Interactive Effects of Biochar and Sewage Sludge on Bioavailability and Plant Uptake of Cu, Fe, and Zn, and Spinach (Spinacia oleracea L.) Yields under Wastewater Irrigation
Round 1
Reviewer 1 Report
The research work described the interactive effects of co-application of the biochar and sewage sludge on bioavailability and uptake of trace metals and spinach yields in two different soils. The paper presents an interesting research topic and good ideas. But some analyses are missing, e.g., plant growth parameters. I have listed some comments which help authors to improve their manuscripts.
Comments
Lines 14-15: "Therefore, this field experiment was conducted on a Luvisol and Cambisol to investigate the bioavailability and uptake of some micronutrients and spinach yields" grown in soil amended with biochar and sewage sludge?
Line 16: RCBD, randomized complete block design
Lines 43-52: Please add recent reports
Line 83: Sewage sludge and biochar. Please add source, biochar production, pyrolysis process etc.
Please add for field trials, climatic conditions, temperature, dates etc.
Line 84: Spinach (Spinacia oleracea), please add source
Line 139-142. Why citations were given in the result section published data?
Line 225-232: Can you please add recent studies as well
This study doesn't demonstrate the effect of various treatments on plant biomass, root, and ´shoot growth? But the only yield was presented. Please add plant growth parameters, if possible. It is interesting to see if there are correlations between soil properties, plant performance indicators, and plant nutrient acquisition.
Author Response
Please see attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript is written in good style, without linguistic errors. The subject matter is very interesting, but the results and the way they are presented and interpreted need to be explained, completed or corrected. Below are my initial comments:
Introduction
Line 38: Please provide more recent reference
Line 43: Please remove “,” before “and”
Line 43: Please provide more recent reference
Line 47: Please provide more recent reference
Line 50: Please provide more recent reference
Materials and Methods
Line 91: It seems to be double space between words “application” and “Bioavailable”
Line 92: Please shortly describe the Mehlich III extraction
Line 94: Please provide more recent reference
Line 97: Please shortly describe the method of biochar pH determination
Lina 99: Please provide more recent reference
Lines 102-104: Please shortly describe the used methods
Line 108: Please provide concentration, purity and producer of nitric acid
Lines 131-133. Which test was used for determination of normality of the distribution of results?
Results
Line 140: Please provide more recent reference
Lines 132-184: In my opinion, the results should be supplemented by the total content of microelements in the soil and the microelements available in biochar and sludge. It can be seen that as the dose of biochar increases, the amount of extractable microelements usually increases. Therefore, the question arises whether it is the effect of biochar or the effect of co-application of biochar and sludge. At the moment this is not clear to me. My doubt is most evident in the case of zinc, where it is not the effect of SS and BC co-application, but the BC additive, which carries a certain amount of bioavailable Zn.
In addition, please give the same number of significant figures. It is not acceptable to give the result 6 and the standard deviation 2.3. This suggests that the measurement is not consistent with the significant figures.
Lines 159-161 and Lines 202-204 and Line 213 – Please explain meaning of letters A, B,C….
Discussion:
Line 227: Please provide more recent reference
Line 255: Please check the correctness of the statistics.
Firstly, with such a huge standard error, statistically significant differences should not be visible. What is the distribution of results? Normal? What statistical test was used to show statistically significant differences? Why is the standard error so great with a simple pH measurement?
In the case of Organic C and CEC, what is the point of showing statistical differences if there are no statistical differences?
The significant figures for correction.
Line 296 Concentration refers to solutions. For dry matter we use the word content. Please check the entire manuscript for correctness.
Line 300 A brave statement. It may be true, but it must be supported by something. Either you have to give the heavy metal content of the root, or you have to show that there was a high concentration of heavy metals in the soil and in soil additives, which blocked the metabolic and transport pathways of trace elements in favour of heavy metals.
Conclusions
Line 336: It is obvious that it increases the bioavailability of heavy metals, because they are introduced with sludge and biochar.
Author Response
Please see attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
I would like to thank the authors for preparing comprehensive answers, which are mostly satisfactory to me.
At the moment I have one comment to make in order to present statistically significant differences.
I would ask you to add appropriate captions under tables and diagrams which present statistically significant differences. For example: Table 4 contains statistically significant differences between two types of soil. This has not been signalled anywhere, and in my opinion this is necessary for the reader to be able to clearly interpret the results. Without a proper signature, it looks like it is unclear whether to interpret columns, rows or random results. A clear explanation and an appropriate signature are required. The same applies to diagrams, because the number of letters and bars, without a caption, makes the results unreadable.
Author Response
We analysed the data for the two soil types simultaneously. Therefore, for each variable, the Duncan’s multiple range statistic was used to rank the 20 treatment means (10 for each soil type) simultaneously. For example, when considering significant differences between means for Mehlich extractable Cu (Figure 1), the alphabetical letters denote simultaneous ranking of treatment means for both sites.
Author Response File: Author Response.pdf
