Chinese Violet Cress (Orychophragmusviolaceus L.) Yield and Nitrogen Balance in Response to Coupling Effects of Water–Nitrogen Application—A Case Study Using ¹⁵N Tracing Technique

Round 1

Reviewer 1 Report

Reviewed manuscript “Chinese violet cress (Orychophragmus violaceus. L) yield, ni-
trogen use and soil nitrogen balance in response to coupling
 effects of water-nitrogen application- A case study using 15N
 tracing technique” is an original and interesting study. Authors comprehensively demonstrated the effects of water-nitrogen application. Study is very interesting and it would add scientific contribution in literature. Authors collected lot of data with strong reasoning. I would suggest minor revision.

Following are some suggestions for further improvements:

First few lines of the abstract should be about the importance of study.

Lines 60-63: Consider revising the lines.

Lines 65-67: Consider revising the lines.

Lines 70-73: Consider revising the lines.

Introduction and Discussion section needs to further strengthen by latest studies on the subject. Improve the discussion section.

At some places in the text, there are grammatical mistakes that need to be corrected by some native English colleague. Please summarize the conclusion.

To further strengthen introduction, following latest studies etc. are suggested to cite for the effects of water-nitrogen application for sustainable productivity.

Author Response

First few lines of the abstract should be about the importance of study.

Thank you for your comments. Indeed, the research should be of great significance rather than necessary, we have revised it in the abstract.

Lines 60-63: Consider revising the lines.

Thank you for your suggestion, we have revised it.

Lines 65-67: Consider revising the lines.

Yes, thank you. “Green” is incorrect, we have revised: it germinated in winter and flowering in spring with a long flowering period

Lines 70-73: Consider revising the lines.

Thank you for your suggestion. We have revised as you commented in the revised paper.

Introduction and Discussion section needs to further strengthen by latest studies on the subject. Improve the discussion section.

Thank you for your suggestion. We have revised the introduction and discussion as well as cited the latest studies.

At some places in the text, there are grammatical mistakes that need to be corrected by some native English colleague. Please summarize the conclusion.

Thank you for your suggestion. We have examine the paper and made the corresponding revision. As you recommended, we have deleted some unuseful part and summarize the conclusion.

To further strengthen introduction, following latest studies etc. are suggested to cite for the effects of water-nitrogen application for sustainable productivity.

Thank you for your suggestion. We have cited the studies especially the water-nitrogen application  on sustainable agriculture.

Reviewer 2 Report

2.1. Experimental design: The self designed intelligent irrigation device was adopted for the irrigation (Figure 1 a-b). I suggest a more detailed description of the used and presented intelligent irrigation device adopted for the irrigation. Please provide more detailed data on the fertilizers ( urea, diammonium phosphate and potassium sulfate used, the content of macronutrients and the producers of the fertilizers.

Author Response

2.1. Experimental design: The self designed intelligent irrigation device was adopted for the irrigation (Figure 1 a-b). I suggest a more detailed description of the used and presented intelligent irrigation device adopted for the irrigation. Please provide more detailed data on the fertilizers ( urea, diammonium phosphate and potassium sulfate used, the content of macronutrients and the producers of the fertilizers.

Dear reviewer:

  Thank you for your comments. As you can see in the revised paper, we have added the information about the device. This automatic irrigation device is connected to municipal water, so there is no filter. According to the system settings, it can automatically irrigate the plants without manual work. Besides, we have added the chemical formula of the fertilizer. Fertilizer varieties were urea (NH₂CO₂NH₂), diammonium phosphate ((NH₄)₂·HPO₄) and potassium sulfate (K₂SO₄) (produced by Stanley Fertilizer Inc., China).

  Thank you again for your constructive suggestions.

Reviewer 3 Report

The manuscript is focused on the effect of water and nitrogen supply on biomass and nitrogen use of Chinese violet cress using 15N tracing technique. The presented manuscript contains well designed experiment and nice graphic visualization of results. However, I have two main points that should be revised. First, the methodology of the experiment must be improved and secondly, I am not sure what does the chapter about entropy weight coefficient bring something new to the evaluation of the results (there is no mention of this in the Discussion section). In addition, I have some other comments and recommendations for the authors:

Introduction:

P2 L53-63: P2 L53-63: You should extend the part about the effect of irrigation and nitrogen fertilization on root growth. Nitrogen application changes root distribution in the soil and root:shoot ratio of the plants. For example, there are studies showing that under sufficient nitrogen plant roots do not grow into such depths compared to plants growing under water or nutrient stress. In addition, a higher nitrogen supply lead to a higher root biomass, but also to lower root:shoot ratio.

