The Application of Fertilizer Phosphorus Affected Olsen P and the Phosphorus Fractions of Hedley Method in Black Soil

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Title: “The application of fertilizer phosphorus affected Olsen P and the phosphorus fractions of Hedley method in black soil” by Sun and team.

Authors highlighted the importance of phosphorus fertilization and its impact on fractions (labile phosphorus, medium labile phosphorus and stable phosphorus).

Title: Does phosphorus fertilization affect phosphorus pools in black soil?

Abstract: Quantify data is missing, and overall recommendation

Keywords: Ok

Introduction: is well written, overall excellent.

Materials and Methods: Excellent

Add the details of Statistical analysis used.

Result: Excellent

Discussion: need updated literature, and add scientific statement in correlation with results data.

Conclusion: add quantify data, and overall recommendation.

Overall, manuscript is very informative, recommended for publication after minor revision. 

Author Response

Dear Reviewer：

Thank you very much for your careful reading of the whole article again and your valuable suggestions for revision. I tried my best to revise and improve this article carefully which we hope meet with approval. The main corrections and the responds to the reviewer’s comments are as follows:

Reviewer’s comments: Title: Does phosphorus fertilization affect phosphorus pools in black soil?

Author’s response: Many studies showed that phosphorus application could increase soil phosphorus pool, Similarly, this study also showed that the application of phosphorus fertilizer (NPK/MNPK) significantly increased Olsen P and medium labile phosphorus, the treatments without phosphorus application (CK, NK) significantly reduced Olsen P, LP of CK treatment and MLP of NK treatment decreased significantly in black soil. Therefore, the input amount and type of phosphate fertilizer affect the phosphorus pool of black soil.

References:

1. Milića S.; Ninkova J.; Zeremskia T.; Latkovićb D.; Šeremešićb S.; Radovanovićc V.; Žarković B. 2019. Soil fertility and phosphorus fractions in a calcareous chernozem after a long-term field experiment, Geoderma. 339, 9-19.
2. Wu Q H.; Zhang S X.; Zhu P.; Huang S M.; Wang B R.; Zhao L P.; Xu M G. 2017. Characterizing differences in the phosphorus activation coefficient of three typical cropland soils and the influencing factors under long-term fertilization. Plos one. 12(5), e0176437.
3. Shen P.; Xu M G.; Zhang H M.; Yang X Y.; Huang S M.; Zhang S X.; He X H. 2014. Long-term response of soil Olsen P and organic C to the depletion or addition of chemical and organic fertilizers. Catena, 118, 20-27.

Reviewer’s comments: Abstract: Quantify data is missing, and overall recommendation.

Author’s response: The quantitative analysis of data is added (Line 29-35, page1), and the overall recommendations have been added (Line 38-40, page1).

Reviewer’s comments: Add the details of Statistical analysis used.

Author’s response: “2.5. Statistical analyses” is described in detail. Modify as follows: The relationship between the change of Olsen P and P budget in two black soils after long-term continuous fertilization was examined by fitting relationship between linear and curve equation. Among them, the fitting relationship between ΔOlsen P and P budget is fitted with a linear equation (CK, NK, NPK treatment), the fitting equation of MNPK treatment is a S-shaped curves. Data for each measured variable were subjected to one-way ANOVA and significant differences were then compared between treatments the least-significant difference (LSD) at P = 0.05. The correlations between ΔOlsen P and P fractions were determined using the R 3.6.3 language in Figure 5. Redundancy analysis (RDA) was conducted because it is a widely used and adaptive descriptive data analysis tool that permits identification of the structure of the interdependences between the main studied parameters. In this case, these were the soil variables (Organic carbon, Total nitrogen, pH, CaCO₃, Clay, Organic carbon/Total nitrogen, Organic carbon/Phosphorus, Total nitrogen/Phosphorus). The results yielded by such analyses might help identify the most influential factors on the soil parameter variability among the investigated treatments. Canoco5 was used for RDA analysis (Figure 6). All the diagrams were drawn with sigmaplot12.5 and Excel software.

Reviewer’s comments: Discussion: need updated literature, and add scientific statement in correlation with results data.

Author’s response: References were all checked, summaries of each paragraph were added, and sentence descriptions were modified.

Reviewer’s comments: Conclusion: add quantify data, and overall recommendation.

Author’s response: The quantitative data are added as follows:“Long term different fertilization for 30 years, for every 100kg ha^-2 budget of soil P, Olsen P decreased by an average of 1.5 mg kg^-1 in NK treatment, increased by an average of 17.6mg kg^-1 in NPK treatment. The increase curve of Olsen P was similar to an S-curve with periods of rapid growth and periods of equilibrium in MNPK treatment and the equilibrium values were 52.0 and 156.2 mg kg^-1 in Harbin and Gongzhuling..”

Modify the overall recommendation as follows: “However, it is necessary to study the characteristics of P adsorption and desorption in different fertilization stages to fully understand the change characteristics of soil P fractions in other soil types and meteorological conditions in the future.”

Author Response File: Author Response.docx

Reviewer 2 Report (Previous Reviewer 3)

This is the third review on this manuscript and comparing it to the second version, I do not detect much improvement. While some minor mistakes have been corrected, the major problems with the manuscript still persist: The whole discussion is based on very vague assumptions made from R2s that are way too low to deduct these conclusions (check Fig. 2). This is not scientifically sound.

What happened to l. 46-102?

l. 27 Same comment as last time: The abbreviations have to be introduced first - you can do this in line 19 when you first mention the names of the drylands.

l. 134-135 Please read the whole manuscript throughly before you submit it again.

l. 139 Same comment as before: "..., total nitrogen and pH low pH promoted the increase of Olsen P"? Please rewrite this part.

l. 146 Same comment as before: Please give a reference to your soil classification.

l. 146 Same comment as before: Why "can"? Do they represent most soil types in NE China or not?

