Optimizing the N Rate for Maize Forage to Balance Profits and N Ecological Stress

Round 1

Reviewer 1 Report

Overview: in this manuscript (ID: agronomy-1609807), the authors provided useful information regarding the effect of N application rate on the production of whole maize (Zea mays L.) plant (WMP) forage and its impact on the environment. The research work has been executed well, and the overall premise looks promising. However, some points need to be addressed as follows:

• Lines 13 and 55: "WMP and NUE" abbreviations should be defined at first mention and used consistently after that.
• In the abstract, the description of the experimental groups has not been provided. Also, add a short conclusion at the end of the abstract.
• Line 37: Are these statistics for China? Please clarify.
• The hypothesis of the study should be clarified before the aim at the end of the Introduction section.
• Line 95: The authors had to justify on what basis they selected the levels of the N application treatment.
• Line 126-130: references number 27 and 28 are secondary citations, not the original. The citation of forage chemical composition should be made to AOAC. Also, NDF and ADF content should be according to Van Soest et al. (1991).
• Line 173: specify which type of ANOVA did you used? One way or two way ANOVA.
• In all Tables, describe all abbreviations used in the tables' footnotes. Also, the sample size per treatment (n= ?) should be stated. Also, add two columns for the stander error of the mean and p-value for each parameter.

Author Response

Dear reviewer,

We appreciate the Agronomy giving us an opportunity to revise our manuscript.

We thank the knowledgeable reviewer for your work and thoughtful comments on our previous manuscript. We have carefully taken the comments into consideration in preparing this revision, and hope to have produced a paper that is both clearer and more compelling.

We appreciate that you have given us positive comments, which will help us enhance the value of our research. The your work will be very helpful in our future research efforts. We have learned so much from the revision, all the hard work is worth it, and we feel more confident for the manuscript. We are looking forward to receiving the valuable comments from Agronomy. 

According the comments, the reviewer considered that the forage price was established and does not change with changes in feeding quality and forage quality, and feeding quality forage quality belonged animal science community. So, we agree with the comments and deleted the part of forage quality and feeding quality in the paper.

Our responses to the review comments are inserted in the comments.

Thank you very much for all your help.

Best wishes,

Sincerely yours

Liu and Han

Overview: in this manuscript (ID: agronomy-1609807), the authors provided useful information regarding the effect of N application rate on the production of whole maize (Zea mays L.) plant (WMP) forage and its impact on the environment. The research work has been executed well, and the overall premise looks promising. However, some points need to be addressed as follows:

• 1. Lines 13 and 55: "WMP and NUE" abbreviations should be defined at first mention and used consistently after that.

Response: We agree and have revised it according to your comments.

• 2. In the abstract, the description of the experimental groups has not been provided. Also, add a short conclusion at the end of the abstract.

Response: We agree and have revised it according to your comments.

We add “Therefore, in WMP forage production, optimizing N application rate by ecological criteria could maintain a high forage yield and economic profit, but greatly reduce input costs and ecological stress, maximizing ecological profit.” 

• 3. Line 37: Are these statistics for China? Please clarify.

Response: We agree and have revised it according to your comments.

We revised that into “Because of its high yield, its high quality output and its relatively low input requirements, maize is widely used to produce forage worldwidely, especially for the dairy industry [3]. Whole maize plant (WMP) forage is a primary source of energy and fiber for dairy cows [4]. In China, the consumption of maize used as forage increased from 85 million tons in 2000 to 157 million tons in 2018 [5]”

• 4. The hypothesis of the study should be clarified before the aim at the end of the Introduction section.

Response: We agree and have revised it according to your comments.

“To fill in this omission, we carried out a 2-year field study with the aim to (1) measure the effect of the N application rate on the growth, yield and feeding quality of WMP forage, (2) estimate the N losses, ecological costs from N pollution and economic and ecological profits, and propose an optimized N application rate, and (3) confirm whether applying ecological criteria is an efficient way to gauge its efficiency.” was revised into “To address this issue, we carried out a 2-year field study with the aim to (1) study the effect of the N application rate on the growth and yield of WMP forage, the ecological costs from N losses, and economic and ecological profits, (2) propose an optimized N application rate, and (3) evaluate the efficiency of ecological criteria in WMP forage production.”

• 5. Line 95: The authors had to justify on what basis they selected the levels of the N application treatment.

Response: On the base of our previous research, N application rate exceeding about 300 kg N ha^-1 did not improve maize yield (Han, 2020). Therefore, N application rate ranged from 0 to 400 kg N ha^-1 for optimizing N application rate. We declared that in the text.

