Round 1

Reviewer 1 Report

Dear Authors,

The subject of the manuscript corresponds to the subject of the journal. However, I believe that you have to revise your manuscript. Below I have given a few comments that should be corrected before publication.

1. The introduction can be improved. Please review the introduction again. You need to more clearly identify the background for your research. The hypothesis and objectives are formulated well enough, but they are poorly justified by previous experience.

2. Line 95 - typo (whea = wheat?)

3. Line 116 - Please, provide more information about principles of this method

4. Please provide information on the statistical treatment of the results in a separate paragraph.

5. Lines 223-226 - The sentence must be edited

6. Line 294 - typo (20 kg P)

 

In general, I hope that your manuscript will be interesting to readers.

Yours faithfully,

Reviewer

Author Response

Authors’ reply

Manuscript ID sustainability-822847entitled ‘Mineral fertilizer demand for optimum biological nitrogen fixation and yield potentials of legumes in northern Ethiopia

Dear Editor and Reviewers,

We thank you for the critical comments. The comments are essential to improve quality of our manuscript. We have now thoroughly incorporated all the comments and significantly improved our manuscript. In this authors reply, we tried to give a reply point by point for each reviewer’s comment. Reviewers’ comments are written in black text and authors reply is written in red text. In the upload section, revised manuscript with changes evident using track change showing all changes has been uploaded. Deleted tables and figures are not indicated in through track changes because table are replaced with new table.

Reviewer 1

Comments and Suggestions for Authors

Dear Authors,

The subject of the manuscript corresponds to the subject of the journal. However, I believe that you have to revise your manuscript. Below I have given a few comments that should be corrected before publication.

1. The introduction can be improved. Please review the introduction again. You need to more clearly identify the background for your research. The hypothesis and objectives are formulated well enough, but they are poorly justified by previous experience.

Reply = L 46 to 89 The introduction part is revised through editing grammar, adding important research backgrounds and literatures of the study area and research experiences in the study area. The problem statement and research gaps of the study area are elaborated. The hypothesis of this study is clearly included in the revision.

2. Line 95 - typo (whea = wheat?)

Reply = L 144:   whea is replaced with wheat

3. Line 116 - Please, provide more information about principles of this method

Reply = L 166 to 173: = effective nodules were determined by cutting nodules of the sampled plants to observe color inside the nodule. Effective or active nodules were identified by a pink to reddish internal color.  The percentage of effective nodules was then calculated through the ratio of effective nodule to total nodules per plant for each plot.

4. Please provide information on the statistical treatment of the results in a separate paragraph.

Reply = The statistical treatments of the agronomic parameters, nodulation, BNF and others are presented in terms of the treatments (different N and P fertilizer rates)

5. Lines 223-226 - The sentence must be edited

Reply = L 326 to 329: The sentence is edited and improved like; application of N and/or P fertilizers had comparable effects on legumes dry biomass and grain yield. The highest dry biomass and grain yields of faba bean, field pea and dekeko were obtained in the interaction of 20 kg N ha^-1 and 20 kg P ha^-1.

6. Line 294 - typo (20 kg P)

Reply = L 448: 20 kg N ha^-1 is replaced by 20 kg P ha^-1

In general, I hope that your manuscript will be interesting to readers.

Yours faithfully,

 

Author Response File: Author Response.docx

Reviewer 2 Report

I've just finished reviewing the paper sustainability-822847 titled: Mineral Fertilizer Demand for Optimum Biological Nitrogen Fixation and Yield Potentials of Legumes in Northern Ethiopia by authors Shimbahri Mesfin, Girmay Gebresamuel, Mitiku Haile, Amanuel Zenebe and Girma Desta.

The study does contain originality, it is fairly well-established experimental study. I believe that it can contribute as a significant reference to the potential readers. The language of manuscript is quite clear and understandable. Discussion sections supported with clear and new references. In addition to these comments it could be more focused on the variations in soil textural properties of studied soils. Consider change keyword " biological nitrogen fixation ". It is in the title.

In presented form, the manuscript satisfied criteria to be published in the journal Sustainability.

