Nutrient Potential Leachability in a Sandy Soil Amended with Manure-Based Fertilisers
Round 1
Reviewer 1 Report
The paper has to be revised extensively. The main critics are the lack of an adequate control and the lack of sufficient descriptions of Math. and Meth.
1. The first sentence of the introduction has non- justified statements. First, soil P contents increased strongly after WWI in most European soils. Second, the link between mineral fertilizers and decreasing SOC contents is not evident, as shown by long-term field trials (see. Körschens et al., 2014, Arch. Agron. Soil Sci., 60, 1485- 1517). Correct, clarify and improve the sentence.
2. Use P and K not P2O5 and K2O.
3. What is available P? Explain!
4. L 138/139: Give the detailled calculation.
5. I assume "Soil" is reference soil? However reference would be the same nutrients applied in inorganic form.
6. L 255/256: P as nitrification inhibitor is highly speculative and cannot be derived from the results. Omit!
7. Fig. 2: P and K concentrations are given as mg/kg soil, therefore no concetrations are reported. Give the P and K concentrations in the leachate in mg/dm3!
8. L 280: The sentence is wrong for two reasons. P is not the second most important macronutreint, it is as important as N, K, Mg, S, Ca. Second not only P in the soil solution is available P, (see e.g. Gerke, 2015, J. Plant Nutr. Soil Sci., 178, 351- 364).
9. L 281 ff.: In most soils P is rather strongly bound to the soil surface, the P retention capacity being much higher than the actual coverage. P elution into groundwater is relevant mainly in soils with high cattle, pig slurry or poultra manure application over decades.
10. Without results on a adequate refernce soil conclusions drawn here are speculative.
Author Response
Answers to the Questions of Reviewer #1:
#Question 1. The paper has to be revised extensively. The main critics are the lack of an adequate control and the lack of sufficient descriptions of Math. and Meth.
Response: Dear reviewer, a deep revision of our manuscript has been performed to attend all the reviewers queries and clarify some questions. The Material and Methods sections has been improved with more details. Regarding the lack of an adequate control, it has been emphasized in the introduction that the main objectives of the paper was First, the MBFs will be compared to the original raw manure to identify if the addition of mineral fertilizer induce an increase of the potential leaching compared to the raw manure. Secondly, the MBFs will be compared within the same N:P ratio to identify which of the proposed MBF lead to the lower potential losses by leaching. Considering these specific objectives, we believe that the treatments including the raw manure acted as a proper control.
#Question 2. The first sentence of the introduction has non- justified statements. First, soil P contents increased strongly after WWI in most European soils. Second, the link between mineral fertilizers and decreasing SOC contents is not evident, as shown by long-term field trials (see. Körschens et al., 2014, Arch. Agron. Soil Sci., 60, 1485- 1517). Correct, clarify, and improve the sentence.
Response: We agree with the reviewer’s remark, thank you for bringing it to our attention; the structure of the former sentence misled the reader. We have rephrased the first paragraph to be clearer.
#Question 3. Use P and K not P2O5 and K2O.
Response: We have used P2O5 and K2O to express P and K in the manure-based fertilizer composition, since that is the usual form of expressing P and K concentrations in mineral fertilizers, as well as to provide plant nutrient necessities to farmers (Table 1). Therefore, although agreeing with the reviewer’s request, we have maintained that information only to be easier to interpret the manure-based fertilizer composition. However, to attend the reviewer’s request, Table 1 also provides the amount of phosphorous and potassium supplied by the manure-based fertilizer as P (mg P kg-1) and K (mg K kg-1)(not P2O5 and K2O) (last two columns in Table 1). Therefore, Table 1, allows both perspectives, and it will be possible to relate the amount of nutrients supplied by the manure-based fertilizer applied to the column, with the amounts of phosphorous and potassium leached, which are all expressed in P and K.
#Question 4. What is available P? Explain!
