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Soil Organic Carbon Stocks Under Daylily Cultivation and Their Influencing Factors in the Agro-Pastoral Ecotone of Northern China

Agronomy 2025, 15(3), 756; https://doi.org/10.3390/agronomy15030756

by Zhen Wang¹, Zelong Yao¹, Hongfen Zhu¹

and Rutian Bi^1,2,*

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Reviewer 4:

Ronaldo Luiz Mincato

Agronomy 2025, 15(3), 756; https://doi.org/10.3390/agronomy15030756

Submission received: 26 February 2025 / Revised: 15 March 2025 / Accepted: 18 March 2025 / Published: 20 March 2025

(This article belongs to the Special Issue New Pathways Towards Carbon Neutrality in Agricultural Systems)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review Report

Manuscript ID: agronomy-3525436

Title: Soil organic carbon stocks under daylily cultivation and its influencing factors in the agro-pastoral ecotone of northern China

Authors: Zhen Wang, Zelong Yao, Hongfen Zhu, Rutian Bi

Dear Authors,

I saw a few details that need to be improved or corrected. I described these details in the reviewer's comments in the pdf file.

Detailed comments:

Title

Authors

Affiliations

Abstract

Keywords

Introduction

Line 48: (Hemerocallis citrina Baroni) → (Hemerocallis citrina Baroni) (the arrow → means: the entry should be changed to)
Please use italic font for the species name. In botanical nomenclature, author citation is a way of citing a person or group of people who have properly published a botanical name, i.e. who were the first to publish the name while meeting the formal requirements set out in the International Code of Nomenclature for Algae, Fungi and Plants (ICN). The name or abbreviation of such a person is usually given after the taxon name in italics, in parentheses, i.e. Hemerocallis citrina (Baroni)

Materials and Methods

2.1. Site Description

Line 103: of the area → of the presented district area.

2.2. Soil Sampling

Line 115: Please provide information on whether the same variety of daylily was grown at each of the sites assessed?

Line 118: Was manure fertilized for daylily cultivation? In perennial crops (perennial plants), manure is used to provide plants with nutrients for many years. In the case of lilies, relatively deep cultivation is used and manure goes quite deep, sometimes this depth reaches 40-50 cm. Please state whether organic fertilization was used in daylily cultivation?

Line 119: Please indicate whether organic fertilization was used in the cultivation of corn. We know that corn is a plant under which organic fertilization is used, e.g. manure. It also tolerates fertilization with liquid manure (slurry) derived from breeding pigs and dairy cows. Did the authors of the study pay attention to this?

Line 123: ring knife → ring-knife soil sampler

Line 127: “The fully mixed sample was divided…”
Please explain why samples taken from each layer after transporting to the lab after removing rocks, roots, nodules, after drying were fully mixed? This part is unclear. Were three subsamples mixed (from each layer) or were all subsamples mixed? Please write it in a way that is understandable.

Line 129: retention → reserve (backup) sample?

Table 1: As usual when specifying geographic coordinates, please first provide Latitude and then Longitude in this table
Please provide the latitude and longitude in degrees, minutes, and seconds as you did in Site description line 97. The coordinates provided are currently inaccurate. Provide the soil sampling points with an accuracy of seconds, e.g. 40°06'00.22"N 113°34'12.18"E

2.3. Analysis of Soil Physical and Chemical Parameters

Line 144: Please add the potentiometer model, type, producer

Line 146: Please add the flame photometer model, type, and producer as you did in line 140 for Mastersizer 3000 analyzer

Line 147: Please see the comment, line 146

2.4. Statistical Analysis

Line 149: SOC density is calculated as follows → SOC density was calculated as follows

Line 154: is the same → was performed analogously.

Line 156: SOC stocks is calculated → SOC stocks were calculated

Line 179: longitude, latitude → latitude and longitude

Line 189: Please add (IBM, Armonk, NY, USA),
AMOS 21.0 → AMOS (Analysis of Moment Structures) 21.0 module of SPSS.

Results

3.1. Effects of Planting Daylilies on SOC Stocks at 0–100 cm Depth

Table 2: Tables and figures included in the manuscript must be legible even when read separately, therefore it is recommended to provide explanations of abbreviations for each table and figure separately. Therefore, please provide explanations of site/village abbreviations: ZGZ, Zhong Gao Zhuang; XYJ, Xia Yu Jian; DS, Du Shu; GJYT, Guo Jia Yao Tou; SYJ, Shang Yu Jian; SZZ, Shan Zi Zao; XJB, Xu Jia Bao; SJZ, Su Jia Zhai.

Discussion

Line 346: “…and quality.” I would be careful with such a statement. Did the authors assess the quality of soil carbon? If they did so in another publication, please cite that publication. If other authors reached such conclusions, then please cite the publication of those authors.

