Physico-Chemical Properties and Phosphorus Solubilization of Organomineral Fertilizers Derived from Sewage Sludge

Round 1

Reviewer 1 Report

The manuscript entitled "Physico-chemical properties and phosphorus solubilization of organomineral fertilizers derived from sewage sludge" is a good study aimed at explaining the possibility of increasing the efficiency of P use in tropical soils using slow or controlled release fertilizers. For this purpose, sewage sludge was used, in some combinations additionally enriched with phosphorus, which are products with a slow release of ingredients and at the same time enable the use of nutrients from local waste.

This study appears to have been conducted correctly and the results presented are interesting. I think the manuscript falls under Soil Systems. This knowledge may be of practical importance in improving the fertilization of plants with phosphorus and provides the opportunity to recycle nutrients, preventing environmental pollution.

The article presented to me for review contains all the key elements required in scientific work and in the editorial office of the journal. Overall, the manuscript is good and clearly written. However, after reviewing the manuscript, I have some minor suggestions for improving it:

Abstract:

Suggestion to provide the future prospects and potential benefits of this study in one line at the end of the abstract.

Introduction

The introduction should state the specific purpose of the research.

Results

When describing the results, there are incorrect references to the numbering of figures (example: line 307 should be Figure 1B and there is 2B; : line 341 should be Figure 2C and there is 2B), I suggest checking and correcting them carefully.

In some cases, there is no reference to a table or figure when describing the results, which makes it difficult for the reader to interpret them.

Conclusions:

Conclusions should include a comparison of the therapy and the potential benefits of choosing the best solution, as well as recommendations and prospects for the future. Meanwhile, they look more like a summary of the results.

References

Line 523 - no publishing house available: Syers, J.K.; Johnston, A.E.; Curtin, D. Efficiency of Soil and Fertilizer Phosphorus Use; 2008;

Author Response

Thank you very much for the considerations and suggestions made to improve the work, I tried my best to make changes to adapt the manuscript to the observations made.The following changes were made:

Future perspectives and benefits brought by the research carried out were added to the abstract.

The specific objectives of the research were indicated

The numbering of the figures has been corrected, as well as the references.

The conclusion has been changed, including the relevance of the information obtained in this study and future perspectives.

L523 - ISBN: 9789251059296   FAO (2008)

Reviewer 2 Report

Review of the manuscript titled “Physico-chemical properties and phosphorus solubilization of organomineral fertilizers derived from sewage sludge”

The research study reported in this manuscript examined the P solubility of developed sewage sludge compost-based organomineral fertilizer in addition to its physico-chemical properties in comparison with conventional fertilizers.

The manuscript was well-written and reported important information regarding P recycling and use efficiency.

My minor comments are presented below:

Convert the P unit applied and in the leachate to mg P/ kg soil instead per column.

L44: The P use efficiency is usually less in 50%, and this percentage seems high and may be based on generalized assumptions. Please check this information and better to provide a range.

L96-98: Provide the total P.

L143: Table 1 title is not correct. This has to be soil characteristics. Also, units of soil parameters provide here are not the common ones used in this kind of studies. Please change.

L272-275: the pH in the control changed from about 5 in the beginning to 7.4 near the end. A clear explanation for this change has to be provided.

L285-287: This implies that anaerobic conditions were created in this study. Does water field capacity create anaerobic conditions in soil? Clarify this statement and provide support from the literature.

L392-393: Use the term "fixation" or "sorption" in this type of study as “immobilization” term is usually used for microbial process where the nutrient is being tied-up by soil microbes.

L485: This section should include values of the key findings.

L487-489: rewrite this statement for a better clarity.

L490-492: This statement exaggerates the findings of this study at this stage. Further studies in presence of plants are required to reach such a conclusion.  These statements need to be modified.

Author Response

Thank you very much for the care you took with the review and for the notes you made to improve the article. Below are some explanations of notes made regarding the text and also the changes made:

Thank you for your observation, it really is a pertinent issue regarding the unit of measurement that was used, but I believe it is important to maintain the absolute values of applied phosphorus (mg per column) to make sense of the phosphorus balance at the end. With concentration values (mg/kg) it would not be possible to calculate the addition and subtraction of the remaining phosphorus in the soil and leachate and thus quantify from the total P applied to the column, how much was lost or remained in the system. Articles with this same unit have been published in this type of test, i.e. reference [47].

L44 - These values are averages of the main crops planted in Brazil, there really are crops where the efficiency is less than 50% such as sugar cane, beans and oranges (18-40%), average in soybeans, wheat and rice (45- 60%), but in the case of corn, the efficiency is higher (60-90%).

L 96-98 - In these lines, parameters related to the maturation and biosafety of the compound produced were presented. Nutrient contents are in table 2.

L143 Thank you very much for the notes, the table title has been corrected and the measurement units changed.

L 272-275 - an explanation was provided based on current literature

L 285-287 - The statement was actually made incorrectly, thank you very much for the correction. It was not maintained at field capacity, in fact the amount of water applied (30 mL) saturated the soil columns, it was observed daily that a layer of water formed on the surface of the columns for a period of time until all the water infiltrated , which may have created an environment of reducing conditions. Changes were made to this part of the text to better reflect the actual conditions of the experiment.

L 392-393 - the appropriate terms have been exchanged.

L485 - 492 Changes were made to improve the conclusion.

Reviewer 3 Report

Comments and sugggestions for Authors

The manuscript after minor corrections may be subjected to further publishing procedure. A very interesting and innovative article. 

The content of heavy metals in sewage sludge is missing, very important for the environment.  Please write Latin names in italics, Line: 438, 439.

Line 450 (13 g kg-1) correct and check throughout the work.

Table S1 mg/kg  correct 

Write numbers correctly in tables, remove commas.

Check the literature, e.g. items 26, 27

Author Response

Thank you very much for the corrections and suggestions, they will certainly make the article more complete and some errors that went unnoticed by me are now corrected.

Heavy metal values was added in Table S1 (Suplementary material) with chemical analysis of sewage sludge and compost.

L438-L439 - The species latin names have been corrected.

L450 - unit has been corrected.

The values correspond to the absolute amount of phosphorus present in the leachate and not to the concentration of the solute. The form presented mg of phosphorus per column is important for the phosphorus balance at the end of the experiment, as it is not possible to add the mg/L concentrations while mg/column is a value that can be added and obtain the balance at the end. Other articles published using the same column leaching methodology also presented values in this form, i.e. reference [47] and DOI 10.3390/agronomy10070918.

commas removed

Items 26 and 27 have been checked and are correct.