<figure><img src="image_1.png" /></figure>

HAL
open science

# Soil quality and fertility in sustainable agriculture, with a contribution to the biological classification of agricultural soils

Adriano Sofo, Augusto Zanella, Jean-François Ponge

► To cite this version:

Adriano Sofo, Augusto Zanella, Jean-François Ponge. Soil quality and fertility in sustainable agriculture, with a contribution to the biological classification of agricultural soils. Soil Use and Management, inPress, 38 (2), pp.1085-1112. 10.1111/sum.12702. hal-03180887v2

HAL Id: hal-03180887

https://hal.science/hal-03180887v2

Submitted on 12 Apr 2022

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

Public Domain
1 **Commentary paper**

2

3 Soil quality and fertility in sustainable agriculture, with a

4 biological classification of agricultural soils

5

6 Adriano Sofo¹,*, Augusto Zanella²,*, Jean-François Ponge³

7

8 ¹ Department of European and Mediterranean Cultures: Architecture, Environment, Cultural
9 Heritage (DiCEM), Università degli Studi della Basilicata, Via Lanera 20, 75100 Matera,
10 Italy

10

11 ² Department of Land, Environment, Agriculture and Forestry, Università degli Studi di
12 Padova, Viale dell'Università 16, 35020 Legnaro (PD), Italy

12

13 ³ Muséum National d'Histoire Naturelle, CNRS UMR 7179, 4 avenue du Petit Château, 91800
14 Brunoy, France

14

15

16

17 Corresponding authors: Prof. Adriano Sofo, [adriano.sofo@unibas.it](mailto:adriano.sofo@unibas.it); Prof. Augusto Zanella, [augusto.zanella@unipd.it](mailto:augusto.zanella@unipd.it)

18

19
## Abstract

Soils and crops are nowadays particularly vulnerable to climate change and environmental stresses. In many agrosystems, soil biodiversity and the ecosystem services soil provides are under threat from a range of natural and manmade drivers. Agricultural soils are often subjected to agronomic practices that disrupt soil trophic networks to a large extent, and make soils less and less productive in the long term. In this scenario, sustainable soil uses aimed at improving plant/root status, growth and development play a crucial role, as they have been found to enhance the biological capacity of agricultural soils.

This commentary paper is divided into four main sections:

a) The contentious nature of soil organic matter.

b) Soil biological quality/fertility.

c) Soil classification.

d) Which agricultural practices can be defined as sustainable?

## Highlights

* A crucial question: what really is a sustainable agricultural soil?

* Is it possible to adopt a different paradigm of soil classification?

* The decline in soil fertility is mainly due to the reduction of soil biodiversity and organic matter content.

* Biodiversity and fertility are two sides of the modern concept multifunctional agricultural soils.

* A better stewardship of agricultural soils as a natural capital is urgent and necessary.
53

# 1. Introduction

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

84

Soils are one of our most valuable resources and are fundamental natural capitals at the base of all trophic chains. In agricultural systems, management practices that ensure high production often have negative repercussions on soil health, quality and fertility (Fig. 1). A high number of physicochemical, microbiological and biochemical parameters are responsible for the fertility of a soil (Cheik & Jouquet, 2020; Jiang et al., 2020). However, because of the challenge of considering them altogether, only the most informative and reliable ones can be selected. Soil biological properties are very sensitive to small-scale changes occurring in a soil compared to soil physicochemical parameters. To ensure the long-term sustainability of cropping systems, both the status of soil organisms and crops need to be taken into account (de Vries and Wallenstein, 2017; Pelosi and Römbke, 2018). In this commentary paper, the specific biological indicators of soil health will be discussed together with soil physicochemical parameters and suggestions for soil classification. The core assumption is that healthy soils provide an optimal environment for soil organisms that stimulate plant physiological and biochemical responses to stress (Pinstrup-Andersen and Pandya-Lorch, 1998; Soussana et al., 2019).

The overall message is the urgency of better understanding the effects of soil management practices on the structure of soil microbial and animal communities, and on plant health and production. A high number of physicochemical, biological and biochemical parameters are responsible for the fertility of a soil. However, due to the impossibility of considering all of them, it is inevitable to select the most informative and reliable ones (Gil-Sotres et al., 2005). Generally, the physicochemical parameters are of scarce utility as indicators, as they are altered often when soils are subjected to drastic disturbances (Filip, 2002). On the other side, soil biochemical properties are more sensitive to smaller changes occurring in a soil (Yakovchenko et al., 1996; Wallenstein & Vilgalys, 2005; Muscolo et al., 2015). The selection of biological indicators closely related to soil microbial dynamics is essential for the quantification of soil quality and its resilience to stresses, two basic requisites of soil fertility (Duru et al., 2015; Hopkin, 2008; Schloter et al., 2018; Vogel et al., 2018; Veen et al., 2019). The indicators adopted could provide reliable and easy-to-interpret information on soil and plant status, as they are little affected by the fluctuations related to the season and topographic effects.
Carrying out a representative soil sampling, measuring soil biological indicators, proposing a correct soil classification, and integrating all data in a holistic framework can facilitate the inclusion of soil health, quality and fertility in management decisions made by farmers, land managers, and crop advisers. Understanding the effects of agricultural management practices on soil health, soil microorganisms/animals, and plants is important, but soil health should be included as a factor when management decisions are made by farmers, land managers, and crop advisers.

<figure><img src="image_2.png" /><figcaption>[Figure 1. HERE]</figcaption></figure>

Despite significant data gaps, there is growing evidence that unsustainable agricultural practices not only negatively affect the health and quality of the soils needed to sustain healthy crops and provide nutrient-rich foods, but they can also significantly affect the
integrity and resilience of the ecosystem as a whole. To 'break' the above-cited vicious circle, sustainable solutions are required to facilitate the conservation of soils. But, in order to understand which soils are or can be sustainably managed, soil classification criteria are essential. The founders of the soil classification linked the different units to precise pedogenetic processes (FAO-UNESCO, 1974) to be able to define the functioning of each unit. The advantages of knowing the position of a cultivated field on the map of the distribution of the world's soils remain minimal for the farmer. Scale and micro-morphological or purely local factors intervene and affect the functionality of the soil map. Generally, farmers do not know the name of the soils they are cultivating. Not even many scientists who study natural ecosystems know the name of the soils in which they grow plants or raise livestock.

This article is focused on the most advanced and updated research on the processes occurring at the interface between soil physicochemical aspects, plant roots and soil microorganisms/animals in sustainable agrosystems, and on practices to establish sustainable soils and preserve their fertility. An examination of the published literature has revealed that:

a) soil humus formation, soil compaction and degradation, soil-plant-atmosphere interactions, root development and rhizosphere processes, vegetation types and phytosociology, signaling among plants and organisms, and plant nutrient balance have all crucial roles in making a soil really sustainable;

b) a conspicuous part of soil physical, chemical and biological fertility in agroecosystems can be attributed to the action of soil microorganisms, with a substantial contribution of soil animals;

c) a new paradigm for soil classification is necessary for creating the conditions for soils to be sustainable and able to provide ecosystem services.

In this article, all these aspects are considered in a holistic view, with agrosystems considered as living systems where soil, vegetation, fauna and microorganisms co-evolve and are reciprocally influenced (paragraph 6). In living soils, the key role of microorganisms in agrosystems should be seriously taken into account in land management strategies, focusing not exclusively on crop yield and quality, but also on soil fertility restoration and environmental safety. Moreover, the role of soil fauna, especially considering their
interactions with microorganisms and plant roots, can surely contribute to the long-term
sustainability of agricultural soils.