I could repeat here all my comments that I gave on the revised manuscript before. I do not see that the manusprict improved and I can not recommend it for publication.

Author Response

Dear Reviewer：

Thank you again for reviewing this article and construction comments, we seriously thought again and revised the MS based on your comments, and adjusted the whole structure of the article. A figures and table are added to the article, the data are supplemented and the test year is unified. The main modifications to the article are as follows:

1. The fertilizer application period of the two long-term test sites was revised to be the same, and both selected 30 years, HRB is 1979-2009, and GZL is 1989-2019.
2. In GZL, Olsen P data in 2018 and 2019 are supplemented, while in HRB, data from 1979 to 2009 are selected, the original Figure 2 is modified.
3. The trend chart of cumulative phosphorus surplus and deficit has been added for 30 years fig 3).
4. The two diagrams of P fractions are modified into a table so as to see its dynamic changes more intuitively.

Author Response File: Author Response.doc

Reviewer 3 Report (Previous Reviewer 2)

Dear Authors,

I agree with the changes. The authors heeded my suggestions.

I agree with publishing the article as it is.

Author Response

Thanks again for your review. It's my honor to get your approval.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report (Previous Reviewer 3)

The authors significantly improved the quality of the manuscript. I strongly recommend English language editing or asking a native speaker to go again through the complete manuscript as there are still passages that are not precise enough (e.g. l. 332: "Heuck was also found that long-term nitrogen input reduced the P dissolving..."). And some standard rules are still not considered. For instance, if you use an abbreviation, you introduce it when you use it for the first time and from that point on, you use the abbreviation. When you introduce it, you put it into brackets, like you did in l. 110. In l. 116 for example you did it the other way round.

Again, I ask you to give a reference for the soil classification and make this part more precise. The sentence "The black soil classification in Harbin and Gongzhuling are typical Udic Mollisols..." (l. 97) does not make sense. Moreover, you add a reference to a FAO publication in l. 111, but Mollisols are not included in the WRB, the classification scheme of the FAO.  

I still have a major problem with the fitting equations. It does not help to show other publications when your data tell something different. And I do not unterstand how you could easily "add data and modify" the figure without manipulating your data.

Once these points are clarified, especially the last one, the manuscript should be ready for publication.

Author Response

Thank you again for reviewing this article and construction comments, we hired a native English speaker to revise the language of the article. We rechecked the data of the fitting equation, and explained the reasons.Detailed modification instructions are submitted as follows.

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Manuscript entitled “Fertilization measures affect the fractions of phosphorus in black soil” by Sun & team.

Overall, the manuscript is written very well, for further process please see below minor corrections-:

1.       Improve figure quality,

2.       Major modification in conclusion section add quantify results, correlated with climate change and future recommendations.

3.       Add weather data.

Author Response

Dear Editor and Reviewer：

Thank you for your letter and for the Reviewer’s comments concerning our manuscript entitled “Fertilization measures affect the fractions of phosphorus in black soil (1937549)”. Those comments are all valuable and helpful for improving our paper, as well as the important guiding significance to our researchers. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responses to the reviewer’s comments:

1. Improve figure quality.

Thank you for the suggestion. We have improved resolution of all figures.

2. Major modification in conclusion section add quantify results, correlated with climate change and future recommendations.

The following climate and future recommendations are added to the Conclusion (Line 450-455, page15):

This study gives therefore deeper understanding of the impact of long-term different fertilization measures on the dynamics of different soil P pools, and will guide the sustainable P management in the future. However, it is necessary to further study the characteristics of P adsorption and analysis in different fertilization stages to fully understand the change characteristics of soil P fractions in other soil types and meteorological conditions.

3. Add weather data.

Table 1 is added to supplement climate data (Line 131-133, page3).

Reviewer 2 Report

GENERAL COMMENTS

The work entitled “Fertilization measures affect the fractions of phosphorus in black soil”

RELEVANCE (considering the contribution to the advancement of knowledge): Medio.

ORIGINALITY (considering the problem to be studied and the existing knowledge gaps that justify the study): Medio.

TECHNICAL AND SCIENTIFIC MERIT: Medio.

FINAL OPINION: Authors need to make the following adjustments:

a) Localization map???

b) What kind of soil?

c) What is the soil classification?

Comments for author File: Comments.pdf

Author Response

Dear Editor and Reviewer：

Thank you for your letter and for the Reviewer’s comments concerning our manuscript entitled “Fertilization measures affect the fractions of phosphorus in black soil (1937549)”. Those comments are all valuable and helpful for improving our paper, as well as the important guiding significance to our researchers. We have studied comments carefully and have made correction which we hope meet with approval. Revised portion are marked in red in the paper. The main corrections in the paper and the responds to the reviewer’s comments are in the attachment.

1. Localization map?

Added Figure 1 (Line137-138, page 4).

2. What kind of soil?

Soil type are Udic Mollisols. Tables 1 has been added (Line131-133, page 3).

3. What is the soil classification?

Tables 2 have been added to supplement soil classification and initial soil physicochemical properties (Line133-136, page 3).

Thanks again!

Author Response File: Author Response.docx

Reviewer 3 Report

The authors evaluate the effect of different fertilization patterns on several phosphorus fractions in Chernozems from two sites in China. The used methods are not sufficiently described, only references are given. The rational of the study is widely missing. While the data could be interesting, in the given form this manuscript is far from being ready for publication. The only rational given is that this work has not been done before. The work is neither set into a broader context nor does it address a larger audience. The manuscript is not structured very well. Regarding the methodology, the authors compare two sites with long-term fertilization experiments that have different time ranges, different crop rotations (one with a legume, one without), and different kinds of manure applied. These problems are not addressed properly. Only in the Discussion, the author present information on the differences between the kinds of manure and between the analyzed soils (e.g. CaCO3 content). The respective - and very important - information is not given before. Overall, the authors present a lot of information and a lot of analyses they did only in the Discussion. This is not very helpful as everything relevant for the study should have been described before in the M+M section and resuls should be presented in the Results section. In addition, for some parts of the Discussion it is not clear if the authors discuss their own findings or if they refer to other's people or their own earlier work.
They overestimate findings they deduce from their data, this is especially obvious with regard to Figure 1. As this is the basis of a large parts of the Discussion, this whole line of reasoning needs to be reworked. The authors also name "3) to provide data support for the rational application of P fertilizers" as one of their aims of this study - they never come back to this aim as the results do not allow to provide this information.        