Author Response

Authors’ reply

Manuscript ID sustainability-822847entitled ‘Mineral fertilizer demand for optimum biological nitrogen fixation and yield potentials of legumes in northern Ethiopia

Dear Editor and Reviewers,

We thank you for the critical comments. The comments are essential to improve quality of our manuscript. We have now thoroughly incorporated all the comments and significantly improved our manuscript. In this authors reply, we tried to give a reply point by point for each reviewer’s comment. Reviewers’ comments are written in black text and authors reply is written in red text. In the upload section, revised manuscript with changes evident using track change showing all changes has been uploaded. Deleted tables and figures are not indicated in through track changes because table are replaced with new table.

Review 2

 Comments and Suggestions for Authors

I've just finished reviewing the paper sustainability-822847 titled: Mineral Fertilizer Demand for Optimum Biological Nitrogen Fixation and Yield Potentials of Legumes in Northern Ethiopia by authors Shimbahri Mesfin, Girmay Gebresamuel, Mitiku Haile, Amanuel Zenebe and Girma Desta.

The study does contain originality, it is fairly well-established experimental study. I believe that it can contribute as a significant reference to the potential readers. The language of manuscript is quite clear and understandable. Discussion sections supported with clear and new references. In addition to these comments it could be more focused on the variations in soil textural properties of studied soils.

Consider change keyword " biological nitrogen fixation ". It is in the title.

Reply = L 42: Biological nitrogen fixation is excluded from keyword instead sustainable crop production is added

In presented form, the manuscript satisfied criteria to be published in the journal Sustainability

Author Response File: Author Response.docx

Reviewer 3 Report

General comments:

1. Abbreviations were provided for biological nitrogen fixation (BNF), nitrogen (N) and phosphorus (P), but they were not used consistently throughout the manuscript.
2. Wheat, barley and soybean have no Latin species names provided. Please ensure there are Latin names for all crop species referred to in the text.
3. The presentation of crop response data for the various N and P treatments in complex Tables are indigestible and what does and what doesn’t need to be presented should be re-evaluated.
4. Much of the data presented in the Tables were either mentioned in passing or not subsequently utilised for the Results and Discussion.
5. Identical data are presented in both Tabular and Figure formats.
6. I presume since the same experimental treatments were undertaken in 2017 and 2018 that the data presented in the Tables and Figures represent the average of both years. If so, then some clear statement to that effect must be included in the text.
7. BNF data were presented to a fraction of a kilogram throughout the manuscript and Tables. This is implying an unjustified level of precision and accuracy. Values should be rounded off to the nearest whole number.
8. The Results and Discussion are very repetitive.
9. Some key data on nutritional effects on legume productivity, and legume effects on soil mineral N presented in the Results are not adequately addressed in either the Discussion or Conclusions.
10. Errors were detected in reference details.

The manuscript is not publishable in its current form and would benefit from a major re-write.

Specific comments:

1. Page 1 lines 10-24 – The Abstract details the effect of treatments fertilizer treatments on BNF, but does not quantify the magnitude of grain yield response, nor does it report the observed impacts on soil N availability following legumes.
2. Page 1 line 35 – With regards to BNF potentials I note citation 8 refers to soybean which originated in Asia, so is not an African native legume. Would “food legumes” or “crop legumes” be a better phrase to use than “native legumes”?
3. Page 2 lines 61-70 – I suggest replacing with the following wording to make the justification of the study clearer : “While it has been hypothesized that additional starter N and P fertilizer could improve nodulation and BNF, the actual rates required to optimize BNF, and which legume species might provide the largest inputs of fixed N to support productivity and improve soil N fertility is currently unknown for northern Ethiopia. This study aimed to generate the necessary knowledge to enable the development of informed nutrient management recommendations to guide Governmental public policy and to assist farmer decision-making.”
4. Page 2 lines 77-78 – The sentence commencing …”The main farming system …” is redundant as the same information is repeated in following sentences. Please remove.
5. Page 3 lines 87-104 – Font size not consistent.
6. Page 3 line 94 – Does “at farmers’ field in Alaje, northern Ethiopia” mean 1 farmer’s field or multiple farmers’ fields? If it is the latter please indicate how many farms or fields, otherwise replace with “a farmer’s field in the Alaje district, northern Ethiopia”.
7. Page 3 line 98 - Please indicate the dimensions of each experimental plot.
8. Page 4 line 122-124 – Please indicate the area of the quadrant sample. The current text is a little confusing and I wasn’t exactly sure whether measures of biomass included both shoot and grain or represented just shoot material. Could this please be re-written, so it is clear.
9. Page 4 line 131 – I suggest inserting the following words after citations [28, 29, 30] so the text is more informative about the assumptions behind the N-difference methodology …” by assuming legume BNF was responsible for the differences in plant N and soil mineral N measured between legume treatments and wheat (Eq. 1).”

