Improving Soil Fertility and Forage Production Using Spruce Bark Biochar in an Eastern Newfoundland Podzolic Soil

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The paper addresses a highly relevant issue – improving acidic, nutrient-poor Podzolic soils through biochar and nitrogen fertilization. This is especially important in regions like Newfoundland where soil limitations constrain forage production.

1. Please, make some changes in the Title. It could be: "Improving Soil Fertility and Forage Production Using Spruce Bark Biochar".
2. Please, discuss the limitations of the greenhouse experiment more explicitly. Although pot experiments under controlled conditions are useful for initial screening, they restrict the direct applicability of the findings to field-scale conditions, where soil heterogeneity, climatic variability, and long-term effects play significant roles.
3. Mention that conclusions on long-term soil health cannot yet be drawn. - The experiment lasted from December 2018 to April 2019 (~4 months). Soil-biochar interactions, particularly for carbon sequestration, cation exchange capacity stabilization, and microbial shifts, are often long-term processes.
4. Clarify additive versus synergistic effects more explicitly. The ANOVA was used; the text notes several cases where biochar × nitrogen interactions were non-significant. Yet, conclusions sometimes imply synergistic effects.
5. If it is possible, include or cite detailed characterization. While some chemical properties are provided (pH, CEC, nutrient content), physical properties like surface area, pore size distribution, and stability indices (e.g., H/C and O/C ratios) were not reported. These are critical for comparing results with other studies.

 

Supplementary material

1. Add legends or short explanatory notes under each table. Some readers not familiar with statistical coding (e.g., “B % (v/v)*N (Kg/ha)*Crop”) may struggle to interpret them without context.
2. Statistically significant difference (P < 0.05). Source of variance codes including biochar (B), Crop, and nitrogen (N).” could be better: “Statistical significance was determined at P < 0.05. Sources of variation included biochar (B), crop (C), and nitrogen (N).

Comments on the Quality of English Language

Generally understandable but not fully native-like. Examples:

1. “which reached 184 mg/g for SB550 biochar in a previous experiment” could be better: “which, in a previous experiment, reached 184 mg/g for SB550 biochar.”
2. “The experiment was conducted using a Completely Randomized Design (CRD), with three replicates, resulting in a total of 60 pots, as shown in the experimental layout” → could be simplified: “The experiment followed a completely randomized design (CRD) with three replicates per treatment (60 pots in total).”
3. Repeated “significantly increased…” could be stylistically varied (“markedly increased”, “substantially improved”).

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study evaluated the effects of spruce bark biochar on soil properties, nutrient uptake, and forage quality in podzolic soils through a greenhouse experiment. The introduction provides a convincing rationale for the potential of biochar as a soil amendment. The results section presents rich datasets, and the discussion is well-supported by relevant literature. However, several aspects still require revision:

1. Tables 4 and 5 contain extensive data, but the variation trends are not easy to discern in tabular form. It is recommended to present these results in graphical format to improve clarity and interpretability.
2. Figures 1 and 2 illustrate the same trend, differing only in fresh yield and dry yield. Presenting both does not provide substantial additional insight. It is suggested to either combine these figures or move one to the Supplementary Information. The same recommendation applies to Figures 4 and 5.
3. The beneficial effects of biochar on crops have been extensively reported in previous studies. Please highlight the novelty and specific significance of this work. In addition, discuss the economic feasibility and sustainability of applying spruce bark biochar under actual field conditions.
4. The conclusion section refers to a “synergistic effect” of biochar and nitrogen, whereas the discussion (line 384) states that the effects were “additive rather than synergistic.” This inconsistency should be addressed to ensure the interpretation is aligned throughout the manuscript.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript was investigated the Effects of Spruce Bark Biochar on Soil Fertility, Forage Crop Production, Forage Quality, and Nutrient Uptake in an Eastern Newfoundland Podzolic Soil. It can be accepted after some major revisions. As well I suggest that author do text proofreading. Given below are several critical points to consider for improving the manuscript for publication:

Introduction

• Comment: in the Introduction section, I recommend reorganizing the content to improve clarity and logical flow. Specifically, consider first introducing biochar what it is and its general properties then describe the problem of acidic soils, followed by how the application of biochar can serve as a potential solution. This structure will help readers better understand the context and rationale of your study.