Response: Available P was used here to express the “plant available P”. Although what was measured in the first place was the “nutrients potential leaching”, that fraction of the total concentration that was leached was considered as a surrogate measure of what was “plant available”, and was “used to assess the agronomic efficiency of these MBFs, considering that both macro and micronutrients in the leachate are potentially available to the crop – plant available nutrients”. We have tried to make that more clearer in the Objectives and in the Material and Methods section, and have used that expression now in the whole manuscript – “plant available”.
#Question 5. L 138/139: Give the detailed calculation.
Response: This information was added as requested. Please see the revised manuscript.
#Question 6. I assume "Soil" is reference soil? However reference would be the same nutrients applied in inorganic form.
Response: In this work the main objectives were to compare the manure-based fertilizers with the manure of origin, to properly determine the effects of having N/P from a mineral source mixed with the manure, to enrich it with one of these elements, and secondly to compare the blended MBFs, to understand benefits and risks of each MBFs, within each ratio. Since what we intended was to recycle manure and its nutrients, our “reference” was the raw manure, and not the mineral fertilizer. However, we understand this point of view and it could have been an interesting perspective too, to compare their use with just the mineral fertilizers, but it would imply a different experimental design, and also the assessment of the effects of the different N or P mineral sources, which would increase enormously the number of treatments to be considered in the study.
#Question 7. L 255/256: P as nitrification inhibitor is highly speculative and cannot be derived from the results. Omit!
Response: We agreed and removed the sentence and the related ones also.
#Question 8. Fig. 2: P and K concentrations are given as mg/kg soil, therefore no concentrations are reported. Give the P and K concentrations in the leachate in mg/dm3!
Response: The P and K concentrations in the leachate were analysed in mg/dm3, however, these concentrations were reported, by calculation, to the soil mass used in the leaching events, and reported as mg X/kg soil. Indeed, the objective of our study was not focussed on the water quality, and we did not intend to compare the leachates obtained in each treatment, rather we wanted to compare which combination of soil+MBF would give rise to the higher nutrient emissions. Indeed, the concentration of the leachates relies strongly on the amount of water used for the leaching events and can not be used for extrapolation. By converting the concentrations into mg/kg soil, we were able to understand how much, of P and K, present in the soil (initially present or added via MBF) was lost through leaching.
#Question 9. L 280: The sentence is wrong for two reasons. P is not the second most important macronutrient, it is as important as N, K, Mg, S, Ca. Second not only P in the soil solution is available P, (see e.g. Gerke, 2015, J. Plant Nutr. Soil Sci., 178, 351- 364).
Response: We agreed with the reviewer’s remark and removed the incorrect information. Also, we have clarified the sentence. Please see the revised manuscript.
#Question 10. L 281 ff.: In most soils P is rather strongly bound to the soil surface, the P retention capacity being much higher than the actual coverage. P elution into groundwater is relevant mainly in soils with high cattle, pig slurry or poultry manure application over decades.
Response: Yes, we agree and reinforced that idea in the manuscript, please see the revised manuscript.
#Question 11. Without results on an adequate reference soil conclusions drawn here are speculative.
Response: As previously stated in the first response and response to comment 5, our reference was the raw manure and we consider that all the needed references were present in our study, taking into consideration what were our objectives. We hope that the explanations provided to the questions posed by the reviewer helped to understand why our conclusions were not that speculative.
Reviewer 2 Report
The use of organic fertilizers for fertilizing purposes is not only providing nutrients for plants, but also their mostly positive effect on the physical, chemical and biological properties of the soil. Nutrients applied to the soil along with organic fertilizers may, however, be lost as a result of the leaching process, which causes potential environmental pollution. Taking this into account, I rate the subject matter taken up by the authors very highly. However, after reading the manuscript carefully, I have numerous comments and questions which I present below:
1. Introduction
I believe that this chapter should be significantly increased. It is necessary to provide other average values of coefficients of nutrient utilization from selected organic fertilizers and the factors on which they depend. Figures on leaching of nutrients from different soils should also be provided.