1. Page 4 lines 144-151 – I suggest it would be better for the soil properties measured before sowing to appear in the Materials and Methods. The subsequent impacts of legumes on soil mineral N would perhaps be more appropriate presented after reporting the agronomic parameters.

1. Page 5 Fig. 2 legend – I propose you alter the start of the legend to read “ Increases in post-harvest soil mineral N (0-20 cm) following legume treatments relative to wheat. Difference letters …” The legend should also state the level of soil mineral N detected under wheat plots. Since there are just 4 legume treatments it would be interesting to see the results for both 2017 and 2018.
2. Table 1 - I leave it to the Editor’s discretion, but I find Table 1 unnecessarily complex and I am not convinced that it is essential to present all data collected for every single parameter for every single NxP treatment. Especially when much of the data are not subsequently discussed in any detail. To my mind the Table could be markedly reduced in size and simplified by focusing on the most important data which are biomass dry matter and grain yield for each legume. If the authors’ wish to indicate the basis of biomass production or grain yield responses to nutrient treatments they could refer to height, tiller number, pod number, grain number per pod or 100 grain weight as the main contributing factor(s) as appropriate in the text, and should they so desire this could be accompanied by the relevant mean data in brackets to demonstrate the magnitude of the change. Specific NxP responses such as 20N+20P could still be discussed in the text as they are now in the manuscript. In terms of summary data analyses a synthesis of N and P effects as currently presented is important, but I would also include summarized statistical analyses of NxP interactions. Some comment about year effects would be justified even just to state year effects were not significant. Finally, I must admit to being slightly confused by some of the statistical analyses in Table 1. For example, I don’t understand how so many significant N or P effects (as indicated by different letters) can be reported for biomass where the stated lsd values are so much greater than the differences between the mean data presented. How can this be?
3. Tables 2 and 3 – Similar comments as #11 above concerning the complexity of the Tables and query on whether it is essential to present all data collected for every single parameter for every single NxP treatment; especially since the same data are re-presented in Fig. 3. I don’t believe it is necessary to present 4 different measures for nodules. Total number and dry weight would be more than enough. The number of effective nodules per plant is interesting, but the data would be more useful if re-expressed as a % of total nodule number and any significant treatment effects on % effective nodules noted in the text, rather than present all the detailed values. Unless I am missing something, I don’t see any value in showing nodule volume per plant – are there any insights that can be obtained from volume that isn’t captured by dry weight? In my opinion the most key data are missing. Legume biomass N data and the amounts of N accumulated by wheat are crucial as these (along with soil mineral N) are the basis for the BNF calculations. Yet these values are not included in the present manuscript. If there was a rationalisation of the data presentation as proposed in #11 then perhaps biomass N could be combined for all 4 legumes and wheat into one Table. The calculated estimates of BNF (possibly the amounts fixed AND % legume N derived from atmospheric N2, %Ndfa) could also be presented in the same Table, and the supporting nodule data in a following Table. Alternatively, both the nodule and BNF data for the 4 legumes could then be presented together in a following Table.