“The experiment deployed a randomized complete block design, which included five N application treatments (0, 100, 200, 300 and 400 kg N ha^-1) with three replications.” was revised into “On the base of our previous research, N application rate exceeding 300 kg N ha^-1 did not improve maize yield (Han, 2020). Therefore, five N application treatments (0, 100, 200, 300 and 400 kg N ha^-1) were set in our experiment. The treatments with three replications were randomly.” 

• 6. Line 126-130: references number 27 and 28 are secondary citations, not the original. The citation of forage chemical composition should be made to AOAC. Also, NDF and ADF content should be according to Van Soest et al. (1991).

Response: We agree. Other reviewer stated that forage quality which belongs animal science community didnot help in the paper. So, we deleted the part of forage quality and feeding quality.

• 7. Line 173: specify which type of ANOVA did you used? One way or two way ANOVA.

Response: It is one way ANOVA, and We have revised it.

•  
• 8. In all Tables, describe all abbreviations used in the tables' footnotes. Also, the sample size per treatment (n= ?) should be stated. Also, add two columns for the stander error of the mean and p-value for each parameter.

Response: We agree and have revised it according to your comments. We avoided abbreviations in the table head, and add p-value for each parameter. It seems the stander error of the mean here didnot help, which made table wide, and we had the letters for the data.

Reviewer 2 Report

Overall an interesting paper that addresses a timely issue.  I have noted some editorial and technical comments below.  The authors have done a good job of conducting and summarizing this research.  The English is good but might benefit from a quick review.  I have tried to address most but not all concerns.  I don’t have any major concerns with the conclusions made by the authors.  I would say that in many areas the animal manure is recycled to corn forage production fields and this really reduces or eliminates the need for fertilizer..but also creates other environmental issues.  Perhaps a statement describing the production system that relies mostly on fertilizer would be useful.

Abstract

15 I would add a statement here that describes some of the optimum rates you calculated in Table 4.

Introduction

37 increased instead of “went up”

48 nutritional

56 Not sure what you mean by agronomic efficiency …delete or define better..yield/unit N?

60 maintaining

67 delete “of”

72 To address this issue… might be better than to fill in this omission

74 I might split objective 2 into 2 or 3 objectives and eliminate the “ands”

Materials and Methods

84-87 I might use the past tense for the soil properties   The soil’s physicochemical properties were as follows: the total N concentration was 1.71 g kg-1

96 You probably assigned the treatments randomly in each of the three blocks and did not randomly assign the plots across the three blocks..this would not be a randomized complete block.

132 I would prefer if you used the word estimated rather than determined since you did not measure these.  Then make sure you indicate in the results and discussion that they are estimated.  I would actually label them somehow  like this…. N2O emissions (est.)

146 I think you need a statement here like you had on line 138.

149 I would appreciate some explanation as to how these numbers were derived so I don’t have to read the original paper.  Just a couple sentences.

Results

193 I might use forage DM yield here and in the table header

202 line seems out of place in first three columns in Table 2 Probably only need one kg N ha-1 in header

213 Check the units on the Fertilizer N productivity..I think you should have kg N in the denominator

242 Forage Yield should not be bold or underlined in Table 4. Perhaps there should be a Header title above such as Parameter for the first column.

247 Did you measure any of this or are you speculating about it?  I might add a qualifier like…apparently improved the light interception… or remove the things you didn’t actually measure.

255 Not sure this sentence is needed.  I might delete.

259 to 266 This seems to be a literature review.  I might delete.

267 I would add estimated to the ecological costs and N losses since you did not really measure them

269 I might reorganize this section a to first discuss the impact of increasing N rates on increasing losses, then increasing costs and then decreasing profits.

290 was 21% lower and 37% lower

295 Therefore, using the ecological criteria, the recommended

296 248 and 245 no decimals needed here

297 We also furtherly optimize…change to …We also addressed…. This avoids using optimize twice in the same sentence.

303 omit decimals here too

Author Response

Dear reviewer,

We appreciate the Agronomy giving us an opportunity to revise our manuscript.

We thank the knowledgeable reviewer for your work and thoughtful comments on our previous manuscript. We have carefully taken the comments into consideration in preparing this revision, and hope to have produced a paper that is both clearer and more compelling.

We appreciate that you have given us positive comments, which will help us enhance the value of our research. The work will be very helpful in our future research efforts. We have learned so much from the revision, all the hard work is worth it, and we feel more confident for the manuscript. We are looking forward to receiving the valuable comments from Agronomy. 

According the comments, the reviewer considered that the forage price was established and does not change with changes in feeding quality and forage quality, and feeding quality forage quality belonged animal science community. So, we agree with the comments and deleted the part of forage quality and feeding quality in the paper.

Our responses to the review comments are inserted in the comments.

Thank you very much for all your help.