2. Materials and Methods
This chapter should also be extended to include the basic properties of the soil used in the experiment. This will allow us to better understand the dynamics of nutrient leaching
3. Results and discussion
3.1. Nitrogen potential leachability
1. line 173 - please specify the factors on which the dynamics of organic fertilizers transformation depends and relate it to the fertilizers used in the experiment.
2. I also believe that at the beginning of this subchapter one should write about the factors that determine the rate of nitrogen mineralization in the soil. This will help to understand the process of its leaching from the soil.
3. In this subsection there are many results of own research, but they are not discussed with the research of other authors. This should be supplemented.
3.2 Phosphorus potential leachability
1. line 283 - please specify the factors on which the availability of phosphorus for plants and the rate of its leaching from the soil depends.
2. line 290 -291. Please check the numerical values in table 2
3. As in the previous section, there is also no discussion. The authors present only the results obtained in their own research, but have not made any attempt to explain them. Why, for example, does the addition of ammonium sulphate to PIS increase phosphorus leaching? Is it related to the acid reaction of this fertilizer? Please complete it.
3.3 Potassium potential leachability
There is no discussion in this chapter either. The authors do not explain the results in any way.
3.4 Macronutrients potential leachability
1. Please complete the discussion
2. Line 428- Including information on iron, copper, zinc and manganese in the supplement is redundant because the authors do not discuss them in the body of the manuscript
4 Conclusion
In my opinion, this chapter should be redrafted and include only the most important results obtained in the conducted research. I also propose to include in this chapter the most important practical aspect of the conducted research.
Author Response
Answers to the Questions of Reviewer #2:
The use of organic fertilizers for fertilizing purposes is not only providing nutrients for plants, but also their mostly positive effect on the physical, chemical and biological properties of the soil. Nutrients applied to the soil along with organic fertilizers may, however, be lost as a result of the leaching process, which causes potential environmental pollution. Taking this into account, I rate the subject matter taken up by the authors very highly. However, after reading the manuscript carefully, I have numerous comments and questions which I present below:
#Question 1: Introduction
I believe that this chapter should be significantly increased. It is necessary to provide other average values of coefficients of nutrient utilization from selected organic fertilizers and the factors on which they depend. Figures on leaching of nutrients from different soils should also be provided.
Response: The introduction was improved, to better introduce the purpose of this study, please see the revised manuscript. Nevertheless, it was intentional not to provide a very large introduction.
#Question 2: Materials and Methods
This chapter should also be extended to include the basic properties of the soil used in the experiment. This will allow us to better understand the dynamics of nutrient leaching.
Response: More information was added to the manuscript, namely more information on soil properties, as requested. Please, see the revised version of the manuscript.
- Results and discussion
#Question 3.1: Nitrogen potential leachability
- line 173 - please specify the factors on which the dynamics of organic fertilizers transformation depends and relate it to the fertilizers used in the experiment.
- I also believe that at the beginning of this subchapter one should write about the factors that determine the rate of nitrogen mineralization in the soil. This will help to understand the process of its leaching from the soil.
Response: This information was added to the manuscript to enlighten the readers and facilitate the results interpretation.
- In this subsection there are many results of own research, but they are not discussed with the research of other authors. This should be supplemented.
Response: Doing this study, it was quite difficult to found other studies to corroborate or not the present results. One practice that has been more adopted worldwide, is the combination of manure and mineral fertilizer application, but where the manure is a complement to the normal practices, meaning it is applied in raw form and separately from mineral fertilizers. Finding studies that previously combined manure with mineral fertilizers, by mixing both, was a challenge. This was one of the contributions to the state of the art of this study. Nonetheless, we reviewed this chapter to try to include as much results as possible.
#Question 3.2: Phosphorus potential leachability
- line 283 - please specify the factors on which the availability of phosphorus for plants and the rate of its leaching from the soil depends.
Response: This information was added to the manuscript, please see the revisions made.
- line 290 -291. Please check the numerical values in table 2
Response: The values were checked carefully and no incorrection was observed.