4. Page 21 – current Table 4 – Similar comments to #12 above. I recommend that the authors present no more than 2 measures of nodulation, but I suggest that Table 4 should also include calculated %Ndfa values in addition to the amounts of BNF. The Table legend needs to indicate the data represent the mean for each legume species calculated across all N and P treatments.
5. Pages 21-22 lines 223-236 – I suggest changing title to 4.1 Agronomic responses to nutritional amendments. Remove all mention of nodulation and BNF from this section. The current emphasis on the highest grain yields for all legumes being achieved with 20N+20P is appropriate. However, I suggest you broaden the discussion further by also indicating what the yield benefits over nil N or P treatment actually represents for each legume in terms of kg per ha and/or % improvement. What is the value of this extra grain to farmers’ income as birr per ha? Please also provide a conversion rate for birr to US$ so international readers can have some benchmark for comparison. The value of the additional grain should be compared to the fertilizer costs required to achieve it (please ensure the cost per kg of N and kg P is provided). Does value in additional grain exceed the increased costs of production? Are the rates of 20N+20P required for greatest yield also providing the optimal return to farmers, or would it make more economic sense to use different rates or combinations? The discussion should also address the additional soil mineral N remaining in the soil profile following the legume treatments. What might this be worth in terms of potential benefit for following cereal crops? The wheat response to different N rates observed in the 2017 and 2018 experiments could help inform this part of the discussion.
6. Page 22 lines 238-268 – I consider the discussion in this section is far too focused on too few results, is convoluted and repetitive. For example, the 30 lines of text could easily be replaced by the following: “The highest nodulation and BNF by legumes was achieved with the combination of 20 kg N ha-1 and 20 kg P ha-1 to faba bean, field pea and dekeko, and 10 kg N ha-1 and 10 kg P ha-1 for lentil. The lowest nodulation and BNF on the other hand, were observed where 46 kg N ha-1 was applied regardless of the rate of P supplied. These results are consistent with previous work demonstrating the benefits of low levels of starter N in conjunction with P for enhanced nodulation and BNF by a range of legume crops [8,9,12,14,15,16,32,33], and the well documented inhibitory effects of high soil nitrate on the BNF process [ add citations …]. However, it should also be noted that they are at odds with some studies in N-deficient soils where higher rates of N fertilizer have been reported to be required to boost nodulation [35,36,37]. ”
7. Page 23 Fig. 3 – If my suggestions #12 & 13 above for Tables 2-4 are acted upon then Fig. 3 could be reduced to just 3a and 3d.
8. Page 23 lines 273-289 – The estimation of the relative value of the fixed N based on the equivalent cost N fertilizer-N is a useful one, but again please ensure value is also presented in US$ for the benefit of international readers.
9. Page 24 – Conclusion – I suggest this should also include some commentary about the new insights the experimentation has provided on the relative economics of applying supplementary nutrients to boost legume productivity and BNF, and the demonstrated impacts legume cropping had on soil N fertility.
10. References – I have not checked every reference, but there are obvious errors in 29. (Christian rather than surnames cited, and monograph details incorrect, suspect part of another reference included) and 33. (Gillera should read Giller). It would be worth checking other references for accuracy.