The aim of this commentary paper is therefore to reveal the complex interactions between
soil physical and chemical properties (on which classification is mainly based), soil microbial
diversity, and plant health in sustainable agroecosystems. Nowadays, agricultural activity,
rather than considering just productivity, is focused on the quality of products, natural
resource stewardship and environmental aspects, moving toward sustainable management
techniques. The sustainable, judicious and efficient use of soils is thus essential to support
continued agricultural production and quality. Focusing on sustainable soil use management
and food production, this new type of agriculture can perfectly fit within the background of
natural resources challenge, where positive mutual interactions between soil microorganisms
and cultivated plants play a key role.

143

144

## 2. The contentious nature of soil organic matter

146

Lehmann and Kleber (2015) reject the concept of humus and claim that: "Government-funded research programs must therefore preferentially support science that bridges the gap between detailed and fine-scale mechanistic research at the plant-soil interface and field-scale research relevant to those who manage soils for their multiple ecosystem services". In their "Soil continuum model - Consolidated view" (Fig. 2) they replaced "humification" and "mineralization" with the less precise terms of "formation" and "destruction". Stevenson (1994) founded the organic matter science accurately describing large to small molecules and their specific properties in a model very similar to the one presented as a novelty in 2015 by Lehman and Kleber. With the intention of strengthening our position in defense of humus, we report in Appendix 1 the thought of "The first major critique of the humification concept" (Lehmann and Kleber, 2015). It seems to us that Waksman (1936) predicted soil depletion as a consequence of denying the concept of "Humus as an organic system". The recent acknowledgement of the supramolecular nature of soil humus substances (Drosos et al., 2018; Piccolo, 2002; Pinton et al., 2007) allows to devise a fractionation procedure, called Humeomics, that enables a detailed characterization of the structure of humic molecules in soil. The molecular mass of humic molecules can be increased with repercussions on the amount of carbon stored in the soil (Piccolo et al., 2019).
164

<figure><img src="image_3.png" /><figcaption>[Figure 2. HERE]</figcaption></figure>

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

As for "fine-scale mechanistic research", it reminds us of those who would like to eat the pills that astronauts carry into space, instead of real legumes or cooked meats. It may even happen that they do not understand why they do not feel good in the long term. The concept gets closer when we consider the mass of neurons composing our brains. Via the process of categorization, the brain transforms only some sensory stimulation into information. Only some of the wavelengths of light striking our retinas are transformed into seen objects, and only some of the changes in air pressure registered in our ears are heard as words or music. To categorize something is to render it meaningful (Barrett, 2009). The same neurons produce different thoughts in response to a specific evolution of the entire brain system, that becomes increasingly rich in interconnexions and information. In figurative terms, the functioning of the soil is similar to that of a brain, but instead of generating thought in a living net of neurons, it builds a real complex ecosystem of interconnected living beings in continuous co-evolution.

### 3. Soil physicochemical quality and changes in soil organic matter

One of the main worldwide agricultural problems is the decline in soil fertility, mainly due to the reduction of soil biodiversity, and of nutrient and water content. Agricultural soils
are particularly susceptible to this problem, as they are based on the purposeful simplification of the relationships between the plant and other components of the natural habitat. This simplification should make agricultural ecosystems easier to control, but instead it creates conditions of extreme weakness for plant life. Many studies have shown that the conversion of natural land to agriculture, together with the agricultural intensification that enhances soil organic matter (SOM) depletion, makes the greatest contribution to soil biodiversity loss (Giller et al., 1997; Six et al., 2004; Sofo et al., 2014a; Vitti et al., 2015; Sofo et al., 2020a). The large-scale use of pesticides may also have direct or indirect effects on soil biodiversity, but the lack of data has resulted in contradictory research results (EASAC - European Academies Science Advisory Council, 2018; Silva et al., 2018). SOM, especially its stabilized fraction (humus in chemical sense), plays a crucial role in climate change mitigation and adaptation (Shukla et al., 2020). Amount and types of SOM are principally determined by the continuous physical and chemical action of soil organisms. Soil fauna and microbes are crucial for breaking down, transforming and decomposing SOM (Filser et al., 2016). For this reason, studies focused on understanding soil microorganism-SOM and macrofauna-SOM interactions are needed, and guidelines for future experimentation and best regenerative practices to exploit soil multifunctionality have to be developed, tested and validated.

Soils and crops are vulnerable to climate change and environmental stress, and will be more and more in the near future. Many crops are endangered by increasing water shortage, often due to changes in rainfall frequency, and rise of soil aridity and desertification, eventually resulting in deteriorated soil structure and critically low levels of SOM, macro- and micronutrients, all of which essential for water provision and plant growth (Matson et al., 1997; Sofo et al., 2019a). The frequent and strong soil tillage, typical of intensive agriculture, significantly affects the stability of soil microaggregates, that have a key role in SOM stabilization and support long term carbon sequestration, being more stable than macroaggregates (Filser et al., 2016). This triggers a detrimental vicious circle which ultimately leads to an increase in the use of mineral fertilizers and pesticides, and needs continuous and strong soil tillage to replace the burrowing and aggregating activity of soil animals, again increasing SOM loss (Silva et al., 2019). In brief, such soils become mere "containers" for plant roots and function as a carbon source, worsening the greenhouse effect even further.

Healthy, fertile soils are rich in SOM built of carbon that living plants remove from the atmosphere through photosynthesis. SOM fuels the soil organisms which improve soil
structure and recycle mineral elements that plants take up as nutrients (FAO and ITPS, 2015; Mechri et al., 2017). But soils release carbon, too. The frequent use of tillage and fertilizers, characteristic of modern conventional agriculture, has accelerated SOM degradation, releasing more carbon into the atmosphere. The last IPCC report (Shukla et al., 2020) concludes that, globally, cropland soils have lost 20-60% of their original SOM content. On top of those losses, modern agriculture consumes a lot of fossil fuels to pull plows and manufacture the synthetic nitrogen fertilizers that farmers rely on to coax large harvests from degraded soils. Additionally, restoring soil health would help mitigate the effects of climate change. Increasing the amount of SOM enhances its ability to hold water. Improving soil structure would reduce erosion and retain more rainfall, where it can better sustain crops - especially during drought-stressed years (Sofo et al., 2019b). In addition to benefiting the climate, less fertilizer use will reduce off-farm water pollution (Silva et al., 2019). Land management choices also affect the amount of carbon stored in trees, plants and soil (FAO, 2020). The last IPCC report (Shukla et al., 2020) estimates that serious changes in forestry and agriculture to curtail deforestation and improve soil management could reduce global emissions by 5 to 20 percent. While this won't solve the climate problem, it would represent a significant down payment on a global solution.