- As in the previous section, there is also no discussion. The authors present only the results obtained in their own research, but have not made any attempt to explain them. Why, for example, does the addition of ammonium sulphate to PIS increase phosphorus leaching? Is it related to the acid reaction of this fertilizer? Please, complete it.
Response: The discussion of this chapter was revised. This topic was quite important, still we cannot forget that the amount of mineral fertilizer added to manure was quite small, and the acidification effect might not have occurred with ammonium sulphate, but perhaps might have occurred with phosphoric acid.
#Question 3.3: Potassium potential leachability
There is no discussion in this chapter either. The authors do not explain the results in any way.
Response: This chapter was altered, please see the manuscript.
#Question 3.4: Macronutrients potential leachability
- Please complete the discussion
Response: The discussion in this chapter was revised and the discussion was deepened, please see the manuscript.
- Line 428- Including information on iron, copper, zinc and manganese in the supplement is redundant because the authors do not discuss them in the body of the manuscript
Response: We added discussion in this chapter, please see the manuscript.
#Question 4: Conclusion
In my opinion, this chapter should be redrafted and include only the most important results obtained in the conducted research. I also propose to include in this chapter the most important practical aspect of the conducted research.
Response: The conclusion chapter was revised to contain only the important results and some practical aspects were added, please see the revised manuscript.
Author Response File: 
Author Response.docx
Reviewer 3 Report
The leaching of nutrients into underground water sources is very important, especially in areas with a high concentration of livestock, when it is necessary to supply additional nutrients for good crop growth.
From this point of view, the article is certainly very necessary and it is good that the authors are dealing with this issue.
For my part, the article lacks an effort to understand the principle of leaching in relation to organic compounds and the sorption complex of the substrate. The problem for farmers is also not determining the difference in leaching between individual types of organic fertilizers, since these are determined by the production structure of the company, but comparing alternatives for farmers, which mineral substances and in what quantity are best for which type of organic fertilization. The logic of the article should also correspond to the description of individual MDF substances after the addition of mineral fertilizers, and only then should the overall comparison of MDF with each other follow.
The principle of adding nutrients to organic fertilizing is the right procedure, but it should be supplemented with an explanation in terms of possible chemical-biological links, from which it would be possible to better derive the actual action of mineral fertilizers in MBF and establish preferences for applications.
The principle of comparing leaching of sandy soil alone with leaching of soil with the addition of MDF is unclear to me. In the article it is written that the soil itself was leached together with other samples with MDF. I didn't understand the reason for this comparison, as it stands to reason that the enriched soil must leach significantly more nutrients than the original soil alone. I believe that the subject of the comparison should have been the application of mineral fertilizers to the soil itself in the total required concentration required by the plants. This comparison would then show the real difference in the leaching of the soil itself and the MDF. The article should be supplemented with a justification of the chosen procedure.
The paper's methodology and results are described in detail, but as indicated, further investigation is needed on other soils to compare leaching between MDFs. I believe that for the presentation of the real impact of the enrichment of MDF substances and the impact on leaching in agricultural conditions, a soil with a higher content of clay particles should have been used as an alternative, which represents the opposite conditions of leaching in practice. The article also does not describe the reason why sandy soil was used. I can assume that because of the leach rate assessment, but this was not directly assessed in the results.
The article is very fragmented into individual evaluations, which make it difficult for the reader to find their way around and are primarily of a quantitative nature. I recommend supplementing the article with a finalizing graphic comparison of effects by individual MDF. In these effects, the absolute and relative loss of nutrients of the monitored parameters should be evaluated. Nutrient concentration is important when comparing, and it is not possible to deduce a certain dependence on concentration in the article, it is also necessary to compare objectively.
The article also describes that the pH of the soil at the beginning of the experiment was 5, but in the supplied graphs, the pH of the soil itself at the beginning is about 6.5.
Statistical analysis is described in the article, but it is not documented in the results.