Best wishes,

Sincerely yours

Liu and Han

Abstract

15 I would add a statement here that describes some of the optimum rates you calculated in Table 4.

 Response: We agree and have revised it according to your comments. We described the highest ecological profit in the Abstract.

Introduction

37 increased instead of “went up”41

Response: We agree and have revised it according to your comments.

48 nutritional52

Response: We agree and have revised it according to your comments.

56 Not sure what you mean by agronomic efficiency …delete or define better..yield/unit N?

Response: We agree and have revised it according to your comments.

 “agronomic efficiency” was replaced by yield.

60 maintaining65

Response: We agree and have revised it according to your comments.

67 delete “of”

Response: We agree and have revised it according to your comments.

72 To address this issue… might be better than to fill in this omission

Response: We agree and have revised it according to your comments.

74 I might split objective 2 into 2 or 3 objectives and eliminate the “ands”

Response: We agree and have revised it according to your comments.

“To fill in this omission, we carried out a 2-year field study with the aim to (1) measure the effect of the N application rate on the growth, yield and feeding quality of WMP forage, (2) estimate the N losses, ecological costs from N pollution and economic and ecological profits, and propose an optimized N application rate, and (3) confirm whether applying ecological criteria is an efficient way to gauge its efficiency.” was revised into “To address this issue, we carried out a 2-year field study with the aim to (1) study the effect of the N application rate on the growth and yield of WMP forage, the ecological costs from N losses, and economic and ecological profits, (2) propose an optimized N application rate, and (3) evaluate the efficiency of ecological criteria in WMP forage production.” 

Materials and Methods

84-87 I might use the past tense for the soil properties   The soil’s physicochemical properties were as follows: the total N concentration was 1.71 g kg-1

Response: We agree and have revised it according to your comments.

96 You probably assigned the treatments randomly in each of the three blocks and did not randomly assign the plots across the three blocks..this would not be a randomized complete block.

Response: We agree and have revised it according to your comments.

“The experiment deployed a randomized complete block design, which included five N application treatments (0, 100, 200, 300 and 400 kg N ha^-1) with three replications.” was revised into “On the base of our previous research, N application rate exceeding 300 kg N ha^-1 did not improve maize yield (Han, 2020). Therefore, five N application treatments (0, 100, 200, 300 and 400 kg N ha^-1) were set in our experiment. The treatments with three replications were randomly.”

132 I would prefer if you used the word estimated rather than determined since you did not measure these.  Then make sure you indicate in the results and discussion that they are estimated.  I would actually label them somehow  like this…. N2O emissions (est.)

Response: We agree and have revised it according to your comments. “estimated N₂O emissions, estimated NH₃ volatilization, estimated N leaching, estimated N loss” was used through the paper.

146 I think you need a statement here like you had on line 138.

Response: We agree and have revised it according to your comments.

149 I would appreciate some explanation as to how these numbers were derived so I don’t have to read the original paper.  Just a couple sentences.

Response: We agree and have revised it according to your comments.

“ the ecological cost of N leaching (the abatement cost of reducing N from agricultural drainage water), NH₃ emissions (the cost of human health damage) and N₂O (the cost of climate change) are taken to be 2.71, 1.3 and 1.24 $ (kg N)^-1, respectively” was revised into “the ecological cost of N leaching (the abatement cost of reducing N from agricultural drainage water), NH₃ emissions (the cost of human health damage) and N₂O (the cost of climate change) are taken to be 2.71, 1.3 and 1.24 $ (kg N)^-1, respectively”

Results

193 I might use forage DM yield here and in the table header

Response: We agree and have revised it according to your comments.

202 line seems out of place in first three columns in Table 2 Probably only need one kg N ha-1 in header

Response: We agree and have revised it according to your comments.

213 Check the units on the Fertilizer N productivity..I think you should have kg N in the denominator

Response: We agree and have revised it according to your comments. The unit was correct by $ (kg N)-1.

242 Forage Yield should not be bold or underlined in Table 4. Perhaps there should be a Header title above such as Parameter for the first column.

Response: We agree and have revised it according to your comments.

247 Did you measure any of this or are you speculating about it?  I might add a qualifier like…apparently improved the light interception… or remove the things you didn’t actually measure.

Response: Yes, the data were shown in Table S1.

255 Not sure this sentence is needed.  I might delete.

Response: We agree and have revised it according to your comments.

259 to 266 This seems to be a literature review.  I might delete.

Response: We agree and have revised it according to your comments. We removed some literature review, and made it more concise.

The part was revised into “The economic profit is considered as more important indicator for evaluating agricultural production, compared to agronomic benefits (yield) [14]. However, ecological profit, in which economic profit minuses the ecological cost from N pollution, should be considered together with agronomic benefits and economic profits in the quest to maintain high economic profits while simultaneously reducing environmental pollution.” 