Author Response

Authors’ reply

Manuscript ID sustainability-822847entitled ‘Mineral fertilizer demand for optimum biological nitrogen fixation and yield potentials of legumes in northern Ethiopia

Dear Editor and Reviewers,

We thank you for the critical comments. The comments are essential to improve quality of our manuscript. We have now thoroughly incorporated all the comments and significantly improved our manuscript. In this authors reply, we tried to give a reply point by point for each reviewer’s comment. Reviewers’ comments are written in black text and authors reply is written in red text. In the upload section, revised manuscript with changes evident using track change showing all changes has been uploaded. Deleted tables and figures are not indicated in through track changes because table are replaced with new table.

Review 3

Comments and Suggestions for Authors

General comments:

1. Abbreviations were provided for biological nitrogen fixation (BNF), nitrogen (N) and phosphorus (P), but they were not used consistently throughout the manuscript.

Reply = The biological nitrogen fixation (BNF), nitrogen (N) and phosphorus (P) were fully defined in the first and abbreviation was used consistently in the whole manuscript

 

2. Wheat, barley and soybean have no Latin species names provided. Please ensure there are Latin names for all crop species referred to in the text.

Reply = L 121: Latin names of crops were provided as Wheat = Triticum spp, barley = Hordeum spp., and L 341 = soybean = Glycine max L. Merill

3. The presentation of crop response data for the various N and P treatments in complex Tables are indigestible and what does and what doesn’t need to be presented should be re-evaluated.

Reply = L 215 to 247: The crop responses to different N and P rates were concentrated into grain and dry biomass yields. The complex table (Table 1) is also reduced in size. Accordingly the grain and dry biomass yields were presented in the result and interpreted in the discussion part (L 325 to 365)

4. Much of the data presented in the Tables were either mentioned in passing or not subsequently utilized for the Results and Discussion.

Reply = since, the size of the tables (Table 1 and 2) were reduced and simplified, what is presented in these tables are interpreted in the discussion part (L 315 to 445).

5. Identical data are presented in both Tabular and Figure formats.

Reply = Since Table 2 is similar with Fig 3, Fig 3 is deleted from the manuscript

6. I presume since the same experimental treatments were undertaken in 2017 and 2018 that the data presented in the Tables and Figures represent the average of both years. If so, then some clear statement to that effect must be included in the text.

Reply = Since all data presented in the tables are mean data of the two cropping seasons, it is indicated in the data analysis part (L 202 to 204) as well as in each table captions

BNF data were presented to a fraction of a kilogram throughout the manuscript and Tables. This is implying an unjustified level of precision and accuracy. Values should be rounded off to the nearest whole number.

Reply = Fractions of kilograms are rounded off to the nearest number.

7. The Results and Discussion are very repetitive.

Reply = Repeated results in the discussion part (L 325 to 445) are excluded from discussion

8. Some key data on nutritional effects on legume productivity, and legume effects on soil mineral N presented in the Results are not adequately addressed in either the Discussion or Conclusions.

Reply = the effect of N and P nutrients on legume productivity and its benefits due to the N and P applications are included in the discussion part (L 350 to 366) for yield and, L423 to 425 for soil N and in the conclusion part (L 450 to 455)

9. Errors were detected in reference details.

Reply = Reference number 29 on (L 548 to 550) is corrected

The manuscript is not publishable in its current form and would benefit from a major re-write.

Specific comments:

1. Page 1 lines 10-24 – The Abstract details the effect of treatments fertilizer treatments on BNF, but does not quantify the magnitude of grain yield response, nor does it report the observed impacts on soil N availability following legumes.

Reply = L 21 to 22: effect of N and P fertilizers on grain yield is included in the abstract and the impact of legumes on soil is included in (L 27 to 28) in the abstract

1. Page 1 line 35 – With regards to BNF potentials I note citation 8 refers to soybean which originated in Asia, so is not an African native legume. Would “food legumes” or “crop legumes” be a better phrase to use than “native legumes”?

Reply = L 53: native legume is replaced by legume crops

1. Page 2 lines 61-70 – I suggest replacing with the following wording to make the justification of the study clearer : “While it has been hypothesized that additional starter N and P fertilizer could improve nodulation and BNF, the actual rates required to optimize BNF, and which legume species might provide the largest inputs of fixed N to support productivity and improve soil N fertility is currently unknown for northern Ethiopia. This study aimed to generate the necessary knowledge to enable the development of informed nutrient management recommendations to guide Governmental public policy and to assist farmer decision-making.”

Reply = L 84 to 89: Thank you so much for the nice way of describing the hypothesis and objective and it is incorporated in the mentioned line numbers.

1. Page 2 lines 77-78 – The sentence commencing …”The main farming system …” is redundant as the same information is repeated in following sentences. Please remove.

Reply = L 105 to 106: This sentence is removed from the manuscript

1. Page 3 lines 87-104 – Font size not consistent.

Reply = L 131 to 156: The font size is corrected and consistent with the other text

1. Page 3 line 94 – Does “at farmers’ field in Alaje, northern Ethiopia” mean 1 farmer’s field or multiple farmers’ fields? If it is the latter please indicate how many farms or fields, otherwise replace with “a farmer’s field in the Alaje district, northern Ethiopia”.