I suggest to use another term than Olsen P, e.g. extractable P or available P. At least, Olsen P needs to be introduced at some (early) point. The language is in large parts not sufficient and needs to be checked thorougly. The same is true for the use of abbreviations (introduce them in the first place and use them from that point on) and units. In addition, all references need to be checked, a lot of names are not written correctly. The introduction lacks a lot of information, for instance are at no point the analyzed P fractions described. The Materials and Methods section, especially the Methods part, is way too short. None of the methods are described, only references are given. The content of tables and figures is often not described in detail, the captions contain information that should (also) be contained in the text. Legends are missing.

Title:
I suggest to adjust the title to make it more precise. "Fertilization measures" is very general and "the fractions of phosphorus" sounds like all P fractions are covered.

Abstract:
l. 14/15    Before you start to use P as abbreviation, it should be introduced. Here, it is the other way round.
l. 14/15    Please be consitent: either Olsen-P or Olsen P, don't switch. (This applies to the whole manuscript.)
l. 16        It would be helpful to be more precise: which P fractions?
l. 17        Are HRB and GZL the names of the drylands? You can not use abbreviations without introducing them.
l. 16-19    Why do you name Olsen P twice in this sentence? You start the sentence with "This study investigated changes in Olsen P" and return to "...and analyzed Olsen P" in the next line.
l. 21        How precise is your data? I suppose it is fine to stick to one decimal here ("...average of 1.3 and 4.5...")
l. 20-21    This sentence is not clear to me. The application of NK decreased? This sounds like a passive effect, but I assume that the application of fertilizer is an active operation.
l. 20-21    Same sentence: What decreased by 1.3 and 4.5 mg/kg? Please clarify this.
l. 27-28    "...could lead to zero increase in Olsen P."? Did your date show this or is this your assumption? Please clarify.

Introduction
General:    I strongly recommend to rewrite and restructure the Introduction section. Please use it to introduce your work. Introduce Olsen P and the other P fractions you analyzed, introduce your approach and why you chose it. Give something like a hypothesis or a clear scope. And please name the benefits of your approach instead of just stating that it has not been done before (cf. l. 56-59, l. 60-67).
l. 34        "Analyzing Olsen P and fractions..." - fractions of what? Please be more precise.
l. 35        Please check all of the used references thorougly, many names contain errors (e.g. 1, 10, 20...).
l. 35        A sentence should never start with an abbreviation, please rewrite (e.g. "The application of P...")
l. 38        It would be better to write something like "in order to be able to predict their changes" instead of "then predict their changes".
l. 38/39    What do you mean with "at present"? For this study?  
l. 39-41    How do you select something "through long-term experiment"? I suggest to rewrite the whole sentence and to state here clear what was selected and why and with which aim.
l. 39        It would be helpful to refer here to the duration of the long-term experiment at least shortly.
l. 40        kg hm-2? Why do you use the very uncommon unit hectometer? And why do you use the more common ha at other occasions?
l. 42        Why do you use "would" here?
l. 46        What do you mean with "that the changes should be phased"? That they should be addressed (faced)? Or brought in line (phased)?
l. 47        Why is necessary to use black soil here? Would it not be possible to use another soil type? If you use black soil because of the long-term experiment you should introduce this in the material and methods sections. However, it is not valid to state it like it is necessary to use this type of soil to provide the named theoretical basis.
l. 51        It would be appropriate to use a more basic (= older) reference for this statement. The fact that labile P decreases without P application is not a very recent finding.
l. 52        Which corresponding P components?
l. 51-53    Does this only need to be clarified under this special setting? (long-term fertilization, black soil)
l. 53-54    This sounds like it is a resulte from your study. If you refer to other studies, please address this: "Earlier studies showed..." or something similar.
l. 56-59    I suggest to rewrite this part. It would be helpful to focus on the benefits of your approach instead of stating that it is just something that has not been done before (and please keep in mind that you reference studies that work on P in black soils from long-term experiments, e.g 39).
l. 60-67    If you put it like this, you address a very narrow audience (black soil, long-term fertilization, China) - to raise interest the whole study should be put in a broader context.

Material and Methods
l. 71-78    I stongly suggest to put this information in a table.
l. 83-84    You used different fertilizers? How could you be sure that they don't have different effects? Please explain.
l. 85-88    You used different kinds of manure? Did you cross-check the effects of the particulate kinds of manure?
Table 1        Did you address the possible effects of a legume in the crop rotation?
l. 98        You should at least shortly describe the method.
l. 98-101    Same applies here: do not only name what you did, but how you did. This is the method section.
l. 104-105    Put this clear. "Where Pi represents... and P0..."
l. 107        When, where and how did you measure the total crop P removal?
l. 111-113    What is RDA? Introduce abbreviations before you use them. What approach did you use to determine correlations? Please be more precise.