267 I would add estimated to the ecological costs and N losses since you did not really measure them

Response: We agree and have revised it according to your comments.

269 I might reorganize this section a to first discuss the impact of increasing N rates on increasing losses, then increasing costs and then decreasing profits.

Response: We agree and have revised it according to your comments.

“As N application rate increased, the ecological costs from N pollution increased. ” was revised into “Increasing N rates on resulted in more N losses, and then increased the ecological costs from N pollution, decreasing the ecological profits.” 

290 was 21% lower and 37% lower

Response: We agree and have revised it according to your comments.

295 Therefore, using the ecological criteria, the recommended

Response: We agree and have revised it according to your comments.

296 248 and 245 no decimals needed here

Response: We agree and have revised it according to your comments.

297 We also furtherly optimize…change to …We also addressed…. This avoids using optimize twice in the same sentence.

Response: We agree and have revised it according to your comments.

Author Response File: Author Response.docx

Reviewer 3 Report

I appreciate the application of agronomic research to the producer decision criteria. The optimal rate of N is a worthwhile objective. Incorporating ecological costs is a worthwhile, though challenging, cost to be considered in optimal N decisions.

However, I found the paper confusing because you tried to do too much. I think the paper should have all the information on feeding quality moved to a separate paper. In this paper focus only on the optimal N rate of the forage producer. If you were able to incorporate the feeding value with the market price of the forage, it would be a useful addition to this paper. But, if I understand the paper correctly, the forage price is established and does not change with changes in feeding quality.

I also think that some parts of the paper need more detail. For example, you defined NUE in a way that is used in no other paper I found. NUE usually is expressed as a percentage. You defined it as $/kg. Why? Discuss NUE in more detail and why you would change its common use. Better yet, choose a different term to use. You also introduce “ecological profit” without any explanation other than the equation. Why is that equation proper?

Below are some detailed notes I took as I reviewed the paper.

• Abstract
  1. uses WMP before defining it.
  2. Optimal N eco > optimal N profit > optimal N yield. I think the signs are backwards. Table 4 presents the optimal N rate for ecological profit as less than that for economic profit.
  3. Ecological profit is a confusing term to me. Common in other literature?
• L37 need geographic limits for consumption estimates – China, world, province in China?
• L45 usually in plants I think “fat” is called “oil.”
• Is WMP common term or is silage common in the research literature? I normally see the word “corn silage.”
• L62ff might benefit from a brief discussion of internal and external costs; private and societal costs.
• A confusion of mine that may not be to plant researchers who work in this area. L104 to 109. Initial soil samples at 20 cim, final soil samples at 100 cm. This is used to measure NO3 content (eq 14). Are different depths appropriate? Eq14 uses depth in the equation but the text in L104-109 says there were 5 consecutive 20 mm depths. Which depth is being used? Eq 14 has no summation sign to indicate all depths were used.
• L134
  1. The N losses equations seem simplistic. There are no variables for soil type, precipitation, temperature, etc.
  2. The reference to Cui et al does show these equations in their Extended Data figures.
• L141 The cost of inputs is the same regardless of the N applied. Harvest may be a function of yield. Higher yields will have a higher harvest cost.
• L144 prices of N, P and K are given without references. This makes the analysis questionable. Why those prices chosen? Are they historical or forecasted? In a centrally planned economy, are market prices a given?
• L148 2.71 and 1.3 are from  references within https://doi.org/10.1111/j.1461-0248.2011.01631.x as referenced in [15]. I prefer going to the original source – original data for $2.71 is from 2010 in Missisippi River Basin abatement costs, $1.3 from lower bound of 2011 data of human health costs, 1.24 from 2010 data of anticipated damages of climate change. The author should have a paragraph detailing that the prices are research estimates rather than market estimates and go to the original sources so the dating of the estimates is revealed.
• Eq 6 of ecological profit is new to me. Any other references for this equation? If this is a unique contribution on this paper, spend a little time describing its importance.
• Eq 7-11. My recommendation is that these equations and their subsequent use in this paper be moved to a different paper. Unless you are going to have the price of forage influenced by the feeding characteristics of the forage, it offers no benefit to this paper on optimal N rate.
• L165 NUE = Y/N uptake. The definition of NUE is different than any I have seen. Usually the unit for NUE is kg/kg. You have it as $/kg. Explain why. Should N uptake be N application?
• Eq 13. Yo is ecological profit with N = 0. Should it be compared to the optimal economic N application rate? If not, the fertilizer N productivity may be overestimated.
• L184 discusses forage quality increasing with higher N rates. But I don’t think the value of silage was increased as quality increased.
• L197 is an incomplete sentence.
• Table 2. The values in this table are calculated from Eq 1-3. How can you have statistical significance of modelled estimates? I confirmed that NH3 estimates are the from Eq 2.
• Table 3. Ecological profit is greater than Economic profit at many N levels. If you subtract a cost (see Table 2) from the economic profit, you should see Ecological profit as less than economic profit.
• You reported CP…NFE (line 126) but never reported them in a table. You went straight to using them in an equation. The discussion would be much simpler to give the measured variable statistics and then discuss the direction that GE, ED…GI (eq 7-11) went. I think all equations were monotonic so the direction of movement would be simple to explain without needing a table.
• Discuss ecological profit and ecological cost. Why try to estimate ecological profit when it is just a further adjustment to ecol cost?
• Regression equations in Table S3 are not helpful. They are regressions from modelled data and therefore have a high R2. Results from models give high R2 but provide no data above the underlying data. They give the impression of great fit that doesn’t necessarily exist.
• Table S1 should be in the paper itself.
• Is revenue price x fresh matter (table S1) or times dry matter?
• Table S2 should be in a paper to the animal science community. Putting it here and trying to estimate forage feeding characteristics was too much and too confusing.
• Table 4. The optimized N rate for Forage yield exceeds the rate studied. Can you have out of bounds results. Would that not indicate that you need to have expanded the bounds of your independent variable (N)?