What is it really important to monitor in a soil? Certainly, a comprehensive and in-depth analysis of soil characteristics is required. To do this, correct soil sampling (e.g., by analyzing composite soil samples taken at different soil depths in specific soil horizons) and/or an appropriate pedological excavation are essential. This can allow the definition of physical soil properties (accumulation of salts, soil compaction, reduction of macropores, soil hydraulic conductivity - vertical and horizontal water infiltration), soil macroporosity (with macropores analysis and their shape and size, both relevant for water infiltration), soil moisture, preferably measured by sensors in different soil horizons during the year. Other important parameters for defining soil fertility are the root status, evaluation of the healthy status of the roots and of root morphology (root density, root diameter, amount of white, suberized and dead roots, etc.), microscopic analysis of the roots to observe eventual physical damage of the roots (e.g., necrotic parts, increased lignification, etc.). Among chemical parameters, a key role for the fertility of agricultural soils is played by soil nutrients (particularly nitrogen and phosphorus) and the presence/absence of soil contaminants, such as heavy metals, pesticides and hydrocarbons. Soil gas analyses are also relevant, as the determination of carbon dioxide, nitrogen oxides and methane (and oxygen too, even if it cannot be easily detected) by means
of gas chromatographic techniques or portable laser-based trace gas analyzers will allow us to distinguish between anaerobic and aerobic micro-environments, with the latter able to promote several plant diseases due to pathogenic microbial attacks.

## 4. Soil biological quality/fertility

Soils host a quarter of our planet's biodiversity, but most of it remains unknown (Sofo et al., 2010; Wall et al., 2010; Fierer, 2017; Sofo et al., 2020a). One gram of soil may contain up to one billion bacterial cells, tens of thousands of taxa, up to 200 million of fungal hyphae, and a wide range of invertebrates like earthworms, springtails and nematodes (Wagg et al., 2014), that are all part of a complex and interconnected food web (Lavelle et al., 2014; Wall et al., 2015; Williamson et al., 2017). The health of all multicellular organisms (including plants, animals, and humans) and their surrounding ecosystems are interconnected through a subset of microbial organisms found in the plant and soil compartments, particularly in the rhizosphere. Plants nurture an entire world of soil organisms that feed and protect the plants according to aboveground-belowground, plant-soil feedbacks (PSFs) that have different spatio-temporal scales and are greatly affected by climate-related factors (Ponge, 2013; Veen et al., 2019).

The diverse communities of telluric bacteria and fungi keep the soil healthy and fertile and determine the main biogeochemical processes that make life possible on Earth (Dastgerdi et al., 2020; Sweeney et al., 2020; Wilpiszeski et al., 2019). They play fundamental roles in driving many ecosystem processes on which the functioning of terrestrial ecosystems depends, including soil formation, nutrient and water cycling, climate regulation, carbon storage, production of food, medicine and fibre, disease and pest control, and greater resilience to global change (Bardgett & Van der Putten, 2014; Lavelle et al., 2014). While soil biodiversity represents an important biological and genetic resource for biotechnological innovation with benefits to society, it is increasingly threatened by different forms of land degradation (FAO, 2020; FAO and ITPS, 2015). Soil biodiversity is vulnerable to many human disturbances, including intensive and non-sustainable agricultural practices, land use, climate change, nitrogen-enrichment, soil pollution, invasive species, and sealing of soil (Orgiazzi et al., 2015). Soil microorganisms' dynamics (e.g., mobility, growth, nutrient absorption and respiration), mainly responsible for soil fertility and quality (Bünemann et al., 2018), are strongly affected by the soil management (Enwall et al., 2007; Jeanbille et al.,
2016; Sofo et al., 2020a, 2020 b). When the soil microbial biocenosis is significantly altered, 285 cultivated plants are more susceptible to diseases and display stunted growth. In this respect, 286 correct agronomic techniques (fertilisation, irrigation, soil tillage, etc.) become instruments to 287 recover the disrupted equilibrium. However, the functionality and metabolism of soil 288 microorganisms are related to soil quality and fertility, as they influence and, at the same 289 time, are influenced by the soil carbon and nitrogen contents, bacteria being an essential part 290 of carbon and nitrogen cycling processes (de Vries and Shade, 2013; Mooshammer et al., 291 292 2014; de Vries & Wallenstein, 2017; Li et al., 2018). Microbial interactions play a critical role 293 not only in regulating ecological functions and processes but ultimately in determining the 294 health of plants, animals and humans as components of terrestrial ecosystems (Fierer, 2017; 295 Sofo et al., 2020b; Stevenson et al., 2020). Having co-evolved with a plethora of 296 microorganisms, plants benefit from microbial symbiosis, while simultaneously facing 297 challenges from pathogens. 298

Microbial communities are regulated by the activity of soil animals, some of which play 298 an essential role as ecosystem engineers (Lavelle, 2002). Earthworms, ants and termites (in 299 arid tropical countries) contribute significantly to the creation of an interconnected pore 300 network (Pagenkemper et al., 2015) into which air and water are circulating (Pla et al., 2017), 301 and which are hot spots of microbial activity (Hoang et al., 2016). They also contribute to the 302 creation of soil aggregates (Lavelle et al., 2020), offering a dynamic habitat to microbial 303 colonies (Gupta & Germida, 2015) and preventing loss of carbon, water and nutrients 304 (Pulleman and Marinissen, 2004). Soil engineers and their associated microbiome produce 305 metabolites which exert a hormonal effect on plants (Muscolo et al., 1996) and act as signals 306 which stimulate the defence metabolism of plants (Blouin et al., 2005). Soil animals of 307 smaller size, although not directly involved in the physical transformation of the soil, are the 308 main regulating agents of the microbial compartment. By feeding on fungi and bacteria they 309 contribute to maintaining the microbial biomass in an active state (Kaneda and Kaneko, 310 2008), and decrease competition among microbial strains by feeding preferentially on those 311 growing faster (Newell, 1984). Although still in need of research, it can be expected that 312 selective grazing of microbial colonies by tiny soil animals (nematodes, protozoa, 313 microarthropods, enchytraeids) increases soil microbial biodiversity locally, as this has been 314 shown to occur with grassland vegetation under moderate herbivore grazing. It has even been 315 suggested that some soil animals would consume preferentially microbial pathogens and thus 316 could contribute to decrease soil pathogenicity (Friberg et al., 2005). Soil food webs, from 317
microbes to top predators, include trophic chains (Pollierer et al., 2019) by which fresh organic matter is transformed in humus (Lehmann and Kleber, 2015) at a rate increasing with the number and complementarity of functional niches of soil animals (Heemsbergen et al., 2004).

It is essential to link biodiversity measures with specific soil functions and plant status under particular environmental contexts, particularly in agrosystems (Ramirez et al., 2015). For instance, while some soil functions are driven by a diverse set of organisms that contribute to functional resilience (e.g., decomposition), other soil functions involve a more specific set of organisms (e.g., nitrifiers, bio-control agents) which make them more vulnerable to biodiversity loss. Wagg et al. (2014) showed that soil biodiversity loss or simplification of soil community composition can impair multiple ecosystem functions, including plant diversity, decomposition, nutrient retention, and nutrient cycling. A better understanding of the pivotal roles of soil organisms in mediating soil-based ecosystem services, as affected by ecosystem management approaches and practices adapted to socio-ecological contexts, is also central to guiding biodiversity-friendly agricultural intensification (Lal, 2015; FAO, 2020).

334

335

## 5. Soil classification

337

### 5.1. *Crucial historical legacies*

339

In this section we summarize the historical legacies of two masters of soil classification, Dukuchaev Vasily Vasilyevich (1846-1903), considered the founder of the soil classification in Europe, and Hans Jenny (1899-1992), one of the greatest American pedologists, a Swiss who ended up working in California at Berkeley University.