Reply = L 147 to 148: The experiment was replicated in six farmers’ field during both cropping seasons, now it is clearly described on the mention line number

1. Page 3 line 98 - Please indicate the dimensions of each experimental plot.

Reply = L 148 to 149: the size of the experimental plot was 3 m by 3 m and is included in the mentioned line number

1. Page 4 line 122-124 – Please indicate the area of the quadrant sample. The current text is a little confusing and I wasn’t exactly sure whether measures of biomass included both shoot and grain or represented just shoot material. Could this please be re-written, so it is clear.

Reply = L 178: The area of quadrant is 1 m by 1 m = 1 square meter. It is already mentioned in the manuscript

1. Page 4 line 131 – I suggest inserting the following words after citations [28, 29, 30] so the text is more informative about the assumptions behind the N-difference methodology …” by assuming legume BNF was responsible for the differences in plant N and soil mineral N measured between legume treatments and wheat (Eq. 1).”

Reply = L 189 to 190: We authors appreciate the idea you suggested to put after the citation is added. Accordingly it is included in the given line number

10. Page 4 lines 144-151 – I suggest it would be better for the soil properties measured before sowing to appear in the Materials and Methods. The subsequent impacts of legumes on soil mineral N would perhaps be more appropriate presented after reporting the agronomic parameters.
11. Reply = L 138 to 142: The pre-sowing soil properties of the experiments were taken and placed in the material and method part
12. Page 5 Fig. 2 legend – I propose you alter the start of the legend to read “ Increases in post-harvest soil mineral N (0-20 cm) following legume treatments relative to wheat. Difference letters …” The legend should also state the level of soil mineral N detected under wheat plots. Since there are just 4 legume treatments it would be interesting to see the results for both 2017 and 2018.

Reply = L 295 to 298: the legend is changed and the soil N in the wheat plot was 64 kg N ha^-1 in 2017 cropping season and 58 kg N ha^-1 in 2018 cropping season.

1. Table 1 - I leave it to the Editor’s discretion, but I find Table 1 unnecessarily complex and I am not convinced that it is essential to present all data collected for every single parameter for every single NxP treatment. Especially when much of the data are not subsequently discussed in any detail. To my mind the Table could be markedly reduced in size and simplified by focusing on the most important data which are biomass dry matter and grain yield for each legume. If the authors’ wish to indicate the basis of biomass production or grain yield responses to nutrient treatments they could refer to height, tiller number, pod number, grain number per pod or 100 grain weight as the main contributing factor(s) as appropriate in the text, and should they so desire this could be accompanied by the relevant mean data in brackets to demonstrate the magnitude of the change. Specific NxP responses such as 20N+20P could still be discussed in the text as they are now in the manuscript. In terms of summary data analyses a synthesis of N and P effects as currently presented is important, but I would also include summarized statistical analyses of NxP interactions. Some comment about year effects would be justified even just to state year effects were not significant. Finally, I must admit to being slightly confused by some of the statistical analyses in Table 1. For example, I don’t understand how so many significant N or P effects (as indicated by different letters) can be reported for biomass where the stated lsd values are so much greater than the differences between the mean data presented. How can this be?

Reply = L 238 to 241: Table 1 is reduced its size. Only dry biomass and grain yields are presented in the table. Insignificancy of the effect of years is mentioned in the data analysis as well as in the table caption. Data errors are checked and corrected.

1. Tables 2 and 3 – Similar comments as #11 above concerning the complexity of the Tables and query on whether it is essential to present all data collected for every single parameter for every single NxP treatment; especially since the same data are re-presented in Fig. 3. I don’t believe it is necessary to present 4 different measures for nodules. Total number and dry weight would be more than enough. The number of effective nodules per plant is interesting, but the data would be more useful if re-expressed as a % of total nodule number and any significant treatment effects on % effective nodules noted in the text, rather than present all the detailed values. Unless I am missing something, I don’t see any value in showing nodule volume per plant – are there any insights that can be obtained from volume that isn’t captured by dry weight? In my opinion the most key data are missing. Legume biomass N data and the amounts of N accumulated by wheat are crucial as these (along with soil mineral N) are the basis for the BNF calculations. Yet these values are not included in the present manuscript. If there was a rationalisation of the data presentation as proposed in #11 then perhaps biomass N could be combined for all 4 legumes and wheat into one Table. The calculated estimates of BNF (possibly the amounts fixed AND % legume N derived from atmospheric N2, %Ndfa) could also be presented in the same Table, and the supporting nodule data in a following Table. Alternatively, both the nodule and BNF data for the 4 legumes could then be presented together in a following Table.

