Productivity and Forage Quality of Alfalfa Response to Potassium Fertilizer: A Field Study in Inner Mongolian Plateau

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

First, I would like to thank you for trusting me with the manuscript "_".

The authors of this study explained that soils are poor in K and that it is necessary to determine the dose of post-assic fertilizer to increase alfalfa productivity in an important livestock production region. The justification for the study is very well presented. I would only suggest adding information about the conventional method of alfalfa cultivation in the region, as this may imply a change in fertilizer management. However, the objective is very well established.

The M&M section is well described, with some reservations that I left in comments in the manuscript (transcribed below).

The Results section is well presented, with correct interpretations of the tables and figures, which are important for better understanding.

The discussion is adequate, as is the conclusion.

Below, I transcribe my considerations made in the manuscript (attached).

ABSTRACT: Line 17: add K₂O

KEYWORDS:  Line 27: Some keywords are already in the title, which is also an indexer. Replace them with others

MATERIALS AND METHODS:

1) Line 99: I don't understand! This concentration is too high! For my study conditions and cultures, k availability above 3.5 mmol/dm3 is considered high.

The justification for the study was that the cultivated soils in this region are deficient in K!!!

2) Line 110: In their conclusion, the authors recommend 273 kg/ha of K2O, after conducting an experiment with the proposed splitting (50 + 25 + 25% of the total dose evaluated). Therefore, the conclusion is based on this dose for three years of cultivation, not kg/ha year. I wonder if the alfalfa cultivation method in the studied region is three years of cultivation and then crop renewal? In other words, is it planted and harvested for two years, and then the crop is renewed? If so, I believe it would be interesting to include the cultivation method somewhere in the Introduction.

3) Line 142: and what about means test? Tukey?

4) Line 162: Same as line 142.

5) Line 164: The Y-axis represents the total amount of alfalfa produced per year (kg/ha year). What do the distribution points on the graph correspond to? It looks to me like the six averages of each harvest at each rate (over the two years). So, I can't understand the graph, because it shows the averages of each harvest, and the regression is for annual production (average of the two years).

6) Line 172: Forage yield (kg/ha year) as a function of potassium rate (means of two years).

 

in the X axis: K (kg ha-1 of K2O). I would like the authors to make this modification to all figures.

7) Line 174: I disagree with the title! It's not annual productivity (kg/ha). It's the average cumulative productivity of three harvests over two years. It's not annual productivity over two years.

8) Line 244: Even for such low coefficients of determination, was there significance in the linear regression?

9) Line 268: Same as line 162

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

We sincerely thank you for your positive feedback and valuable suggestion. We have carefully considered the comment regarding the conventional alfalfa cultivation method and have incorporated relevant information into the manuscript. We are pleased that the justification and objectives of the study were clearly conveyed.

We have revised the manuscript accordingly and would be grateful for any further suggestions the reviewer may have. Our point-by-point responses are detailed below.

Comment 1: Line 17: add K₂O

Response 1: Thank you for your advice, we I have add K₂O to the Abstract section.

Comment 2: Line 27: Some keywords are already in the title, which is also an indexer. Replace them with others

Response 2: Thanks, I have changed the keywords, as: “Medicago Sativa; potash fertilizer; yield, yield component; nutrition value”.

Comment 3: Line 99: I don't understand! This concentration is too high! For my study conditions and cultures, k availability above 3.5 mmol/dm3 is considered high. The justification for the study was that the cultivated soils in this region are deficient in K!!!

Response 3: We sincerely apologize for the error. We have re-examined the original soil data and made the necessary corrections. The methodology for soil analysis has also been added, along with the contents of total phosphorus, total potassium, Mg, and Ca. Based on the existing potassium content, the level is considered moderate to low, which met the experimental requirements.

Comment 4: Line 110: In their conclusion, the authors recommend 273 kg/ha of K2O, after conducting an experiment with the proposed splitting (50 + 25 + 25% of the total dose evaluated). Therefore, the conclusion is based on this dose for three years of cultivation, not kg/ha year. I wonder if the alfalfa cultivation method in the studied region is three years of cultivation and then crop renewal? In other words, is it planted and harvested for two years, and then the crop is renewed? If so, I believe it would be interesting to include the cultivation method somewhere in the Introduction.