Results
l. 115        Please check the header.
l. 117-118    "It was similar to the fitting curve of the same fertilization treatment."? Please clarify.
l. 118        What do you mean with "partial" application of NK?
l. 120-121    Why do you use mg/kg in one sentence and in the next sentence, but in the same context, percent? Choose one and stick to it or name both to make the numbers comparable.
l. 125-126    To compare both sites with different crops and different ferilizers/manure is not helpful. In addition, I think it's a problem that you compare different time spans. I'd suggest to take the shorte time span and adjust the data.
Fig. 1        An R2 of less than 0.5 is not convincing. If you look at the distribution (GZL-CK, GZL-NK, HRB-NPK, HRB-MNPK), this looks more like a coincidence than like an appropriate fitting curve. In addition, it is not ideal that the x-axis has different values in each panel - this should at least be addressed in the caption (is also the case in the other figures).
l. 137-138    The abbreviations should have been introduced before.
l. 142-144    Again: here you mix mg/kg, times and percent.
Fig. 2        How did you test for significance? Same here, some of the fitting lines are not very convincing. Where is the legend? What do you mean with "There is a significant difference and there is an equation"? Why do you put the equation in the end (LP=...) only here and do not explain it in the text?
l. 162        What is IP? Did you introduce this abbreviation?
l. 166        In l. 147-158 you state that P had no significant effect on SP - here you state that MNPK had a significant effect. You should address this.
Fig. 3        Same here: why do you name the equations in the end of the caption, but do not explain them in the text.  
l. 183-185    Please rewrite and clarify this sentence. The abbreviation should have been introduced before.
l. 186        You used the abbreviation C/N before.
l. 187        "...the same C/N and C/P"?
Fig. 4        Wher is the legend? You should explain the color ranges and the size of the circles.

Discussion
l. 200        "...showed that fertilization affected the change trend of Olsen P" - please be more precise. What is a change trend? How was it affected?
l. 201        "in NK" sounds strange, it should be something like "under the NK treatment" - this applies to the whole manuscript.
l. 200-202    Regarding the R2 values, this is not valid.
l. 202-204    I am sure that there are older references (than 2014 and 2018) for the finding that no application of P results in a loss of soil P - please do not neglect basic studies.
l. 206-207    Different to what previous research? Once again, given the R2 values, the S shaped curve is not a solid statement. The whole sentence is hard to understand, please rewrite.
l. 210-211    Do you have any references or indications for this assumption? Please name them. What do you mean with "early fertilization", please be precise.
l. 213-215    Do you refer here to your own results or to the given references? Please discuss your own results on the basis of other publications. 
l. 215-216    If you look at Fig. 1 there is no equilibrium, especially not in HRB.
l. 218        You never before mentioned mineral types. How can something from your work show here that P migration was related to OC and mineral types?
l. 222-224    How do you now have data on the subsoil? Please discuss your work.
l. 225-226    Once again: is this your data or the named references?
l. 235-236    You should repeat the respective years here, otherwise it sounds like random years.
l. 251-254    You should discuss the differences between the kinds of manure much earlier. The fact that the manure was analyzed by NMR spectroscopy should be given in the Material section.
l. 259-261    Same here, you should name the soil properties that you already knew from earlier studies in the Material section and not only here. If it deduces from earlier studies, give the respective reference - if it is from your work you should address this both in the M+M and in the Results section.
l. 270-271    Again: never before did you mention the microbial community. If you did this analyses why do you not address them in the M+M section and in the Results?
l. 274-276    Again: is this your data or is it completely taken from the named reference? It must be clear what is your own original work and where you put it in contex with other (also your own previous) publications.
l. 278        The uncertainties and limitation should have been addressed much earlier. In addition, it would be helpful for the placement of your results if you address them throghout the Discussion, not only at the very end.
l. 280-281    If you measured the P concentrations in grains and straw annually put this information in the M+M section and address it in the Results.
l. 289-290     How could data analysis by different people affect the size of the extracted P fractions? If different people did the lab work, you are supposed to follow a strict protocol, which you at least shortly should describe in the M+M section.
l. 297-298    As you have noteworthy differences in the CaCO3 content, you should address this much earlier - together with the differing contents.

Conclusions
General:    Once again, the basis of this Conclusions are the fitting lines that robust as their R2 are way too low. 

Author Response

Dear Editor and Reviewer：
Thank you for your letter and for the Reviewer’s comments concerning our manuscript entitled “Fertilization measures affect the fractions of phosphorus in black soil (1937549)”. I have no experience in writing SCI for the first time. Thank you very much for your careful reading of the whole article and your valuable suggestions for revision. Those comments are all valuable and helpful for improving our paper, as well as the important guiding significance to our researchers. I tried my best to revise and improve this article carefully which we hope meet with approval. Revised portion are marked in red in the paper. 

Thanks again!

(Modification description:The red part is the revised content, The revised line and page number are in brackets.)

Title:

I suggest to adjust the title to make it more precise. "Fertilization measures" is very general and "the fractions of phosphorus" sounds like all P fractions are covered.

The title is changed to:“The application of fertilizer phosphorus affected Olsen P and the phosphorus fractions of Hedley method in black soil(Line 1-5, page 1)”

Abstract:

14/15 Before you start to use P as abbreviation, it should be introduced. Here, it is the other way round.

14/15 Please be consitent: either Olsen-P or Olsen P, don't switch. (This applies to the whole manuscript.)

Added in the first line of the abstract：“Olsen P（labile phosphorus determined by Olsen method） is an important indicator of soil labile phosphorus. (Line 16-17, page 1)”

Revise "Olsen-P" to "Olsen P" in the whole article.

