |
48.9±1.76C |
|
|
|
KY |
145.3±5.82c |
181.8±2.67a |
36.4±3.38a |
68.6±5.02b |
56.6±0.99a |
|
|
|
JY |
154.7±2.65b |
183.8±1.22a |
29.0±1.44b |
76.0±2.18a |
54.9±0.60a |
|
|
|
MeanOQR |
150.0±6.52B |
182.8±2.14A |
32.7±4.67A |
72.3±5.34A |
55.7±1.19B |
Note: Within a column, different lowercase letters between varieties in the same N rate indicate significant differences at the p < 0.05 level; different uppercase letters between varietal types across two N rates indicate significant differences at the p < 0.05 level.
Point 4: Discussion; the discussion should be supported and justified accordingly with some latest references and modern style, and it needs some formatting as the manuscript has been opened in different MS Office.
Response: We have made correction according to the reviewer’s comments. Additions of relevant content are reflected in this section.
Author Response File: Author Response.docx
Reviewer 3 Report
The paper by G. Duan et al. entitled 'Agronomic and physiological performance of high-quality indica rice under moderate and high nitrogen conditions in southern China' is an exciting study on the effect of nitrogen application on grain yield of high-quality indica rice varieties in southern China. The authors found that moderate nitrogen application is better to obtain higher yield in high-quality indica rice than high nitrogen application whereas high nitrogen application is better for ordinary-quality indica rice. The authors also found the important relationship between sink-source balance and rice yield and a better balance between them is favorable to obtain higher yield in high-quality Indica rice. These results are important for rice production in southern China where recently the demand for high-quality rice is steeply increased due to economic development. The method, analysis, and discussion are appropriate. However, the reviewer has some questions and mentions them later.
1) This paper simply compares two nitrogen fertilization methods between two groups of varieties. It only argues that one fertilization method or variety has a higher yield (higher quality) because one measurement is higher or lower than the other. Such methods cannot establish causality. It is necessary to analyze how individual factors combine to cause the high yield of high-quality indica rice by using correlation analysis, regression analysis, multiple regression analysis, or multivariate analysis, especially since there are many measurement items
2) In this paper, the authors only use the data from "http://www.ricedata.cn/" in Table 1 as the basis for their assumption that high-quality indica rice is of higher quality because it has a lower percentage of chalky grains. Certainly, many growing conditions would yield higher quality for these varieties. However, in the present experiment, there was no study of the quality of high-quality indica rice at high and moderate nitrogen fertilization levels. If you now preserve the brown rice grains of this experiment, it is necessary to investigate the quality of the grains, such as the percentage of chalky grains, and to confirm that the quality is indeed higher in the high-quality indica rice under the moderate nitrogen fertilizer application. If it is difficult to check, please note in the discussion that the quality of high-quality indica rice was observed to be higher under the moderate nitrogen fertilizer application, although the authors only visually observed at harvest time.
3) What high quality actually means in this experiment should be properly written in the abstract. There are many parameters for high quality, including appearance such as chalky grains, taste, aroma, nutritional value, digestibility, and suitability for processing. The abstract should clarify what the high quality is that is being discussed in this experiment.
4) The abbreviation "AE" is used in the abstract. However, the abstract does not define what the abbreviation "AE" is. When an abbreviation is used, it must be defined before it is used.
5) In line 84, the authors present the following hypothesis that HQIR and OQIR had similar responses in terms of yield formation under different N application rates. If the authors present such a hypothesis in the introduction, the authors must consider whether this hypothesis was valid in the conclusion or discussion.
6) Physiological mechanisms are very diverse, including photosynthesis, respiration, enzymes, translocation, etc. A very large number of physiological mechanisms are possible. Therefore, it is necessary to write more clearly in the introduction what physiological mechanisms were the focus of this study.
7) In Table 1, the term "length-width ratio" must be clearly stated to be the length-width ratio of the grain.