344

1) From "Zones verticales des sols, zones agricoles, sols du Caucase" (Dokuchaev, 1900), cited in "A l'aube de la Science du sol" (Legros, 2019):

347

a) Climate, biological agents, rock, topography and duration are the factors of soil differentiation, or the factors of pedogenesis.

349
350 b) Climate and corresponding vegetation are the main factors responsible for the
351 organization of soils on a global scale.

352 c) At the field scale, climatic variability does not have to be considered, while
353 topography and variability of the geological substrate can still modify soils.

354 d) Dokuchaev and his students also observed that there were exceptions to climate
355 zonality. Local environmental factors play a predominant role and mask the role of
356 climate. It will take many years to conceptually resolve this problem, as evidenced
357 by the changes in vocabulary introduced on the subject over time. Currently we
358 distinguish between "zonal" soils, that are part of the climatic zonality, "azonal"
359 soils, whenever the rock outcrops directly, and "intra-zonal" soils, whose
360 characteristics are linked to special conditions, such as excess water or salt.

361
362 2) In "Factors of soil formation - A System of Quantitative Pedology" (Jenny, 1941):
363

364 a) The soil system is an open system; substances may be added to or removed from it.
365 Every system is characterized by properties that we may designate by symbols, such
366 as s1, s2, s3, s4, s5, etc. For example, s1 may indicate nitrogen content, s2 acidity,
367 s3 apparent density, s4 amount of calcium, s5 pressure of carbon dioxide, etc. Any
368 system is defined when its properties are stated.

369 b) The initial state of the soil system has been designated as parent material. Climate (cl), Organisms (o), Topography (r), Parent material (p), and Time (t) completely describe the soil system. The total change of any soil property depends on all the changes of the soil-forming factors following a fundamental equation:
370
371
372
373

(1) $s = f(cl, o, r, p, t, \dots)$, where: s stands for "soil property", f for "function of," or "dependent on", dots show that, besides the variables listed, additional soil formers may have to be included. In a more precise differential mathematical formula, the equation (1) becomes:

$$
(2) \quad d s = \left(\frac{\partial s}{\partial cl}\right)_{o, r, p, t} d cl + \left(\frac{\partial s}{\partial o}\right)_{cl, r, p, t} d o + \left(\frac{\partial s}{\partial r}\right)_{cl, o, p, t} d r + \left(\frac{\partial s}{\partial p}\right)_{cl, o, r, t} d p + \left(\frac{\partial s}{\partial t}\right)_{cl, o, r, p} d t
$$

381 c) In selecting cl, o, r, p, and t as the independent variables of the soil system, we do
382 not assert that these factors never enter functional relationships among themselves.
We emphasize the fact that the soil formers may vary independently and may be present in a great variety of combinations, either in nature or under experimental conditions. To find out the role played by each soil-forming factor, it is necessary that all the remaining factors be kept constant. A serious practical difficulty in solving Equation (1) in the field arises from the requirement of keeping the soil formers constant. In laboratory experiments on soil formation, we can exercise rigid control of the conditioning variables (e.g., temperature, moisture, etc.) and thus obtain sets of data that leave no doubt as to the functional relationship between them. Under field conditions, considerable variation in the magnitude of the variables cannot be avoided, in consequence of which we arrive at scatter diagrams rather than perfect functions. Statistical considerations must be introduced, and the resulting equations possess the character of general trends only. Even so, the gain in scientific knowledge fully justifies the mode of approach.

396

## 5.2. Soil and vegetation

398

A major problem with the current system of soil classification is that it is difficult for non-specialists to use and understand. Perhaps it is possible to take an example from botanists and the synthetic methods they have prepared. There are several aspects that vegetation and soil coverings have in common:

a) both are "covers", both correspond to a continuous layer that shows changes inside and outside perceptible to the human eye. If there is more water in the system, for example, the vegetation changes and also the underlying soil; external change can also be seen from satellite; the internal change (structure) is noticed by the naked eye with some training. Of course, the more the water (or other main ecological factors) balance differs, the more the change is visible;

b) in both, the whole cover can be broken down into sub-layers. For example, for vegetation we speak of arboreal, shrubby and herbaceous layers; for the soil of organic, organic-mineral and mineral horizons;

c) in both cases, circumscribing spatial sub-units (horizontal or vertical) is not so simple, because the transition from one to the other unit is rarely abrupt; very often it is gradual and nuanced. It is normal for this to happen, because in the two cases
the factors involved in the distribution of the plant and animal species that inhabit
these two coverages are interdependent and evolving.

We know that using the characteristic species of the phytosociological units to map the forest vegetation, the part of the forest occupied by undefined vegetation types becomes larger than that occupied by known vegetation types (Zanella and Géhu (Directeur), 1994). In fact, to define vegetation units, lists of particular species are needed; these characteristic species are not the most common in each vegetation unit (if they were the most common, they would also be present elsewhere). Thus, by definition, a large part of an area covered by phytosociological units lacks the characteristic species. This prevents phytosociology from best expressing its operationality. A map of the distribution of vegetation units is always ambiguous and nuanced in many transitional places (Bartoli, 1966; Susmel, 1980, 1959). The founding principle (Braun-Blanquet, 1964; Clements, 1936) says that the species lists are repetitive in the space, and therefore it is possible to put a name on each list and produce vegetation maps. We know, however, that for ecological reasons, plant lists can only be partially repetitive. The species respond to the environment and form an unlimited number of combinations that are constantly evolving in space and time (Tansley, 1935). To make an ecosystem survey, in which a given group of plants and animals coevolve, people have to place themselves in the center of an ecologically homogeneous environment. Unfortunately, detecting such ecological homogeneity remains a subjective matter, also because the success of this coexistence can only be discovered in the future, during the succession of an ecosystem.

436

### 5.3. *Classical soil classification*

438

Foresters considered mainly the organic surface part of the soil, calling it the “humus form”, P.E. Müller in Jabiol et al. (2005), whilst agronomists concentrated mostly on the mineral part of the soil (which also contained the organic part buried with the cultivation) which they called “soil”. While foresters selected morpho-functional traits, agronomists focused on climate (USDA) and physical-chemical composition, texture, structure, thickness of various diagnostic horizons (USDA and other National and International classifications), with the scope to provide mineral elements and nutrients for crops. Foresters tried to link humus forms to the floristic composition or soil animal lists (Hartmann, 1965; Hartmann and Marcuzzi, 1970; Klinka et al., 1981) and the ability to regenerate the forest (Toutain, 1981;

447
Bernier and Ponge, 1994; Camaret et al., 2000; Ponge, 2009; Bernier, 2018). Agronomists, on the other hand, linked soil types to the specific climate and needs of crops (Jenny, 1941; Birkeland, 1999; Beaudette et al., 2013; Brenna and Tabaglio, 2013; Berdugo et al., 2020). Each country built its own classifications.