Author Response

Dear reviewer,

We appreciate the Agronomy giving us an opportunity to revise our manuscript.

We thank the knowledgeable reviewer for your work and thoughtful comments on our previous manuscript. We have carefully taken their comments into consideration in preparing this revision, and hope to have produced a paper that is both clearer and more compelling.

We appreciate that you have given us strict criticisms and comments, which will help us enhance the value of our research. The work will be very helpful in our future research efforts. We have learned so much from the revision, all the hard work is worth it, and we feel more confident for the manuscript. We are looking forward to receiving the valuable comments from Agronomy. 

According the comments that the forage price was established and does not change with changes in feeding quality and forage quality, and feeding quality forage quality belonged animal science community. So, we agree with the comments and deleted the part of forage quality and feeding quality in the paper. We replaced NUE by N productivity. N productivity seems more reasonable than NUE. N productivity is the ecological profit produced by per kg N. The conception of ecological profit was used in some paper, i.e., Han et al., 2020. In the research by Gou (2021), “ecological profit” was called by Economic net profit, but readers may feel confused between economic net profit and Economic profit in our paper. So we use ecological profit.

Our responses to the review comments are inserted in the comments.

Thank you very much for all your help.

Best wishes,

Sincerely yours

Liu and Han

Abstract

1. uses WMP before defining it.

Response: We agree and have revised it according to your comments.

2.Optimal N eco > optimal N profit > optimal N yield. I think the signs are backwards. Table 4 presents the optimal N rate for ecological profit as less than that for economic profit.

Response: We agree and have revised it according to your comments.

3.Ecological profit is a confusing term to me. Common in other literature?

Response: The conception of ecological profit was used in some paper, i.e., Han et al., 2020. In the research by Gou (2021), “ecological profit” was called by Economic net profit, but readers may feel confused between Economic net profit and Economic profit in our paper. So we use ecological profit.

Han, K., Yin, F., Liu, P. Planting density and N application rate balance maize agronomic and environmental effect. Nutr. Cycl. Agroecosys.. 2020, 117, 337-349.  

Guo, X., Zhao, D., Zhuang, M., Wang, C., Zhang, F. Fertilizer and pesticide reduction in cherry tomato production to achieve multiple environmental benefits in Guangxi, China. Science of the Total Environment. 2021, 793, 148527.

4. L37 need geographic limits for consumption estimates – China, world, province in China?

Response: We agree and have revised it according to your comments.

 “Because of its high yield, its high quality output and its relatively low input requirements, maize is widely used to produce forage, especially for the dairy industry [3]. Whole maize plant (WMP) forage is a primary source of energy and fiber for dairy cows [4]. The consumption of maize used as forage went up from 85 million tons in 2000 to 157 million tons in 2018 [5],” was revised into “Because of its high yield, its high quality output and its relatively low input requirements, maize is widely used to produce forage worldwidely, especially for the dairy industry [3]. Whole maize plant (WMP) forage is a primary source of energy and fiber for dairy cows [4]. In China, the consumption of maize used as forage went up from 85 million tons in 2000 to 157 million tons in 2018.”

5. 5. L45 usually in plants I think “fat” is called “oil.”

Response: We agree and have revised it according to your comments.

6. 6. Is WMP common term or is silage common in the research literature? I normally see the word “corn silage.”

