Formiguer Fertilization: Historical Agricultural Biochar Use in Catalonia and Its Modern-Day Resource Implications
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
The review paper of Farré and Hoshide provides an interesting overview about historical biochar production technologies in Spain. As most of the knowledge about early production and agricultural application of biochar originates from Amazonia and the local Terra preta, this paper about traditional knowledge from Catalonia / Spain is a valuable contribution to the history of agricultural food production in Europe.
The paper is interesting to read but would deserve some revision work to sharpen the focus on the main topic of the paper. Therefore, the introduction should be shortened considerably. It is not necessary to bring such a broad overview about biochar and soil applications; this could be considered as general knowledge, described elsewhere. There is an abundance of review papers and text books on biochar (e.g. in the two years 2023 and 2024 only, about 15 new biochar books have been published!). It would be better to refer to them, especially as some wording and phrases in the introduction are rather unfortunate and should be improved.
Line 30: The problems start right with the first sentence: the “presence of limited oxygen” sounds rather inconsistent. Why not “under oxygen limitation”? In line 64 the explanation is much better.
Line 43: “support” instead of “accentuate”
Line 50: The use of fire is much older than 11,700 years (at least several 100,000 years). The Holocene is a geological epoch and does not relate well to human activities with fire that have started much, much earlier.
Line 66: Pyrolysis, resulting in more degradation-resistant carbon forms, starts already at 350 to 400 °C.
Line 70: don’t forget how pyrolysis temperature determines the biochar characteristics, too.
Line 76: Strange expression, linguistic problem?
Line 84: this is no good comparison; fresh organic matter can decompose within months, biochar may take centuries or millennia. The sentence also contradicts to line 112.
Line 88-89: the meaning of the sentence is unclear or inconsistent.
Line 102: in fact, this was rather a water vapor activation
Line 128: gaps cannot be fulfilled
Line 135: low-oxygen pyrolysis conditions
Materials and Methods: it is unfortunate that the authors focused on biochar reviews only and neglected meta-analyses. Although they cite a few meta-analyses in the list of references, there exist many more. The frequent lack of numbers about biochar characteristics and biochar effects generally is a weakness of the paper. Meta-analyses could provide quantitative summaries, review papers only qualitative summaries.
Starting with Section 3, the paper becomes much better and more interesting.
Line 189: highly weathered
Line 216: unclear meaning, linguistic problem?
Line 367: did the carbon loss occur in the whole fertilized area or only in the area of the formiguera?
Line 374: typing error
Line 407: 62 tons of biomass (dry matter) is much more than 1 hectare can produce.
Line 412: typing error
Figure 4: the probable competition for space and fertile land with this method looks deterrent
Generally, it would be fine if at least a few analytical data of biochar produced with a formiguera in comparison with “modern” biochar produced from the same feedstock could be provided.
Comments on the Quality of English Language
I recommend that a native speaker should check the manuscript.
Author Response
Comments and Suggestions for Authors
The review paper of Farré and Hoshide provides an interesting overview about historical biochar production technologies in Spain. As most of the knowledge about early production and agricultural application of biochar originates from Amazonia and the local Terra preta, this paper about traditional knowledge from Catalonia / Spain is a valuable contribution to the history of agricultural food production in Europe.
The paper is interesting to read but would deserve some revision work to sharpen the focus on the main topic of the paper. Therefore, the introduction should be shortened considerably. It is not necessary to bring such a broad overview about biochar and soil applications; this could be considered as general knowledge, described elsewhere. There is an abundance of review papers and text books on biochar (e.g. in the two years 2023 and 2024 only, about 15 new biochar books have been published!). It would be better to refer to them, especially as some wording and phrases in the introduction are rather unfortunate and should be improved.
We have shortened the Introduction as requested and improved the wording and phrasing. We have summarized and cited recently published meta-analyses articles related to agricultural use of biochar and its impacts on crop production, soil nutrients and properties, and agro-environmental impacts as a newly added Table 1 (added to Introduction section with updated methods on how this was done in the Methods section).
Line 30: The problems start right with the first sentence: the “presence of limited oxygen” sounds rather inconsistent. Why not “under oxygen limitation”? In line 64 the explanation is much better.