To make it clearer to you I suggested that text from L51 to L57 (“Biochar is a carbon-rich product derived from the pyrolysis of agricultural biomass, such as crop residues, wood, and waste, under controlled conditions involving high temperatures and limited oxygen supply. It is considered a modern advancement in soil management practices [8, 9]. Biochar has been widely studied for its multiple environmental and agricultural benefits, including improving soil fertility, enhancing nutrient retention, mitigating climate change through carbon sequestration, and remediating contaminated soils [10].”) put at the beginning of the Introduction to inform readers what biochar is, and then go what it is a problem i.e., acidic soil from L39 – L50 (“Soils in Newfoundland and Labrador (NL), Canada, are generally characterized by very high acidity, low fertility, low CEC, low SOM, very coarse texture, and a high proportion of stones, all of which negatively impact forage crop production. Acidic soils typically exhibit low fertility due to high concentrations of Al and Mn and limited availability of P, Ca, and Mg, resulting in reduced crop productivity [1]. Applying biochar as a soil amendment presents a promising strategy for improving forage crop productivity in such challenging soils. Biochar can enhance CEC and SOM, thereby improving the soil’s nutrient retention capacity [2, 3]. Its application to the top 0-15 cm of very acidic soils has been shown to significantly increase soil pH and the availability of nutrients, particularly Ca, K, S, and Mn [4]. Similarly, biochar amendments have been found to raise K, Ca, and levels in surface soils [5]. while other studies report improvements in CEC, SOM, and nutrient availability (e.g., P and K), leading to better crop growth and yields [6, 7].”), and then L 57 – 84 (“The effectiveness of biochar in agricultural systems depends heavily on its feedstock and production conditions, which determine its chemical and physical properties. For instance, biochar derived from poultry litter, peanut hulls, or pine chips differs significantly in elemental content, affecting its influence on soil nutrient availability [5, 11]. Studies have shown that biochar can release essential nutrients such as K, Ca, Mg, 61 Mn, Cu, and Zn into the soil, which supports plant growth. It also plays a critical role in salt-affected soils by reducing Na uptake and improving K availability, thus alleviating salt stress [1]. Beyond fertility improvement, biochar can immobilize heavy metals in contaminated soils. For example, Lu et al. (2017) reported that rice straw biochar reduced Cd, 65 Cu, Pb, and Zn concentrations by 11–34% when applied at 5% [12]. Chicken manure biochar has also been shown to increase shoot and root biomass in Indian mustard due to reduced metal toxicity and improved P and K availability [13]. Recent studies have also explored the use of biochar as a nutrient source. Peanut hull biochar, for instance, increased surface soil concentrations of K, Ca, and Mg, while pine chip biochar had limited effects beyond Ca [5]. Although some biochars show minimal impact on plant tissue nutrient concentrations, application rate is a key factor. In tropical regions, plant productivity improved significantly with higher biochar rates [11]. For example, rice husk biochar increased rice yield by approximately 100% in Japanese paddy fields when applied at 74 g pot⁻¹ [14], and willow biochar at 5% (w/w) increased spinach growth by over 100% in spring and 353% in autumn [15]. These findings demonstrate that the ideal biochar application rate should be tailored to specific soil types and regional conditions to maximize benefits. This optimization can reduce costs, labor, and potential negative impacts, while improving soil health, crop yield, and quality. Therefore, the objective of this study was to evaluate the effectiveness of biochar as a soil amendment for improving soil fertility, forage yield, forage quality, and nutrient uptake in the podzolic soils of eastern Newfoundland. The findings of this research are expected to support the expansion of local agricultural production and contribute to improving food security in the province.”).

Materials and Methods

• Comment: on line L97 when mentioning the SEM, please include the manufacturer, city, country of origin. For consistency, ensure that this information is provided for all instruments used in the study. For example: “Mettler Toledo MPC 227 instrument (Mettler-Toledo, Columbus, Ohio, USA).”
• Comment: please ensure consistent use of dashes throughout the manuscript. For example, in line 105 you use an en dash (“18–20 °C”), while in line 123 a hyphen is used instead (“2.5-3.0 cm”). Choose one style (preferably an en dash for ranges) and apply it consistently. Additionally, ensure there is a space between numbers and measurement units throughout the text (e.g., “20 °C” instead of “20°C”). This formatting should be uniform across the entire manuscript, including text, tables, and figures.
• Comment: please ensure that the text font is consistent throughout the entire manuscript. For example, the font used in Table 1 differs from that used in the main text, and the same issue appears with Table 2 and possibly others. All tables and text should use the same font style and size in accordance with the journal’s formatting guidelines.
• Comment: please move Table 1 to the end of the subsection 2.1. Biochar production and characterization, as it is first referenced and discussed within that paragraph. Positioning the table immediately after the relevant content will improve the logical flow and readability.
• Comment: please on line L144 correct 35○C, into 35 °C.
• Comment: please revise the text on lines 148–150. Instead of: “Soil samples were air-dried at 35 °C, sieved through a 2-mm mesh, and analyzed for texture, pH, SOM, CEC, total N, total C, and available nutrients (P, K, Ca, Mg, S, Zn, Cu, Na, Fe, B, Mn, and Al).”