Response 4：We sincerely thank the reviewer for this valuable suggestion. Indeed, a crop rotation system is practiced in this region. After three years of alfalfa cultivation, the experimental field was switched to potato in 2025. Relevant details have been added to the latter part of the Introduction.

Comment 5: Line 142: and what about means test? Tukey?

Response 5：We performed Tukey's honestly significant difference (HSD) test for mean separation following a significant ANOVA result (P < 0.05). This has been explicitly stated in the revised manuscript.

Comment 6: Line 162: Same as line 142.

Response 6: We performed Tukey's honestly significant difference (HSD) test for mean separation following a significant ANOVA result (P < 0.05).

Comment 7: Line 164: The Y-axis represents the total amount of alfalfa produced per year (kg/ha year). What do the distribution points on the graph correspond to? It looks to me like the six averages of each harvest at each rate (over the two years). So, I can't understand the graph, because it shows the averages of each harvest, and the regression is for annual production (average of the two years).

Response 7: Each data point represents the sum of the three harvest yields per replicate under the same treatment, i.e., the annual forage yield of each individual replicate. With three replicates per treatment over two years, there are a total of six replicates per treatment, hence six data points for each treatment. The corresponding description has been revised in the caption of Figure 1.

Comment 8:  Line 172: Forage yield (kg/ha year) as a function of potassium rate (means of two years).  in the X axis: K (kg ha^-1 of K₂O). I would like the authors to make this modification to all figures.

Response 8: Thank you for your suggestion. We have made this modification to all relevant figures.

Comment 9: Line 174: I disagree with the title! It's not annual productivity (kg/ha). It's the average cumulative productivity of three harvests over two years. It's not annual productivity over two years.

Response 9: We have revised the title to” Regression equations for estimating the K fertilizer application rates on the average cumulative productivity of three harvests over two years” to be more specific.

Comment 10: Line 244: Even for such low coefficients of determination, was there significance in the linear regression?

Response 10: We confirm that the linear regression relationships are indeed statistically significant (P < 0.01), even for the models with lower coefficients of determination (R²). In agricultural research, a low R² value can occur when the independent variable has a real but minor effect on the dependent variable, which is often the case for factors like plant density. The consistently high significance (P < 0.01) across all models strongly suggests that the observed relationships are not due to chance. Most importantly, the analysis effectively reveals that mass per shoot (mass shoot⁻¹) is the dominant yield component, whereas plant density and shoot density make relatively minor contributions.

Comment 11: Line 268: Same as line 162

Response 11: We performed Tukey's honestly significant difference (HSD) test for mean separation following a significant ANOVA result (P < 0.05).

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

First, I would like to express my gratitude for the opportunity to review the manuscript entitled "Productivity and forage quality of alfalfa response to potassium fertilizer in Inner Mongolian Plateau."

The topic of the manuscript is relevant and seeks answers to questions that are important from an agronomic perspective.

 

I have the following comments regarding the manuscript:

 

Abstract:

In line 22-23: K fertilization...: the results do not support this statement.

Instead of abbreviations, the full names of the parameters should be written out when they first appear, so in this section (Crude protein=CP, etc.).

Line 26: Since soil quality, type, and K content cannot be the same throughout the entire region, it would be an oversimplification to apply this statement to the entire region.

Materials and methods

The experimental soil has a high K content. How could this have affected the results of the experiment? Why are there no more favorable results without K supplementation?

Lines 133-137: How many independent samples were used to determine the quality parameters described?

 

Results:

I suggest revising Figures 2-5 so that they show the differences between the various K doses rather than the different harvest times. It should also be noted in a footnote that the different letters indicate these differences.

3.3.: Which of the regression equations refers to which parameter? This should be indicated after the equations!

3.4.: The analysis of the effect of K-dosing on quality parameters does not contain any well-founded conclusions, either in the Results or in the Discussion section. Results that do not differ significantly from each other cannot be interpreted as different.

What could be the reason for the different results of the effect of K-dosing on quality parameters in the two study years?