Methods:

It is not clear from the methodology whether it is a field or laboratory experiment. If it is an experiment in growth chambers, you have to add the size of the pots, soil substrate, climatic conditions, etc. If it is a field experiment, you have to explain how you arranged the control treatment (rain out schelters or there was any ambient precipitation during the experiment?).

P2 L90-93: You mentioned the average rainfall, sunshine duration, extreme temperatures, but you should also add the mean air temperature in the region.

P4 L127-129: You wrote: “…samples of Chinese violet cress plants were collected and fresh weight was measured”, but there is not clear if it is only above-ground biomass or total biomass with roots. You should add how you cut the biomass and from what area (2x2-m?).

Results:

Results are clear and well written.

You should add in all tables and figures that data are means and S.E. or S.D.

P7-9 (chapter 3.5). I am not sure if this chapter contributes to something new to the results found and, in addition, these results (entropy weight coefficients) are not subject to further evaluation in the discussion section and conclusions. I recommend deleting this part or discussed these results in Discussion.

Discussion and Conclusions:

P10 L323-329: You should more discussed potential effect of nitrogen application (positive and also negative) on root spatial distribution and following utilization of water from deeper soil layers.

Conclusions are clear and sufficient.

Author Response

The manuscript is focused on the effect of water and nitrogen supply on biomass and nitrogen use of Chinese violet cress using 15N tracing technique. The presented manuscript contains well designed experiment and nice graphic visualization of results. However, I have two main points that should be revised. First, the methodology of the experiment must be improved and secondly, I am not sure what does the chapter about entropy weight coefficient bring something new to the evaluation of the results (there is no mention of this in the Discussion section). In addition, I have some other comments and recommendations for the authors: Introduction:P2 L53-63: P2 L53-63: You should extend the part about the effect of irrigation and nitrogen fertilization on root growth. Nitrogen application changes root distribution in the soil and root:shoot ratio of the plants. For example, there are studies showing that under sufficient nitrogen plant roots do not grow into such depths compared to plants growing under water or nutrient stress. In addition, a higher nitrogen supply lead to a higher root biomass, but also to lower root:shoot ratio.

Thank you for your suggestion. Indeed, root characteristics under the influence of water and nitrogen are very important for crop water and nitrogen absorption. We have also paid attention to some articles that studying the effect of water, nitrogen or water and nitrogen coupling on crop root and root-shoot ratio. So we added relevant contents in the introduction: Some studies have shown that different water and nitrogen supply may affect root depth, root weight and root-shoot ratio, thus affecting the plant utilization efficiency for water and nitrogen. At the same time, the detailed discussions have been added to the Discussion section.

Methods:It is not clear from the methodology whether it is a field or laboratory experiment. If it is an experiment in growth chambers, you have to add the size of the pots, soil substrate, climatic conditions, etc. If it is a field experiment, you have to explain how you arranged the control treatment (rain out schelters or there was any ambient precipitation during the experiment?).

Thank you for your opinion, yes, we didn't express it clearly. The experiment was conducted using the field block planting, with a single block area of 2 m × 2 m. Each treatment occupied three blocks, and the total experimental area covered an area of 120 m².The experimental site was not isolated from natural rainfall, and CK treatment did not accept additional irrigation water. We have revised it in the paper.

P2 L90-93: You mentioned the average rainfall, sunshine duration, extreme temperatures, but you should also add the mean air temperature in the region.

Yes, we missed the information, thank you for pointing out. In recent years, the extreme maximum temperature is 38.6 ℃, the extreme minimum temperature is -5.8 ℃, and the mean air temperature is 23.6 ℃.

P4 L127-129: You wrote: “…samples of Chinese violet cress plants were collected and fresh weight was measured”, but there is not clear if it is only above-ground biomass or total biomass with roots. You should add how you cut the biomass and from what area (2x2-m?).

Thank you for pointing out this problem. It is true that we have not clearly stated whether it is the whole plant or the aboveground part, and where to sample the plant. In the revised version, we added relevant content. We digged out the samples of the whole plant from the micro-area.