I suggest replacing it with: “Soil samples at harvest were analyzed using the same procedures and methods as those applied to the soil before the addition of any amendments.” This wording is clearer and avoids unnecessary repetition.

• Comment: in Table 2, please format all measurement units consistently by placing them in parentheses, as done for CEC (cmol/kg). For example, revise “Sand %” to “Sand (%)”, and apply the same formatting to all other parameters in the table to ensure clarity and consistency.
• Comment: on line 161 I suggest replacing the term “final soils” with “soil samples at harvest,” as previously used in lines 148–150. Consistent terminology throughout the manuscript helps avoid confusion and improves clarity for the reader. On line L163 I think it’s extractable elements, not ex-tractable elements.
• Comment: on line 165 for the Teledyne Prodigy ICP instrument, please include the manufacturer’s name, city, country, and model, as mentioned in my earlier comment. Apply this formatting consistently to all other instruments cited throughout the manuscript (e.g., lines 162, 166, etc.) to meet standard reporting requirements. (e.g., L 162, 166 etc.,).
• Comment: on line L185 start sentences: „For example, N and C contents were determined following...“
• Comment: on line 210 please italicize the p in the p-value. Ensure this formatting is applied consistently throughout the entire manuscript, in accordance with scientific writing conventions.
• Comment: on lines 210–216 I recommend moving the equations and detailed explanation of the two-way and three-way ANOVA to the supplementary material or removing them altogether. This level of detail is not essential in the main text, as ANOVA is a standard statistical method widely understood by the scientific community. Keeping the main text concise will improve readability and focus.

Results

• Comment: on line 218 please revise the subheading “3.1. Status of soil nutrient” to a more precise and descriptive title, such as “3.1. Chemical characterization of acid Podzolic soil.” This will better reflect the content of the section and improve clarity for the reader.
• Comment: on line 200 please specify by how much pH, CEC, and SOM increased in each treatment compared to the control (provide numerical values or percentages where applicable).
• Comment: on line 222 clearly state the increase in nutrient concentrations for each nutrient across treatments compared to the control.
• Comment: on line 224 indicate the reduction in Fe and Al concentrations, specifying the treatments in which these decreases occurred, and provide exact values or percentages. The current phrasing (“it is known”) is vague and not sufficiently informative.
• Comment: on lines 228–229 for SOM, please clarify which treatments led to significant increases compared to the control and provide the numerical values. For results that are not statistically significant, there is no need to highlight changes.
• Comment: on lines 230–231 please revise the title of Table 4 for improved clarity and consistency in terminology. For example, instead of using “final soil,” you could write:

“The impact of biochar at various doses (0.0 – Control, 2, 5, 8, and 10%) on chemical properties of acid soil, 4 months after biochar application (Mean ± SE, n = 3; p < 0.05).”

Ensure consistent use of terms (e.g., “acid soil” instead of “final soil”) and appropriate statistical notation throughout the table title.

• Comment: on Table 4 please correct the font to ensure it matches the rest of the manuscript, following the journal’s formatting guidelines. Also, format all measurement units consistently by placing them in brackets (e.g., “pH (–)”, “CEC (cmol/kg)”). Additionally, revise the table caption and footnotes according to the journal’s instructions, this may include italicizing statistical notations (e.g., p < 0.05) and formatting the overall description appropriately. Apply these formatting corrections consistently to all other tables in the manuscript (e.g., Table 5, etc.).
• Comment: on Table 5 (L232 – 233) improve title of the Table 5 according to suggestion for Table 4.
• Comment: on Table 5 please put measurement units for nutrients in the table, correct the font.
• Comment: lines 234–236 please specify by how much soil pH values at the 8% and 10% [v/v] biochar application rates were significantly higher compared to the 2% and 5% [v/v] rates. Include the exact numerical values and statistical significance where applicable.