 

Discussion:

Typos:

Line 343: fertilization instead of fertility

Line 387: Olsen should be deleted, or it should be written that according to Olsen

 

Conclusion:

ctrl c - ctrl v Abstract or vice versa:

This section needs to be reworded or omitted!

Author Response

Dear Reviewer,

We sincerely thank you for your positive assessment of the manuscript's relevance and agronomic importance, as well as for your thorough and constructive comments. We have carefully considered each point and have revised the manuscript accordingly. Our point-by-point responses are detailed below.

Abstract:

Comment 1: line 22-23: K fertilization...: the results do not support this statement. Instead of abbreviations, the full names of the parameters should be written out when they first appear, so in this section (Crude protein=CP, etc.).

Response 1：We agree and have rephrased the relevant sentence to accurately reflect the specific findings presented in the manuscript. We have ensured that all abbreviations (e.g., CP for crude protein, TDN for total digestible nutrients, NDF for neutral detergent fiber, ADF for acid detergent fiber, RFV for relative feeding value) are now clearly defined upon their first use in the abstract.

Comment 2: Line 26: Since soil quality, type, and K content cannot be the same throughout the entire region, it would be an oversimplification to apply this statement to the entire region.

Response 2: We agree with this important point. The concluding statement has been modified to specify that the recommended application rate is suggested as a reference for local alfalfa production under the specific experimental conditions of this study, rather than for the entire region.

Materials and methods

Comment 3: The experimental soil has a high K content. How could this have affected the results of the experiment? Why are there no more favorable results without K supplementation?

Response 3: We apologize for the error in the original potassium content data. We have re-examined the original soil records and corrected the soil information throughout the manuscript.

Comment 4: Lines 133-137: How many independent samples were used to determine the quality parameters described?

Response 4: We have added this information to the methods section 2.2. Quality parameters were determined using a composite sample from the first harvest per plot, with three independent replicates (plots) per treatment.

Results:

Comment 5: I suggest revising Figures 2-5 so that they show the differences between the various K doses rather than the different harvest times. It should also be noted in a footnote that the different letters indicate these differences.

Response 5: We thank the reviewer for this suggestion. We have revised the titles of Figures 2-5 to highlight the differences between various K application rates (e.g., "Plant density of alfalfa under different K fertilizer rates in two years"). Additionally, we have added a note to each figure caption to clarify that different lowercase letters indicate significant differences among K treatments within the same harvest period (e.g., "Different lowercase letters indicate significant differences in plant density among different K application rates at the same harvest period (P < 0.05).").

Comment 6: 3.3.: Which of the regression equations refers to which parameter? This should be indicated after the equations!

Response 6: Thanks. We have clearly explained the meaning of each variable in the equations prior to presenting the regression models. For instance, we defined the variables as follows: plants m⁻² (D), shoots m⁻² (S), mass shoot⁻¹ (SM), height shoot⁻¹ (H), and forage yield (Y).

Comment 7: 3.4.: The analysis of the effect of K-dosing on quality parameters does not contain any well-founded conclusions, either in the Results or in the Discussion section. Results that do not differ significantly from each other cannot be interpreted as different.

What could be the reason for the different results of the effect of K-dosing on quality parameters in the two study years?

Response 7: Thank you for your comments. We have thoroughly revised this section and the corresponding discussion. For 2023 data where differences were not significant, we now focus on describing the numerical trends without implying statistical differences. More importantly, we have added a substantive discussion on the potential reasons for the stronger response in 2024, linking it to climatic differences and possible depletion of the soil's native K reserve. Please refer to the third paragraph of Section 4.3 for details.

 Discussion:

Comment 8: Line 343: fertilization instead of fertility

Response 8: Done.

Comment 9: Line 387: Olsen should be deleted, or it should be written that according to Olsen.

Response 9: Done.

Conclusion:

Comment 10: ctrl c - ctrl v Abstract or vice versa: This section needs to be reworded or omitted!