We have corrected this as requested so there is more consistency later on in the Introduction section.
Line 43: “support” instead of “accentuate”
This is corrected.
Line 50: The use of fire is much older than 11,700 years (at least several 100,000 years). The Holocene is a geological epoch and does not relate well to human activities with fire that have started much, much earlier.
We have corrected this by writing the following ‘Regular use of fire and charcoal associated with human activities can be dated back to a period of time between 400,000-350,000 years.’ sourced from the following source from the following research article published in PNAS https://doi.org/10.1073/pnas.2101108118
Line 66: Pyrolysis, resulting in more degradation-resistant carbon forms, starts already at 350 to 400 °C.
We have clarified this temperature range here as the start of pyrolysis.
Line 70: don’t forget how pyrolysis temperature determines the biochar characteristics, too.
We have clarified that temperature also impacts biochar characteristics.
Line 76: Strange expression, linguistic problem?
We have re-phrased this expression regarding value proposition at the start of the sentence so that the writing is less normative and more positive (e.g., direct to point with no value judgements).
Line 84: this is no good comparison; fresh organic matter can decompose within months; biochar may take centuries or millennia. The sentence also contradicts to line 112.
We have removed this contrast in this sentence due to the issues brought up with the comparison.
Line 88-89: the meaning of the sentence is unclear or inconsistent.
We have corrected it to read the following “Controlled burning of forest residues and waste can help reduce the negative impacts of wildfires on food production and the environment.”
Line 102: in fact, this was rather a water vapor activation
We have clarified this as water vapor activation rather than partial gasification.
Line 128: gaps cannot be fulfilled
We have clarified this sentence saying that the gaps in research and further development of the technology that need to be fulfilled.
Line 135: low-oxygen pyrolysis conditions
We have made the clarification of conditions.
Materials and Methods: it is unfortunate that the authors focused on biochar reviews only and neglected meta-analyses. Although they cite a few meta-analyses in the list of references, there exist many more. The frequent lack of numbers about biochar characteristics and biochar effects generally is a weakness of the paper. Meta-analyses could provide quantitative summaries, review papers only qualitative summaries.
We have cited more meta-analysis journal articles quantitatively summarized the percent impacts of agricultural biochar on crop production, agronomy, and the environment in a newly added Table 1. This adds to the pre-existing synopses of the qualitative summaries from the qualitative review articles previously cited.
Starting with Section 3, the paper becomes much better and more interesting.
Line 189: highly weathered
We have changed from high to highly.
Line 216: unclear meaning, linguistic problem?
We have decided to remove the sentence “In actuality, the many ways these ideas are expressed reflect various conceptualizations of the interactions between humans and nature.” This sentence does not really add to the paragraph writing flow of the points being made.
Line 367: did the carbon loss occur in the whole fertilized area or only in the area of the formiguera?
We have corrected this by clarifying the 33% general decrease of organic carbon was referring to the soil cover of the formiguer.
Line 374: typing error
We have corrected the mis-spelled word and changed to “Environmental.”
Line 407: 62 tons of biomass (dry matter) is much more than 1 hectare can produce.
We have clarified the wording of the sentence as it appears that our use of language was ambiguous and made the wrong point.
Line 412: typing error
We streamlined the writing on this line.
Figure 4: the probable competition for space and fertile land with this method looks deterrent
We agree with this argument and have added this qualification to the writing in the Discussion section at the end of the 1st paragraph in sub-section 5.3.2. Industrial upscaling of formigueras.
Generally, it would be fine if at least a few analytical data of biochar produced with a formiguera in comparison with “modern” biochar produced from the same feedstock could be provided.
These studies have not been done as Olarieta et al. 2011 who produced biochar with a formiguera did not contrast their biochar with modern biochars. We have added a statement on this in the Conclusions section as an avenue for future research.
Comments on the Quality of English Language
I recommend that a native speaker should check the manuscript.
The second co-author is a native English speaker who has checked the manuscript for English.
