Digital Soil Mapping of Soil Macronutrients (N, P, K) in Emilia-Romagna (NE Italy): A Regional Baseline for the EU Soil Monitoring Law
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe main research refers to the digital soil mapping (DSM) of macronutrients (N, P, K) in the Emilia-Romagna region of Italy. The study aims to provide regional baseline data for the EU Soil Monitoring Law, which utilized multiple data sources, including high-resolution digital elevation models (DEM) and remote sensing images from the Sentinel-2 satellite, to assess the distribution of macronutrients in the soil. The article provides a detailed analysis of the distribution of macronutrients in the region's soil and offers important baseline data for future soil management and policy-making. Additionally, the research has clear significance and purpose and is innovative to some extent. However, before it can be further processed, the authors still need to address the following issues:
1. There is a fundamental difference in the spatial distribution of nutrients between the regional soil database (RER, N=34,750) and LUCAS data (e.g., the proportion of phosphorus exceeding the standard in the plain area differs by 76.75%). This reflects the insufficiency of large-scale data in regional applications, but the root causes of the differences in data sampling design or analysis methods have not been deeply explored. EU-level data (LUCAS) cannot accurately reflect the regional soil nutrient status, leading to deviations in the policy reference baseline; at the same time, there is a lack of in-depth analysis of the causes of data differences (such as sampling density, analysis methods) and cross-scale integration solutions, which limits the direct application of the results in the implementation of the EU Soil Monitoring Law (SML). The authors should fully consider and explain this issue.
2. The paper has obvious deficiencies in providing timely validation of regional baselines, multi-scale data integration solutions, and the implementation of regulatory standards, weakening its direct support for the EU Soil Monitoring Law. Its core value lies in revealing the regional applicability risks of continental-scale models (such as LUCAS data bias), but it does not provide a systematic solution.
3. The introduction lacks precise positioning of research gaps, and the literature review is superficial, failing to establish a solid theoretical foundation and methodological basis, which affects readers' judgment of the research value. Especially as a policy-oriented study (in response to EU laws), the failure to link existing literature with policy practices is a significant defect. In addition, when introducing digital soil mapping (DSM) technology, the introduction does not cite the foundational research in the DSM field, nor does it comment on the shortcomings of traditional mapping methods, weakening the necessity of method innovation. These issues should be given attention and revised.
4. In terms of experimental design and methods, the sampling design makes it impossible to analyze the dynamic changes of nutrients and the impact of land use history. The experimental design emphasizes simplicity and interpretability, but this may sacrifice the ability to capture all relevant variations (especially those driven by recent human activities). Moreover, while the study successfully implemented regional-scale DSM, it strongly revealed the severe inapplicability and risks of using continental-scale data (LUCAS) for regional regulation through comparison.
5. The chart design of the data results does not fully compensate for data deficiencies (such as temporal and spatial deviations and insufficient visualization of policy comparisons). These deficiencies affect the assessment of the applicability of soil nutrient baselines to the EU Soil Monitoring Law (as clearly stated in the conclusion section from lines 1130 to 1134).
6. The paper compared the prediction results based on the LUCAS and RER datasets, but only presented the differences in the proportion of areas where soil phosphorus (P) concentration exceeded the threshold under different datasets. It lacks in-depth exploration of the reasons for such differences and does not analyze which factor (such as data collection methods, sample representativeness, analysis techniques) led to the different results. Furthermore, when discussing soil nitrogen (N) and potassium (K) concentrations, only the insufficiency of the LUCAS-based Digital Soil Mapping (DSM) assessment in detecting concentration hotspots was mentioned, but no specific details were provided regarding the characteristics of these hotspots, the influencing factors, or the specific impacts of this insufficiency on soil quality and land management. Meanwhile, although the paper referred to the requirements of the EU Soil Monitoring Law (SML) proposal for monitoring nitrogen and phosphorus concentrations, it failed to discuss the potential difficulties in the actual implementation of this proposal, the possible differences among member states in its implementation, and the comprehensive impact of this proposal on soil management in different regions.