Response 10: We agree and have completely rewritten the conclusion section. It now presents a more succinct synthesis of the findings compared to the Abstract, utilizes different terminology and sentence structures, and incorporates a perspective on future research directions.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Dear authors,

The paper is based on a lot of experimental data, but not all the details of the statistical interpretation are provided. The significance of the established correlations is not clear. It is important to clarify this aspect, especially since, in conclusion, the recommended dose is based on a regression curve.

Below I present other aspects that require attention, clarification, or correction:

The abbreviation for temperature is temp., not tem. (see Table 1)

It is not clear whether the applied potassium doses are actually potassium sulfate doses or potassium ions: 0, 100, 200, 300, 400 kg ha^-1. If it is about potassium sulfate doses, then the corresponding K⁺ doses should also be calculated, and these should be mentioned in graphs and tables. (see table 2, figure 3….etc).

Line 193: The same as below???

Figure 2: It must be specified in the legend what the letters on the graph represent.

Figure 3, Figure 4, Figure 5: Eror bars? The letters? What do they represent?

Chapter 3.3: The significance is not calculated for each coefficient of determination (R²). A significance threshold of p<0.01 is mentioned for linear regression, but the R² value of 0.078 seems a bit low to me to be a significant dependence. It would be clearer if the significance threshold was calculated for R² or for the Pearson simple correlation coefficient (r).

It is necessary to check the bibliography and correct errors.

Author Response

Dear Reviewer,

We sincerely thank you for taking the valuable time to review our manuscript and for providing constructive feedback. We have thoroughly considered all your suggestions and have revised the paper accordingly. We hope that the revised version meets with your approval, and we welcome any further comments you may have. Our point-by-point responses are detailed below.

Comment 1: The abbreviation for temperature is temp., not tem. (see Table 1)

Response 1: We apologize for this oversight. The abbreviation in Table 1 has been corrected to "Temp." throughout the manuscript.

Comment 2: It is not clear whether the applied potassium doses are actually potassium sulfate doses or potassium ions: 0, 100, 200, 300, 400 kg ha^-1. If it is about potassium sulfate doses, then the corresponding K+ doses should also be calculated, and these should be mentioned in graphs and tables. (see table 2, figure 3….etc).

Response 2: We thank the reviewer for this important clarification. The applied doses refer to K₂O kg ha^-1, as is standard practice in agronomic literature for fertilizer recommendations. This has been explicitly stated in the "Experimental design and sampling" section (Line 116 in the revised manuscript). For absolute clarity, we have also added a sentence noting that the source was K₂SO₄ (52% K₂O). In each chart, we have also converted the unit of K fertilizer to kg ha^-1 of k₂O.

Comment 3: Line 193: The same as below???

Response 3: We have removed the phrase "The same as below" and have reformulated the figure captions and notes based on the specific details of each figure.

Comment 4: Figure 2: It must be specified in the legend what the letters on the graph represent.

Response 4: Thanks. Different lowercase letters indicate statistically significant differences among potassium application rates within the same harvest period (Tukey's test, P < 0.05).

Comment 5: Figure 3, Figure 4, Figure 5: Eror bars? The letters? What do they represent?

Response 5: In Figure3-5: Error bars represent the standard error of the mean (SEM). Different lowercase letters indicate statistically significant differences among potassium application rates within the same harvest period (Tukey's test, P < 0.05).

Comment 6: Chapter 3.3: The significance is not calculated for each coefficient of determination (R2). A significance threshold of p<0.01 is mentioned for linear regression, but the R2 value of 0.078 seems a bit low to me to be a significant dependence. It would be clearer if the significance threshold was calculated for R2 or for the Pearson simple correlation coefficient (r).

Response 6: We confirm that the linear regression relationships are indeed statistically significant (P < 0.01), even for the models with lower coefficients of determination (R²). In agricultural research, a low R² value can occur when the independent variable has a real but minor effect on the dependent variable, which is often the case for factors like plant density. The consistently high significance (P < 0.01) across all models strongly suggests that the observed relationships are not due to chance. Most importantly, the analysis effectively reveals that mass per shoot (mass shoot⁻¹) is the dominant yield component, whereas plant density and shoot density make relatively minor contributions. We appended P<0.01 and n=90 to each of the equations.

Comment 7: It is necessary to check the bibliography and correct errors.