Reviewer 2 Report
Comments and Suggestions for Authors
The main question raised in the manuscript is whether it is possible to produce biochar in underdeveloped areas without large economic outlays in order to improve food security. As a reader, I understood the authors' intentions in this way.
The methodology in the manuscript is very limited, it basically consists of searching for available publications on biochar by keywords. It is a review paper based entirely on reports from other authors. As I wrote earlier, the manuscript is more like a popular science article.
The topic is not original and does not introduce any spectacular or innovative methods, but it gives hope that perhaps in countries with food shortages, biochar production could be implemented to improve soil quality and thus increase agricultural production in these areas.
Is it really Educador or maybe Ecuador line 212
Figure 1. Foriguera or formiguera, no uniformity in naming. The drawing is not very professional, as if drawn by a child. What do the colors of the arrows mean?
Figure 2 Below the photo And there is an error in the caption, it is historical and it should be historical? The drawing is signed Foriguera, in the title of the manuscript there is formiguera, Please standardize.
The description refers to Figure 1A. There is no Figure 1A in the manuscript, there is Figure 1 - line 251
Change of keywords: écobuage; formigueras; hormigueros – incomprehensible words for the reader
Author Response
Comments and Suggestions for Authors
The main question raised in the manuscript is whether it is possible to produce biochar in underdeveloped areas without large economic outlays in order to improve food security. As a reader, I understood the authors' intentions in this way.
The methodology in the manuscript is very limited, it basically consists of searching for available publications on biochar by keywords. It is a review paper based entirely on reports from other authors. As I wrote earlier, the manuscript is more like a popular science article.
The topic is not original and does not introduce any spectacular or innovative methods, but it gives hope that perhaps in countries with food shortages, biochar production could be implemented to improve soil quality and thus increase agricultural production in these areas.
Thank-you for pointing out this short-coming in the manuscript. By adding a new Table 1 quantitatively summarizing recent meta-analysis journal articles on the topic of production, agronomic, and environmental impacts of agricultural biochar as well as integrating this in with the writing, we hope that we have increased the value of this review manuscript to other researchers.
Is it really Educador or maybe Ecuador line 212
We have corrected the spelling for Ecuador.
Figure 1. Foriguera or formiguera, no uniformity in naming. The drawing is not very professional, as if drawn by a child. What do the colors of the arrows mean?
Thanks very much for catching this typo and we have corrected the spelling of formiguera in both captions for Figure 1 and Figure 2. We have also updated the drawings in Figure 1 to look more professional. The colors have no explicit meaning so we changed the color to uniform grey shaded arrows.
Figure 2 Below the photo And there is an error in the caption, it is historical and it should be historical? The drawing is signed Foriguera, in the title of the manuscript there is formiguera, Please standardize.
Thanks very much for catching this typo and we have corrected the spelling of formiguera in both captions for Figure 1 and Figure 2.
The description refers to Figure 1A. There is no Figure 1A in the manuscript, there is Figure 1 - line 251
We have corrected this to read Figure 1 and not Figure 1A.
Change of keywords: écobuage; formigueras; hormigueros – incomprehensible words for the reader
We had decided to not include these 3 keywords since most readers would not use these words in their literature searches.
Reviewer 3 Report
Comments and Suggestions for Authors
Comments and suggestions
This study provides a well-researched and comprehensive overview of the historical use of biochar through the formiguera method in Catalonia, linking it to modern-day sustainability practices. It offers valuable insights into how traditional methods can inform contemporary solutions for improving soil health and managing agricultural ecosystems more sustainably, which is highly significant for advancing modern agricultural practices. I have the following comments and suggestions for this manuscript:
- Line 146-148: "Biochar was not used in traditional Chinese agricultural systems, which relied on aerobically burning crop residues, applying dredged nutrient-rich canal sediment, and composting plant wastes, animal manure, and human manure." This statement is not entirely accurate. In fact, fire-mixed soil composting practices have been quite common in my hometown (Songzi County, Hubei Province, China, 30.1805° N, 112.8962° E) since my childhood. The local farming method involves first laying a layer of soil in the fields, building ridges, and then covering them with dry weeds, small trees, twigs, and fallen leaves collected from the edges of the fields. Farmers may also add rice straw, wheat stalks, and similar materials. Afterward, another layer of soil is added, and the biomass is sealed as tightly as possible to reduce the supply of oxygen. Under oxygen-deficient conditions, the biomass slowly burns. Once the process is complete, liquid pig manure or other liquid fertilizers are applied, and the mixture is later used as compost. Local farmers consider this to be the highest quality fertilizer. This practice was popular in some other provinces in China, including Hunan, Sicuan etc. However, it is prohibited by local government because they think open firing and smoking may cause environment pollution issue. Unfortunately, this practice has rarely been systematically documented or studied by agricultural scientists, and relevant literature is scarce.
