Long-Term Nitrogen Fertilization Impacts on Soil Bacteria, Grain Yield and Nitrogen Use Efficiency of Wheat in Semiarid Loess Plateau, China

Round 1

Reviewer 1 Report

The article has novelty of the content, potential impact in the relevant field of research, and study design and appropriate methodology.

Author Response

Review 1:

• The article has novelty of the content, potential impact in the relevant field of research, and study design and appropriate methodology.

Authors’ response: Thank you for your approval!

Reviewer 2 Report

 

The manuscript “Long-term nitrogen fertilization impacts on soil  bacteria, grain yield and nitrogen use efficiency of wheat in semiarid Loess Plateau, China” represents an interesting study and is generally well written. It is highly relevant showing on the background of increasing demand for food and related nitrogen fertilisation that optimum levels for spring wheat mono cropping are about half of the average amounts applied. N fertilization rate of 105 kg  N per ha and year was most suitable for improving spring wheat yield and Nitrogen use efficiency (NUE), and maintain a diversified soil bacterial community. Still the relationship between soil bacteria community and grain yield and NUE was non-significant.

At this point the manuscript remains inconclusive and the study and discussion of the results shows deficits. Although yield plays a central role for optimum fertilization no data are given on quantity and stability over the observed 16 year time period. Stability is almost as import to farmers as quantity and needs to be discussed. The 105 kg N per ha are not related to the amount of N removed from the field, so it is unclear how much needs to be replaced and which amount stays within the field system. Furthermore soil bacterial community diversity is often discussed with plant health as another important factor for yield. No information is given on diseases and pest management apart from the use of herbicides. Overall the soil bacterial community is likely to be fluctuating within the season and over the time of the experiment so minor differences between the treatments are more than likely to detect. The study presents only a single measurement at the end of the experiment and lacks the discussion of the fluctuation on the significance of the results. Apart from this the relevance of the cited literature for the context of this study could be improved in terms of what were the findings or conclusion in the citation and how does this specifically relate to the presented study. The manuscript remains occasionally with rather general statements, which are difficult to follow and relate.

Due to these deficits I cannot recommend this manuscript for publication.

Some remarks and typos with reference to Line

28 typo no instead of No

51 For readability NUE abbreviation should be explained introduction and longer text passages and not only in the abstract and Material and Methods part 

75 typo soils instead of solis

103-104 fungicides, insecticides? More importantly which pests were present and how did they get controlled? ( eg Septoria, Ptr, Take All)

101 same variety for 16 years?

103 sampling area or plots?

141 chimers?

107 only single timepoint for soil sampling. root biomass was removed, but not measured?

153-4 every year or in 2018 only

190 what was the average grain yield, how did this vary over the years

277 please add numbers to relatively

291-3 sentences are unclear. please rephrase.

 

Figure 2 similar x axis (unit-distance) would facilitate the comparison. Then differences in units makes it difficult to recognise and compare major and minor effects.

Author Response

Review 2:

• The manuscript “Long-term nitrogen fertilization impacts on soil bacteria, grain yield and nitrogen use efficiency of wheat in semiarid Loess Plateau, China” represents an interesting study and is generally well written. It is highly relevant showing on the background of increasing demand for food and related nitrogen fertilisation that optimum levels for spring wheat mono cropping are about half of the average amounts applied. N fertilization rate of 105 kg N per ha and year was most suitable for improving spring wheat yield and Nitrogen use efficiency (NUE), and maintain a diversified soil bacterial community.

 Authors’ response: Thank you for your approval!

• Still the relationship between soil bacteria community and grain yield and NUE was non-significant. At this point the manuscript remains inconclusive and the study and discussion of the results shows deficits.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 35-42, 503-514).

• Although yield plays a central role for optimum fertilization no data are given on quantity and stability over the observed 16 year time period. Stability is almost as import to farmers as quantity and needs to be discussed.

Authors’ response: Thank you for this suggestion. Grain yield in 2018 was provided in Table 2, and previous test information had been reported in previously published article and detailed in the discussion section of this article, which we have followed (Lines: 222-223, 418-421, 493-495).

• The 105 kg N per ha are not related to the amount of N removed from the field, so it is unclear how much needs to be replaced and which amount stays within the field system.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 293-294, 418-421, 491-495, 509-511, 538-543).