Conclusions

References

Yours sincerely

Reviewer

Comments for author File: Comments.pdf

Author Response

Dear reviewer 1,

Thank you for your letter and for the reviewers’ comments concerning our manuscript entitled " Soil Organic Carbon Stocks Under Daylily Cultivation and Its Influencing Factors in the Agro-Pastoral Ecotone of Northern China ". Those comments are important for guiding significance to our researches. We have made corrections which we hope meet with approval. Revised portion have been marked in yellow in the paper. The main corrections in the paper and responds to the comments of editor and reviewers are as following:

Introduction

Response: Thank you for your comments. We have replaced the previous term with "Hemerocallis citrina Baroni" in the manuscript. The change can be found in line 50, which was highlighted for your review as follows:

Like other perennial crops, the daylily (Hemerocallis citrina Baroni), a perennial root herb, typically grows for 12–15 years, thriving over multiple growing seasons without the need for annual replanting.

Materials and Methods

2.1. Site Description

Line 103: of the area → of the presented district area.

Response: We have replaced the previous expression with "of the presented district area" in the manuscript. The change can be found in lines 107-108, which was highlighted for your review as follows:

The dominant soil type, Chestnut-Calcareous, which is characterized by high pH, poor water retention, and low SOC content, covers 86.33% of the presented district area.

2.2. Soil Sampling

Line 115: Please provide information on whether the same variety of daylily was grown at each of the sites assessed?

Response: In our study, the same variety of daylily was grown at all the sites assessed. Relevant research has indicated that apart from four daylily germplasms from Fengyu Village and Hedian Village, the remaining 134 germplasms from Yunzhou District, Datong City, are all the “Datong Huanghua” variety [1].

Response: During sampling, we inquired with the farmers and learned that no manure was applied in the cultivation of daylilies; instead, compound fertilizers containing nitrogen, phosphorus, and potassium, as well as urea, were mainly used.

Response: Thank you for your comment. We apologize for the omission in the original manuscript. No manure was used in the cultivation of corn. Instead, formula fertilizers and urea were primarily applied. This aspect was considered in the experimental design, but it was omitted in the text. We have now added the necessary clarification in lines 121-122, which we have highlighted for your review as follows:

To ensure the comparability of the results, all sample sites met the following criteria: (1) they were geographically close to each other (within 200 m) to minimize the impact of factors such as elevation and soil type, (2) the crops were growing robustly, reducing the influence of tillage management practices on the experimental results, and (3) no organic fertilizer was used during the planting process to avoid interference with the experimental results.

Line 123: ring knife → ring-knife soil sampler

Response: We have replaced the previous expression with "ring-knife soil sampler" in the manuscript. The change can be found in line 130, which was highlighted for your review as follows:

In each layer of soil, we used a ring-knife soil sampler with a volume of 200 cm³ to collect the undisturbed soil, and sampling was performed thrice per layer.

Response: Thank you for your comments. We apologize for the lack of clarity in the original description. We have revised the text to better explain the procedure in lines 133-138, which was highlighted for your review as follows:

Additionally, composite soil samples were separately collected from each layer. After removing rocks, roots, nodules, the stratified soil samples were dried naturally under ventilation conditions. The well-mixed sample was divided into two parts: one was ground and passed through a 2-mm sieve for subsequent determination of physical and chemical properties, the other copy was kept as a reserve (backup) sample.

Line 129: retention → reserve (backup) sample?

Response: We have replaced the previous expression with "reserve (backup) sample" in the manuscript. The change can be found in line 137, which was highlighted for your review as follows:

The well-mixed sample was divided into two parts: one was ground and passed through a 2-mm sieve for subsequent determination of physical and chemical properties, the other copy was kept as a reserve (backup) sample.

Table 1: As usual when specifying geographic coordinates, please first provide Latitude and then Longitude in this table

Response: Thank you for your comments. We have revised Table 1. The change was highlighted for your review as follows:

Table 1. Sampling point description (0–10 cm).

Site /village	Latitude (°N)	Longitude (°E)	Elevation (m)	Aspect (°)	Slope (°)	SOC (g kg^-1)	BD (g cm^-3)	SWC (%)	pH
ZGZ	40.10	113.57	1108.85	170.88	3.25	9.80	1.39	9.26	9.27
XYJ	40.09	113.54	1076.44	237.84	3.59	8.49	1.41	5.91	8.96
DS	40.08	113.46	1047.08	274.11	2.62	9.13	1.25	9.43	8.61
GJYT	40.03	113.51	1020.86	266.75	6.06	8.29	1.41	5.61	9.53
SYJ	40.11	113.55	1116.84	253.73	4.05	7.96	1.36	3.68	8.63
SZZ	40.08	113.70	1155.64	126.38	4.05	8.49	1.25	5.06	9.13
XJB	39.92	113.69	1078.61	206.44	2.45	7.65	1.35	4.45	9.20
SJZ	39.99	113.48	1000.97	269.53	1.40	6.79	1.39	5.92	8.73

Note: ZGZ is the abbreviation for Zhong Gao Zhuang Village, XYJ for Xia Yu Jian Village, DS for Du Shu Village, GJYT for Guo Jia Yao Tou Village, SYJ for Shang Yu Jian Village, SZZ for Shan Zi Zao Village, XJB for Xu Jia Bao Village, and SJZ for Su Jia Zhai Village. Aspect refers to the orientation of a slope, measured in degrees (°). It is defined with north as 0° or 360° and increases in a clockwise direction. For example, 90° indicates an east-facing slope, 180° indicates a south-facing slope, and 270° indicates a west-facing slope.