16 It would be helpful to be more precise: which P fractions?

“Determining the effect of fertilization on Olsen P and P fractions can guide the application of phosphate(P) fertilizer.” is revised to “Determining the effect of fertilization on Olsen P and P fractions（labile phosphorus, medium labile phosphorus and stable phosphorus） can guide the application of phosphate(P) fertilizer. (Line 17-18, page 1)”

17 Are HRB and GZL the names of the drylands? You can not use abbreviations without introducing them.

16-19 Why do you name Olsen P twice in this sentence? You start the sentence with "This study investigated changes in Olsen P" and return to "...and analyzed Olsen P" in the next line.
“This study investigated changes in Olsen P at the 0-20 cm in two drylands (HRB, GZL) with long-term fertilization in China, and analyzed Olsen P, P fractions and the application factors of NK (nitrogen, potassium), NPK (nitrogen, phosphorus, potassium) and MNPK (manure, nitrogen, phosphorus, potassium).” is revised to “This study investigated changes in Olsen P and P fractions at the 0-20 cm in two drylands (Harbin, Gongzhuling) with long-term fertilization in China, and analyzed the application factors of NK (nitrogen, potassium), NPK (nitrogen, phosphorus, potassium) and MNPK (manure, nitrogen, phosphorus, potassium). (Line 20-24, page 1)”

21 How precise is your data? I suppose it is fine to stick to one decimal here ("...average of 1.3 and 4.5...")
20-21 This sentence is not clear to me. The application of NK decreased? This sounds like a passive effect, but I assume that the application of fertilizer is an active operation.
20-21 Same sentence: What decreased by 1.3 and 4.5 mg/kg? Please clarify this.

“The results showed that the application of NK, Olsen P and medium labile P(MLP) decreased by an average of 1.31 and 4.5mg kg^-1 for every 100kg ha^-2 loss of soil P.” is revised to “The results showed that the application of NK, because of the continuous absorption of P by crops, Olsen P and medium labile P(MLP) decreased by an average of 1.3 and 4.5mg kg^-1 for every 100kg ha^-2 loss of soil P. (Line 24-26, page 1)”

27-28 "...could lead to zero increase in Olsen P."? Did your date show this or is this your assumption? Please clarify.

“Long-term combined application of MNPK could lead to zero increase in Olsen P.” is revised to“Long term combined application of MNPK could lead to the growth of Olsen P to remain constant. (Line 32-33, page 1)”

Introduction

Rewrited and restructured the Introduction section. (Line 37-102, page 1-3)

**34."Analyzing Olsen P and fractions..." - fractions of what? Please be more precise.

“Analyzing Olsen P and fractions and predicting their change trends can guide the application of P fertilizer and improve crop yield.” is revised to “Analyzing Olsen P and P fractions（labile P, medium labile P and stable P） and predicting their change trends can guide the application of P fertilizer and improve crop yield. (Line 39, page 1)”

**35. Please check all of the used references thorougly, many names contain errors (e.g. 1, 10, 20...).

All references were rechecked.

**35. A sentence should never start with an abbreviation, please rewrite (e.g. "The application of P...")

“P application caused a large amount of P accumulation in farmland, increasing of Olsen P would lead to the loss of P, resulting in wasted resources and environmental pollution.” is revised to “The application of P caused a large amount of P accumulation in farmland, increasing of Olsen P would lead to the loss of P, resulting in wasted resources and environmental pollution. (Line 41, page 1)”

**38. It would be better to write something like "in order to be able to predict their changes" instead of "then predict their changes".

“Therefore, it is necessary to clarify the effect of fertilization on Olsen P and P fractions, then predict their changes.” is revised to “Therefore, it is necessary to clarify the effect of fertilization on Olsen P and P fractions, so the change of Olsen P can be calculated by fitting the equation, which can predict the recent change and provide data for fertilization. (Line 45-53, page 2)”

**38-39. What do you mean with "at present"? For this study?

**39-41. How do you select something "through long-term experiment"? I suggest to rewrite the whole sentence and to state here clear what was selected and why and with which aim.
**39. It would be helpful to refer here to the duration of the long-term experiment at least shortly.
**40.kg hm-2? Why do you use the very uncommon unit hectometer? And why do you use the more common ha at other occasions?

**42. Why do you use "would" here?

38-42 is revised as follows:

“At present, different fertilization treatments were selected through long-term experiment to calculate the change of Olsen P per 100 kg hm^-2 of soil P budget, predict their future change trends and adjust the fertilizer application.” is revised to “Different fertilization treatments were selected through long-term experiments(>15 years) to calculate the change of Olsen P per 100 kg ha^-2 of soil P budget, predict their future change trends and adjust the fertilizer application. (Line 45-53, page 2)”

**46. What do you mean with "that the changes should be phased"? That they should be addressed (faced)? Or brought in line (phased)? “However, long-term continuous fertilization caused constant changes in Olsen P and P fractions, and we believe that the changes should be phased.” is revised to “However, long-term continuous fertilization caused constant changes in Olsen P and P fractions, which we predict should be of stage type. (Line 59, page 2)”

**47. Why is necessary to use black soil here? Would it not be possible to use another soil type? If you use black soil because of the long-term experiment you should introduce this in the material and methods sections. However, it is not valid to state it like it is necessary to use this type of soil to provide the named theoretical basis.

Added description in 95-100 lines

**51. It would be appropriate to use a more basic (= older) reference for this statement. The fact that labile P decreases without P application is not a very recent finding.

**52. Which corresponding P components?
**51-53. Does this only need to be clarified under this special setting? (long-term fertilization, black soil)
**53-54. This sounds like it is a resulte from your study. If you refer to other studies, please address this: "Earlier studies showed..." or something similar.
**56-59. I suggest to rewrite this part. It would be helpful to focus on the benefits of your approach instead of stating that it is just something that has not been done before (and please keep in mind that you reference studies that work on P in black soils from long-term experiments, e.g 39).

**60-67. If you put it like this, you address a very narrow audience (black soil, long-term fertilization, China) - to raise interest the whole study should be put in a broader context.

The original 49-67 lines are described again, and the new line number is 63-103.

Material and Methods

**71-78    I stongly suggest to put this information in a table.

Add Table 1 and Table 2. (Line 132-137, page 3)

**83-84. You used different fertilizers? How could you be sure that they don't have different effects? Please explain. **85-88. You used different kinds of manure? Did you cross-check the effects of the particulate kinds of manure? Table1. Did you address the possible effects of a legume in the crop rotation?

