the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 17 Jan 2025
On soil health and the pivotal role of proximal sensing
Abstract. Soil underpins the functioning of all terrestrial ecosystems. Sustainable soil management is crucial to preventing further degradation of the non-renewable soil resources and achieving sustainability. The soil health concept has gained popularity as a means to this end and has been integrated into the policies of many countries and supranational organisations. We need an accurate definition and scientifically robust assessment framework for effectively measuring, monitoring and managing soil health, a framework that can effectively be communicated to the policy arena and to stakeholders. Linking soil health to the provision of ecosystem services in line with selected UN Sustainable Development Goals (SDGs) provides an effective link with the policy arena focusing on sustainable development. This is needed because lack of operational procedures to measure soil health leads to policies that ignore soils and focus on management measures. We review the literature on soil health, its conceptualisation, the current criteria for selecting indicators and thresholds, as well as the implementation of different soil health assessment frameworks. Most published studies on soil health focus on agriculture; however, a broader perspective that includes various terrestrial ecosystems is needed. Soil health assessments should not be limited to agricultural contexts. We highlight the significant potential of advanced sensing technologies to improve current soil health evaluations, which often rely on traditional methods that are time-consuming and costly. We propose a soil health assessment framework that prioritises ecological considerations and is free from anthropogenic bias. The proposed approach leverages modern technological advancements, including proximal sensing, remote sensing, machine learning, and sensor data fusion. This combined use of technologies enables objective, quantitative, reliable, rapid, cost-effective, scalable, and integrative soil health assessments.
Competing interests: At least one of the (co-)authors is a member of the editorial board of SOIL.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Comment on egusphere-2024-3939', Anonymous Referee #1, 28 Feb 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3939/egusphere-2024-3939-RC1-supplement.pdf
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AC2: 'Reply on RC1', Yang Hu, 25 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3939/egusphere-2024-3939-AC2-supplement.pdf
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AC2: 'Reply on RC1', Yang Hu, 25 Jun 2025
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RC2: 'Comment on egusphere-2024-3939', Anonymous Referee #2, 23 May 2025
There is lots of good information in this manuscript and it is generally well written. The biggest problem with this manuscript is that feels like it is two different papers. One idea is a review of the current lab-based assessment of soil health vs the proximal sensing of soil health. Both approaches have advantages and disadvantages, but they are both assessment framework neutral. This feels really valuable especially the discussion of how multiple sensors can be used. The other paper is about the author’s suggestion for a more inclusive ecologically based soil health assessment approach. This second idea is underdeveloped and not directly related to the first idea. They provide a conceptual figure, but no actual guidance for how to do this other than “By directly measuring and monitoring soil properties linked to processes and functions.” The sensor methods don’t necessarily provide more direct measurements, they just make it possible to do a lot more measurements in space in time. My recommendation would be to remove the bulk of the discussion of soil health frameworks including the idea for a new framework and do a more coherent review of the measurements. For example, what are the citations that Vis-NIR or MIR can directly measure labile carbon and nitrogen or nitrogen mineralization? Finally, the paper delineates all the challenges of using the lab measurements and not any of the advantages, and then all the advantages of using sensors, but none of the challenges. A more balanced review is in order.
L18-24. This paragraph is problematic. It starts by talking about soil health. Then it switches to the connection between soil and human health. However, it doesn’t make the connection between soil health (as generally discussed) and human health. There are soil contamination issues with toxins and pathogens, but that is not typically what is measured in any soil health assessment. It’s fine to discuss all the functions of soils, but don’t conflate soil health assessment with soil assessment. None of the later discussion talks about pathogens or toxins, so either take this out or explain more concretely how soil health is related to human health.
L28 Similarly, this paragraph and the next one are about soil degradation, but the authors state without any citations that soil health is central to soil degradation. Are they just the converse of each other or is soil degradation a subset of soil health or vice versa. Please explain the relationship between soil health and degradation.
L42-43 What are “the broader, multifaceted dimensions of soil health?” Does policies in this sentence refer to the previous sentence or is this just policies in general? Is the problem that they only focus on agricultural land or only certain functions. Either add more context or take this sentence out.
L48-49 What are “ecological needs of ecosystems?”