Author Response
Responses to Reviewers' Comments
Reviewer #1
We thank the reviewer for acknowledging that the work provides a detailed analysis of the distribution of macronutrients in Emilia-Romagna soil and offers important baseline data for future soil management and policymaking. We also thank the reviewer for stating that the work has a clear significance and purpose and is innovative to some extent. We did our best to respond to their issues and requests for revision.
Rewiers' Comments
Comments 1, 2, 4, 6 (Thematic): The paper highlights the LUCAS-RER discrepancy but doesn't deeply analyse the root causes, provide cross-scale solutions, or fully explore the policy implications. This weakens its direct support for the implementation of the EU Soil Monitoring Law (SML) at regional scale.
Response
We thank the reviewer for these insightful comments, which allowed us to clarify and significantly improve the core contribution of our work. Our primary goal was to provide a rigorous, high-resolution regional assessment to serve as a benchmark for evaluating continental-scale models like LUCAS. In response, we have substantially strengthened the discussion to explicitly address the points raised.
We have added a new subsection (4.2. Root Causes of the LUCAS-RER Discrepancy and its DSM Implications) where we systematically analyse the root causes: (1) Sampling density, (2) Scale of covariates and model generalization, and (3) Inability to capture specific pedolandscape units.
Furthermore, in the new subsection 4.3. Direct Implications for the EU Soil Monitoring Law and Regional Management, we now explicitly quantify the policy consequences (e.g., a potential 76% misclassification of the plain's area for P) and argue for a hybrid "top-down/bottom-up" monitoring approach, citing relevant EU initiatives (FAO-GSP, EJPSOIL), thereby providing a clear pathway forward.
Changes in Manuscript
Introduction: Sharpened the research gap.
New Section 4.2 & 4.3: Added in-depth analysis of root causes and policy implications.
Throughout Discussion: Reinforced the narrative that our work provides the essential evidence base for the necessity of regional data within the SML framework.
In Section 4.3 New figure (Figure 11) added showing the distribution of the P concentrations > 50 mg/kg according to the RER and LUCAS P2O5 maps to improve the visualization of policy comparisons.
Comment 3. The introduction lacks precise research gaps, a solid theoretical DSM foundation, and links to policy practice.
Response
We thank the reviewer for this suggestion. We have entirely restructured the Introduction to:
- More precisely define the research gap: the critical void at the regional scale for implementing broad EU policies.
- Cite foundational DSM literature (e.g., McBratney et al., 2003; Wadoux et al., 2020) and recent reviews to establish a solid methodological context.
- Strengthen the narrative connecting DSM capabilities, policy needs (SML, Nitrates Directive), and the specific lack of regional data.
Changes in Manuscript
The entire Introduction has been rewritten to address these points directly.
Introduction: Sharpened the research gap.
New Section 4.2 & 4.3: Added in-depth analysis of root causes and policy implications.
Throughout Discussion: Reinforced the narrative that our work provides the essential evidence base for the necessity of regional data within the SML framework.
In Section 4.3 New figure (Figure 11) added showing the distribution of the P concentrations > 50 mg/kg according to the RER and LUCAS P2O5 maps to improve the visualization of policy comparisons.
Comment 5. Chart design doesn't compensate for data deficiencies (temporal, spatial) or visualize policy comparisons well.
Response
We agree that enhanced visualization strengthens the message.
We have:
- Improved the legibility of Figure 3 (classed post-plots) by increasing symbol size and providing new legends.
- We discussed the policy implications of P thresholds numerically and in the revised text. As for visualization we provided a comparison of relative differences between the RER and the LUCAL macronutrients maps at pedolandscapes and agricultural districts level (summarised in Figure 10) providing a visual comparison of aggregated values stemming from the two datasets. In addition we added a new figure in the revised version of the manuscript (Figure 11)
Eventually, Figure 5S shows the relative differences in estimated macronutrient concentrations between the LUCAS and the RER datasets highlighting the occurrence of areas where LUCAS estimates are systematically above or below the RER estimates.