- In the Introduction section, the authors connect the historical use of biochar, particularly in Amazonian terra preta, to the formiguera method in Catalonia, making a compelling case for how ancient practices can inform modern solutions to soil degradation and climate change. However, it would enhance the manuscript if the authors could provide more information on the specific challenges that the formiguera method addresses compared to modern agricultural practices, beyond just chemical fertilizers. This discussion could also be included in the Discussion section.
Author Response
Comments and Suggestions for Authors
Comments and suggestions
This study provides a well-researched and comprehensive overview of the historical use of biochar through the formiguera method in Catalonia, linking it to modern-day sustainability practices. It offers valuable insights into how traditional methods can inform contemporary solutions for improving soil health and managing agricultural ecosystems more sustainably, which is highly significant for advancing modern agricultural practices. I have the following comments and suggestions for this manuscript:
We thank the reviewer for extremely informative suggestions for edits and for educating us more about traditional Chinese agricultural practices that are not systemically documented in the literature. We have integrated, documented, and cited traditional Asian (e.g., Chinese, Japanese) agricultural soil paring and burning processes and updated this in the writing and in Table 2.
- Line 146-148: "Biochar was not used in traditional Chinese agricultural systems, which relied on aerobically burning crop residues, applying dredged nutrient-rich canal sediment, and composting plant wastes, animal manure, and human manure." This statement is not entirely accurate. In fact, fire-mixed soil composting practices have been quite common in my hometown (Songzi County, Hubei Province, China, 30.1805° N, 112.8962° E) since my childhood. The local farming method involves first laying a layer of soil in the fields, building ridges, and then covering them with dry weeds, small trees, twigs, and fallen leaves collected from the edges of the fields. Farmers may also add rice straw, wheat stalks, and similar materials. Afterward, another layer of soil is added, and the biomass is sealed as tightly as possible to reduce the supply of oxygen. Under oxygen-deficient conditions, the biomass slowly burns. Once the process is complete, liquid pig manure or other liquid fertilizers are applied, and the mixture is later used as compost. Local farmers consider this to be the highest quality fertilizer. This practice was popular in some other provinces in China, including Hunan, Sicuan etc. However, it is prohibited by local government because they think open firing and smoking may cause environment pollution issue. Unfortunately, this practice has rarely been systematically documented or studied by agricultural scientists, and relevant literature is scarce.
We have added writing on this as well at the end of the 2nd paragraph in the 5.1. Formiguera Compared to Similar Historical and Current Practices sub-section prior to Table 2.
- In the Introduction section, the authors connect the historical use of biochar, particularly in Amazonian terra preta, to the formiguera method in Catalonia, making a compelling case for how ancient practices can inform modern solutions to soil degradation and climate change. However, it would enhance the manuscript if the authors could provide more information on the specific challenges that the formiguera method addresses compared to modern agricultural practices, beyond just chemical fertilizers. This discussion could also be included in the Discussion section.
Thank-you have requesting this clarification. We have emphasized the applicability of this historic Catalonian process to small shareholder agricultural producers in developing nations due to its low capital requirements (see second paragraph in the Discussion section in the sub-section 5.3.1. Formiguera), particularly small shareholder agricultural producers that do not use chemical fertilizers.
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
The authors have fully considered the suggestions of the reviewers. The manuscript has improved considerably and has developed into a highly interesting paper.
Author Response
Thank you very much for taking the time to review our manuscript. Your edits and suggestions have substantially increased the quality of this work.
