The Mineral Biochar Alters the Biochemical and Microbial Properties of the Soil and the Grain Yield of Hordeum vulgare L. under Drought Stress

Round 1

Reviewer 1 Report

The manuscript entitled "The mineral biochar alters the biochemical and microbial properties of the soil and the grain yield of barley (Hordeum vulgare L.) under drought stress" addresses an important thematic, the use of biochar as soil amendment to mitigate the negative effects of drought stress. Thus, the subject of this manuscript is very interesting and suitable material for publication in Land. The manuscript is presented in a well-structured manner. However, there are some issues that the authors need to address before the manuscript is accepted for publication.

-      - Please revise the language of this manuscript to prevent minor grammar mistake. The English must be improved.

- Line 26-27. The authors use both % and percent. I suggest to uniformize to %. The same for Line 40 and Line 51. This should be checked in all manuscript.

- Line 117. Change 22 nd to 22^nd.

-  Line 242. Change Drought to drought.

- Line 250-256. These abbreviations were already mentioned in Materials and Methods section. The authors should use the abbreviated format in all the manuscript (for example, SIR); Same to line 263 and 360. Apply this to all the manuscript.

- Line 353-356. The English is not correct. The authors should reformulate these sentences.

- Line 354-356. This sentence is not noticeable to the readers. What do the authors mean by adequate soil? Authors should be more specific.

- All references should be carefully checked, according to the requirements of Land journal. Journal names should be changed to the abbreviated form.

-  Pay attention to the reference number 1, doi is repeated.

Author Response

REVIEWER#1

The manuscript entitled "The mineral biochar alters the biochemical and microbial properties of the soil and the grain yield of barley (Hordeum vulgare L.) under drought stress" addresses an important thematic, the use of biochar as soil amendment to mitigate the negative effects of drought stress. Thus, the subject of this manuscript is very interesting and suitable material for publication in Land. The manuscript is presented in a well-structured manner. However, there are some issues that the authors need to address before the manuscript is accepted for publication.

Please revise the language of this manuscript to prevent minor grammar mistake. The English must be improved.

AUTHORS: We thank the Reviewer for his comments, major grammatical and typo errors corrected as requested. Further corrections may be performed by the MDPI language office if the manuscript passes peer review.

- Line 26-27. The authors use both % and percent. I suggest to uniformize to %. The same for Line 40 and Line 51. This should be checked in all manuscript.

AUTHORS: the Reviewer's observation is pertinent and corrections have been made in all points indicated.

- Line 117. Change 22 nd to 22^nd.

AUTHORS: the correction has been done

-  Line 242. Change Drought to drought.

AUTHORS: the correction has been done

- Line 250-256. These abbreviations were already mentioned in Materials and Methods section. The authors should use the abbreviated format in all the manuscript (for example, SIR); Same to line 263 and 360. Apply this to all the manuscript.

AUTHORS: the Reviewer's observation is pertinent and corrections have been made in all points indicated.

- Line 353-356. The English is not correct. The authors should reformulate these sentences.

AUTHORS: The sentence has been revised as requested

- Line 354-356. This sentence is not noticeable to the readers. What do the authors mean by adequate soil? Authors should be more specific.

AUTHORS: The reviewer's observation is correct. The sentence has been corrected, the sentence referred to “moisture of the soil”

- All references should be carefully checked, according to the requirements of Land journal. Journal names should be changed to the abbreviated form.

-  Pay attention to the reference number 1, doi is repeated.

AUTHORS: all references have been corrected and updated.

Reviewer 2 Report

In this study, the authors conducted a randomized complete block design with four replications in 23 experimental glasshouses at the University of Zanjan in 2022. The study involved two irrigation regimes and four levels of natural mineral biochar. According to the results, drought significantly reduced the organic carbon content of the soil and grain yield, while increasing the available phosphorus, soil carbohydrate content, and microbial biomass of the soil. The addition of biochar improved the measured soil parameters and could be considered a viable strategy for increasing plant resistance to drought. While the manuscript is well-organized, it requires a more in-depth discussion. The following are some questions that need clarification before publication:

1. The introduction states that drought is one of the most serious obstacles to agricultural productivity, but there is a lack of discussion related to drought stress. It is suggested that the authors add relevant concepts related to drought stress in the introduction.

2. The manuscript mentions mineral biochar from natural minerals, but it does not describe in detail how biochar is extracted from natural minerals or what is done with the biochar after it is obtained. The authors are advised to provide more information on the production process and applications of biochar.

3. The manuscript lacks relevant characterization of biochar, such as SEM, TEM, and other data. It is suggested that the authors add this information to the manuscript.

4. In the results section, it is noted that 1% is the maximum level of biochar used. It is suggested that the authors investigate whether there is a sweet spot or if higher levels of biochar could further improve soil parameters.

5. In Section 4.2, the manuscript states that biochar raises soil pH, but it does not explain why. The authors are advised to provide an explanation for this observation.

6. The format of all headings should be checked, and any formatting errors should be corrected. If section 4.4 is missing, it should be added to the manuscript.