15. Reply = L 254 to 262: Table 2 is also reduced its size. Number of nodules, dry weight of nodules and BNF are presented in the table. Mean values of the two years were presented and is mentioned in the data analysis as well as in the table caption. Some errors are also corrected

 

1. Page 21 – current Table 4 – Similar comments to #12 above. I recommend that the authors present no more than 2 measures of nodulation, but I suggest that Table 4 should also include calculated %Ndfa values in addition to the amounts of BNF. The Table legend needs to indicate the data represent the mean for each legume species calculated across all N and P treatments.

Reply = L 305 to 312: In Table 3, nodule number, dry weight of nodules, Ndfa,  BNF and Soil N after harvest (kg ha^-1) are presented.  The data represent the mean for each legume species calculated across all N and P treatment rates is also indicated in the table caption.

1. Pages 21-22 lines 223-236 – I suggest changing title to 4.1 Agronomic responses to nutritional amendments. Remove all mention of nodulation and BNF from this section.

Reply = L 325:  4.1 Agronomic parameters is replaced by “Agronomic responses to nutritional amendments.” The nodulation and BNF are excluded from this section

The current emphasis on the highest grain yields for all legumes being achieved with 20N+20P is appropriate. However, I suggest you broaden the discussion further by also indicating what the yield benefits over nil N or P treatment actually represents for each legume in terms of kg per ha and/or % improvement. What is the value of this extra grain to farmers’ income as birr per ha? Please also provide a conversion rate for birr to US$ so international readers can have some benchmark for comparison. The value of the additional grain should be compared to the fertilizer costs required to achieve it (please ensure the cost per kg of N and kg P is provided). Does value in additional grain exceed the increased costs of production? Are the rates of 20N+20P required for greatest yield also providing the optimal return to farmers, or would it make more economic sense to use different rates or combinations? The discussion should also address the additional soil mineral N remaining in the soil profile following the legume treatments. What might this be worth in terms of potential benefit for following cereal crops? The wheat response to different N rates observed in the 2017 and 2018 experiments could help inform this part of the discussion.

Reply = Reply = L 350 to 366: The discussion is broaden through adding the yield increment of legumes due to the N and P fertilizers and their inter actions. The benefits of these increased legume yields at current market price (Ethiopian Birr and US$) is also included in the discussion part.  The price of increased legume yields is by far higher than the price of applied fertilizers.

L 423 to 446: the role of legumes for soil N accumulation is discussed well. The contribution of legumes in storing soil N for the next crop is clearly incorporated in this discussion part

1. Page 22 lines 238-268 – I consider the discussion in this section is far too focused on too few results, is convoluted and repetitive. For example, the 30 lines of text could easily be replaced by the following: “The highest nodulation and BNF by legumes was achieved with the combination of 20 kg N ha-1 and 20 kg P ha-1 to faba bean, field pea and dekeko, and 10 kg N ha-1 and 10 kg P ha-1 for lentil. The lowest nodulation and BNF on the other hand, were observed where 46 kg N ha-1 was applied regardless of the rate of P supplied. These results are consistent with previous work demonstrating the benefits of low levels of starter N in conjunction with P for enhanced nodulation and BNF by a range of legume crops [8,9,12,14,15,16,32,33], and the well documented inhibitory effects of high soil nitrate on the BNF process [ add citations …]. However, it should also be noted that they are at odds with some studies in N-deficient soils where higher rates of N fertilizer have been reported to be required to boost nodulation [35,36,37]. ”

Reply = L 369 to 377: Thank you for your well articulating this long discussion. Accordingly, this is well incorporated in the mentioned line number in this revision.