Overall, I recommend reworking the article for a more appropriate evaluation of the data found in graphic and statistical form.
Comments for author File: Comments.docx
Author Response
Answers to the Questions of Reviewer #3:
Nutrient potential leachability in a sandy soil amended with manure-based fertilizers
The leaching of nutrients into underground water sources is very important, especially in areas with a high concentration of livestock, when it is necessary to supply additional nutrients for good crop growth.
From this point of view, the article is certainly very necessary, and it is good that the authors are dealing with this issue.
#Question 1: For my part, the article lacks an effort to understand the principle of leaching in relation to organic compounds and the sorption complex of the substrate. The problem for farmers is also not determining the difference in leaching between individual types of organic fertilizers, since these are determined by the production structure of the company, but comparing alternatives for farmers, which mineral substances and in what quantity are best for which type of organic fertilization. The logic of the article should also correspond to the description of individual MDF substances after the addition of mineral fertilizers, and only then should the overall comparison of MDF with each other follow.
Response: We understand this point of view, however, we are at a preliminary stage in the use of MBFs, where it is necessary to determine if the MBFs did not lead to a higher risk of leaching than the original raw manure and, secondly, identify, for the same N:P ratio, which of the three MBFs tested have the most interesting outcome, and only later we will compare the performance of MBFs with the mineral fertilizers. Indeed, manure application is already associated with environmental problems, such as nitrate leaching and, in this first stage, we needed to prove that the MBFs tested, enriched with nutrients from a mineral source, would not lead to an increase in nutrients leaching, even more negative to the environment than the impacts from the manure.
#Question 2: The principle of adding nutrients to organic fertilizing is the right procedure, but it should be supplemented with an explanation in terms of possible chemical-biological links, from which it would be possible to better derive the actual action of mineral fertilizers in MBF and establish preferences for applications.
Response: We agree with the reviewer but, as stated before, we believe that such assessment, to evaluate the biological links between the different MBFs and crops, considering different soils types and different crops, are the next step of our research. At this stage, we did not perform these tests, and any reference to the biological link would be speculative.
#Question 3: The principle of comparing leaching of sandy soil alone with leaching of soil with the addition of MDF is unclear to me. In the article it is written that the soil itself was leached together with other samples with MDF. I didn't understand the reason for this comparison, as it stands to reason that the enriched soil must leach significantly more nutrients than the original soil alone. I believe that the subject of the comparison should have been the application of mineral fertilizers to the soil itself in the total required concentration required by the plants. This comparison would then show the real difference in the leaching of the soil itself and the MDF. The article should be supplemented with a justification of the chosen procedure.
Response: In this study, the main objectives were to compare the manure-based fertilizers with the manure of origin, to properly determine the effect of having different N/P mineral sources mixed with the manure, and secondly, to compare the MBFs within each ratio, to understand which MBFs would increase nutrients leaching. Since the main idea, subjacent to the study, is to recycle manure and its nutrients, our references were the raw manure. We compared whether different materials applied to a sandy soil would promote greater nutrient leaching, in relation to each other within each ratio, and comparing with the raw materials, and always having, as the base line, the soil without any material applied. Using the soil alone, gives the amount of soil native nutrients leached, reason why it was important to choose a poor soil, to avoid any misleading result. At this stage, proving that the MBFs were more sustainable than the raw manure, was a more important information, since it would be a start to increase the use of manure or derive products and reduce the environmental impacts.
#Question 4: The paper's methodology and results are described in detail, but as indicated, further investigation is needed on other soils to compare leaching between MDFs. I believe that for the presentation of the real impact of the enrichment of MDF substances and the impact on leaching in agricultural conditions, a soil with a higher content of clay particles should have been used as an alternative, which represents the opposite conditions of leaching in practice. The article also does not describe the reason why sandy soil was used. I can assume that because of the leach rate assessment, but this was not directly assessed in the results.
Response: We used a sandy soil to maximize the leaching potential, which would represent the situation with a higher leachability risk. This information was now added to the material and methods section.