8) In Figure 1, the graph of solar radiation is very difficult to read. We think it would be better to display it as a moving average in 5-day increments so that we can simply see the trend and the difference between the two years. For the reader's convenience, it would be better to include information on dates of heading and harvest, and so on in Figure 1.
9) In the survey of yield components, it is necessary to clearly depict how the filled grains were determined. The reader will not understand a description that the authors investigate filled grains only by a machine. The results of the survey of the filled grains will vary greatly depending on the survey method. It is necessary to clearly state whether the grains were selected by saltwater selection, wind selection, or sieving selection according to the thickness of the grains.
10) In the biomass measurement, the author states that the leaves, stems, and panicles were separated and dried in a forced-air dryer. In rice, however, the leaf is composed of the leaf blade and leaf sheath. In general, the leaf sheath is weighed together with the stem (culm) in the dry matter weight survey of rice. If the leaf blade and leaf sheath are measured together as leaves, this is an inappropriate method of measuring biomass. The average rice scientist usually measures biomass by dividing the rice plants into panicles, leaf blades, and leaf sheaths and culms. In some cases, roots are also measured.
11) Pre-anthesis AE is based solely on the reduction in biomass between heading and maturity, however, this measurement is not valid. Biomass in leaf sheaths and culms decreases after heading, usually reaching a minimum at 20 to 25 days after heading, the mid-ripening stage, and then increases with reaccumulation. If the authors want to measure the contribution to yield of biomass accumulated in leaf sheaths and culms before heading, the authors must measure the biomass of leaf sheaths and culms at the mid-ripening stage. The present method underestimates the contribution of pre-heading biomass to yield and overestimates the contribution of post-heading photosynthesis. This is because biomass in leaf sheaths and culms generally decreases and reaches a minimum during the mid-ripening stage, after which biomass is reaccumulated by photosynthesis during ripening.
12) The numbers of data in the tables are too fine. They do not need to be displayed to the second decimal place; in many cases, one decimal place is sufficient. Please check the significant figures properly. It should be easier for the reader to understand if you do not put data to unnecessary digits.
13) In table 2, the unit of the grain yield is in t hm-2, is it not a mistake for t ha-1?
14) The chlorophyll value (SPAD) is influenced by the thickness of the leaf blade. Please describe how the leaf blade thickness is nearly identical in all varieties used in this experiment.
15) Even if the absorbed solar radiation and leaf area index are the same, the radiation use efficiency will be different if the leaf erectness (angle) and canopy structure are different. If you have any data on canopy structure and leaf angle for the cultivars used in this study, please describe them in the discussion.
Author Response
Response to Reviewer 3
Point 1: This paper simply compares two nitrogen fertilization methods between two groups of varieties. It only argues that one fertilization method or variety has a higher yield (higher quality) because one measurement is higher or lower than the other. Such methods cannot establish causality. It is necessary to analyze how individual factors combine to cause the high yield of high-quality indica rice by using correlation analysis, regression analysis, multiple regression analysis, or multivariate analysis, especially since there are many measurement items.
Response: This study was performed based on our previous study, in which we found that grain yield of selected twenty HQIR varieties significantly increased from 105 kg N ha−1 to 165 kg N ha−1, while most varieties show no increase or even decrease in grain yield from 165 kg N ha−1 to 225 kg N ha−1. However, many studies showed that grain yield of OQIR varieties still significantly increased from 165 kg N ha−1 to 225 kg N ha−1. Therefore, the objective of this study was to explore the different agronomic and physiological responses of HQIR and OQIR varieties to moderate (165 kg N ha−1) and high (225 kg N ha−1) nitrogen application rates. These results directly indicate that HQIR varieties cannot obtain higher grain yield under high N application rate because of carbon metabolic deterioration and imbalance of source-sink relationship.