• Furthermore soil bacterial community diversity is often discussed with plant health as another important factor for yield. No information is given on diseases and pest management apart from the use of herbicides.

Authors’ response: Thank you for this suggestion. There was no serious pests and diseases occurred during the entire test period, so relevant data were not provided. However, the prevention and control management of field diseases and pest were described in the article, which we have followed.(Lines: 112-116).

• Overall the soil bacterial community is likely to be fluctuating within the season and over the time of the experiment so minor differences between the treatments are more than likely to detect. The study presents only a single measurement at the end of the experiment and lacks the discussion of the fluctuation on the significance of the results.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 474-526).

• Apart from this the relevance of the cited literature for the context of this study could be improved in terms of what were the findings or conclusion in the citation and how does this specifically relate to the presented study. The manuscript remains occasionally with rather general statements, which are difficult to follow and relate.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 408-411, 418-421, 447-457, 479-514 ).

• 28 typo no instead of No.

Authors’ response: Thank you for this question, which we have followed. (Lines: 31).

• 51 For readability NUE abbreviation should be explained introduction and longer text passages and not only in the abstract and Material and Methods part.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 58, 216, 237, 321, 419, 529, 540).

• 75 typo soils instead of solis.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 83).

• 103-104 fungicides, insecticides? More importantly which pests were present and how did they get controlled? ( eg Septoria, Ptr, Take All).

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 112-116).

• 101 same variety for 16 years?

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 110).

• 103 sampling area or plots?

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 112).

• 141 chimers?

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 156).

• 107 only single timepoint for soil sampling. root biomass was removed, but not measured?

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 119-125).

• 153-4 every year or in 2018 only.

Authors’ response: Thank you for this suggestion, which we have followed. (Lines: 169).

• 190 what was the average grain yield, how did this vary over the years.

Authors’ response: Thank you for this question. Grain yield in 2018 was provided in Table 2, and previous test information had been reported in previously published article and detailed in the discussion section of this article, which we have followed (Lines: 222-223, 418-421, 493-495).

• 277 please add numbers to relatively.

Authors’ response: Thank you for this question, which we have followed. (Lines: 427-434).

• 291-3 sentences are unclear. please rephrase.

Authors’ response: Thank you for this question, which we have followed. (Lines: 450-457).

• Figure 2 similar x axis (unit-distance) would facilitate the comparison. Then differences in units makes it difficult to recognise and compare major and minor effects.

Authors’ response: Thank you for this suggestion, which we have followed. (Fig. 2, Lines: 263-265).

 

Reviewer 3 Report

Long-term field evaluation of N fertilizing. very good time line from 2003 to 2018. 

reccomendation and questins:

• row 43 - from 112,5 mil tons to 112,8 mil tons??? some mistake!
• in chapter 2: results of soil analyses from 2003 is OK, and information about bacteria content from 2003??
• experimantal design - what was precrops?? in each experimental year the same??
• little surprise, that authors study spring wheat. Because in Europe more important is winter wheat for food processing. 
• soil analyses, grain yields etc. were evaluated each year?? Or only in 2018?? 
• Please what is average grain yield from different N levels?  Do you have some info about changes during all experimental  period?
• Ok, conclusion about 100 kg N per year is fine, but from different studies no so new

Author Response

Review 3:

• Long-term field evaluation of N fertilizing. very good time line from 2003 to 2018.

Authors’ response: Thank you for your approval!

• row 43 - from 112,5 mil tons to 112,8 mil tons??? some mistake!

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 50).

• in chapter 2: results of soil analyses from 2003 is OK, and information about bacteria content from 2003??

Authors’ response: Thank you for this suggestion. The long-term nitrogen fertilizer experiment was established in 2003 to study the effects of long-term quantitative nitrogen application on soil properties and microorganisms. So at the beginning of the experiment (2003), we only measured basic physicochemical properties because the basic soil is uniform.

• experimantal design - what was precrops?? in each experimental year the same??

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 110-112, 528).

• little surprise, that authors study spring wheat. Because in Europe more important is winter wheat for food processing.

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 54).

• soil analyses, grain yields etc. were evaluated each year?? Or only in 2018??