#Question 5: The article is very fragmented into individual evaluations, which make it difficult for the reader to find their way around and are primarily of a quantitative nature. I recommend supplementing the article with a finalizing graphic comparison of effects by individual MDF. In these effects, the absolute and relative loss of nutrients of the monitored parameters should be evaluated. Nutrient concentration is important when comparing, and it is not possible to deduce a certain dependence on concentration in the article, it is also necessary to compare objectively.
Response: We agree with the reviewer’s remark and appreciate the suggestion. We added now a figure with the total quantity of macronutrients leached in the supplementary material (Figure S1).
#Question 6: The article also describes that the pH of the soil at the beginning of the experiment was 5, but in the supplied graphs, the pH of the soil itself at the beginning is about 6.5.
Response: The pH shown in the graphs thar were provided was the pH of the leachate, and not the pH of the soil itself. Since we used a sandy soil, the contact time between the water and the soil was short. Hence, the pH of the leachate was close to the pH of the distilled water used in the leaching events, and not to the soil pH.
#Question 7: Statistical analysis is described in the article, but it is not documented in the results. Overall, I recommend reworking the article for a more appropriate evaluation of the data found in graphic and statistical form.
Response: We added the statistical analyses referring to the last part of statistical analyses, which was the Tukey test, to compare the means. In the figures, we chose to add the standard error from the homogeneity test, which quantifies the certainty of the result of the comparison of the means test. In the tables, we used different letters to represent the significant statistical differences. Nevertheless, we have checked the figures and table legends, and all have this information.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The paper should not be published since no adequate reference treatment exists.
Author Response
- In the 1st round of review, reviewer 1 raised a considerable number of questions, which were fully answered, and the manuscript was improved taking these suggestions into account;
- in the 2nd round of review, reviewer 1 did not contest our responses, explanations or improvements made to the manuscript, which resulted from its first review. Reviewer 1 only presents 1 argument to suggest rejection of the manuscript: "The paper should not be published since no adequate reference treatment exists." but reviewer 1 did not make any further comments or suggestions.
- Regarding the "reference treatment" issue, in the response to reviewer 1 in the first round of review, we already clarified that, in our opinion, the reference treatment are the modalities with "raw manure". In response to Question 1 of the 1st review by reviewer 1, we wrote the following:
" Regarding the lack of an adequate control, it has been emphasized in the introduction that the main objectives of the paper was First, the MBFs will be compared to the original raw manure to identify if the addition of mineral fertilizer induce an increase of the potential leaching compared to the raw manure. Secondly, the MBFs will be compared within the same N:P ratio to identify which of the proposed MBF lead to the lower potential losses by leaching. Considering these specific objectives, we believe that the treatments including the raw manure acted as a proper control”.
- The authors, reviewer 2 and reviewer 3 agree that, given the objective of this work, the modalities with "raw management" are the "reference treatment", disagreeing with the opinion of reviewer 1;
- The suggested "reference treatment" proposed by reviewer 1 was not considered in the trial design, therefore, there is no data to be included in this manuscript.
Reviewer 2 Report
I recommend the manuscript for publication.
Author Response
Reviewer 2, who raised more questions in the first review, agreed with our answers, explanations and improvements made to the manuscript and recommends publication: “I recommend the manuscript for publication”.
Reviewer 3 Report
The authors' answers were sufficient, although it is still crucial to work with other types of soil, where the results found can potentially be fundamentally shifted in terms of reduced nutrient leaching. I understand the laboriousness of the experiment used, but in my opinion, the use of sandy soil greatly reduces the importance of the sorption complex of the soil and also the importance of work, which would benefit from the use of at least both opposite poles - sandy and clay soil.
Comments for author File: Comments.docx
Author Response
Reviewer 3 agrees with our responses, explanations and improvements made to the manuscript, stating: the authors' answers were sufficient. The reviewer only presents suggestions for future work, namely the "use of at least both opposite poles - sandy and clay soil".