For the soil, the need for unification was necessary when international organizations wanted to map soils at planet level. A summary of the history of soil classification can be found in the FAO-website portal. The FAO-Unesco Soil Map of the World (1974) is structured in 10 Volumes composed of a common Legend (Volume 1) and nine sections corresponding to different areas of our planet (http://www.fao.org/soils-portal/data-hub/soil-maps-and-databases/faounesco-soil-map-of-the-world/en/). The authors of the cartography tried to respect the principles mentioned above (5.1. Crucial historical legacies). In FAO-UNESCO (1974) we can read: "The number of soil units which compose the legend of the Soil Map of the World is 106. The legend sheets present these soil units in an order which reflects the general processes of soil formation. The basic principles which underlie the separation of these soil units and their definitions are discussed in Chapter 3. Areas of "non soil" are shown on the map as miscellaneous land units." It sounded very promising. Unfortunately, the agreement was only apparent. It hid strong differences of thought that later revealed themselves in the construction of different national operational classification systems. The USA built their own classification (Soil Survey Staff, 1975, 1999, 2003, 2010, 2014, 2015; Soil Science Division Staff, 2017), FAO and IUSS another (Jahn et al., 2006; WRB, 2006; IUSS Working Group WRB, 2007; IUSS Working Group WRB, 2010; IUSS Working Group WRB, 2015; Charzyński et al., 2017), and many states operated independently in their countries, often agronomists on one side and foresters on the other, for example in France (Afes, 2009). In Italy, for historical reasons, the classification of soils depends on the region in which it is practiced: in the North West, the French system prevails, even for humus forms, in the North East, the German or USDA systems are adopted but an ancient Austrian system (Hartmann and Marcuzzi, 1970) was until recently used for humus forms, and in the Central-South often the USDA is preferred sometimes that of IUSS Working Group, while for humus it is not uncommon to refer to a Canadian manual (Klinka et al., 1981).

Even worse, when there are more than three variables interacting, and in the soil there are dozens, a natural system ends up in chaotic and unpredictable movement (Mayr, 1942; Lorenz, 1963). Soil profiles, as other natural systems, are all different and impossible to classify through a list of characters subdivided in categories as foreseen by Jenny (1941). It is
thus impossible to give a name to the soil by fixing the position of a diagnostic horizon in the profile, or the color of this horizon using a panel of reference colors (Munsell), or the content of clay of this horizon. Each variable depends on so many other variables that, in a given point in the field, the combination of them is very large and unpredictable (Equation 1 or 2). However, soil scientists decided to separately improve existing classifications. The result was that the national classifications diverged over time, making it impossible to merge them into a single reference.

For some years now, the specialists of the different classification schools have been organizing joint outings, such as soil classification IUSS activities. The best attempt to make the classification easier to understand to other natural science specialists is that of the Soil Survey Staff (Staff Soil Survey, 2015), which proposed a beautiful Illustrated Guide to Soil Taxonomy (version 2) based on the American system. The corresponding model of the World Reference Base Working Group was published in 2018 (Blum et al., 2018). What is most surprising in these manuals is the almost absence of information on soil biology, zero pages in the Staff Soil Survey (2015), four pages in the Blum et al. (2018), even if the “fathers” of soil science put soil organisms in second position, after the climate. And we know how much the climate itself is connected to the living beings of our planet, which have modified it to make it suitable for their development (Lenton et al., 2016).

500

### 5.4. Is there a way to classify soil that is useful and also accessible to non-specialists?

501

To classify the soil in a simple way, it is necessary to define from the outset the purpose of the classification and the “limits of the boxes” in which it is useful to put the soils. The Unified Soil Classification System (USCS), for example, is a standardized method used in engineering and geology to describe the texture and grain size of a soil. It can be applied to most unconsolidated materials and is represented by a two-letter symbol. A similar “logical” model is already used for agricultural soils. The owner of a crop sends the soil sample to the laboratory which does the analysis and classifies that soil for that specific crop, and reports how much nutrients are missing to optimize its production. Although you may disagree on the principle that knowing what plants are made of makes possible to calculate what needs to be put into the soil (Fusaro, 2015; Lowenfels, 2017), with adjustments of doses and nutrients distributed over time, and crop rotation, the method works. There is now an important amount of research results on the biological quality of the soil. Some of the thousands of articles on
the subject include historical context (Magdoff and Weil, 2004; Wander et al., 2019); European references (Parisi, 1974, 2001; Chaussod, 1996; Balbo et al., 2006; Ponge et al., 2013) and climate change implications (Brussaard et al., 2007; Bispo et al., 2018; Yin et al., 2020).

In few words, a QBS index (Biological Quality of the Soil) is calculated by sampling soil animals, especially arthropods and worms. These animals are sorted into functional groups and studied in different types of soils. It can be seen if one soil is richer in functional biodiversity (which guarantees the functioning of the soil, with the right proportion between mites and springtails, for example) than another (Angelini et al., 2002; Ruiz-Camacho, 2011; Nuria et al., 2011). Similarly, soil microorganisms are classified into functional groups designed to reflect soil management (Torsvik and Øvreås, 2002; Nesme et al., 2016).

In summary, there are many useful ways to classify the soil, but none which satisfy what the founders of the soil science wished, that is to understand the soil on a planetary level and to appreciate how this system was distributed/developed on the planet in harmony with life. There is perhaps a way to get to this; not to attempt to circumscribe the infinite final soil types, but to identify a small number of soil-forming processes to which more soil types are arbitrarily assigned.

## 5.5. Soil and humus

When an artificial crop system is compared to a forest, things change. We think of a whole system composed of species that have historically come together to collaborate and optimize energy resources. Forest managers call the attempt to mathematically imitate the achievement of a balanced forest ecosystem in terms of age, number and size of trees as "normalization" (Susmel, 1980; Phillips et al., 2004; Pan et al., 2011; Oldeman, 2012; Reinmann and Hutyra, 2017; Hasan et al., 2017; Mahdavi et al., 2019). The cycle concerns a part of the forest surface, a mosaic piece that regenerates when an old tree die and leads to the stability of the forest mosaic as a whole. The number of trees on the surface under renewal must decrease exponentially following a known curve with parameters related to the species and called the "norm". Soil plays a fundamental role in the cycle, and it is the superficial part of the soil profile composed of organic (O or H) and organo-mineral (A) horizons that changes most rapidly, the whole profile following within a much longer time (Achat et al.,
546 2015; Baldrian, 2017; Bernier and Ponge, 1994; Osman, 2013; Poeplau et al., 2020; Takahashi et al., 2019; Zanella et al., 2001, 2018a).

548 The need to have one international system for classification of all humus forms is quite recent. Unification began in July 2003, with a meeting in Trento (Italy) of 26 European specialists with the specific aim of arriving at a European proposal for the classification of humus forms. The need for unification arose from the necessity to accurately calculate the carbon cycle at the level of several European countries. The profile of a natural soil is very complex, and it is not enough to take samples at predefined depths to know the amount of carbon that it stores. It is better to subdivide the soil into horizons and then take a sample in each of them. With 1/2 or more of the carbon being concentrated in the organic and organo-mineral horizons, which correspond to the humus forms, it was decided to try to classify them in a standardized way. In 2018, the summary of the work (Fig. 3) was collected in three Applied Soil Ecology special issues (Zanella and Ascher-Jenull, 2018a, 2018b, 2018c).

559

<figure><img src="image_4.png" /><figcaption>[Figure 3. HERE]</figcaption></figure>

560

561

562

563 The soil develops and changes with the system that contains it, and depending on the space-time scale with which one looks at it (Zanella et al., 2018e, 2018b). It seems like a trivial matter; in reality it changes the perspective with which one has to look at the soil when wanting to classify it. One way to classify soil taking into account its dynamics is to break it down into three layers which are evolving and influencing each other but which remain and can be classified independently (Fig. 4).