Response 7: We have meticulously checked the entire reference list and corrected any formatting errors, ensuring consistency with the journal's guidelines. All in-text citations have been verified against the reference list. In addition, we have supplemented the reference list with relevant literature from recent years to enhance the timeliness and relevance of the research.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

ID:agronomy-3879805

Comments:

1. Tittle, abstrct: One or two years of field experiment is too little to generalize the title and final conclusion for the whole region, i.e. to the Inner Mongolian Plateau.
2. Keywords cannot be identical to the title and vice versa.
3. Lines 38-51; too much academic content.
4. There is a lack of information about the specificity, climate and soil conditions (deeper data) of the Inner Mongolian Plateau.
5. There is a lack of data on methods for determining the chemical properties of soil.
6. Table 1 lacks data on the amount and timing of irrigation.
7. Table 2 and others: full analysis of variance, including the Year × K dose interaction, is missing.
8. The analysis of Figures 2 and 3 does not show that Figure 1 is statistically reliable.
9. Line 243: some of these equations are statistically insignificant; the number of observations, n, is missing.
10. In this type of fertilizer experiment, chemical analysis results cannot be ignored. At a minimum, data should be provided for N, P, K, Mg, and Ca. It is the relationships between these factors that significantly influence the qualitative characteristics of the crop.
11. This manuscript, without taking into account the characteristics mentioned in point no. 10, does not contribute anything to the state of knowledge about the role of K in alfalfa production.
12. This type of article should include data on the content of at least mineral N, avilabele K, Ca, and Mg in the soil, at least at final harvest. Only by simultaneously analyzing the soil and the plant can the trend in alfalfa's response to K doses be explained.
13. The discussion, without the data mentioned in points 10-12, is meaningless. It is merely an expanded version of the research results chapter.
14. The literature is sufficiently rich, but there are no citations of the latest articles in this field.

Author Response

Dear Reviewer,

We sincerely thank you for your thorough and constructive comments, which have been invaluable in improving the quality of our manuscript. We have carefully considered all the points raised and have revised the manuscript accordingly. We would be grateful for any further suggestions the reviewer may have.

The main modifications are summarized below:

Comment 1: Tittle, abstrct: One or two years of field experiment is too little to generalize the title and final conclusion for the whole region, i.e. to the Inner Mongolian Plateau.

Response 1: We thank the reviewer for this comment. In response, we have revised both the title and the abstract. The title has been changed to "Productivity and forage quality of alfalfa response to potassium fertilizer: A field study in Inner Mongolian Plateau" to avoid being overly broad. Additionally, the abstract has been modified by qualifying the recommended application rate to better reflect the specific experimental conditions.

Comment 2: Keywords cannot be identical to the title and vice versa.

Response 2: We thank the reviewer for this suggestion. We have revised the keywords to avoid overlap with terms already present in the title. Keywords have been revised to: “Medicago Sativa; potash fertilizer; yield; yield component; nutrition value”

Comment 3: Lines 38-51; too much academic content.

Response 3: The excessive academic content in the introduction has been condensed.

Comment 4: There is a lack of information about the specificity, climate and soil conditions (deeper data) of the Inner Mongolian Plateau.

Response 4: We have added a dedicated paragraph describing the specific climatic conditions (arid climate, significant temperature variations, strong winds, short frost-free period) and soil properties (sandy loam, low fertility, risk of salinization) of the experimental site in the Inner Mongolian Plateau.

Comment 5: There is a lack of data on methods for determining the chemical properties of soil.

Response 5: The methodology for soil chemical analysis has been explicitly stated. We now specify that soil properties were determined following standard Chinese methods (e.g., GB/T 22108-2008). And, we also added the contents of total phosphorus, total potassium, Mg, and Ca.

Comment 6: Table 1 lacks data on the amount and timing of irrigation.

Response 6: We have added specific irrigation timing and amount details in the paragraph preceding Table 1. The text has been revised as follows: " The plots were irrigated both in spring during green-up and after the first two harvests in 2023 and 2024, as well as during the growing periods with no rainfall for approximately ten days. The irrigation method employed was drip irrigation, with each irrigation amount being approximately 50 mm."

