A Mixture of Green Waste Compost and Biomass Combustion Ash for Recycled Nutrient Delivery to Soil
Round 1
Reviewer 1 Report
The article “The Mixture of Green Waste Compost and Biomass Combustion Ash for Recycled Nutrient Delivery to Soil” reports the results of a 2-year in-field experimental campaign aimed at evaluating the effect of green waste compost and biomass combustion ash utilization on the soil and on crops’ yield increase. The article can be of interest for the readers of Agronomy journal, reports novel information and is written in a coherent way. There are some minor aspects to be fixed before publication (see in the following the main comments), consequently I recommend a minor revision.
- Lines 174-175: The possibility of enhancing the low C/N ratio with the addition of other carbon-rich substrates (e.g. biochar, granular activated carbon, digestate from anaerobic digestion process) could be mentioned in the text to enhance the discussion (e.g., see doi.org/10.1016/j.jece.2019.103184).
- Results and discussion: at the end of the section, it would be beneficial to add a short paragraph summarizing the main obtained outputs and their usefulness for other researchers in the field. Also, the future perspectives of this research should be highlighted (i.e., will longer studies be conducted in the future? Will the experimental campaign be supported by an economic analysis regarding the application of these bio-based fertilizers in comparison with traditional mineral fertilizers?)
- English language has to be improved: revision by a native English speaker would be beneficial to this purpose.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
- Please unify treatments abbreviations. It would be better to use the + sign or the word and instead of a forward slash (L.71-72).
- On what basis were the rates of green waste compost selected? (L. 69-71)?
- Please correct and organize the subsections in the Materials and Methods section. Subsections should concern material applied to the soil, soil, plants and statistical analysis. In the present version of the manuscript there are 3 subsections concerning material applied to the soil (2.1.-2.3.) and 2 subsections (2.4. and 2.5) with the same title. There is also a lack of information on the collecting of the plant material. How the plant yield was determined?
- All abbreviations and acronyms used in tables and figures should be defined in the table notes or figure captions.
- Have nitrogen and carbon been determined in the soil and plants? This was not mentioned in the Materials and Methods section.
- Max allowable limits are given in units other than the rest of the data (Table 3). Please use European or Lithuanian standards.
- There is a lack of statistical analysis of the data on the Figure 2. Why did authors write: After spring wheat harvest, the amount of mobile forms of all nutrients (K2O, P2O5, Ca, Mg) differed significantly.
- Please unify units of element contents in the manuscript.
Author Response
Response to Reviewer 2 Comments
Point 1: Please unify treatments abbreviations. It would be better to use the + sign or the word and instead of a forward slash (L.71-72).
Response 1: abbreviations for treatments were unified throughout the text. Selected to use + sign (corrected throughout in the text and figures).
Point 2: On what basis were the rates of green waste compost selected? (L. 69-71)?
Response 2: the rate of GWC was calculated based on the maximum permitted N rate of 170 kg ha-1, as it was indicated in the EC Directive 91/676/EEC [16] (page 2, L. 85-87).
Point 3: Please correct and organize the subsections in the Materials and Methods section. Subsections should concern material applied to the soil, soil, plants and statistical analysis. In the present version of the manuscript there are 3 subsections concerning material applied to the soil (2.1.-2.3.) and 2 subsections (2.4. and 2.5) with the same title. There is also a lack of information on the collecting of the plant material. How the plant yield was determined?
Response 3: the section in the Materials and Methods was corrected and organized.
The subsection “Physicochemical characterization” was moved to 2.1 subsection “Materials and physicochemical characterization” (L. 62). The subsection “Physicochemical characterization” text “A chemical analysis of the recycled materials used in the field experiments was carried out. The samples were ground, sieved and extracted with aqua regia. Atomic Absorption Spectroscopy (AAS) was used to find the concentration of Ca and Mg, flame photometer (FP) of K, UV–VIS spectrophotometer of P and inductively coupled plasma mass spectrometry (ICP-MS) of heavy metals (Cu, Cd, Cr, Ni, Pb, Zn) [14]” moved to L. 69-73.
Subsection 2.4 renamed to Meteorological conditions (L. 135).
The text “The GWC rate of 20 t ha-1 corresponded to 60 kg of test GWC per field (30 m2). BA (3 t ha-1) 9 kg, respectively. In mixtures with 7%, 13% and 18% ash: GWC 60 kg+BA 4.5 kg, GWC 60 kg+BA 9 kg, GWC 60 kg+BA 13.5 kg.” from “Field experiment description and experimental design” was moved to "BA and GWC mixtures for composting" (L. 82-85).
We added to page 3 (L. 123-124) text “Crop yield was determined by weighing. Spring wheat and spring triticale grain and straw from each experimental plot were collected and weighed separately.”
Point 4: All abbreviations and acronyms used in tables and figures should be defined in the table notes or figure captions.
Response 4: all abbreviations were defined in the figure captions. We have added the following text to the table notes and figure captions: “BA – biofuel ash; GWC – green waste compost; GWC+BA1.5 – green waste compost (20 t ha-1) + biofuel ash (1.5 t ha-1); GWC+BA3.0 – green waste compost (20 t ha-1) + biofuel ash (3.0 t ha-1); GWC+BA4.5 – green waste compost (20 t ha-1) + biofuel ash (4.5 t ha-1)” in all the figure captions.
Point 5: Have nitrogen and carbon been determined in the soil and plants? This was not mentioned in the Materials and Methods section.
Response 5: Yes, the nitrogen and carbon were determined in the soil and plants. We have mentioned it in the Materials and Methods section:
L. 73-76: Total nitrogen (Ntot) was determined using by the Kjeldahl nitrogen distiller and organic carbon (Corg) determined by a dry combustion method using a total carbon analyzer Liqui TOC II [15]. (in green waste compost).
L. 128-130: Mineral nitrogen (Nmin) was determined using laboratory prepared spectrometric method LVP-D-05:2017 (in soil).
L. 131-132: The Kjeldahl method was used to determine total nitrogen (Ntot) in spring wheat and spring triticale grain and straw (in plant).
Point 6: Max allowable limits are given in units other than the rest of the data (Table 3). Please use European or Lithuanian standards.
Response 6: the max allowable limits (mg kg-1) in compost are listed according to the limits allowed in Lithuania (Table 3, L. 205-207).
The amount of heavy metals inserted into the soil (kg ha-1) are not regulated in Lithuania and Europe. Therefore, we left the US standard (Table 4, L. 218-219).
Point 7: There is a lack of statistical analysis of the data on the Figure 2. Why did authors write: After spring wheat harvest, the amount of mobile forms of all nutrients (K2O, P2O5, Ca, Mg) differed significantly.
Response 7: statistical analysis of the data was performed (Figure 2, page 7, L. 248).
"After spring wheat harvest, the amount of mobile forms of all nutrients (K2O, P2O5, Ca, Mg) differed significantly from the corresponding control soil" because it can be seen in Figure 2 (4 months after the start of the experiment).
Point 8: Please unify units of element contents in the manuscript.
Response 8: units of element contents in the manuscript were unified. Due to the high content of nutrients in the ash, the results are given as a percentage (Table 2). The content of heavy metals in soil and plants is given in mg kg-1 (Figure 3, Figure 5b), and due to the high content of nutrients in plants - g kg-1 (Figure 5a).
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
The authors have addressed all the comments and suggestions I made in the first review. I have no further suggestions.
Author Response
Dear Reviewer,
Thank you for your time.