Results:Results are clear and well written.You should add in all tables and figures that data are means and S.E. or S.D.

Thank you for your affirmation. Indeed, a well presented table or figure should contain the information of S.E. or S.D. We explained that in Table 3, some of the evaluation data were from the earlier part, where we have gave the S.E. information. Figure 5 was the calculation result of the entropy method without an S.E.

P7-9 (chapter 3.5). I am not sure if this chapter contributes to something new to the results found and, in addition, these results (entropy weight coefficients) are not subject to further evaluation in the discussion section and conclusions. I recommend deleting this part or discussed these results in Discussion.

Thank you for your suggestion. According to your comments (these results (entropy weight coefficients) are not subject to further evaluation), we have added the description of the entropy results (The evaluation result by entropy weight coefficient in this study can be used as assistance for the practical scheme decision, while when formulating a water-nitrogen strategy, the parameters might need to make minor changes), and added the following discussion:

In this paper, the entropy weight coefficient evaluation method was used to select the most suitable water-nitrogen coupling mode for the Chinese violet cress. Since the selection of the Chinese violet cress water-nitrogen coupling mode involved multiple schemes and multiple indicators, only relying on subjective decision has various limitations, the entropy weight coefficient model provided a relatively more scientific pathway for the selection. However, it should be noted that the accuracy of the entropy weight coefficient evaluation model was affected by multiple factors such as the data quantity, scheme number and the weight distribution. A greater data quantity and scheme number combined with a more reasonable weight distribution led to a more accurate calculation result of the entropy weight coefficient. The evaluation result by entropy weight coefficient in this study can be used as assistance for the practical scheme decision, while when formulating a water-nitrogen strategy, the parameters might need to make minor changes.

Thank again for this very useful suggestion.

Discussion and Conclusions:P10 L323-329: You should more discussed potential effect of nitrogen application (positive and also negative) on root spatial distribution and following utilization of water from deeper soil layers.

Thank you for your suggestion. Indeed, we missed these contents in the original paper. In the revised version, we have added: In addition, water and nitrogen have a significant impact on plant root length and root-shoot ratio, thus affecting the plant water and nitrogen utilization. A study shows that the root and shoot biomass significantly varied with N rates. Another study points out that the root-shoot relationship is more affected by the planting pattern than by the N application rate. Increasing N supply may improve root length density, surface area and root dry weight. However, it should be noticed that compared to under water or nutrient stress, the plant roots under sufficient nitrogen will not grow into such depths.

Round 2

Reviewer 3 Report

In this corrected version of manuscript I have only two comments on the methodology:

L107-108: You write: “The experimental site was not isolated from natural rainfall, and CK treatment did not accept additional irrigation water”. Do you know the amount of ambient precipitation during the experiment? You should mention this in the methods.

L142-143: You write: “…samples of the whole Chinese violet cress plants were digged out from the micro-zone and the fresh weight was measured.” If I understand well, you collected total biomass with roots. You should write: “…samples of the whole Chinese violet cress plants were digged out from the micro-zone and the fresh weight of total biomass was measured.” In addition, you should explain whether you washed the roots with water before weighing or how you proceeded this.

Author Response

In this corrected version of manuscript I have only two comments on the methodology:

L107-108: You write: “The experimental site was not isolated from natural rainfall, and CK treatment did not accept additional irrigation water”. Do you know the amount of ambient precipitation during the experiment? You should mention this in the methods.

Dear editor: thank you for your comments. We have a small weather station to record the monthly rainfall. The total rainfall during the whole experimental period was 255.5 mm, and the lowest rainfall occurred in February 2021, only 4.6 mm and the highest was 68.2 mm in July 2021. We have added.

L142-143: You write: “…samples of the whole Chinese violet cress plants were digged out from the micro-zone and the fresh weight was measured.” If I understand well, you collected total biomass with roots. You should write: “…samples of the whole Chinese violet cress plants were digged out from the micro-zone and the fresh weight of total biomass was measured.” In addition, you should explain whether you washed the roots with water before weighing or how you proceeded this.

Thank you for your reminding. We have added as you pointed. 

Chinese violet cress biomass (fresh weight) (t/ha): At the end of the flowering period (May 27), samples of the whole Chinese violet cress plants were digged out from the micro-zone, the plant root was washed using clean water and then the fresh weight of whole plant was measured.