Please provide the latitude and longitude in degrees, minutes, and seconds as you did in Site description line 97. The coordinates provided are currently inaccurate. Provide the soil sampling points with an accuracy of seconds, e.g. 40°06’00.22"N 113°34’12.18"E

Response: We have revised the coordinates to ensure they are accurate and presented in the format of degrees, minutes, and seconds in line 101. The change was highlighted for your review as follows:

Yunzhou District (40°06’00.22"N, 113°34’12.18"E), one of China's four main daylily production areas, is located in the middle of the agricultural-pastoral ecotone in northern China (Figure 1), covering 1478 km².

2.3. Analysis of Soil Physical and Chemical Parameters

Line 144: Please add the potentiometer model, type, producer

Line 146: Please add the flame photometer model, type, and producer as you did in line 140 for Mastersizer 3000 analyzer

Line 147: Please see the comment, line 146

Response: We have added the detailed information of the potentiometer, including its model, type, and producer, in lines 158-166. The changes were highlighted for your review as follows:

Soil pH was measured by potentiometric method (soil:water ratio was 1:2.5) using a STARTER3100 Portable pH Meter (Ohaus International Trading (Shanghai) Co., Ltd., Shanghai, China) [2]. Soil available phosphorus (AP, mg kg^-1) was determined using the sodium hydrogen carbonate solution-Mo-Sb anti spectrophotometric method with a 722E Visible Spectrophotometer (Shanghai Spectrum Instrument Co., Ltd., Shanghai, China) [2]. Soil available potassium (AK, mg kg^-1) was determined using the Flame photometer method with an FP640 Flame Photometer (Shanghai INESA Analytical Instruments Co., Ltd., Shanghai, China) [2].

2.4. Statistical Analysis

Line 149: SOC density is calculated as follows → SOC density was calculated as follows

Response: We have replaced the previous expression with "SOC density was calculated as follows" in the manuscript. The change can be found in line 168, which was highlighted for your review as follows:

SOC density was calculated as follows

Line 154: is the same → was performed analogously.

Response: We have replaced the previous expression with "was performed analogously" in the manuscript. The change can be found in line 174, which was highlighted for your review as follows:

SOC stocks at 0–100 cm depth is the sum of SOC density of soil layers 0–100 cm, and the calculation of SOC stocks at 0–30 cm depth and SOC stocks at 30–100 cm depth was performed analogously.

Line 156: SOC stocks is calculated → SOC stocks were calculated

Response: We have replaced the previous expression with "SOC stocks were calculated" in the manuscript. The change can be found in line 175, which was highlighted for your review as follows:

The relative change of SOC stocks were calculated as follows

Line 179: longitude, latitude → latitude and longitude

Response: We have replaced the previous expression with "latitude and longitude" in the manuscript. The change can be found in line 198, which was highlighted for your review as follows:

the correlation between SOC stocks at 0–100 cm depth and latitude and longitude, elevation, aspect, or slope was analyzed, ...

Line 189: Please add (IBM, Armonk, NY, USA),
AMOS 21.0 → AMOS (Analysis of Moment Structures) 21.0 module of SPSS.

Response: We have revised the previous expression in lines 208-210, which was highlighted for your review as follows:

General statistical analysis was performed using SPSS 27 (IBM, Armonk, NY, USA). SEM was performed using AMOS (Analysis of Moment Structures) 21.0 module of SPSS.

3 Results

3.1. Effects of Planting Daylilies on SOC Stocks at 0–100 cm Depth

Response: We have revised the Table 2 to include explanations of the site/village abbreviations. The change was highlighted for your review as follows:

Table 2. SOC stocks at 0–100 cm depth at each sampling point (kg m^-2).

Treatments	Site / village								Mean
Treatments	ZGZ	XYJ	DS	GJYT	SYJ	SZZ	XJB	SJZ	Mean
LD	5.37	5.28	6.78	5.43	5.50	4.98	6.40	5.50	5.66 A
SD	4.87	5.22	5.84	4.89	4.68	4.41	5.42	5.35	5.09 AB
CK	4.08	5.24	5.28	4.79	4.11	4.02	5.33	4.92	4.72 B
Mean	4.77 bc	5.25 abc	5.97 a	5.04 abc	4.77 bc	4.47 c	5.72 ab	5.26 abc	5.15

Note: Different capital letters indicate that there are significant differences in different treatments at p < 0.05 level; Different lowercase letters indicate significant differences at p < 0.05 at different sampling points. ZGZ is the abbreviation for Zhong Gao Zhuang Village, XYJ for Xia Yu Jian Village, DS for Du Shu Village, GJYT for Guo Jia Yao Tou Village, SYJ for Shang Yu Jian Village, SZZ for Shan Zi Zao Village, XJB for Xu Jia Bao Village, and SJZ for Su Jia Zhai Village.