569
<figure><img src="image_5.png" /><figcaption>[Figure 4. HERE]</figcaption></figure>

Living organisms organize the superficial part of the Earth's crust into layers that are visible to the naked eye. If we consider the soil as a living ecosystem, it begins with the colonization process of the rock by microorganisms (time 1 on Fig. 4). In time 2, we can see an organic matter that begins to bond with the mineral one and form aggregates (OA horizon), and the rock fragments generating an initial Lithopedon (C). In time 3, the organo-mineral aggregates become well amalgamated and form a structured A horizon. In time 4, a new layer called Copedon begins to form between well-developed Humipedon and Lithopedon; it arises from the interaction of them. In time 5, Copedon (horizon B) increases in volume and takes on a mature form. In time 6, we arrive at a complete, mature soil profile, where the Copedon can also present an E horizon.

It is possible to break down the soil profile into three main sections: Humipedon (organic O and/or organic-mineral A horizons); Copedon (mineral horizons E and/or B); Lithopedon (mineral horizons C and R). The advantage is that of being able to study these parts of the soil as if they were relatively independent (Zanella et al., 2018d). In the natural environment, the formation of the soil profile can stop at the Humipedon stage (in films of microorganisms on bare rock, or in soil crust), or also comprise a Lithopedon (sometimes very thick in soils at high altitude, such as Rendzina or Rakers, for example), or form an additional Copedon (as in the most common mature soils) which may be very deep in tropical soils (Fig. 4, time 5 and 6); eroded soils often lost their whole Humipedon.
Moving on to classification, morpho-functional diagnostic horizons were chosen for each Humipedon. As an example, the Mull system contains those humus forms that are able to integrate into an organic-mineral horizon all the litter annually produced by the ecosystem in which they develop. As consequence, all the humus forms belonging to a Mull system are characterized by 1. the absence of the last stage of litter transformation (corresponding to a diagnostic horizon called OH, made of organic thin fragments, mixed with small animal droppings) and 2. the presence of an organic-mineral A horizons made of zoogenic large aggregates. In the same way, other morpho-functional, organic and organo-mineral, zoogenic and non-zoogenic horizons were defined to classify each Humipedon in five Terrestrial humus systems (Mull, Moder, Mor, Amphi and Tangel). In each humus system the relative thickness of the diagnostic horizons allows to individuate 3-4 finer humus forms.

TerrHum, a free available Android app, can help to remember the diagnostic characters and horizons (https://play.google.com/store/apps/details?id=fr.inra.terrhum) corresponding to each humus system and forms. The same reasoning was done for submerged (Histic) tidalic seaside (Aqueous) and initial, or man-modified, or artificial (Para) humus systems. The classification method is very similar to that described in the FAO-UNICEF map legend: to circumscribe a soil ecosystem at the top of the Earth crust, that grows over time and evolves following a pedogenetic process, dependent on those same soil forming-factors reported in the preceding Crucial historical legacies. The recognition of morpho-functional elements then makes it possible to identify humus systems and forms.

To obtain a classification of the whole soil profile, it would be enough to do the same proceeding for the Copedon and Lithopedon, and to identify some morpho-functional diagnostic horizons corresponding to given processes of pedogenesis. This work is already present and explicitly reported in the FAO-UNICEF first world soil maps. As if the soil could not correspond to a real ecosystem, recent classifications have given up looking for a purpose in the evolution of the soil.. We think it is a serious fundamental error, which generates confusion and misunderstanding. We suggest assigning the classic pedogenesis processes to Copedon, in order to recover much of the classification work that is also found in recent soil classifications (examples: Eluviation/Illuvation, with the formation of an E horizon in missing the finished in Bt clay and genesis of a Luvisol profile; Podzolization, with formation of Bhs or/and Bs horizons and genesis of a profile of Podzol; Brunification/weathering, with formation of Bw horizons and genesis of a profile of Cambisols, and so on). It is a question of
returning to the origin of Pedology, where pedogenesis processes were established, and which implies that the soil is a real evolving ecosystem.

A classification of the Lithopedon would help to distinguish parent material from substrate. In addition, Lithopedon physical and chemical qualities certainly influence the cycles of nutrients, carbon, air and water in the soil (Cremeens et al., 1994; Gupta et al., 2008). (Juilleret et al., 2014; Moragues-Quiroga et al., 2017) Juilleret et al. (2014) suggest to implement four “subsolum materials” in the WRB as qualifiers; Moragues-Quiroga et al. (2017) suggest to survey potential geochemical tracers of exchange processes at the water-mineral interface, suggest to differentiate surface organic compartment, upper horizons with presence of atmosphere-derived particles, lower horizons characterized by a mineralogical composition pointing to ancient events.

In Figure 5, the subdivisions (which are rarely abrupt) within the three soil layers (Humipedon, Copedon and Lithopedon) are expressed with colors. The arrows correspond to the interrelationships between the subsystems (Humi- Co- and Litho-pedon) of the soil. These have their own dynamics which are partly independent of the whole, but which can be detected with the naked eye by looking for signs of co-evolution (pedological processes), which ultimately generate each particular soil profile.

Examples of PEDOGENETIC PROCESSES

<figure><img src="image_6.png" /><figcaption>[Figure 5. HERE]</figcaption></figure>
The forms of humus are directly linked to particular groups of soil animals (Ponge, 2003, 2013; Zanella et al., 2018b) and agents of biodegradation which are in turn linked to soil microorganisms (Sofo et al., 2014, 2019; Bispo et al., 2018; Bayat et al., 2018; Karimi et al., 2018, 2019; Liang et al., 2019). This connection could have very important consequences on the management of forest and agricultural soils to stop the climate from warming. The ultimate goal could be to integrate in the new classification all those data relating to biological functioning that are now collected by people who already practice a non-specialized soil classification.

From another point of view, which is the one concerning agricultural soil, soil that produces food for humans and domesticated animals, it was thought that to transform/modify/till such type of soil was an economically very profitable action. At the time of maximum expansion of the technological revolution of agriculture, Hans Jenny became aware of the possible misunderstanding, and in 1980 defined soil as follows: "Soil is more than farmer's dirt, or a pile of good topsoil, or engineering material; it is a body of nature that has its own internal organization and history of genesis" (Jenny, 1980). In a letter to Science of the same year, he even wrote: "Because of a possible climatic warm-up, we do not wish accelerate humus oxidation and the concomitant flux of carbon dioxide from soil into the atmosphere... The humus capital, which is substantial, deserves to be maintained because good soils are a national asset".

## 6. Which agricultural practices can be defined sustainable?

### 6.1. Conventional or sustainable agriculture?

Nowadays, agricultural production is at risk due to many adverse abiotic and biotic factors. Furthermore, climate change can potentially decrease the effectiveness of plant defence mechanisms and increase the risk of diseases through excess growth and physiological alteration of cultivated plants (Vitti et al., 2016). In terms of increased temperature and extreme precipitation regimes, whether aridity or flooding, climate change will have detrimental agricultural consequences due to the interrelations between climate, land and water use, soil degradation and landscape changes (Dale, 1997; Tsiafouli et al., 2015). Nowadays, food security is an increasing concern in a growing number of countries.
This situation calls for a relevant appraisal of factors that could affect crop production. One of the factors promoting a sustainable food production system is soil biodiversity (Sofo et al., 2020b). Unfortunately, despite the promotion of sustainable soil management by the Global Soil Partnership since 2012, in many cases soil management is still focused on directly managing soil fertility, rather than on protecting soil biodiversity as a whole or single species individually, although soil biodiversity is known to be a main agent of soil fertility (Altieri et al., 2015).