Point 2: In this paper, the authors only use the data from "http://www.ricedata.cn/" in Table 1 as the basis for their assumption that high-quality indica rice is of higher quality because it has a lower percentage of chalky grains. Certainly, many growing conditions would yield higher quality for these varieties. However, in the present experiment, there was no study of the quality of high-quality indica rice at high and moderate nitrogen fertilization levels. If you now preserve the brown rice grains of this experiment, it is necessary to investigate the quality of the grains, such as the percentage of chalky grains, and to confirm that the quality is indeed higher in the high-quality indica rice under the moderate nitrogen fertilizer application. If it is difficult to check, please note in the discussion that the quality of high-quality indica rice was observed to be higher under the moderate nitrogen fertilizer application, although the authors only visually observed at harvest time.
Response: We have presented the discussion of the quality performance of high-quality indica rice under moderate and higher N fertilizer application rates.
Point 3: What high quality actually means in this experiment should be properly written in the abstract. There are many parameters for high quality, including appearance such as chalky grains, taste, aroma, nutritional value, digestibility, and suitability for processing. The abstract should clarify what the high quality is that is being discussed in this experiment.
Response: We have made correction according to the reviewer’s comments. High quality rice usually has higher appearance and eating quality.
Point 4: The abbreviation "AE" is used in the abstract. However, the abstract does not define what the abbreviation "AE" is. When an abbreviation is used, it must be defined before it is used.
Response: We have made correction according to the reviewer’s comments.
Point 5: In line 84, the authors present the following hypothesis that HQIR and OQIR had similar responses in terms of yield formation under different N application rates. If the authors present such a hypothesis in the introduction, the authors must consider whether this hypothesis was valid in the conclusion or discussion.
Response: We have changed the description in this paragraph.
Point 6: Physiological mechanisms are very diverse, including photosynthesis, respiration, enzymes, translocation, etc. A very large number of physiological mechanisms are possible. Therefore, it is necessary to write more clearly in the introduction what physiological mechanisms were the focus of this study.
Response: We have made correction according to the reviewer’s comments.
Point 7: In Table 1, the term "length-width ratio" must be clearly stated to be the length-width ratio of the grain.
Response: We have made correction according to the reviewer’s comments.
Point 8: In Figure 1, the graph of solar radiation is very difficult to read. We think it would be better to display it as a moving average in 5-day increments so that we can simply see the trend and the difference between the two years. For the reader's convenience, it would be better to include information on dates of heading and harvest, and so on in Figure 1.
Response: Considering all comments from reviewers, we deleted the Figure 1 and showed the temperature and solar radiation in Table 3. The dates of heading and harvest (physiological maturity) were presented in “Experimental design” section.
Point 9: In the survey of yield components, it is necessary to clearly depict how the filled grains were determined. The reader will not understand a description that the authors investigate filled grains only by a machine. The results of the survey of the filled grains will vary greatly depending on the survey method. It is necessary to clearly state whether the grains were selected by saltwater selection, wind selection, or sieving selection according to the thickness of the grains.
Response: Considering the reviewers’ comments, we have supplemented a method for separating filled and unfilled grains.
Point 10: In the biomass measurement, the author states that the leaves, stems, and panicles were separated and dried in a forced-air dryer. In rice, however, the leaf is composed of the leaf blade and leaf sheath. In general, the leaf sheath is weighed together with the stem (culm) in the dry matter weight survey of rice. If the leaf blade and leaf sheath are measured together as leaves, this is an inappropriate method of measuring biomass. The average rice scientist usually measures biomass by dividing the rice plants into panicles, leaf blades, and leaf sheaths and culms. In some cases, roots are also measured.
Response: We apologize for the confusion caused to the experts due to the poor sentence presentation, and we have further described and corrected the sentence. In fact, our treatment of rice biomass is the same as the expert's view.
Point 11: Pre-anthesis AE is based solely on the reduction in biomass between heading and maturity, however, this measurement is not valid. Biomass in leaf sheaths and culms decreases after heading, usually reaching a minimum at 20 to 25 days after heading, the mid-ripening stage, and then increases with reaccumulation. If the authors want to measure the contribution to yield of biomass accumulated in leaf sheaths and culms before heading, the authors must measure the biomass of leaf sheaths and culms at the mid-ripening stage. The present method underestimates the contribution of pre-heading biomass to yield and overestimates the contribution of post-heading photosynthesis. This is because biomass in leaf sheaths and culms generally decreases and reaches a minimum during the mid-ripening stage, after which biomass is reaccumulated by photosynthesis during ripening.