The determination of manure composition is added. (Line 121-125, page 3) The different effects of particulate kinds of manure and legumes are not supported by data in this study.

**98. You should at least shortly describe the method. **98-101. Same applies here: do not only name what you did, but how you did. This is the method section.

Redescribed "2.3. Soil sampling and data"(Line 156-175, page 4-5)

**104-105. Put this clear. "Where Pi represents... and P0..."**107. When, where and how did you measure the total crop P removal?

“2.4. Formula calculation and statistical analysis” is described in detail again. (Line 178-191, page 5)

**111-113. What is RDA? Introduce abbreviations before you use them. What approach did you use to determine correlations? Please be more precise.

2.5. Statistical analyses is revised to: The relationship between the change of Olsen P and P budget in two black soils after long-term continuous fertilization was examined by using the fitting relationship between linear and S-shaped curves. Data for each measured variable were subjected to one-way ANOVA and significant differences were then compared between treatments the least-significant difference (LSD) at P = 0.05. The correlations between ΔOlsen P and P fractions were determined using the R 3.6.3 language, and Canoco 5 was used for RDA (Redundancy analysis) analysis. All the diagrams were drawn with sigma plot 12.5 and Excel software. (Line 194-200, page 5)

Results

**115. Please check the header. **115. “3.1Δ. Olsen P and P budget” is revised to “3.1 ΔOlsen P and P budget”. **117-118. "It was similar to the fitting curve of the same fertilization treatment."? Please clarify. **118. What do you mean with "partial" application of NK? **120-121. Why do you use mg/kg in one sentence and in the next sentence, but in the same context, percent? Choose one and stick to it or name both to make the numbers comparable. **125-126. To compare both sites with different crops and different ferilizers/manure is not helpfu**In addition, I think it's a problem that you compare different time spans. I'd suggest to take the shorte time span and adjust the data.

Legend and equation description are standardized.

Redescribed "3.1 ΔOlsen P and P budget” (Line203-223, page 5-6)

Fig

Fig. 1. An R2 of less than 0.5 is not convincing. If you look at the distribution (GZL-CK, GZL-NK, HRB-NPK, HRB-MNPK), this looks more like a coincidence than like an appropriate fitting curve. In addition, it is not ideal that the x-axis has different values in each panel - this should at least be addressed in the caption (is also the case in the other figures).

The names of Figures 1, 2 and 3 are modified to show the difference of P budget.

Figures is revised to:

Figure 2. Relationship between ΔOlsen P and different P budget. (Line225, page 6)

Figure 3. Relationship between fractions and different P budget. (Line244, page 8)

Figure 4. Relationship between fractions% and different P budget. (Line263, page 10)

**137-138. The abbreviations should have been introduced before.stable phosphorus (SP) has not been introduced before.

“The continuous changes of soil labile phosphorus (LP), medium labile phosphorus (MLP) and stable phosphorus (SP) could better reflect the impact on fractions of long-term fertilization (Fig.2).” is revised to “The continuous changes of soil LP, MLP and stable phosphorus (SP) could better reflect the impact on fractions of long-term fertilization (Fig.2).” (Line231-233, page 6-7)

**142-144. Again: here you mix mg/kg, times and percent.

“The MLP decreased significantly by 17.5% on average compared with the initial value in NK treatment. For every 100kg ha^-2 loss of P, the MLP decreased by 4.5mg kg^-1 on average. NPK treatment significantly increased LP by 1.45-2.98 times, 17.4mg kg^-1 for every 100kg ha^-2 surplus of P, and MLP by 50.3% on average.” is revised to “According to the slope calculation of linear fitting equation: For NK, every 100kg ha^-2 of P loss, MLP decreased by 3.5mg kg^-1 at HRB and 5.5 mg kg^-1 at GZL. For NPK, every 100kg ha^-2 of P surplus, LP increased by 12.0mg kg^-1 at HRB and 29.9 mg kg^-1 at GZL. MLP increased by 10.3 mg kg^-1 at HRB and 79.5 mg kg^-1 at GZL.” (Line235-238, page 7)

Fig. 2. How did you test for significance? Same here, some of the fitting lines are not very convincing. Where is the legend? What do you mean with "There is a significant difference and there is an equation"? Why do you put the equation in the end (LP=...) only here and do not explain it in the text?

Legend added in Figure.

The significance test method is added in 2.5 statistical analysis, as follows: Data for each measured variable were subjected to one-way ANOVA and significant differences were then compared between treatments the least-significant difference (LSD) at P = 0.05. (Line193-201, page 5)

According to the slope calculation of linear fitting equation:

"LP=Resin-P+NaHCO3-P; MLP=NaOH-P+DHCl-P; SP=CHCl-P+Residual-P." is added to the text description in Figure. (Line233, page 7)

The description of the equation is added to the description of the figure, as follows:

y₁, y₂ and y₃ are the fitting equations of LP, MLP and SP. (Line253,271, page8,10)

**162. What is IP? Did you introduce this abbreviation?

Write error, modify all IP addresses to SP. (Line260-261, page 8)

**166. In **147-158 you state that P had no significant effect on SP - here you state that MNPK had a significant effect. You should address this.

In the discussion, the explanation of this part is supplemented.

The content added in the discussion is: For MNPK treatment, fertilization increased all forms of phosphorus in black soil, SP increase was not significant, but SP% decreased significantly, indicating that long-term manure combined with NPK increased LP and MLP in black soil more than SP, resulting in significant increase of LP+MLP and (LP+MLP) %, so SP% decreased significantly. (Line367-371, page 13)

Fig. 3. Same here: why do you name the equations in the end of the caption, but do not explain them in the text.