4 Discussion

Response: Thank you for your insightful comment. The statement regarding the “quality” of SOC was not directly assessed in our study. We have removed the phrase “and quality” from the sentence to ensure that our conclusions are accurately and appropriately supported by the data presented in this study. The change can be found in lines 371-372 and is presented as follows:

This result may reflect the deeper roots of daylilies and the higher turnover and secretion rate of fine roots, which increase the quantity of the SOC input.

References

1.Wang, L.W.; Hou, F.F.; Wu, J.; Gao, Y.; Zhang, W.; Wang, J.Y.; Yang, W.J.; Li, S.; Xing, G.M. Investigation and analysis of daylily resources in Yunzhou District, Datong. Shanxi Agricultural Sciences 2023, 51, 663–675. (in Chinese).

2.Bao, S. Soil Agro-chemistrical Analysis; China Agriculture Press (in Chinese): Beijing, 2008.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

article agronomy-3525436

Soil Organic Carbon Stocks Under Daylily Cultivation and Its Influencing Factors in the Agro-Pastoral Ecotone of Northern China

Zhen Wang ¹, Zelong Yao ¹, Hongfen Zhu ¹, and Rutian Bi ^{1, 2,*}

¹College of Resources and Environment, Shanxi Agricultural University, Taigu, Shanxi 030801, China;

s20222278@stu.sxau.edu.cn (Z.W.); 20232284@stu.sxau.edu.cn (Z.Y.)

² Datong Daylily Industrial Development Research Institute, Datong 037004, China

* Corresponding author: brt@sxau.edu.cn (R.B.)

General assessment of the subject studied

In this study, the authors emphasize the significant role that the daylily crop has, after a crop period of over 10, in increasing soil organic carbon stocks in the Agro-Pastoral Ecotone of Northern China, thus contributing to climate change mitigation. Through a fine-grained statistical analysis, the authors particularly highlighted the geographical importance of site on soil organic carbon stocks at 0-100 cm depth, compared to crop types in different geographical locations. In what is presented in this article, we found a rigorous scientific documentation, which was the basis of the objective taken in the study and which substantiated from a scientific point of view the results obtained, by citing in the paper 63 bibliographic titles, of which approx. 46% represent scientific novelties obtained in the last 5 years.

There are a few observations and suggestions, which I will present below:

Abstract:

R22: The acronyms: TN, AP, AK, SWC should also be explained in the summary, although they are explained in point 2.3. Analysis of Soil Physical and Chemical Parameters

Materials and Methods

R 132: Explain in the text what the 5th column of table 1 – „Aspect (°)” represents??

R 143-146: Please cite references regarding the working methods for the determination of: SOC, TN, pH and AP

Results

R216: Correct the SD value (5.08 kg m-²) in the text because in table 2 it is SD= 5.09 kg m-²

Figure 4: Write on the graphs in figures 4a, 4b, 4c, 4d and 4e, the shape of the linear or polynomial functions and the value of the correlation coefficients (r) to understand the significance of the SOC correlation according to the 24 cases of longitude, latitude, elevation, aspect, and slope.

R269-270: Attention!!!: Silt and sand indicate distinctly significant correlations with TN in the SD variant. Please correct!!

R284-288: Correct the total effect of the soil physicochemical properties on SOC, by writing the negative sign („-”) of the values in the text, according to the trend in Figure 7, as follows:

- in the LD variant: pH (-0.311), SWC (-0.152), BD (-0.021)

- in the SD variant: SWC (-0.429), pH (-0.166) and BD (-0.062)

- in the AK variant: SWC (-0.307), BD (-0.093) and pH (-0.061)

Figure 7/R301: Explain the SEM indices, respectively: RMSEA (Root Mean Square Error of Approximation); GFI (Goodness of Fit Index); NFI (Normed Fit Index); TLI (Tucker Lewis index); CFI (Comparative Fit Index) in subsection 2.4. Statistical Analysis / R162.... Structural equation model (SEM)….

Date: March 10, 2025 Review - v1

Author Response

Dear reviewer 2,

General assessment of the subject studied

There are a few observations and suggestions, which I will present below:

Abstract:

R22: The acronyms: TN, AP, AK, SWC should also be explained in the summary, although they are explained in point 2.3. Analysis of Soil Physical and Chemical Parameters

Response: Thank you for your comment. We have revised in the summary section in lines 22-24 to ensure clarity and completeness. The change was highlighted for your review as follows:

At the same location, SEM revealed that soil factors influenced SOC differently across treatments: for LD, soil total nitrogen (TN) > pH > soil water content (SWC); for SD, TN > SWC > soil available phosphorus (AP); for CK, TN > soil available potassium (AK) > SWC.