Response: WMP forage is common term in maize forage production. Corn silage is the harvested maize plants that is stored and fermented, while the forage refers to the fresh plants (i.e., the whole maize plant, maize straw, or maize grain) or treated plants. In our study, we used the whole maize plant including ear and straw as forage, so WMP forage is more reasonable.

7. 7. L62ff might benefit from a brief discussion of internal and external costs; private and societal costs.

Response: We agree and have revised it according to your comments.

“On top of that, increasing the N input beyond this threshold reduces the NUE and increases the economic cost, which negatively affects the agronomic efficiency (i.e., yield) and economic profit” was revised into “On top of that, increasing the N input beyond this threshold reduces the N use efficiency and increases the economic cost, which negatively affects forage yield and economic profit (income subtracts productive cost)”

8. 8. A confusion of mine that may not be to plant researchers who work in this area. L104 to 109. Initial soil samples at 20 cim, final soil samples at 100 cm. This is used to measure NO3 content (eq 14). Are different depths appropriate? Eq14 uses depth in the equation but the text in L104-109 says there were 5 consecutive 20 mm depths. Which depth is being used? Eq 14 has no summation sign to indicate all depths were used.

Response: In field study, soil physical and chemical properties should be shown to make sure that the experiment could be recurred. Before planting, the 20 cm surface soil is sampled (n=5) in the whole field to detected the soil physical and chemical properties. In our study, we studied on the soil NO₃^-1 leaching, so we should detect the soil NO₃^-1 in maize rhizosphere soil layers in each plots before planting and after harvesting. Most of maize root distributs in 0-100cm soil layers. So we sampled 5 consecutive 20 mm depths in 0-100cm soil layers to detect soil NO₃^-1 leaching.

9. 9. L134

(1) The N losses equations seem simplistic. There are no variables for soil type, precipitation, temperature, etc.

(2) The reference to Cui et al does show these equations in their Extended Data figures.

Response: In field study, the actual measured data is the closest to the truth and is the best choice. It is also a valid choice to use reliable formulas and models in the absence of measured data. The formula of N loss by Cui et al. is based on the experiment of summer maize in North China plain for multiple locations over the years and is a reliable formula of N loss in this area. Therefore, the experiment of N loss in this area fits this equation, which is inculded the average state of the climatic and soil factors in this area. Therefore, in our study, the use of this formula to estimate nitrogen loss can reflect certain facts. Even when relevant nitrogen loss data were measured, they were within the significance range for these equations.

10. L141 The cost of inputs is the same regardless of the N applied. Harvest may be a function of yield. Higher yields will have a higher harvest cost.

Response: In the practical production, the harvest price was measured by land area, not by weight. The harvest price measured by weight would affect work efficiency.

11. L144 prices of N, P and K are given without references. This makes the analysis questionable. Why those prices chosen? Are they historical or forecasted? In a centrally planned economy, are market prices a given?

Response: The price of N, P and K fertilizer fluctuated due to the market factors. The price of N, P and K fertilizer was their average price obtained by the market survey in the local market during the two years experiment. We declared that in the text.

“The price of N, P and K fertilizer was 0.651 $ (kg N)^-1, 1.7 $ (kg P₂O₅)^-1 and 1.56 $ (kg K₂O)^-1, respectively” was revised into “Depending on the market survey in the study period, the price of N, P and K fertilizer was 0.651 $ (kg N)^-1, 1.7 $ (kg P₂O₅)^-1 and 1.56 $ (kg K₂O)^-1, respectively.”

12.·L148 2.71 and 1.3 are from  references within https://doi.org/10.1111/j.1461-0248.2011.01631.x as referenced in [15]. I prefer going to the original source – original data for $2.71 is from 2010 in Missisippi River Basin abatement costs, $1.3 from lower bound of 2011 data of human health costs, 1.24 from 2010 data of anticipated damages of climate change. The author should have a paragraph detailing that the prices are research estimates rather than market estimates and go to the original sources so the dating of the estimates is revealed.

Response: We agree and have revised it according to your comments. We cited the original references.

the ecological cost of N leaching, NH₃ emissions and N₂O are taken to be 2.71, 1.3 and 1.24 (kg N)^-1, respectively” was revised into “the ecological cost of N leaching (the abatement cost of reducing N from agricultural drainage water), NH₃ emissions (the cost of human health damage) and N₂O (the cost of climate change) are taken to be 2.71, 1.3 and 1.24 (kg N)^-1, respectively”.

13.·Eq 6 of ecological profit is new to me. Any other references for this equation? If this is a unique contribution on this paper, spend a little time describing its importance.