The application of pesticides, herbicides and mineral fertilizers, typical of conventional agriculture, cannot be considered an eco-friendly approach for crop production and defence, as their overuse can provoke water contamination, air and water pollution, and release of harmful residues and by-products into the soils (Blouin 2018; Korkina and Vorobeichik 2018; Van Groenigen et al., 2019). A decrease in soil quality due to conventional soil management negatively influences important ecosystem processes, like nutrient cycling and carbon sequestration (Blouin et al., 2005; Bampa et al., 2019). On the other side, sustainable agriculture offers new chances to mitigate the effects of climate change. In sustainable agroforestry systems, management practices are able to increase carbon inputs into the soil and possibly reduce greenhouse gases (GHGs) emissions due to some revised field operations, e.g. by irrigation, use of recycled water, pest and disease management, fertilization, and soil and plant farming systems (Mutuo et al., 2005). In turn, carbon enrichment increases biological activity by improving soil structure, as well as soil moisture and nutrient content that are beneficial to plant growth and production (Marinari et al., 2000). As Lago et al. (2020) recently indicated, there is clear evidence that more environmentally friendly land management represents a promising strategy to increase soil carbon sequestration.

6.2. Soil and vegetation coevolve

Soil functions as a living system. Climate, organisms, topography, parent material and time completely describe the soil system. Soil and vegetation co-evolve implementing other living beings and creating the well-known zonation of biomes of planet Earth. In recent years, soil quality has been recognized to play a double role in the entire agroecosystem: it is important for a good production as well as for a healthy environment (Doran and Zeiss, 2000). In conventional agriculture, still adopted by most farmers, frequent soil tillage strongly
711 reduces the complexity and diversity of soil microbiota (Adl et al., 2006). For this reason, 712 conventional, non-sustainable agronomic practices should evolve into a more sustainable 713 management addressed to ameliorate the ecological networks and nutrient cycles, in which 714 soil microorganisms are involved. The adoption of sustainable soil management practices and 715 organic agriculture can be eco-friendly and include safe methods to ameliorate plant 716 physiological status, reduce plant disease incidence, and increase yield and quality without 717 side damages to the environment and human health. For instance, it would be possible to 718 adopt a sustainable approach that enriches the soil with biocontrol microorganisms with 719 action against pests (El-Tarabily and Sivasithamparam, 2006), plant-growth-promoting 720 microorganisms able to promote plant growth and development (Abhilash et al., 2016), and 721 microorganisms able to increase the availability and uptake of essential nutrients in plants, 722 e.g. mycorrhiza for phosphorus and nitrogen-fixing bacteria for nitrogen (Bolan, 1991). 723

723 In this scenario, the advantages of the adoption of a sustainable management (or 724 conservation and regeneration agriculture), that includes no/minimum tillage, cover crop 725 application, incorporation of grass and crop residues into the soil, and endogenous and 726 exogenous soil carbon inputs (Palm et al., 2014) can be a key factor to enhance soil 727 quality/fertility and production in a sustainable way, preserving natural resources and 728 avoiding detrimental effects on the environment. Such benefits include a high level of soil 729 microbial genetic/functional diversity and complexity both in the soil (bulk soil and 730 rhizosphere) and in the plant (phyllosphere, carposphere, and endosphere), a faster carbon and 731 nitrogen turnover, higher levels of SOM and soil water content, and better soil physical and 732 chemical characteristics (Fausto et al., 2018). Inappropriate or exploitative crop 733 agroecosystems represent a key threat for soil degradation through erosion, nutrient depletion 734 or structural collapse (Didden et al., 1994). Increasing our knowledge on biochemical 735 processes of soil microorganisms and animals involved in carbon and nitrogen dynamics, that 736 influence in turn their availability for plants (Shaffer et al., 2001), will lead to optimized 737 management strategies for a multifunctional concept of agriculture. 738

738

### 6.3. Sustainable agriculture application and monitoring

740

741 Addressing knowledge gaps of sustainable practices is of fundamental importance as an 742 entry point to improve growing techniques and for understanding wider soil processes, such 743 as consequences of land use or climatic change on both biodiversity and soil ecosystem
services. The research should be focused on developing an ecological and holistic approach that combines traditional soil health assessment with sensitive indicators of the effects of the soil environment on soil microbial and faunal communities and cultivated plants, such as community dynamics (taxonomic, genetic, functional and metabolic) and plant stress physiology, mostly assessed by growth/yield, hormone levels and photosynthetic capacity (e.g., photosystem II activity). The sustainable approach will lead to a better understanding of the effects of management practices on soil organisms and plants. In the long-term, soil health should be included as a factor when management decisions are made by farmers, land managers and crop advisers. The studies should not be designed for a systematic monitoring of the differential effects of each component of sustainable practices such as soil cover, manuring, reduced pesticide use or reduced tillage (Hobbs et al., 2008), but with these practices in combination, in order to have an overall vision of the agrosystem, and how to manage it sustainably (Fig. 6). In this view, the metagenomics (that is the microbial identities and functional gene information) and the metagenomics (that is the product of the combined genetic potential of the microbiome and resources) of bacteria or fungi (Fierer, 2017; Jansson and Hofmockel, 2018) would allow to define the microbial communities living in the different soil layers. The DNA/RNA-based identification of specific alive and active bacterial/fungal taxa, according to their functional distinction (aerobic/anaerobic, saprophytic/parasitic/pathogenic, autotrophic/heterotrophic) can be of key importance for defining the microbiological fertility of a soil and its response to agricultural practices (Crecchio et al., 2004; Badagliacca et al., 2020). Identification by DNA fingerprinting, originally developed for the identification of poorly culturable microbial strains, has become a rapid and cost-effective method of current use in agricultural soils. It has been extended to the current assessment of nematode communities (Wang et al., 2008) and its application to other soil fauna is promising, although still not in current use (Orgiazzi et al., 2015). Finally, eventual pathogenic organisms and mycorrhization index should be monitored, identifying probable microbial pathogens and/or anaerobic microorganisms by a culture based-approach (*Phytophthora, Clostridium, Bacillus*, etc.) and presence and types of mycorrhiza, including DNA analysis of eventual pathogenic microorganisms during the growing season.

The application of endogenous and exogenous carbon inputs would be necessary for improving soil status. Using specific commercial products containing biostimulants and biocontrol agents to improve physicochemical and microbiological properties of the soils, could increase resistance against eventual pathogens and enrich soil microbial communities.
The application of compost, manure, soil management techniques for facilitating water horizontal movement in the soil, use of decompacting plants (e.g., *Raphanus* spp. or other Brassicaceae) would facilitate water vertical movement in the soil, both directly (Whelan et al., 2013) and through a favorable influence on earthworms (Pérès et al., 1998). On this basis, sustainable management is a key factor for increasing the functionality and diversity of soil biota that enhance soil biological fertility. This amelioration leads to a higher soil quality, stability and multifunctionality, positively affecting plant physiological status and crop productivity.

