the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Jul 2026
An operational definition of absolute soil quality and soil health, and why we need both in practice
Abstract. The concept of soil health is becoming increasingly popular. Yet, the way to measure it remains unclear, which hinders its effective consideration in decision-making processes. We propose a general framework to interpret soil data, including the scoring of absolute soil quality (the state of an indicator representative of a soil function regarding an absolute maximum) and (ii) the scoring of soil health (the relative level of an indicator with respect to soil intrinsic potential). We underline that the scoring of soil quality and potential quality is central in land planning and excavated soil reemployment (i.e., matching land future use with soil capabilities) whereas soil health, as the mirror of soil degradation, is essential for soil restoration and sustainable management. We illustrate the approach with saturated hydraulic conductivity as an indicator of soil infiltration capacity for 42 measurements from contrasting soil types and uses, and demonstrate that the approach can be generalized to other soil indicators and functions. Overall, we outline the need to refine target or threshold values for the scoring of both soil quality and soil health, thereby better equipping stakeholders for sustainable soil management and land planning.
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Status: open (until 17 Sep 2026)
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RC1: 'Scientists should not be requested to answer meaningless, unscientific questions. (Comment on egusphere-2026-3765)', Philippe Baveye, 20 Aug 2026
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AC1: 'Reply on RC1', Brieuc Hardy, 04 Sep 2026
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We thank Reviewer 1 for starting this important discussion. We note that much of the review focuses on the general legitimacy of the concept of “soil health” rather than on the specific argument developed in this short note, and we would like to clarify several elements of the proposed framework that, in our view, deserve more direct examination. We acknowledge the reviewer’s long-standing reservations regarding soil health, but our objective here is to assess how a concept now firmly established in scientific, policy, and regulatory frameworks, including the Soil monitoring law, can be made more explicit, more coherent, and more defensible from an operational standpoint. This is also where our positions diverge. We share the reviewer’s commitment to scientific rigor. At the same time, soil science is an applied science, and decisions affecting soil degradation, protection, management, and land-use planning are being taken every day by administrations, planners, land managers, farmers, architects, and other stakeholders. In our view, scientific uncertainty is a reason to make our assumptions, limitations, and decision rules explicit and to improve them progressively, rather than a reason to stand back until every conceptual and methodological question has been settled. Remaining outside these operational frameworks would, we believe, leave soil science with very little influence on the real-world processes that drive soil degradation. We would rather contribute to shaping them, even imperfectly, than accept that outcome.
The point of divergence therefore concerns less the existence of conceptual and methodological difficulties, which we readily acknowledge, than the conclusion to be drawn from them. Reviewer 1 considers that these difficulties currently prevent a meaningful operationalization of soil health and of “absolute” soil quality. We argue instead that an operational and scientifically sound assessment is, at least conceptually, feasible, and that it is necessary if soil science knowledge is to be translated into usable information for the actors who directly influence soil degradation, protection, sustainable management and land-use planning.
In the manuscript, we explain why we strongly believe that soil health should not remain a fuzzy concept, and we propose a framework designed to address the difficulties raised by both soil management and land-use planning, including situations involving a change of land use. We totally recognize that soil quality and soil health depend on both (i) soil type and inherent constraints and (ii) current and/or projected land use. This is precisely what the concept aims to tackle. Specifically, we propose that (i) soil functions are defined and estimated independently from one another; and (ii) the soil functions considered to soil health/soil quality are selected according to current or projected land use; and (iii) soil quality and soil health are clearly distinguished. We would add an important clarification here: “absolute” soil quality, in our framework, does not mean a universally optimal quality independent of use. It refers to the evaluation of a soil's capacity to provide each individual function, before those functions are selected or weighted for a given land use. The land-use dependence highlighted by the reviewer thus enters the framework at a later stage, and does not invalidate the concept. Such organization also substantially reduces the issues arising from indicator collinearity and from the interpretation of a single indicator as a proxy for multiple distinct soil functions. The resulting soil diagnosis is deliberately flexible: functions can be retained, discarded or weighted differently depending on whether the objective is soil management under an existing use or land-use planning open to future changes.