Changes in Manuscript
Figure 3 has been regenerated for clarity, and a new figure has been added (Figure 11). The policy comparison is now central to the revised Discussion (Section 4.3).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors write about their experience in investigating a comprehensive survey to fill the knowledge gaps regarding the concentration values (layer 0-30 cm) of macroelements (N, K, P) in the soils of the Emilia-Romagna region (Italy). The article should be of interest to readers, because the analysis of nutrients addressed here is in line with scientific research or official European publications, as well as the Proposal for a Directive of the "Soil Monitoring Act" (COM (2023) 416 final - 2023/0232 (COD). Thus, this work, in my opinion, has great promise and will significantly advance the field. Very interesting is the comparison of the maps of topsoil macronutrients based on the LUCAS survey data at the EU-scale for Emilia-Romagna, along with the corresponding maps based on regional data (RER maps), highlighting the degree of the overestimation observed for the LUCAS-based concentration maps. However, after carefully reading the paper, I have a few modest comments.
Line 14. What is the difference between agronomic interventions and soil management.
Excessively long sentences that make reading the manuscript very unappealing and understandable. For example
-Line 76. However the full implementation of several EU environ- 76 mental regulations targeting water, soil and environmental quality [14-16], based on the 77 reduction of emissions from agriculture, still requires knowledge gaps to be filled at the 78 national and regional scales to manage the impacts of nutrient losses on terrestrial and 79 aquatic ecosystems and human health [17,18]. Please rewrite.
-Line 94. In Italy the objective of protecting waters from pollution caused by nitrates and ex- 94 cess nutrients from wastewater sources is entrusted to the administrative Regions (NUTS2 95 according to the EU Nomenclature of Territorial Units for Statistics), which defines the dis- 96 cipline on the agronomic use of livestock effluents, vegetation waters from oil mills and waste waters from agricultural and agri-food companies, on the basis of the criteria and general technical standards contained in the Ministerial Decree of 25/02/2016, as provided for by the "Consolidated Environmental Law" ( Testo Unico sull’Ambiente, Legislative Decree 152/2006), in application of the EU "Nitrates Directive" (Dir. 91/676/EEC). Please rewrite.
This sentence is not clear: Line 140..… identifies 466 soil typological units which can be grouped in 22 pedolandscapes or soil provinces (reference scale 1:1,000,000): ten in the alluvial plain and four, five and three, respectively, in the low (150-450 m a.s.l.), medium (450-900 m a.s.l.) and high (>900 m a.s.l.) Apennines (Figure 1). But especially explain in more detail the concept of soil province:… is a geographical area defined by relatively uniform soil characteristics, which are influenced by a relatively uniform combination of climate, vegetation, and parent material. Please rewrite.
The strange thing is that nowhere does the type of soil appear by an international system such as FAO WRB or Soil Taxpnomy. Any reason?
The maps in Figure 3 are practically illegible. Please improve.
Consider making sentences more concise for clarity and precision. The long sentence between lines 781 and 821 should be broken up.
Part of the Results section includes a discussion. And it is unacceptable not to show a conclusions section. In fact, section 4, Discussion and Conclusions, should be broken up appropriately. Precision must be exercised to reduce the lengthiness of these sections.
Please state the novelty of this study on an international scale.
Limitations of the study should be highlighted.
Author Response
Responses to Reviewers' Comments
Reviewer #2
We thank the reviewer for their positive and constructive response, judging that the work has great promise and will significantly advance the field, and finding very interesting the comparison of the maps of topsoil macronutrients based on the LUCAS survey data at the EU-scale for Emilia-Romagna with the corresponding maps based on regional data. We did our best to respond to their issues and requests for revision.
Rewier’s Comments
Comment 1. General: Excessively long sentences make the manuscript hard to read. Specific examples given.
Response
We thank the reviewer for this critical feedback on clarity. We have gone through the entire manuscript and broken down long, complex sentences into shorter, more direct statements. The specific examples provided by the reviewer have been rewritten.