Sections 3-4 have lots of useful information, but it isn’t clear how switching to sensor based measurements addresses any of the difficulties associated with the current assessment frameworks described here.
L170 One attempt to do this was published in https://doi.org/10.1016/j.soisec.2023.100084
Section 6. Why is this section only about the field measurements? Aren’t all these decisions about where to sample and how to standardize across equipment/users just as relevant for for sensors. MIR is a lab-based technique, so it still relies on collecting samples and processing them. For decades people have been studying variability among types of penetrometers (e.g. FRITTON, D. D.2. A STANDARD FOR INTERPRETING SOIL PENETROMETER MEASUREMENTS. Soil Science 150(2):p 542-551, August 1990). Field respiration varies from day to day and diurnally.
Section 7 – 9 . Once again, there is useful information in this section, but how is it relevant to the review of lab vs sensor methods?
L314-315 It is confusing whether the authors are talking about soil sensing or proximal soil sensing which some of the co-authors have been instrumental in defining (e.g. “the use of field-based sensors to obtain signals from the soil when the sensor's detector is in contact with or close to (within 2 m) the soil” Viscarra Rossel et al 2011). The title of the manuscript suggests proximal soil sensing, but then this sentence and the last paragraph of section 11 suggests that sensing can be in the laboratory too. For example, there is a much more robust history of using MIR in the lab than the field, so it would be really valuable to highlight the promising data from the field applications and for which measurements it seems to work as well as in the field as in the lab. A full discussion about the tradeoffs in data quality and cost/sample size even within the world of soil sensors would be extremely valuable and seems appropriate for a review paper.
L329 This is more of the most valuable components of sensor based methods. Many of the frameworks that the authors describe need texture, but if that can be measured in the field, that is a huge benefit.
L348-349. One of the criteria is practicality/affordability. The authors should be more explicit that using proximal sensing would be a very different approach to soil health sampling. Half of the rows of affordable in figure 4 suggest that the measurements aren’t affordable. Is it just a question of the cost of technology coming down or will these always just be for research and not widely used? The traditional lab based techniques permit anyone to collect and submit a sample while the lab has the expensive equipment. There are efforts to try to make soil health sampling very inexpensive for small holder farmers to do themselves (e.g. https://doi.org/10.1016/j.geoderma.2020.114539). The proximal sensing approach would require there to be companies that had the expertise to do the field sampling got hired to do the sampling and analysis, but do is require such specialized equipment and expertise that it wouldn’t be possible for the technology to be widely available.
Section 12. It would be really valuable if the review could discuss all the sensors/indicators in Figure 4. That would be the most novel and valuable part of the review and most useful to soil health practitioners. It would be especially valuable if there could be a comparison of the methods that do similar indicators. For example, Vis-NIR and MIR look identical in the table, but there are advantages and disadvantages to the two approaches. It would also be valuable if there was some discussion about how “good” these measurements are. For example, there has been way more work on trying to predict SOC than nitrogen mineralization.
Figure 4. It is surprising to see infrared CO2 gas analyser in here. Soil respiration varies so much based on field conditions, it doesn’t seem to fit with the other methods. Most of the current frameworks that do a measurement of respiration do a lab-based approach under standardized conditions. The difference between the green and the yellow is unclear. What does a direct measurement mean in this context? While the spectral techniques for SOC are based on the fact that different organic functional groups respond at particular wavelengths, the measurements is based on complicated algorithms and calibrations. This seems much less direct than combusting a sample and measuring the CO2. Similarly, the camera based techniques for structural stability really are directly measuring stability.
L404-405 I don’t understand this sentence. Section 12 is all about the ways in which sensing is better at measuring the same indicators. It’s not about new indicators. How does sensing changing the “selection of indicators.”
L431-434 There was nothing in section 12 about integrating lab measurements and field measurements. This would be a valuable contribution to discuss which measurements are still hard to do with sensing and should be done in the lab.
Citation: https://doi.org/10.5194/egusphere-2024-3939-RC2 -
AC1: 'Reply on RC2', Yang Hu, 25 Jun 2025
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2024-3939/egusphere-2024-3939-AC1-supplement.pdf
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AC1: 'Reply on RC2', Yang Hu, 25 Jun 2025
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