We find the reviewer’s comparison between soil health and human health particularly relevant, because the two are indeed analogous in many respects. Human health is not assessed through a single universal variable: different components are evaluated through different indicators, interpreted against reference values that depend on the characteristics of the individual. Athletic capacity, for instance, is evaluated through VO2max, strength, power, speed, and endurance; general clinical state through vital signs such as temperature, heart rate, blood pressure, respiratory rate, and SpO2; and nutritional status through BMI, waist-to-height ratio, body-fat percentage, or growth velocity. The interpretation of these indicators must consider characteristics of the studied individual (sex, age, etc.) to be compared to relevant benchmarks and for a relevant diagnosis. The same logic underpins our framework: distinct soil function (e.g., nutrient supply, water supply, biodiversity habitat, maintaining soil structure, carbon storage, etc.) cannot be assessed with the same indicators, and their interpretation must account for soil type and the inherent determinants constraining a soil’s achievable potential. Not every function is equally relevant when assessing whether a soil meets the expected requirements for a given land use, whereas considering the full range of functions is meaningful in land-use planning, where future uses remain open. The reviewer’s vineyard-versus-wheat example therefore illustrates precisely why the framework separates soil functions, inherent constraints and land-use requirements, rather than contradicting it. Fertility requirements clearly differ among vineyards, arable crops, pastures, and forests. The interpretation of fertility-related indicators must accordingly rely on use-specific targets and thresholds. We agree that robust target and threshold values are still lacking for many indicators in a given soil use context; this reflects the current state of knowledge, and we are hopeful that soil science will continue to progress on this front, particularly as efficient digital data-management systems develop.
We also agree that saturated hydraulic conductivity (Ksat) should not be regarded as a universally valid proxy for infiltration or water-regulation functions. Here, however, the criticism assigns to this example a role it does not play in the manuscript. First, the evaluation of one soil function should rely on a set of mutually reinforcing indicators. Second, the most suitable indicators should be adapted to local pedoclimatic conditions, which is fully consistent with the proposed approach. Third, the present short note is a proof of concept, with Ksat used as an illustrative example rather than an universally accepted solution to assess soil water infiltration potential in every context.
We thank Reviewer 1 for providing additional literature that we will consider carefully in the revision. We believe that progress toward a robust operational soil-health assessment has been slower than we would have liked, and that significant scientific challenges remain. Our disagreement concerns the implications of this observation: in our view, the persistence of these challenges does not make operationalization futile, but rather reinforces the need for explicit conceptual frameworks that can be tested, criticized, and improved as knowledge advances. This short note offers a deliberately modest contribution in that direction. We do not claim to resolve all the issues raised by the reviewer, but we do believe that the distinctions we propose can help make the concepts of soil quality and soil health less ambiguous and more useful for soil protection, sustainable management, and land-use planning.
Citation: https://doi.org/10.5194/egusphere-2026-3765-AC1
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AC1: 'Reply on RC1', Brieuc Hardy, 04 Sep 2026
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RC2: 'Comment on egusphere-2026-3765', Anonymous Referee #2, 03 Sep 2026
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Thank you for this study presenting a different perspective on soil health and soil quality. I have a few questions to better understand the proposed approach.
- I am a little confused about the definition of soil quality. Soil quality is generally defined as the capacity of a soil to function within ecosystem and land use boundaries, and therefore it is usually linked to a specific function or purpose. For example, Doran and Parkin (1994) defined soil quality as the capacity of a soil to function within ecosystem and land-use boundaries to sustain biological productivity, maintain environmental quality, and promote plant and animal health. Hoewver, in the proposed framework, “absolute soil quality” seems to represent the absolute performance of a particular soil function based on an individual indicator. Could the authors please clarify how this definition is related to the established definition of soil quality? I am also wondering whether a term such as “absolute functional performance” would be more appropriate here.