Author Response

REVIEWER#2

In this study, the authors conducted a randomized complete block design with four replications in 23 experimental glasshouses at the University of Zanjan in 2022. The study involved two irrigation regimes and four levels of natural mineral biochar. According to the results, drought significantly reduced the organic carbon content of the soil and grain yield, while increasing the available phosphorus, soil carbohydrate content, and microbial biomass of the soil. The addition of biochar improved the measured soil parameters and could be considered a viable strategy for increasing plant resistance to drought. While the manuscript is well-organized, it requires a more in-depth discussion. The following are some questions that need clarification before publication:

1. The introduction states that drought is one of the most serious obstacles to agricultural productivity, but there is a lack of discussion related to drought stress. It is suggested that the authors add relevant concepts related to drought stress in the introduction.

AUTHORS: In the introduction we have included some aspects regarding drought and plant response as follows:

 “Drought is one of the most destructive stresses for wild plants and agronomic crops [4,5,17]. Drought stress affects crop yields, especially in arid and semi-arid regions of the world [8,10]. The intensity and frequency of drought periods are increasing due to climate change as recently reported [19,20]. Scarce rainfall induces different physiological and metabolic responses in plants such as the closure of the stomata, resulting in reduced growth and a low photosynthetic rate [21]. The first biological mechanisms compromised by drought concern the reduction of cell expansion and cell divisions, two primary processes involved in plant growth [6,16]. If water stress continues, the impairment is more profound and conditions photosynthesis and cellular respiration influencing critical processes, such as germination, emergence, leaf expansion, root and shoot development, dry matter accumulation, floral initiation, pollination, fertilization, seed growth and seed yield [16,22,23]. Indeed, water stress by reducing the size and number of cells leads to reduced leaf area, reduced plant height and stem development. Furthermore, a shortening of the period from floral initiation was observed, resulting in a lower yield in terms of seed production [17,24,25].”

2. The manuscript mentions mineral biochar from natural minerals, but it does not describe in detail how biochar is extracted from natural minerals or what is done with the biochar after it is obtained. The authors are advised to provide more information on the production process and applications of biochar.

AUTHORS: Some aspects associated with biochar characteristics have been integrated in the materials and methods section.

3. The manuscript lacks relevant characterization of biochar, such as SEM, TEM, and other data. It is suggested that the authors add this information to the manuscript.

AUTHORS: The Reviewer's considerations are pertinent and valid. However, the objective of the manuscript was not the chemical-physical characterization of the biochar but the contribution of the amendment on some plant growth parameters and on the effects on the soil and the microbiome. SEM or TEM microscope observations are fundamental for understanding the structure of biochar and its physical interaction with the soil system. In the specific case of our manuscript, our goal was to improve the response of the plant to different degrees of irrigation and different concentrations of biochar. The analysis of the biochar structure will be used for future structural characterization studies.

Below we report only three examples of recent manuscripts in which the authors evaluate the effects of biochar on plant growth parameters and do not consider SEM and TEM measurements.

Frimpong KA, Phares CA, Boateng I, Abban-Baidoo E, Apuri L. One-time application of biochar influenced crop yield across three cropping cycles on tropical sandy loam soil in Ghana. Heliyon. 2021 Feb 17;7(2):e06267. doi: 10.1016/j.heliyon.2021.e06267

Thomas Kätterer, Dries Roobroeck, Olof Andrén, Geoffrey Kimutai, Erik Karltun, Holger Kirchmann, Gert Nyberg, Bernard Vanlauwe, Kristina Röing de Nowina, Biochar addition persistently increased soil fertility and yields in maize-soybean rotations over 10 years in sub-humid regions of Kenya, Field Crops Research, Volume 235, 2019, Pages 18-26, ISSN 0378-4290, https://doi.org/10.1016/j.fcr.2019.02.015.

Losacco, D.; Tumolo, M.; Cotugno, P.; Leone, N.; Massarelli, C.; Convertini, S.; Tursi, A.; Uricchio, V.F.; Ancona, V. Use of Biochar to Improve the Sustainable Crop Production of Cauliflower (Brassica oleracea L.). Plants 2022, 11, 1182. https://doi.org/10.3390/plants11091182

4. In the results section, it is noted that 1% is the maximum level of biochar used. It is suggested that the authors investigate whether there is a sweet spot or if higher levels of biochar could further improve soil parameters.

AUTHORS: The reviewer's comment is pertinent. However, in the literature there are many experimental protocols that involve the use of a wide range of types of biochar different from ours. In addition, many researchers create mixtures with soil (sometimes including multiple soil types) that also include higher concentrations of biochar. The use of higher concentrations, or the use of other types of biochar do not ensure success in crop growth and yield. For this reason, our manuscript focused on a typology of biochar, which we chemically characterized, and we evaluated the effects of its use on some soil parameters under drought stress conditions.

In the light of the Reviewer's considerations, we have inserted two sentences in the conclusions, adding very recent references.

5. In Section 4.2, the manuscript states that biochar raises soil pH, but it does not explain why. The authors are advised to provide an explanation for this observation.

AUTHORS: More details of the effects of biochar on soil acidity have been added in the text.

6. The format of all headings should be checked, and any formatting errors should be corrected. If section 4.4 is missing, it should be added to the manuscript.

AUTHORS: Paragraph subtitles have been updated.

Round 2

Reviewer 1 Report

The paper can be accepted without any further changes.