Changes in Manuscript
Main text: The entire manuscript has been edited for conciseness. Specific problematic sentences have been simplified and split.
The sentences at lines 76 and 194 were rewritten and split (Lines 64-67, and lines 69-77)
The long sentences between lines 781 and 821 were broken up (Lines 770-804, revised version).
Comment 2. Clarification: The concept of "soil province" needs a clearer explanation.
Response
We thank the reviewer for pointing this out. We have expanded the explanation of a "soil province" (pedolandscape) in the Section 2.1 to make it clearer. We also decided to use the term “pedolandscape” to avoid confusion with administrative units (provinces). Similar higher association and soil organization levels are recognized through by number of pedologists acting in different regions of the world (Wadoux et al. 2024, doi.org/10.1016/j.geoderma.2024.117065).
Changes in Manuscript
Section 2.1: The definition has been rewritten as: "These pedolandscapes represent distinct geographical units where soil characteristics are relatively uniform, as they develop under a consistent combination of climate, vegetation, and parent material." (Lines 116-118 , revised version)
Comment 3. Methodology: the type of soil do not appear by an international system such as FAO WRB or Soil Taxonomy
Response
This is a very valid point. We have now added a new figure in the supplementary materials with the distribution of the FAO-WRB Major Soil Groups in the pedolandscapes of Emilia-Romagna. Soil Taxonomy classification (12th Edition, 2014) for the dominant soil types in each pedolandscape unit have been updated and is provided in the supplementary material (Table S1). In the analysis of results and in the discussion, we did not focus on individual soil typological unit but rather on pedolandscapes to keep the focus on the regional scale. Nevertheless, for some pedolandscapes (A2, A6) detailed information about soil units and their classification were provided in the text
Changes in Manuscript
Supplementary Material: A new figure (Figure S1) has been added with the FAO-WRB classification. The Soil Taxonomy (12th Edition, 2014) classification of the soil types is reported in Table S1 where soil are listed in order of prevalence. This is referenced in the main text (Lines 172-176, Section 2.1).
Main text: In the revised version of the manuscript we have added the reference to the soil classification system (ST, 12th Ed., 2014) where specific soil types are mentioned (e.g., Lines 996-998; 1008-1010; ).Comment 5. Chart design doesn't compensate for data deficiencies (temporal, spatial) or visualize policy comparisons well.
Comment 4. Structure: The Results section includes discussion, and the Discussion & Conclusions section is too long and should be separated.
Response
We agree with this suggestion for improving the manuscript's flow. We have:
- Removed interpretive language from the Results section, making it a purely factual presentation of the findings.
- Split the single "Discussion and Conclusions" section into two distinct sections: "4. Discussion" and "5. Conclusions".
Changes in Manuscript
Sections 3 & 4: The Results section has been edited to be as descriptive as possible. The former Section 4 has been formally split into "4. Discussion" and "5. Conclusions".
Comment 5. Novelty & Limitations: Please state the novelty and highlight the study's limitations.
Response
We thank the reviewer for this suggestion. We have now explicitly stated the international novelty of our work in the Conclusions and have expanded the discussion of limitations in a dedicated subsection (4.4. Communication of Uncertainty and Study Limitations).
Changes in Manuscript
Section 4.4: Added a dedicated paragraph on study limitations (temporal data, topsoil focus).
Section 5 (Conclusions): Clearly states the novel contribution.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsManuscript No. land-3906366 tilted “Digital Soil Mapping of Soil Macronutrients (N, P, K) in Emi-lia-Romagna (NE Italy): A Regional Baseline for the EU Soil Monitoring Law" presented the maps of three macronutrients, i.e. N, K, and P, in the topsoils (layer 0-30 cm) of the Emilia-Romagna (21710.1 km2) region in NE Italy. According to the primary goal of the current study, which is indicated in lines 114–117, I am unable to propose the current article for publication. It seems like a report or survey should be submitted to the government. The abstract did not involve information regarding the status of other macronutrients, such as P. The introduction was very lengthy and should be shortened. Lines 94-101 without citations. Lines 102-112 are without citations. The abbreviation “NUTS3” appeared suddenly in line 61 without prior interpretation. The authors should separate the Discussion from the Conclusions.