Response: We agree with reviewer’s opinion. So, in this study, the pre-anthesis AE is an apparent exportation of pre-anthesis stem and leave blades dry matter, which was referenced from Liu et al. (2019).
Liu, K.; Yang, R.; Lu, J.; Wang, X.; Lu, B.; Tian, X.; Zhang, Y. Radiation use efficiency and source-sink changes of super hybrid rice under shade stress during grain-filling stage. Agron. J. 2019, 111, 1788-1798.
Point 12: The numbers of data in the tables are too fine. They do not need to be displayed to the second decimal place; in many cases, one decimal place is sufficient. Please check the significant figures properly. It should be easier for the reader to understand if you do not put data to unnecessary digits.
Response: We have made correction according to the reviewer’s comments.
Point 13: In table 2, the unit of the grain yield is in t hm-2, is it not a mistake for t ha-1?
Response: We have made correction according to the reviewer’s comments.
Point 14: The chlorophyll value (SPAD) is influenced by the thickness of the leaf blade. Please describe how the leaf blade thickness is nearly identical in all varieties used in this experiment.
Response: We have presented this description in “Sampling and measurements” section. In this study, YXY and JY have nearly identical leaf blade thickness (370 mg cm-2), but are lower than WXY and KY (410 mg cm-2)
Point 15: Even if the absorbed solar radiation and leaf area index are the same, the radiation use efficiency will be different if the leaf erectness (angle) and canopy structure are different. If you have any data on canopy structure and leaf angle for the cultivars used in this study, please describe them in the discussion.
Response: We agree with reviewer’s opinion. Nevertheless, the canopy structure and leaf angle for two type of rice varieties had not been measure in this study, we will focus on these parameters in future study.
In addition, the other revisions suggested by the reviewer were all done.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The latest version of the submitted manuscript has substantially improved compared to the previous version.Author Response
Dear reviewer:
Thank you very much for your kind work and consideration on publication of our paper. On behalf of my co-authors, we would like to express our great appreciation to reviewers.
Thank you and best regards.
Yours sincerely,
Gangqiang Duan
Reviewer 2 Report
Dear Authors
I would like to acknowledge and appreciate your efforts in addressing all my concerns and comments. It’s my pleasure to inform you that the corrected version of your manuscript has been revised and accepted by my side to be considered for publication since your revisions have greatly improved the quality of the manuscript.
Best regards,
Saif
Author Response
Dear reviewer:
Thank you very much for your kind work and consideration on publication of our paper. On behalf of my co-authors, we would like to express our great appreciation to reviewers.
Thank you and best regards.
Yours sincerely,
Gangqiang Duan
Reviewer 3 Report
When you have revised your manuscript in accordance with the reviewer's comments, please indicate in the response letter what part of the manuscript you have revised and what line in the new manuscript corresponds to the revised part.
About Pont 12: Whether or not the first or second decimal place is written in the table figures is trivial, but the reviewer does not find that it has been corrected in accordance with the comment.
About Point 13: The reviewer did not find the revision about the unit (t hm-2).
Author Response
Dear Reviewer:
We are very sorry for the confusion caused to you due to our negligence in submitting an incorrect version. The new revised manuscript has been submitted as required, please check the attachment. And the responds to the reviewer’s comments are as following:
Response to Reviewer 3
Point 12: The numbers of data in the tables are too fine. They do not need to be displayed to the second decimal place; in many cases, one decimal place is sufficient. Please check the significant figures properly. It should be easier for the reader to understand if you do not put data to unnecessary digits.
Response: We have made correction according to the reviewer’s comments.
Point 13: In table 2, the unit of the grain yield is in t hm-2, is it not a mistake for t ha-1?
Response: We have made correction according to the reviewer’s comments.