Materials and Methods

R 132: Explain in the text what the 5th column of table 1 – “Aspect (°)” represents??

Response: We have added an explanation in lines 147-150. The change was highlighted for your review as follows:

Aspect refers to the orientation of a slope, measured in degrees (°). It is defined with north as 0° or 360° and increases in a clockwise direction. For example, 90° indicates an east-facing slope, 180° indicates a south-facing slope, and 270° indicates a west-facing slope.

R 143-146: Please cite references regarding the working methods for the determination of: SOC, TN, pH and AP

Response: We have added the relevant references in lines 157-163, which was highlighted for your review as follows:

SOC (g kg^-1) content was determined using dichromate oxidation method [1]. Soil total nitrogen (TN, g kg^-1) was determined using the Kjeldahl method [1]. Soil pH was measured by potentiometric method (soil:water ratio was 1:2.5) [1]. Soil available phosphorus (AP, mg kg^-1) was determined using the sodium hydrogen carbonate solution-Mo-Sb anti spectrophotometric method [1]. Soil available potassium (AK, mg kg^-1) was determined using the Flame photometer method [1].

Results

R216: Correct the SD value (5.08 kg m-²) in the text because in table 2 it is SD= 5.09 kg m-²

Response: We have corrected the SD value in the text to match the value reported in Table 2 (SD = 5.09 kg m⁻²). The change can be found in line 242, which was highlighted for your review as follows:

At soil depth of 0–100 cm, the SOC stocks of LD (5.66 kg m^-²) increased by 19.63% and SD (5.09 kg m^-²) increased by 7.60%, compared with that of CK (4.72 kg m^-²) (Table 2 and Figure 3c).

Figure 4: Write on the graphs in figures 4a, 4b, 4c, 4d and 4e, the shape of the linear or polynomial functions and the value of the correlation coefficients (r) to understand the significance of the SOC correlation according to the 24 cases of longitude, latitude, elevation, aspect, and slope.

Response: Thank you for your suggestion regarding Figure 4. We have made the following revisions to address your concerns:

1) We have added the equations of the fitted linear or polynomial functions to the graphs in Figures 4 to clearly indicate the relationship between SOC and the variables (longitude, latitude, elevation, aspect, and slope).

2) To avoid confusion, we have changed the notation from “ r²” (which may be interpreted as the correlation coefficient squared) to “ R²”, representing the coefficient of determination, which measures the goodness of fit for the regression models. The revised figure is as follows:

Figure 4. Relationship between SOC stocks at 0–100 cm depth and (a) longitude, (b) latitude, (c) elevation, (d) aspect, and (e) slope.

R269-270: Attention!!!: Silt and sand indicate distinctly significant correlations with TN in the SD variant. Please correct!!

Response: Thank you for pointing out the issue. We have revised the text to accurately reflect the findings in lines 293-296, which was highlighted for your review as follows:

Under CK treatment, soil texture (clay, silt, and sand) showed significant correlations with SOC density (p < 0.05), whereas no significant correlations were observed between soil texture and SOC density under LD or SD treatments.

R284-288: Correct the total effect of the soil physicochemical properties on SOC, by writing the negative sign (“-”) of the values in the text, according to the trend in Figure 7, as follows:

- in the LD variant: pH (-0.311), SWC (-0.152), BD (-0.021)

- in the SD variant: SWC (-0.429), pH (-0.166) and BD (-0.062)

- in the AK variant: SWC (-0.307), BD (-0.093) and pH (-0.061)

Response: Thank you for your detailed feedback. We appreciate your attention to the presentation of the total effects of soil physicochemical properties on SOC. To ensure clarity and avoid potential confusion, we have revised the text to focus on the ranking of the total effects rather than on their specific magnitudes. The change can be found in lines 310-313, which was highlighted for your review as follows:

Regarding the total effect of soil physicochemical properties on SOC, LD was the most affected by TN, followed by pH, SWC, AK, BD and AP (Figure 7b). For SD, TN had the largest effect, followed by SWC, AP, AK, pH, and BD (Figure 7d). For CK, TN had the largest effect, followed by AK, SWC, AP, BD, and pH (Figure 7f).

Figure 7/R301: Explain the SEM indices, respectively: RMSEA (Root Mean Square Error of Approximation); GFI (Goodness of Fit Index); NFI (Normed Fit Index); TLI (Tucker Lewis index); CFI (Comparative Fit Index) in subsection 2.4. Statistical Analysis / R162.... Structural equation model (SEM)….

Response: We have added explanations for the SEM indices in subsection 2.4. Statistical Analysis. The descriptions can be found in lines 209-213, which was highlighted for your review as follows:

SEM was performed using AMOS (Analysis of Moment Structures) 21.0 module of SPSS. Model fit was evaluated by: χ²/df (ideal range: 1–3), RMSEA (Root Mean Square Error of Approximation; ≤0.08), GFI (Goodness-of-Fit Index; ≥0.90), NFI (Normed Fit Index; ≥0.90), TLI (Tucker Lewis Index; ≥0.90), CFI (Comparative Fit Index; ≥0.95).