- I also have a similar question regarding the definition of soil health. In this manuscript, soil health is defined as the relative level of an indicator compared with its soil specific potential, and therefore it is closely related to soil degradation. Could the authors provide more justification for this definition? For example, if one indicator reaches 100% of its potential, does this mean that the related soil function is fully healthy, or does this score only represent the condition of that individual indicator? If the framework is later used to assess overall soil health, how would the different physical, chemical and biological indicators or soil functions be combined?
- Regarding Ksat, I agree that it can be a useful indicator of soil functioning or soil health. However, the soil-health benchmark for Ksat appears to be mainly based on soil texture. Ksat is also strongly influenced by soil structure, macroporsity, organic matter, stone content etc. Why is texture alone considered sufficient to define the achievable potential? Also, about half of the soils reached or exceeded 100% soil health. Could this indicate that the reference values may not fully represent the actual soil-specific potential? I think this point needs some more discussion.
- The distinction between inherent soil properties or soil potential and the current soil condition has already been proposed in previous frameworks, including Vogel et al. (2019), which is also cited in the manuscript. Could the authors clarify more clearly what is new in the proposed framework compared with these previous approaches? In particular, what is the advantage of defining these components as “absolute soil quality” and “soil health”?
- The scoring approach for Ksat assumes that a higher Ksat gives a higher score. However, many soil indicators do not follow a simple “higher is better” relationship. For example, pH has an optimum range, while available phosphorus or nitrogen can be too low or too high. Even for Ksat, very high values may increase the risk of nutrient leaching. How would the proposed scoring approach be applied to indicators where there is an optimum range or where both low and high values can be undesirable? This is important because the authors mentioned that this framework could also be extended to other soil indicators and functions.
Doran, J. W., & Parkin, T. B. (1994). Defining and assessing soil quality. Defining soil quality for a sustainable environment, 35, 1-21.
Vogel, H. J., Eberhardt, E., Franko, U., Lang, B., Ließ, M., Weller, U., ... & Wollschläger, U. (2019). Quantitative evaluation of soil functions: Potential and state. Frontiers in Environmental Science, 7, 164.
Citation: https://doi.org/10.5194/egusphere-2026-3765-RC2
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Despite the title I gave to my review, I will try to be as constructive as possible, to assist the authors. Given the topic at hand, about which I have never made it a secret that I did not think it made sense (in particular in an article that the authors cite), that will require some mental gymnastics on my part…
The reason I am even trying to be constructive is that I suspect that the authors, like many of our colleagues in virtually every country now, are under heavy pressure from public officials, decision makers, and stakeholders (e.g., farmers), to come up with a sound scientific basis for the concept of soil health, or at least with an objective way to standardize its measurement. When the concept first surfaced, scientists should have said, loud and clear, that unless one could define clearly and operationally what was meant by it, in more than a metaphorical way, there was no need to go further. Instead of that, a bunch of people went around happily applauding the supposedly new vision… I guess that, in order to get their names on a Nature paper, some people are willing to write anything, including the fact that in science, we don’t really need to define clearly what we are talking about, and that some totally fuzzy, “feel-good” concept will do. Anyway, because it was not stopped in time, the “soil health” craze has gained ground (no pun intended), and now members of the public are requesting soil scientists to put some science behind it, and to come up with ways to measure it unambiguously. I guess that is a good illustration of the fact that lack of scientific rigor comes back to haunt you in the end… The authors seem to be very well aware of this, when they write: “The lack of an operational definition prevents objective quantification, which discourages stakeholders from incorporating soil health into management plans”. This, 26 years (!!!!) after Doran and Zeiss (2000) supposedly defined soil health… Way to go…
With a clear sense of pity for the authors, who clearly had to satisfy some demand to make sense of soil health, I have attempted to find out what could be salvaged of their efforts, after they are reframed along a more reasonable path. I believe that if the authors are willing to rewrite their narrative, not as a way to come up, arbitrarily, with a way to measure soil health, but as an analysis of why such a futile effort does not really make sense at this stage, the resulting article, once published, would be a positive and very valuable contribution to the discipline.