Response: The conception of ecological profit was used in some paper, i.e., Han et al., 2020. In the research by Guo (2021), “ecological profit” was called by Economic net profit, but readers may feel confused between economic net profit and Economic profit in our paper. So we use ecological profit.

Han, K., Yin, F., Liu, P. Planting density and N application rate balance maize agronomic and environmental effect. Nutr. Cycl. Agroecosys.. 2020, 117, 337-349.  

Guo, X., Zhao, D., Zhuang, M., Wang, C., Zhang, F. Fertilizer and pesticide reduction in cherry tomato production to achieve multiple environmental benefits in Guangxi, China. Science of the Total Environment. 2021, 793, 148527.

14.·Eq 7-11. My recommendation is that these equations and their subsequent use in this paper be moved to a different paper. Unless you are going to have the price of forage influenced by the feeding characteristics of the forage, it offers no benefit to this paper on optimal N rate.

Response: We agree and have revised it according to your comments. The message of forage quality was deleted.

15.·L165 NUE = Y/N uptake. The definition of NUE is different than any I have seen. Usually the unit for NUE is kg/kg. You have it as $/kg. Explain why. Should N uptake be N application?

Response: We replaced NUE by N productivity. N productivity seems more reasonable than NUE. N productivity is the ecological profit produced by per kg N.

16. Eq 13. Yo is ecological profit with N = 0. Should it be compared to the optimal economic N application rate? If not, the fertilizer N productivity may be overestimated.

Response: I do not understand the comments. The ecological profit with N rate of x subtracted the ecological profit without N application, and difference value was the ecological profit produced by N application with N rate of x. So it wascalled fertilizer N productivity.

17.·L184 discusses forage quality increasing with higher N rates. But I don’t think the value of silage was increased as quality increased.

Response: We agree and have revised it according to your comments. The message of forage quality was deleted.

18.·L197 is an incomplete sentence.

Response: We agree and have revised it according to your comments. 

“When N application rates increased from 0 to 400 kg N ha^-1, N₂O emissions, NH₃ volatilization, N leaching, N loss and ∆Soil NO₃^--N” was revised into “When N application rates increased from 0 to 400 kg N ha^-1, N₂O emissions, NH₃ volatilization, N leaching, N loss and ∆Soil NO₃^--N increased” 

19. Table 2. The values in this table are calculated from Eq 1-3. How can you have statistical significance of modelled estimates? I confirmed that NH₃estimates are the from Eq 2.

Response: We agree and have revised it according to your comments. The letters were deleted.

20. Table 3. Ecological profit is greater than Economic profit at many N levels. If you subtract a cost (see Table 2) from the economic profit, you should see Ecological profit as less than economic profit.

Response: We thank you so much, and we re-checked and correct it. And we also correct the regression equations of ecological profit, as well as the ecological profit in Table 4.

21.·You reported CP…NFE (line 126) but never reported them in a table. You went straight to using them in an equation. The discussion would be much simpler to give the measured variable statistics and then discuss the direction that GE, ED…GI (eq 7-11) went. I think all equations were monotonic so the direction of movement would be simple to explain without needing a table.

Response: We agree and have revised it according to your comments. The message of forage quality was deleted.

21.·Discuss ecological profit and ecological cost. Why try to estimate ecological profit when it is just a further adjustment to ecol cost?

Response: We estimate the ecological cost, which is essentially the loss of the economy. The purpose of agricultural production is to obtain food and produce economic value, but agricultural production will produce ecological cost and cause economic loss. Therefore, the combination of agricultural economic value and ecological cost is the net value created by agricultural production, which is ecological benefit in our paper.

22. Regression equations in Table S3 are not helpful. They are regressions from modelled data and therefore have a high R2. Results from models give high R2 but provide no data above the underlying data. They give the impression of great fit that doesn’t necessarily exist.

Response: Regression equations were obtained on the base of our measured data. Regression equations was the deep analysis on measured data. We only set N treatment in 0, 100, 200, 300, 400 kg N ha^-1, and we just judge the highest yield in the five pionts. But, i.e., the 320 kg N ha^-1 might produce the highest yield, which could not be known by the measured data. If we used regression equations of measured data, we could find the highest yield and the N rate. That could help farmers optimized their production. Therefore, regression equations were still valuable for evaluating forage production in our paper.

23.Table S1 should be in the paper itself.

Response: We agree and have revised it according to your comments. It was combined into Table 1.

24.Is revenue price x fresh matter (table S1) or times dry matter?

Response: When maize forage was sold, maize forage was fresh matter. But water content would be considered, and the price depended on fresh matter with 60% water content.

25.Table S2 should be in a paper to the animal science community. Putting it here and trying to estimate forage feeding characteristics was too much and too confusing.

Response: We agree and have revised it according to your comments. The message of forage quality was deleted.