References

1.Bao, S. Soil Agro-chemistrical Analysis; China Agriculture Press (in Chinese): Beijing, 2008.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The research topic is interesting and relevant to the current issue of soil health management. Some issues of the manuscript need to be addressed and explained reasonably as follows.

Line25 , first key word is long

In the beginning of the introduction, it would be nice to mention how perineal plants contribute to increase soil carbon.

Line 59-61, move this sentence to materials and method 2.1 sub section. And line 61 to 67 merge to the last paragraph of the introduction section.

Line 136-147, Cite the methods used for soil analysis.

Lines, 150-157, Provide reference for equation 1&2

Discussion

The section effectively explains the results and contextualizes them within existing literature. It follows a logical structure, moving from SOC stock comparisons to influencing factors and broader implications.

The discussion references relevant studies to support findings, enhancing credibility. The discussion addresses vertical SOC distribution, influencing environmental factors, and management practices. The final section ties the study’s findings to real-world applications, emphasizing the significance of LD for carbon sequestration and soil health.

One more thing can be added to lines 382-384 about the accumulation of SOC with management activities, such as adding soil amendment products such as char materials that do not decompose readily in the soil. You can refer to the latest research (https://www.mdpi.com/2571-8789/8/3/82 ), which indicated a significant increase in SOC with char amendments.

Conclusion

Overall, it looks good and suggests providing recommendations and future research directions in the field of study to advance scientific knowledge in the field.

Comments on the Quality of English Language

Overall, the English language looks good; however, Some redundancies were noticed in the introduction and the discussion section.

Author Response

Dear reviewer 3,

Comments and Suggestions for Authors

The research topic is interesting and relevant to the current issue of soil health management. Some issues of the manuscript need to be addressed and explained reasonably as follows.

Line25 , first key word is long

Response: Thank you for pointing out the issue. We have revised lines 27-28. The change was highlighted for your review as follows:

Keywords: Daylily; Crop comparison; Subsoil carbon; Ecological restoration; Structural equation model

In the beginning of the introduction, it would be nice to mention how perennial plants contribute to increase soil carbon.

Response: We have revised the beginning of the Introduction section to highlight how perennial plants contribute to increasing soil carbon. The change can be found in lines 31-32 and is as follows:

Perennial crops often develop deep root systems, which contribute to enhanced soil structure and the continuous input of organic matter.

Line 59-61, move this sentence to materials and method 2.1 sub section. And line 61 to 67 merge to the last paragraph of the introduction section.

Response: Thank you for your suggestions regarding the organization of the text. The modifications have been made to enhance the logical consistency of the manuscript as follows:

(1) L84-90: Owing to the long-term effects of drought, strong winds, and unsustainable human activities—such as intensive farming, overgrazing, and overharvesting—the agro-pastoral ecotone in northern China is sensitive to environmental changes and has low ecological resilience, making it ecologically fragile [1]. We hypothesize that despite these challenging environmental conditions, daylily cultivation could still improve SOC stocks resulting in the enhancement of soil structure, thereby contributing to the ecological protections of the area. Therefore, the objectives of this study are to: (1) investigate the characteristics of SOC stocks at depths of 0–100 cm under short-term and long-term daylily cultivation, compared to the dominant local annual crop of maize, (2) identify the influencing factors of SOC stocks across different geographic locations, and (3) examine the effects of SOC variation between daylily and maize cultivation under similar geographic conditions.

(2) L98-100: The agro-pastoral ecotone in northern China, located in semi-arid and arid zones with an annual precipitation of 300–400 mm, is characterized by the overlap of agriculture and animal husbandry both spatially and temporally [2,3].

Line 136-147, Cite the methods used for soil analysis.

Response: We have added the relevant references in lines 157-166, which was highlighted for your review as follows:

SOC (g kg^-1) content was determined using dichromate oxidation method [4]. Soil total nitrogen (TN, g kg^-1) was determined using the Kjeldahl method [4]. Soil pH was measured by potentiometric method (soil:water ratio was 1:2.5) [4]. Soil available phosphorus (AP, mg kg^-1) was determined using the sodium hydrogen carbonate solution-Mo-Sb anti spectrophotometric method [4]. Soil available potassium (AK, mg kg^-1) was determined using the Flame photometer method [4].

Lines, 150-157, Provide reference for equation 1&2

Response: We have added the relevant references for equation 1&2, which was highlighted for your review as follows:

SOC density was calculated as follows [5]:

(1)

where SOC density_i is SOC density (kg m^-2) of layer i, SOC_i is SOC content (g kg^-1) of layer i, BD_i is BD (g cm^-3) of layer i, and D_i is the soil layer thickness (cm) of layer i.

SOC stocks at 0–100 cm depth is the sum of SOC density of soil layers 0–100 cm, and the calculation of SOC stocks at 0–30 cm depth and SOC stocks at 30–100 cm depth was performed analogously.