In order to achieve this, a first aspect to be discussed is the notion that the adjective “absolute” could be meaningfully associated with either soil quality or soil health. For soil quality, that question has been addressed rigorously by Sojka and Upchurch (1999) and Letey et al. (2003), who concluded that an “absolute” soil quality did not make practical sense. Only a “quality” relative to some proposed use of a soil made sense. A good illustration of this is that a soil could provide good growing conditions for a vineyard, but be terrible to grow wheat or sugar beets. And that is just in the context of one of the services that soils render to human populations… The question is whether the concept of soil health should also be relative to a particular use. Ultimately, to answer it one needs to define clearly what makes a soil “healthy”. We know that to be healthy for a human being depends on what s/he wants to do. Healthy for someone running marathons, is not necessarily the same as healthy for a weightlifter or an office worker… One could argue that the same should be true of soils.
The second aspect that needs to be addressed is the notion of potential, to which the authors refer often. It is appealing conceptually to imagine the amount of a particular service that a soil could provide if all the conditions were ripe, and then to compare it with the actual amount the soil is capable to deliver. The problem, with the overwhelming majority of the functions/services of soils is that we are not able at this point to measure them at all, let alone whether or not they are “achievable”. There are mentions of that problem in two articles I published in the past ( Baveye et al., 2016; Baveye, 2017). More recently, we have discussed this point in detail in a manuscript that is under review for publication in Soil (Baveye et al., 2026). You can find it here: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-3485/.
The purpose of that article is to try to evaluate when an “indicator”, in particular of a soil ecosystem service, is a good one. The authors consider that using such indicators is a good way to access the potential of soils in different respects. However, it is not clear to me how a soil parameter we measure can be a good indicator for something that we do not measure at all, and for which we therefore do not have a mechanistic model, linking service and indicator. In that context, the recent article of Yosef et al. (2026) is particularly interesting and relevant. They used a detailed process-based model to investigate “the relationships between soil properties and provision of water regulation ecosystem services across three contrasting pedo-climatic regions in Austria, Italy, and Tunisia”. One of their conclusions is that “several widely used indicators exhibited weaker or inconsistent relationships with water-related processes than commonly assumed”. These included the saturated hydraulic conductivity, often regarded as a key predictor of infiltration rates and water-regulation ecosystem services.
Not surprisingly under these conditions, the authors conclude an illustrative attempt to estimate the soil achievable potential relative to water infiltration by admitting that “defining [the] soil achievable potential for a given indicator is often not straightforward and remains a major challenge to implement robust soil health scoring systems”. Perhaps the fact that what was a challenge when the research was conceived still remains a challenge when the research is done should be the key message of a revised version of the manuscript. Sure, one can arbitrarily call soil health anything one wants, even if the link to
health” is elusive and not very convincing, but in the end, one is still faced with problems for which, at the moment, there is not clear solution, at least not the kind of simplistic solution that seems to be sought when one asks for the “absolute” “health” score of a soil.
References cited
Baveye, P. (2017). Quantification of ecosystem services: Beyond all the “guesstimates”, how do we get real data?.Ecosystem Services, 24, 47-49.
Baveye, P. C., Baveye, J., & Gowdy, J. (2016). Soil “ecosystem” services and natural capital: critical appraisal of research on uncertain ground. Frontiers in Environmental Science, 4, 41.
Baveye, P., Scammacca, O., & Chalhoub, M. (2026). Fundamental conditions" indicators" should meet to be objective and to guide practice reliably. EGUsphere, 2026, 1-12.
Letey, J., Sojka, R. E., Upchurch, D. R., Cassel, D. K., Olson, K. R., Payne, W. A., ... & Triplett, G. B. (2003). Deficiencies in the soil quality concept and its application. Journal of soil and water conservation, 58(4), 180-187.
Sojka, R. E., & Upchurch, D. R. (1999). Reservations regarding the soil quality concept. Soil Science Society of America Journal, 63(5), 1039-1054.
Yosef, B. A., Basile, A., Coppola, A., Ungaro, F., Zucca, C., & Bancheri, M. (2026). Soil indicators for ecosystem services: a focus on water regulation. Soil, 12(1), 347-369.