Comment 7: Table 2 and others: full analysis of variance, including the Year × K dose interaction, is missing.

Response 7: The statistical analysis has been re-performed using a two-way ANOVA to include the Year × K dose interaction. The new supplementary tables (Table S1 and Table S2) presenting the full ANOVA results have been added.

Comment 8: The analysis of Figures 2 and 3 does not show that Figure 1 is statistically reliable.

Response 8: We explicitly state that the statistical significance of Figure 1 (regression of two-year average yield) is based on the robustness of the combined two-year dataset. Figures 2 and 3, however, illustrate the dynamics of plant density and shoot density, respectively. The incomplete consistency between Figures 2 and 3 is possible because yield is not solely determined by plant density and shoot number. This is verified by the regression analysis in Section 3.3, which demonstrates that forage yield is primarily determined by mass per shoot, while the contributions of plant density and shoot number, though present, are relatively minor.

Comment 9: Line 243: some of these equations are statistically insignificant; the number of observations, n, is missing.

Response 9: We confirm that the linear regression relationships are indeed statistically significant (P<0.01), even for the models with lower coefficients of determination (R²). In agricultural research, a low R² value can occur when the independent variable has a real but minor effect on the dependent variable, which is often the case for factors like plant density. The consistently high significance (P<0.01) across all models strongly suggests that the observed relationships are not due to chance. Most importantly, the analysis effectively reveals that mass per shoot (mass shoot⁻¹) is the dominant yield component, whereas plant density and shoot density make relatively minor contributions. We appended P<0.01 and n=90 to each of the equations.

Comment 10-13：In this type of fertilizer experiment, chemical analysis results cannot be ignored. At a minimum, data should be provided for N, P, K, Mg, and Ca. It is the relationships between these factors that significantly influence the qualitative characteristics of the crop.

This manuscript, without taking into account the characteristics mentioned in point no. 10, does not contribute anything to the state of knowledge about the role of K in alfalfa production.

This type of article should include data on the content of at least mineral N, avilabele K, Ca, and Mg in the soil, at least at final harvest. Only by simultaneously analyzing the soil and the plant can the trend in alfalfa's response to K doses be explained.

The discussion, without the data mentioned in points 10-12, is meaningless. It is merely an expanded version of the research results chapter.

Response 10-13: We thank you for your comments and agree with that the lack of detailed soil and plant nutrient analysis (for N, P, K, Mg, and Ca) is a significant limitation of our study, preventing a deeper investigation into the nutrient interactions the govern crop quality. We recognize that this omission constrains the mechanistic depth of our discussion.

In response, we have substantially revised the manuscript. While we cannot retroactively include this data, we have:

• The contents of total phosphorus, total potassium, Mg, and Ca have been added to the original soil parameters.
• Notwithstanding the aforementioned limitations, we have striven to conduct a more in-depth discussion of the results based on the available data and by citing some latest literature. We have moved beyond merely describing the results to instead interpreting them within the specific context of the aridand cold environment of the Inner Mongolian Plateau. For instance, when discussing the more pronounced quality response in 2024, we linked this phenomenon to the distinctive precipitation pattern of that year and the hypothesis of possible depletion of the soil potassium pool.
• Strengthened the discussion by citing relevant literature on potassium cycling and crop response to provide a more robust context for our findings, moving beyond a mere description of the results.

The primary contribution of this work is therefore positioned as providing a practically valuable fertilizer recommendation for alfalfa production under the specific soil and climatic conditions of the experimental area, based on a two-year field study. We explicitly state that future research should incorporate the detailed nutrient monitoring suggested by the reviewer to fully elucidate the physiological mechanisms involved.

We believe these revisions have improved the intellectual honesty and academic value of the manuscript, despite the acknowledged limitation.

Comment 14：The literature is sufficiently rich, but there are no citations of the latest articles in this field.

Response 14: Thank you for your suggestion. We have updated a portion of the references, adding several recently published within the last five years that are related to potassium fertilizer or alfalfa production.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for taking my suggestions into consideration, which I hope have helped to present the work more effectively.

Reviewer 4 Report

Comments and Suggestions for Authors

The authors have revised.