Author Response
Responses to Reviewers' Comments
Reviewer #3
We thank the reviewer for their comments, which have helped us to further refine the focus and increase the technical accuracy of the manuscript. We did our best to respond to their issues and requests for revision.
Rewier’s Comments
Comment 1. General (Major Critique): “According to the primary goal of the current study, which is indicated in lines 114–117, I am unable to propose the current article for publication. It seems like a report or survey should be submitted to the government”.
Response
We thank the reviewer for this perspective. We have reframed the narrative to emphasize the scientific contribution. The policy context is now presented as the motivation, while the core of the paper is the methodological and evidence-based scientific contribution of testing the limits of continental models and providing a robust, uncertainty-quantified baseline.
Changes in Manuscript
Abstract & Introduction: Reworded to lead with the scientific challenge of cross-scale DSM accuracy. The goal of the work has been rewritten as follows (Lines 83-93, revised version):
“The goal of this work is to fill this knowledge gap by providing a high-resolution (100 m) assessment of topsoil macronutrients (N, P, K) in Emilia-Romagna using a robust DSM approach based on a large regional soil database (N = 34,750). Our specific objectives are to:
- Produce and validate maps of N, P, and K concentrations and their associated un-certainty using Quantile Random Forests.
- Identify the environmental covariates that most strongly influence the spatial patterns of each nutrient.
- Critically compare our regional maps with the existing LUCAS-based continental maps to quantify discrepancies and evaluate the implications for regional soil health assessment within the framework of the proposed EU Soil Monitoring Law.”
Comment 2. Abstract: Does not involve information on P.
Response
We thank the reviewer for this observation. To ensure all key findings are prominent, we have revised the abstract to give P its own distinct statement, making the results for phosphorus more prominent.
Changes in Manuscript
Abstract: Revised to state: "A stark contrast was observed for available phosphorus (P), with mean values of 40.4 ± 11.0 mg kg⁻¹ in the alluvial plain, dropping to 15.2 ± 6.1 mg kg⁻¹ in the Apennines."
Comment 3. Introduction: Very lengthy, should be shortened. Lines 94-101 and 102-112 lack citations.
Response
We agree. We have significantly shortened and streamlined the Introduction. We have also added relevant citations to the previously unsupported statements regarding Italian and regional regulations.
Changes in Manuscript
Introduction: The introduction has been condensed. Appropriate citations have been added to the paragraphs on Italian and regional regulations.
Comment 4. Abbreviation: "NUTS3" appears without definition.
Response
We apologize for this oversight. The abbreviation has now been defined upon its first use (Line 71, revised version).
Changes in Manuscript
Line 71: Added the full definition: "...administrative regions, i.e., at NUTS2 level (Nomenclature of Territorial Units for Statistics, level 2) [23]..."
Comment 5. Structure: Separate Discussion from Conclusions.
Response
As also requested by Reviewer #2, we have split the "Discussion and Conclusions" section into two separate sections.
Changes in Manuscript
Sections 4 & 5: The single section is now "4. Discussion" and "5. Conclusions".
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsMost of my concerns have been covered accordingly. I believe that the manuscript has been well improved, It's OK for me.
Reviewer 2 Report
Comments and Suggestions for AuthorsI recommend publication, my comments were taken into consideration.
Reviewer 3 Report
Comments and Suggestions for AuthorsI read the response of the authors on manuscript land-3906366 V2 titled “Digital Soil Mapping of Soil Macronutrients (N, P, K) in Emilia-Romagna (NE Italy): A Regional Baseline for the EU Soil Monitoring Law ". Unfortunately, the author's response did not convince me, and I am still insisting that the present work did not show any innovation; it seems like a report or survey that should be submitted to the government or decision-makers to take action.