Lines 236–243: provide precise values to clearly show how the measured parameters increased or decreased across treatments. Avoid general statements, specific data improves the clarity and usefulness of the results.

Lines 236–237: clearly state the exact values by which all biochar treatments differed significantly from the control (0% biochar). Numerical results are necessary to fully support your conclusions.

• Comment: please italicize p throughout the manuscript in accordance with scientific writing standards (e.g., p < 0.001). There is no need to write “p-value”; simply use the format "p < 0.001" or similar. Apply this correction consistently in all sections of the manuscript, including tables, figures, and text.
• Comment: on line 225 please remove the phrase “Supplementary Materials” from the citation “Table 5 & Supplementary Materials, Table S2,” so it simply reads “Table 5 & Table S2.” Apply this correction consistently throughout the manuscript (e.g., lines 242, 245, 252, 286, etc.), as per the journal's citation style.
• Comment: the results in the text on the lines L244 – 264 please improve according to my previous comment i.e., write exact values how much significantly increased or decreased. Do that in all manuscript where you report the results.
• Comment: on line L 249 please correct word “bio-char” to biochar. There is no need for “-“.
• Comment: on line 282 please correct word “be-tween”.
• Comment: please move Figure 1 and Figure 2 to the end of the paragraph titled “3.2. Treatment effects on forage crop yield,” as they are first mentioned in that section. This will improve the logical flow and alignment between text and figures. Ensure this placement practice is consistently applied throughout the manuscript, following the journal’s formatting guidelines.
• Comment: please move Figure 3 into the paragraph “3.3. Treatment effects on SPAD,” as it is first mentioned in that section. Currently, it appears two paragraphs later, which disrupts the flow of the manuscript. Figures should be positioned close to their first mention in the text to improve readability and clarity. Please ensure this is corrected according to the journal’s formatting guidelines.
• Comment: please put Table 6 into end of paragraph 3.4. Treatment effects on forage quality. Please do correction in all manucript according to the instructions.
• Comment: in paragraph 3.4. Treatment effects on forage quality, please revise the results according to my previous comments. Specifically, report the exact values showing how much each treatment significantly increased or decreased the observed variables. Clearly state which treatment caused which effect, and by how much, rather than using general statements. This level of detail is necessary for all reported significant results throughout the manuscript to ensure transparency and scientific rigor.
• Comment: in Figure 1, please italicize the n in “n = 3” to follow standard scientific formatting. Apply this correction consistently in Figure 2, Figure 3, and throughout the entire manuscript wherever n is used.
• Comment: on line L320 correct “Mate-rials“, into materials. Please find the same mistakes in all manuscript and correct it.
• Comment: on lines 318–330 please revise this section in accordance with my earlier comments regarding the reporting of results. Clearly state which specific treatment caused an increase or decrease in each nutrient, and by how much. For example, you could write: “The 5% biochar application rate significantly increased Ca, Mg, and K concentrations by up to 3-fold compared to the control (0% biochar).” Use precise numerical values wherever possible. This will improve clarity, transparency, and the scientific quality of the results section.

Disscussion

• Comment: relate the findings to existing literature and theoretical frameworks. How do these results align with or diverge from previous studies? What do they suggest about the mechanisms underlying biochar effects on soil properties?

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

Please review and correct Table 5, as there appears to be a formatting issue. The values seem misaligned or mixed up, and it is unclear where the data for certain nutrients such as K (potassium) are presented. Ensure that all values are correctly positioned under their respective headings and that the table layout is clear and easy to interpret. Please check the formatting of the entire table and make necessary adjustments to improve clarity.

Author Response

Comments 1: [Please review and correct Table 5, as there appears to be a formatting issue. The values seem misaligned or mixed up, and it is unclear where the data for certain nutrients, such as K (potassium), are presented. Ensure that all values are correctly positioned under their respective headings and that the table layout is clear and easy to interpret. Please check the formatting of the entire table and make necessary adjustments to improve clarity.

Response 1: [Thank you for pointing out the formatting issue in Table 5. We have carefully reviewed the table and corrected the alignment of all values to ensure they are placed under the appropriate headings. The data for each nutrient, including K (potassium), have now been clearly presented. We have also revised the overall layout of the table to improve clarity and readability.

Author Response File: Author Response.pdf