The description of the equation is added to the description of the figure, as follows:

y₁, y₂ and y₃ are the fitting equations of LP, MLP and SP. (Line253,271, page8,10)

**183-185. Please rewrite and clarify this sentence. The abbreviation should have been introduced before.

“In order to clarify the impact of soil physical and chemical properties on Olsen P and the fractions, from Figure 4, ΔOlsen P and its significantly related fractions were selected for redundancy analysis (RDA) (Figure 5).” is revised to “In order to clarify the impact of soil physical and chemical properties on Olsen P and its related P fractions, we conducted RDA analysis on two groups of variables (Figure 6).” (Line283-285, page 10-11)

**186. You used the abbreviation C/N before.

“The results showed that for NK, carbon/nitrogen (C/N) and carbon/phosphorus (C/P) had greater effect on Olsen P, and the total contribution rate was 43.2%;” is revised to “The results showed that for NK treatment, C/N and C/P had greater effect on Olsen P, and the total contribution rate was 43.2%;” (Line287-289, page 11)

**Fig. 4. Wher is the legend? You should explain the color ranges and the size of the circles.

Figure 4 is changed to Figure 5, Figure 5 was revised to make it clearer and the legend figures were enlarged. (Line296-297, page 11)

Added note to Figure 5：

The red indicates positive correlation, the blue indicates negative correlation, the larger the circle area, the stronger the correlation, the * in the circle indicates significant correlation, and the value on the left of the figure indicates R². (Line300-302, page 12)

Discussion

**200. "...showed that fertilization affected the change trend of Olsen P" - please be more precise. What is a change trend? How was it affected?

“The results of this study showed that fertilization affected the change trend of Olsen P.” is revised to “The results of this study showed that different fertilization measures affected the change trend of Olsen P during P budget. Olsen P decreased significantly without P application in black soil, while Olsen P with P application increased.” (Line307-309, page 12)

**201.  "in NK" sounds strange, it should be something like "under the NK treatment" - this applies to the whole manuscript.

The whole article changes NP to NK treatment.

**200-202.  Regarding the R2 values, this is not valid. **202-204.  I am sure that there are older references (than 2014 and 2018) for the finding that no application of P results in a loss of soil P - please do not neglect basic studies.

“The results of this study showed that fertilization affected the change trend of Olsen P. Olsen P showed a significant linear decreasing trend in NK, a significant linear increasing trend in NPK, and a similar S-shaped curve in MNPK. Similar to the results of previous studies, no application of P would lead to loss of soil P and decrease of Olsen P, while P application would cause increase of Olsen P in P surplus.” is revised to “The results of this study showed that fertilization affected the change trend of Olsen P. Olsen P showed a linear decreasing trend in NK treatment, a linear increasing trend in NPK, and a similar S-shaped curve in MNPK. Similar to the results of previous studies, Continuous application of P will increase P surplus in black soil, while P application would cause increase of Olsen P in P surplus.” (Line310-314, page 12)

**206-207.  Different to what previous research? Once again, given the R2 values, the S shaped curve is not a solid statement. The whole sentence is hard to understand, please rewrite.
“Olsen P still showed a linear upward trend in 29 and 36 years of continuous fertilization. Different from the previous research, the increase of Olsen P in stages in MNPK, similar to an S-shaped curve.” is revised to “During 29 and 36 years of continuous fertilization, Olsen P still showed a linear upward trend for NKP treatment. However, the growth trend of Olsen P in MNPK is different from that in previous studies, which shows a phased increase, similar to an S-shaped curve.” (Line315-318, page 12)

**210-211.  Do you have any references or indications for this assumption? Please name them. What do you mean with "early fertilization", please be precise.

“This may be because the soil P had been consumed too much before the experiment, so the early fertilization may increase the fixation of P.” is revised to “At the beginning of the experiment, the initial value of Olsen P was 11.8 mg kg^-1, much lower than that of 22.2mg kg^-1 in HRB (Table 2). The HRB was higher than GZL10.4 mg kg^-1, and there might be a consumption of soil P at GZL, Therefore, at the beginning of the experiment, a large amount of P fertilizer input increased P fixation, and Olsen P increased slowly.” (Line321-326, page 13)

**213-215.  Do you refer here to your own results or to the given references? Please discuss your own results on the basis of other publications.

“At the same time, the increase of soil organic matter increased labile P and P activation coefficient, reduced the adsorption of P, and improved the desorption capacity of P.” is revised to “At the same time, the increase of soil organic matter increased labile P and P activation coefficient, reduced the adsorption of P, and increased Olsen P rapidly.” (Line329-331, page 13)

**215-216.  If you look at Fig. 1 there is no equilibrium, especially not in HRB.

“At the later stage of MNPK, the increase of Olsen P reached equilibrium. The possible reason was that continuous fertilization would lead to saturation of P adsorption in the soil [30], and lead to infiltration and loss of Olsen P.” is revised to “At the later stage of MNPK, especially in GZL, the increase of Olsen P reached equilibrium. The possible reason was that continuous fertilization would lead to saturation of P adsorption in the soil [30], and lead to infiltration and loss of Olsen P.” (Line331-337, page 13)

**218.  You never before mentioned mineral types. How can something from your work show here that P migration was related to OC and mineral types?

Table 2 has been added to describe the physical and chemical properties of soil.

“It showed that P migration was related to organic carbon and mineral types.” is revised to “It showed that P migration was related to organic carbon and mineral types. There are differences between soil calcium carbonate and clay particles in the two test sites, especially calcium carbonate (Table 2).” (Line337-339, page 13)

**222-224.  How do you now have data on the subsoil? Please discuss your work.

“The loss of Olsen P ranges from 39.9 to 90.2 mg kg^-1 [29]. Therefore, compared with the input of fertilizer P, manure application increased the proportion of Olsen P in the subsoil [23,33].” is revised to “Diego showed that compared with the input of fertilizer P, manure application increased the proportion of Olsen P in the subsoil [29]. Similarly, Olsen P in 20-40cm soil of GZL treated with CK, NPK and MNPK was measured in 2000, with the mean values of 2.1, 5.5 and 9.5mg kg^-1. Olsen P in MNPK was significantly higher than that in NPK. Soil organic carbon, total nitrogen and C/N had the greatest effects on Olsen P and P fractions. Yang et al.'s research on black soil showed that the increase of soil organic matter increased Olsen P and P activation co-efficient, and improved the desorption capacity of P [30].” (Line345-350, page 13)

**225-226.  Once again: is this your data or the named references?

Remove this description.