1. Page 23 Fig. 3 – If my suggestions #12 & 13 above for Tables 2-4 are acted upon then Fig. 3 could be reduced to just 3a and 3d.

Reply = since, the information of Fig 3 is presented in Table 2 and Table 3, it is deleted from the manuscript

1. Page 23 lines 273-289 – The estimation of the relative value of the fixed N based on the equivalent cost N fertilizer-N is a useful one, but again please ensure value is also presented in US$ for the benefit of international readers.

Reply = L 437to 441: Thank you very much for your concern, we also mention the Ethiopian BIRR in terms of US$. This is important for readers. It is described both interms of Ethiopian money (BIRR) and US$.

1. Page 24 – Conclusion – I suggest this should also include some commentary about the new insights the experimentation has provided on the relative economics of applying supplementary nutrients to boost legume productivity and BNF, and the demonstrated impacts legume cropping had on soil N fertility.

Reply = L 451 to 453:  The effect of N and P supply on grain yield increment over the nil plots is included in the conclusion part. In addition in L 454 to 456:  effects of legumes on soil N accumulation compared to the wheat plot which can be very important for subsequent cereal production is added in the conclusion part in the revision.

1. References – I have not checked every reference, but there are obvious errors in 29. (Christian rather than surnames cited, and monograph details incorrect, suspect part of another reference included) and 33. (Gillera should read Giller). It would be worth checking other references for accuracy.

Reply = Whole references list are checked and some errors are corrected. Reference number 29 is also corrected.

 

Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

The manuscript is much improved; especially with the inclusion of economic analyses which provides highly relevant information that can assist farmer adoption of the proposed new practices. Only a few minor comments:

1. I still found the English a little awkward in places and suggest replacing the text Lines 35-40 with the following rewording: “Since the study area has potential for expansion of legume cropping, the findings from this study has important implications for the development of government policy and farmer guidelines. The intensification of the use of legumes supplied with starter N and P fertilizers in northern Ethiopian cropping systems has the dual benefit of enhancing inputs of fixed N and improving soil N status for following crops and represents a future option for sustainable soil fertility management practices.
2. Figure 2 – The current choice of colours would be problematic for colour-blind readers. I suggest using a dashed line for one of the temperature tracks.
3. Line 352 – Typographical error “increment”

Author Response

Authors’ reply to the second revision

Manuscript ID sustainability-822847 entitled ‘Mineral fertilizer demand for optimum biological nitrogen fixation and yield potentials of legumes in northern Ethiopia

Dear Editor and Reviewer,

We thank you for the important comments. The comments are essential to improve the quality of paper. We have now thoroughly incorporated all the given comments and other additional editorial comments.  In a reply point by point for each reviewer’s comment were given. In the manuscript all previous changes with track change were accepted and new comments were showed by track change in this second revision.

Review 3

Comments and Suggestions for Authors

1. The manuscript is much improved; especially with the inclusion of economic analyses which provides highly relevant information that can assist farmer adoption of the proposed new practices. Only a few minor comments: I still found the English a little awkward in places and suggest replacing the text Lines 35-40 with the following rewording: “Since the study area has potential for expansion of legume cropping, the findings from this study have important implications for the development of government policy and farmer guidelines. The intensification of the use of legumes supplied with starter N and P fertilizers in northern Ethiopian cropping systems has the dual benefit of enhancing inputs of fixed N and improving soil N status for following crops and represents a future option for sustainable soil fertility management practices

Reply = L29 to 34: Thank you so much for improving these sentences and we incorporate your comment and improve idea of the paragraph

2. Figure 2 – The current choice of colours would be problematic for colour-blind readers. I suggest using a dashed line for one of the temperature tracks

Reply = L94 to 97: The color of figure 2 is changed into dashed lines

3. Line 352 – Typographical error “increment’’

Reply = L29 to 34: icrement is replaced by ‘increment’

NB: In this version some additional minor editorial changes have also been made to the whole manuscript.

 

 

 

Author Response File: Author Response.docx