26.·Table 4. The optimized N rate for Forage yield exceeds the rate studied. Can you have out of bounds results. Would that not indicate that you need to have expanded the bounds of your independent variable (N)?

Response: The optimized N rate for forage yield is obtained by equation regression, which is reliable even though it is out of range because the regression equation is significant. When the optimized N rate for forage yield exceeding 300 kg N ha^-1, the improvement in yield limited. So we didnot set the treatment of 500 kg N ha^-1.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors adequately responded to all comments and performed all required modifications

Author Response

Dear reviewer,

 We appreciate that you have given us positive comments, which will help us enhance the value of our research. The work will be very helpful in our future research efforts. 

Thank you very much for all your help.

Hope everything goes well

Sincerely yours

Liu and Han

Reviewer 3 Report

I am amazed at the speed with which you revised the paper. I don't know if the other reviewers had as extensive of edits as I suggested but you seemed to do a good job of taking into account my major concerns.

My remaining concerns are:

1. the prices (L157) requires a citation in my opinion. The prices of P2O5 and K2O are vastly different than the prices you would find in the U.S. I have no knowledge of fertilizer prices in Asia or Europe but as an American reading the paper, the prices stood out to me. The entire analysis depends on prices used. Different prices will yield different conclusions.
2. the prices for pollution (Eq 5) are from credible citations but very different times and locations. I'm not sure they are appropriate for this analysis.
3. L236. A regression of N on profit is not necessary or valid. The prices should be applied to a regression of N on yield. The only observed data that needs to be used in regression is contained in Table 1. Once the yield regression is completed, you can apply prices to it to get estimated profits.
4. I would put the assumed costs of N, P2O5, K2O, forage and N pollution as a footnote in Table 4. The entire analysis depends on the price relationships used so it needs to be clear that these results are only for this pricing scenario.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 We thank the knowledgeable reviewer for your work and thoughtful comments on our previous manuscript. We have carefully taken their comments into consideration in preparing this revision, and hope to have produced a paper that is both clearer and more compelling.

 Our responses to the review comments are inserted in the comments.

Thank you very much for all your help.

Best wishes,

Sincerely yours

Liu and Han

1. the prices (L157) requires a citation in my opinion. The prices of P2O5 and K2O are vastly different than the prices you would find in the U.S. I have no knowledge of fertilizer prices in Asia or Europe but as an American reading the paper, the prices stood out to me. The entire analysis depends on prices used. Different prices will yield different conclusions.

Response: Different prices will yield different conclusions, we agreed that. So, we used the average price during the two years experiment, which more reflect the local practical production in China, compared to a citation. The prices in a citation is its local prices which is different with ours. In different countries, the prices vary greatly, but we use our local prices to reflect the forage production in China. If the U.S. farmer read the paper, they could evaluate the profit using their local prices.

2. The prices for pollution (Eq 5) are from credible citations but very different times and locations. I'm not sure they are appropriate for this analysis.

Response: it is not the best choice that we used, but there is not relevant prices research in China. The citations is alternative for us. The prices still could reflect same truth. In different countries, the prices vary greatly, but the difference does not affect the effect tendency of N rate on profits. Therefore, it is still significative for maize forage production.

3. A regression of N on profit is not necessary or valid. The prices should be applied to a regression of N on yield. The only observed data that needs to be used in regression is contained in Table 1. Once the yield regression is completed, you can apply prices to it to get estimated profits.

Response: Profit is improtant for farmers. The farmers used their prices instead of ours using the regressions. The difference does not affect the effect tendency of N rate on profits. Therefore, it is still significative for maize forage.

4. I would put the assumed costs of N, P2O5, K2O, forage and N pollution as a footnote in Table 4. The entire analysis depends on the price relationships used so it needs to be clear that these results are only for this pricing scenario.

Response: We agree and have revised it according to your comments. The assumed costs of N, P₂O5, K₂O, forage and N pollution were added as a footnote in Table 4.

Line 41: Response: We agree and have revised it according to your comments.

“worldwidely” is revised into “worldwide”.

Line 62-63: Response: We agree and have revised it according to your comments.

“which negatively affects biomass yield and economic profit (income subtracts productive cost)” is revised into “which negatively affects biomass yield and economic profit (income minus production)”.

Line 62-63: Response: We agree and have revised it according to your comments.

“The treatments with three replications were randomly.” Was deleted

Line 157: Response: We agree and have revised it according to your comments.

“Depending on the market survey in the study period” is revised into “According a market survey of Chinese fertilizer prices during 2017-2018.”

Line 250: Response: We agree and have revised it according to your comments.

“optimized” was deleted

Table 1-3: Response: We agree and have revised it according to your comments.

p value for N rate were deleted