**235-236.  You should repeat the respective years here, otherwise it sounds like random years.

“The P fractions and their proportions were analyzed over six years from 1990 to 2013.” is revised to “The P fractions and their proportions were analyzed over six years from 1990 to 2013 (1990, 1995, 2000, 2005, 2010 and 2013).” (Line361-362, page 13)

**251-254.  You should discuss the differences between the kinds of manure much earlier. The fact that the manure was analyzed by NMR spectroscopy should be given in the Material section.

Put this part into the material method. (Line121-125, page 3)

**259-261.  Same here, you should name the soil properties that you already knew from earlier studies in the Material section and not only here. If it deduces from earlier studies, give the respective reference - if it is from your work you should address this both in the M+M and in the Results section.

Table 2 is added to describe the physical properties of soil. (Line135-137, page 3)

**270-271.  Again: never before did you mention the microbial community. If you did this analyses why do you not address them in the M+M section and in the Results? **274-276.  Again: is this your data or is it completely taken from the named reference? It must be clear what is your own original work and where you put it in contex with other (also your own previous) publications.

Remove this part: “Secondly, the input of soil C, N and P affected the microbial community structure. The P dissolving microorganisms were studied in HRB. It was found that long-term nitrogen input reduced the P dissolving and mineralization capacity of microorganisms. In addition, the uneven distribution of nutrients affected the diversity of microorganisms in black soil. Its abundance was significantly positively correlated with soil TN and SOC. The P dissolving capacity of microorganisms was mainly regulated by C/P [40,41].” (Line403-409, page 14)

**278.  The uncertainties and limitation should have been addressed much earlier. In addition, it would be helpful for the placement of your results if you address them throghout the Discussion, not only at the very end.

Remove this part “4.3. Uncertainties and limitations.” (Line421-449, page 14-15)

**280-281.  If you measured the P concentrations in grains and straw annually put this information in the M+M section and address it in the Results.

The following description is added to "2.3. Soil sampling and data and 2.4. Formula calculation and statistical analysis":

**289-290.  How could data analysis by different people affect the size of the extracted P fractions? If different people did the lab work, you are supposed to follow a strict protocol, which you at least shortly should describe in the M+M section.

The following description is added to "2.3. Soil sampling and data":

All the data of soil physical and chemical properties in this paper are from two long-term experiments. All dynamic data are summarized by annual monitoring data. (Line172-175, page5)

**297-298.  As you have noteworthy differences in the CaCO3 content, you should address this much earlier - together with the differing contents.

Add description: “However, in RDA analysis, the contribution of CaCO3 and clay is far lower than that of organic carbon and total nitrogen, and it is likely that their impact on P fractions is limited to the initial stage of the test.” (Line391-395, page14)

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The authors improved their manuscript somehow. However, they failed in correcting the part that contains the major problem: they base their discussion on fitting equations with R2s that are way to low to deduce the conclusions they do. Therefore, the manuscript is still not ready for publication.

Title       

The title improved, but I suggest to change it again to make it clearer: "The application of phosphorus fertilizer affected both Olsen P and phosphorus fractions of the Hedley method in black soil"

The language needs to be checked thoroughly again for grammar (past/present tense...) and spelling.  

Abstract
l. 27        The abbreviations have to be introduced first - you can do this in line 19 when you first mention the names of the drylands.

Introduction
l. 38-41    This sentence needs to be rewritten, maybe it could help to split it into two sentences.
l. 62        Shouldn't it be "...the accumulated P budget"?
l. 69-70    What do you mean with "...which we predict should be of stage type"?
l. 78        Better than what?
l. 79-80    "...was first fast and then slow..."
l. 83-84    What do you mean with "...and whether its increase trend was phased needs to be evaluated again."?
l. 85-86    The references 13 and 14 refer to the Hedley method and Tiessen's modification, but not to the statement that the method was widely used.
l. 97        "..., total nitrogen and pH low pH promoted the increase of Olsen P"? Please rewrite this part.
l. 102        Please give a reference to your soil classification.
l. 102-103    Why "can"? Do they represent most soil types in Northeast China or not?

Material and Methods
l. 161        "for Table 1 and Table 2"?
l. 162        Please add spectroscopy after NMR.
Table 1 + 2    I suggest to use "site" instead of "place". As header I'd suggest "Soil type, geographical location and climate of the two experimental sites HRB and GZL" or something similar (for Table 2 as well).
l. 239-240    "shall be measured"? Are they measured every year or not?
l. 267-269    "...were then compared between treatments the least-significant..." There is something missing.
l. 270-272    It is common to name the manufacturer also for software etc.

Results
l. 275-276    This sentence needs to be rewritten. I suggest to use the term "long-term experiment sites" instead of "long-term experiments"
l. 278-280    "...will continuously lose P." - This part needs to be rewritten as well, I suggest something like "will lead to a continuous loss of P."
l. 280-282    Same here. Both sentences are not clear and need to be clarified.
l. 285        I still think that the use of different time frames is problematic.
Figure 2    You did not change anything here and the conclusions are still not valid. R2 of 0.213 (GZL-CK) is nothing what you can base your argumentation on, same is true for GZL-NK, HRB-NPK, and especially HRB-MNPK.  "MNPK" is still not added to GZL.

At this point, I stop the review as this means all the discussion is still based on this very vague assumptions based on R2s that are way too low to deduct
these conclusions. We had this in the review before and as this is not changed, the manuscript will for sure not be ready for publication.