Authors’ response: Thank you for this suggestion. The data before 2018 had been reported in previously published article and elaborated in the discussion section of this article, which we have followed (Lines: 418-421, 493-495).

• Please what is average grain yield from different N levels? Do you have some info about changes during all experimental period?

Authors’ response: Thank you for this suggestion. Grain yield in 2018 was provided in Table 2, and previous test information had been reported in previously published article and detailed in the discussion section of this article, which we have followed (Lines: 418-421).

• Ok, conclusion about 100 kg N per year is fine, but from different studies no so new.

Authors’ response: Thank you for this suggestion. In this study, we found that the N fertilization rate of 105 kg N ha⁻¹ yr⁻¹ maintained a diversified soil bacterial community, and was most suitable for improving spring wheat yield and nitrogen use efficiency, which attributed to the higher phyla Verrucomicrobia and Planctomycetes, and lower Proteobacteria abundance, and thereby assist sustainable intensification of wheat production in semi-arid Loess Plateau of China.

 

Reviewer 4 Report

 Long-term nitrogen fertilization impacts on soil bacteria, grain yield and nitrogen use efficiency of wheat in semiarid Loess Plateau, China

Major:

This manuscript tried to identify the long-term nitrogen fertilization (2003-2018) impact on a number of soil properties. However, I have a major concern that authors only collected soil samples in 2018 and did the analysis. They further established the correlation between these chemical and biological characters. Although not all the correlation analysis did make a sense, some of them may be valuable in the field. The point here is if the authors could provide additional information (such as the data in previous years between 2003-2018), it could validate the application. Or at least they need to point out the changing trend during the experimental period. It seems that authors only presented the initial (2003) and final (2018) data, which may be devalued the long-term experiment result. Next, when the authors established the correlation by using NH₄-N and NO₃-N with other property, it should be noted that NH₄-N and NO₃-N concentrations are changeable in a large degree. Your result in this category cannot be convincing. At least, you need to mention this in your discussion session.

Minor:

 

Line 33:

KD4_96 (definition first time used).

Line 71: LAI (definition first time used).

Lines 111-112: One subsample was stored at -80 ℃ (make sure?) for molecular analysis and soil moisture determination.

Lines 115-116: Soil pH was measured using a glass combination electrode in a suspension of soil and water at a ratio of 1:1 (try other ratios)?

 

Author Response

Review 4:

• This manuscript tried to identify the long-term nitrogen fertilization (2003-2018) impact on a number of soil properties. However, I have a major concern that authors only collected soil samples in 2018 and did the analysis. They further established the correlation between these chemical and biological characters. Although not all the correlation analysis did make a sense, some of them may be valuable in the field. The point here is if the authors could provide additional information (such as the data in previous years between 2003-2018), it could validate the application. Or at least they need to point out the changing trend during the experimental period. It seems that authors only presented the initial (2003) and final (2018) data, which may be devalued the long-term experiment result. Next, when the authors established the correlation by using NH₄-N and NO₃-N with other property, it should be noted that NH₄-N and NO₃-N concentrations are changeable in a large degree. Your result in this category cannot be convincing. At least, you need to mention this in your discussion session.

Authors’ response: Thank you for this suggestion! The data before 2018 had been reported in previously published article and elaborated in the discussion section of this article, which we have followed (Lines: 418-421, 493-495).

• Line 33: KD4_96 (definition first time used).

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 506-507).

• Line 71: LAI (definition first time used).

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 79).

• Lines 111-112: One subsample was stored at -80 ℃ (make sure?) for molecular analysis and soil moisture determination.

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 125-127).

• Lines 115-116: Soil pH was measured using a glass combination electrode in a suspension of soil and water at a ratio of 1:1 (try other ratios)?

Authors’ response: Thank you for this suggestion, which we have followed (Lines: 130).

Round 2

Reviewer 4 Report

The revised version has addressed the reviewers' major concern. It seems that the manuscript is acceptable with minor English grammar, style, etc. requested. 

Author Response

Dear reviewer, 

Thank you very much for your effort to improve the MS, we went through the whole MS and revised the language, 1 authors of this article is American, we also asked a Ghanaian went through the whole manuscript and revised the English, however, not under track change, sorry for that. 

 

Once again, thank you very much for review our MS.