The relative change of SOC stocks were calculated as follows [5]:

(2)

where Relative Change of SOC stocks is the relative change (%) of the SOC stocks of the treatment group versus the SOC stocks of the control group. SOC stocks_t and SOC stocks_c were SOC stocks in treatment group and control group, respectively. LD and SD were the treatment groups, while CK was the control group.

Discussion

Response: We have added the relevant references about the accumulation of SOC with management activities, which was highlighted for your review as follows:

On the other hand, management activities such as fertilization, irrigation, and soil erosion control increase the accumulation of organic carbon [6,7].

Conclusion

Overall, it looks good and suggests providing recommendations and future research directions in the field of study to advance scientific knowledge in the field.

Response: Thank you for your positive feedback. We have included recommendations and future research directions in Section 4.3 Significance and Limitations of our manuscript in lines 464-471.

Although this study highlights the positive effects of daylily cultivation on increasing SOC stocks, further research is needed to explore its underlying mechanisms. Future studies could focus on various aspects, including differences in aboveground and belowground biomass, the accumulation and transformation of different carbon fractions, and the roles of root systems and microbial activity in carbon cycling. These investigations would provide a theoretical foundation for a more comprehensive understanding of the impact of daylily cultivation on SOC accumulation and offer practical guidance for soil carbon management and ecological restoration.

References

1.Guo, Z.C.; Li, Y.Q.; Wang, X.Y.; Gong, X.W.; Chen, Y.; Cao, W.J. Remote Sensing of Soil Organic Carbon at Regional Scale Based on Deep Learning: A Case Study of Agro-Pastoral Ecotone in Northern China. Remote Sens. 2023, 15. DOI: 10.3390/rs15153846.

2.Wang, X.Y.; Li, Y.G.; Gong, X.W.; Niu, Y.Y.; Chen, Y.P.; Shi, X.P.; Li, W. Storage, pattern and driving factors of soil organic carbon in an ecologically fragile zone of northern China. Geoderma 2019, 343, 155-165. DOI: 10.1016/j.geoderma.2019.02.030.

3.Lu, H.Y.; Chen, X.Y.; Ma, K.; Zhou, S.W.; Yi, J.L.; Qi, Y.J.; Hao, J.L.; Chen, F.; Wen, X.Y. Soil health assessment under different soil and irrigation types in the agro-pastoral ecotone of northern China. Catena 2024, 235. DOI: 10.1016/j.catena.2023.107655.

4.Bao, S. Soil Agro-chemistrical Analysis; China Agriculture Press (in Chinese): Beijing, 2008.

5.Xu, Y.; Zhou, J.; Liu, C.Y.; Jia, R.; Ji, H.J.; Dippold, M.A.; Zhao, T.; Pavinato, P.S.; Peixoxo, L.; Yang, Y.D.; et al. Long-term rotational and perennial cropping benefit soil organic carbon stocks and ecosystem multifunctionality. Industrial Crops and Products 2024, 209. DOI: 10.1016/j.indcrop.2023.117980.

6.Lal, R. Soil carbon sequestration impacts on global climate change and food security. Science 2004, 304, 1623-1627. DOI: 10.1126/science.1097396.

7.Thapa, R.B.; Budhathoki, S.; Shilpakar, C.; Panday, D.; Alsunuse, B.; Tang, S.X.; Stahl, P.D. Enhancing Corn Yield and Soil Quality in Irrigated Semiarid Region with Coal Char and Biochar Amendments. Soil Systems 2024, 8, 82. DOI: 10.3390/soilsystems8030082

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Review ID: agronomy-3525436 “Soil Organic Carbon Stocks Under Daylily Cultivation and Its Influencing Factors in the Agro-Pastoral Ecotone of Northern China”

The article addresses the influence of short- and long-term perennial crops on the increase in soil organic carbon in the agro-pastoral ecotone in northern China. The study was carried out in an experimental area to evaluate the long-term impact, greater than 10 years, of short-term, approximately 5 years of daylily cultivation on SOC stocks and in an area of long-term maize cultivation.

The article addresses a relevant topic in the context of climate change and the importance and increase in SOC stocks in soils.

The article is didactically written and organized, with an adequate experimental design. The figures and tables are all necessary.

Only a few considerations for fine-tuning the article remain.

- Despite the list of acronyms at the end of the text, the abstract uses several acronyms that should be previously explained.

- In the keywords, terms and expressions that are part of the title should be avoided.

- In Figure 1, the acronyms are not explained explicitly, but they are explained in Table 1. I recommend that you mention Figure 1, which describes the acronyms in Table 1.

In the text, in lines 234 to 242 and Figure 4, the low r2 (between 0.12 and 0.33) should be better explained or justified, even considering the ,

In Figure 6, there is the acronym SOSD without meaning and not identified in the figure. It is necessary to improve the explanation of this calculation to avoid the effect of different depths. But, shouldn't the different depths have different effects or show differences in soil properties and carbon storage capacity?

Despite the few errors, it is necessary to review and adjust the references according to the journal's standards.

Comments for author File: Comments.pdf

Author Response

Dear reviewer 4,

The article addresses a relevant topic in the context of climate change and the importance and increase in SOC stocks in soils.

The article is didactically written and organized, with an adequate experimental design. The figures and tables are all necessary.

Only a few considerations for fine-tuning the article remain.

Despite the list of acronyms at the end of the text, the abstract uses several acronyms that should be previously explained.

Response: Thank you for your comment. We have revised in the abstract section in lines 22-24 to ensure clarity and completeness. The change was highlighted for your review as follows:

In the keywords, terms and expressions that are part of the title should be avoided.

Response: Thank you for pointing out the issue. We have revised the keywords in lines 27-28. The change was highlighted for your review as follows:

Keywords: Daylily; Crop comparison; Subsoil carbon; Ecological restoration; Structural equation model

In Figure 1, the acronyms are not explained explicitly, but they are explained in Table 1. I recommend that you mention Figure 1, which describes the acronyms in Table 1.

Response: We have revised the Figure 1 to include explanations of the site/village abbreviations. The change was highlighted for your review as follows:

Figure 1. Geographical location and sampling points in the study area. Note: ZGZ is the abbreviation for Zhong Gao Zhuang Village, XYJ for Xia Yu Jian Village, DS for Du Shu Village, GJYT for Guo Jia Yao Tou Village, SYJ for Shang Yu Jian Village, SZZ for Shan Zi Zao Village, XJB for Xu Jia Bao Village, and SJZ for Su Jia Zhai Village.

In the text, in lines 234 to 242 and Figure 4, the low r² (between 0.12 and 0.33) should be better explained or justified, even considering the ,

Response: Thank you for your insightful comments. In response to your suggestion, we have added a detailed explanation for these low R² values in lines 393-400 to better clarify the reasons behind these results. The change was highlighted for your review as follows:

The relatively low R² values obtained from the correlation analysis between geographical factors and SOC stocks in Figure 4 indicate that SOC storage is influenced by a complex interplay of multiple factors, and individual geographical factors have limited explanatory power [1]. However, this does not imply that the model is invalid. Instead, it highlights the necessity to incorporate additional potential influencing factors, such as vegetation types and soil nutrients [2], to provide a more comprehensive interpretation of the spatial distribution of SOC stocks.

Response: In response to your concerns, we have made the following revisions and explanations:

(1) In Figure 6, we have corrected “SOSD” to “SOS density” in line 319. The change was highlighted for your review as follows:

Figure 6. Relationship between SOC density and soil physicochemical properties under (a) LD, (b) SD, and (c) CK. Note: SOS density was processed during the correlation analysis to eliminate the effect of different sampling intervals.

(2) SOC density was calculated as follows [3]:

(1)

where SOC density_i is SOC density (kg m-2) of layer i, SOCi is SOC content (g kg-1) of layer i, BD_i is BD (g cm-3) of layer i, and D_i is the soil layer thickness (cm) of layer i.

(3) We acknowledge that soil properties and carbon density may vary across different depths. However, the objective of our study is to investigate the impact of different treatments (LD, SD, and CK) on SOC density through soil physicochemical properties, rather than examining the influence of soil properties at different depths on SOC density. Consequently, we adopted a uniform depth range of 0–100 cm for SOC density calculation to ensure the comparability and consistency of our study.

Despite the few errors, it is necessary to review and adjust the references according to the journal's standards.

Response: Thank you for your comments. We have carefully reviewed and adjusted the references according to the journal's standards.

References

1.Nan, F.S.; Li, Z.X.; Zhang, X.P.; Cui, Q.; Li, Y.C.; Xiong, X.T.; Yang, X.J.; Yang, A.L. Spatial Distribution Characteristics and Influencing Factors of Soil Organic Carbon Density in Yellow River Basin Based on MGWR Mode. Environmental Science 2023, 44, 912-923. DOI: 10.13227/j.hjkx.202203091.

2.Yang, J.G.; Zhang, L.W.; Guo, X.; Lu, Y.X.; Guo, H.; Zhang, Y.M.; Zhou, X.B. Vertical Distribution Characteristics and Influencing Factors of Soil Organic Carbon under Biological Soil Crusts in the Gurbantunggut Desert. Acta Ecol. Sin. 2024, 44, 2946-2954. DOI: 10.20103/j.stxb.202308101722.

3.Xu, Y.; Zhou, J.; Liu, C.Y.; Jia, R.; Ji, H.J.; Dippold, M.A.; Zhao, T.; Pavinato, P.S.; Peixoxo, L.; Yang, Y.D.; et al. Long-term rotational and perennial cropping benefit soil organic carbon stocks and ecosystem multifunctionality. Industrial Crops and Products 2024, 209. DOI: 10.1016/j.indcrop.2023.117980.

Author Response File: Author Response.pdf

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Soil Organic Carbon Stocks Under Daylily Cultivation and Their Influencing Factors in the Agro-Pastoral Ecotone of Northern China

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