<figure><img src="image_7.png" /><figcaption>[Figure 6. HERE]</figcaption></figure>

Over the last decades, intensive agricultural practices (e.g., continuous soil tillage, high inputs of mineral fertilizers, application of low-quality irrigation water, removal of pruning residues) have determined the loss of soil fertility and the depletion of soil organic matter (SOM), with negative effects on both productivity and soil conservation (Bonanomi et al., 2011). Many conventional agronomic practices have a negative impact on SOM (Arrouays and Pelissier, 1994), the soil microbiome (Lupatini et al., 2017) and soil trophic networks (Tsiafouli et al., 2015), causing a decline in fertility: soil leveling (with consequent elimination of the organic horizon in many areas of the plant), deep tillage with a surface
carryover of mineral horizons (non-organic), soil sterilization with destruction of
microbiological diversity, the continuous and massive use of herbicides, mineral fertilizers
and pesticides with biocidal action, and so on. Sustainable agronomic practices foresee a
reworking of agronomic management which includes the reduction of the use of mineral
fertilizers and pesticides (including cupric products), the rationalization of irrigation, the
management - and not the elimination - of spontaneous vegetation and the contribution of
different types of organic matter to restore the ecosystem complexity and heterogeneity,
without leaving aside a careful analysis of the fields and the state of the plants, of the
environmental conditions (pedological, microbiological, orographic and microclimatic), and,
above all, of the agronomic and ecological history of the fields. The correct use of
formulations of materials of natural origin, specially designed and processed according to the
different cultivation and business conditions, can quickly re-establish the trophic balance and
soil-plant compatibility, reactivating the nourishment of the crops and increasing their
resistance to pathogens and parasites. Thus, soils rich in organic matter, or regularly fertilized
organically with compost and vegetable residues (possibly not coming from the same crop),
have a greater microbiological biodiversity. Crop rotation with phylogenetically distant
species, the practice of fallow and crop associations make it possible to prevent or eliminate
the decrease in soil fertility, and the use of graft carriers with tree crops can be helpful to
mitigate problems of replanting of the same species. The crop succession, the inter-cropping
of different species, the use of rootstocks phylogenetically distant from the cultivated variety
make it possible to overcome the problems related to the decline in soil fertility. A very
effective sustainable technique appears to be the use of compost tea, infused or more
commonly fermented with compost, which has already been the subject of growing scientific
and applicative interest for several years (Scheuerell and Mahaffee, 2002; St. Martin et al.,
2020; Villecco et al., 2020). The technique is based on the use of different compost, specially
selected (and sometimes, according to the needs of the plant, combined with non-composted
organic substance), placed in infusion under aerobic conditions.

6.4. Soil functions as a living system

Nowadays, there is evidence that sustainable management practices (e.g. no-tillage,
supply of organic fertilizers, mulching of pruning residuals and cover crops, reduction or even
suppression of pesticide use) can contribute to re-carbonize soils and reduce soil CO2
emissions, recover soil fertility, and increase yield. In sustainable agrosystems, because of the
composition of the recycled biomass (pruning residuals, leaf fall, cover crops) and of newly
supplied (e.g. compost, manure), a huge amount of nutrients is released if external supply of
mineral fertilizers could successfully be replaced. However, considering processes
determining nitrogen availability (organic matter mineralization, leaching, cover crops uptake,
etc.), interactions among nutrients (e.g., antagonistic effects), variability of soil moisture, and
mineral nutrition, particular attention is required. Sustainable agriculture can give benefits to
plant growth, such as increased biomass and productivity, enhanced photosynthesis and
carbohydrate allocation, better regulation of root respiration and higher defenses against pests
and diseases, with more soil microorganisms and fauna, and thus more efficient trophic
networks. Mycorrhizal fungi, being involved in many ecosystem services (Stevenson et al.,
2020), are important in many types of soil. Besides well-known negative effects of
conventional practices (Verbruggen et al., 2010), in over-exploited, conventionally managed
agricultural landscapes, habitat loss and fragmentation prevent dispersal and are major threats
to mycorrhizas (Longo et al., 2016).

Human societies benefit from a multitude of ecosystem services from both natural and managed ecosystems, to which soil organisms make a crucial and distinctive (Stevenson et al., 2020). Unfortunately, it is well recognized that humans are changing the global environment at an unprecedented rate. An increasing proportion of the world's population is urban or suburban. For this reason, the demand to extend cultivated areas in cities is increasing, prompting to establish, restore and sustain urban ecosystems. In these new anthropogenic environments, the application of organic inputs and bio-products, included in sustainable agricultural practices, can be crucial for plants' survival. Sustainable agriculture can cause recreational, human health, economic and environmental benefits. The latter also includes lower GHGs emissions because of reduced use of synthetic fertilizers and pesticides, lower leaching losses to groundwater (e.g., nitrates and nitrites), and no eutrophication of ponds and streams because of excess phosphorus and nitrogen. Comparisons of soil biota across wild, rural and urban habitats have revealed dramatic differences between sustainably managed and conventionally managed areas, with the lowest biodiversity in the latter (Stevenson et al., 2020).

Regardless of practical challenges, there is untapped potential for sustainable agricultural
practices to influence environmental outcomes, citizens' consciousness and market's trends
soon (Scotti et al., 2015; Stevenson et al., 2020). The results of many recent studies encourage
862 the use of sustainable agricultural practices able to enhance soil fertility (Diacono and Montemurro, 2010; Kassie et al., 2013; Scotti et al., 2015). The ultimate goal is to convince farmers to adopt a sustainable farming system as a whole, and not just as individual elements/practices, in order to promote good-quality production without negative effects on the environment. For achieving this, the approaches should not be 'top down', but they must be 'bottom up', where farmers and citizens help to co-design and co-deliver soil management and food production systems (Ajayi, 2007; Kassie et al., 2013). It is time to switch to a modern and multifunctional concept of agriculture based not only on the production but above all on product quality, environmental protection, resource saving and promotion of human health.

872

873 6.5. Soil is organized into layers

874

875 The complexity is such that the time distinguishes at least three groups of layers in the soil: Humipedon, Copedon and Lithopedon. Microorganisms and plants condition the Humipedon evolution by generating a known series of systems that starts on mineral substrate and divides in two series, in submerged environment (Archeo, Anaero, Histo and Aqueous systems) and out of water in aerated sites (Crusto, Bryo, Rhizo, main Terrestrial systems) (Zanella et al., 2018d). Animals interact with microrganisms and plants in each system. Each system is structured around particular organisms and which have coevolved for millions of years.

882
883
884
885
886
887
888
889
890
Microorganisms and plants condition the Humipedon. Mineralogical aspects and more related to soil physics are more decisive in Copedon. The geological history of the soil and the cycles of some minerals are much more important in Lithopedon. The time separates the studies of these three soil layers, handing them over to specialists who meet periodically to make the right synthesis. The soil is a single body that reacts as if it were composed of superimposed organs. Soil classification must take this crucial aspect into account. Humipedon reacts over the years and up to a few decades; Copedon takes from decades to hundreds of years; the Lithopedon centuries to millennia.

891 We must no longer think we can move, manipulate, destroy, create soil as if it were an inanimate object. Soil has its own internal, historical and precious organization: what we need to do is discover it and use it well. It is necessary to understand these processes well before intervening with means that risk destroying the "superimposed organs" of the soil.
Agrosystems (crop soils) correspond to artificially simplified natural systems (in general Mull Humipedons). When artificialization is extreme, we talk about Techno systems (hydroponic or compost are examples of that). These phrases hide an underestimated truth of intrinsic value. Agro-systems are not alternative systems, but old systems reorganized by man (Zanella et al., 2018f). The soil system incessantly tries to return to its original organization, made of different overlapping layers, but the work of using its stored energy takes it back annually in time. At the end of a conventional exploitation process there is a soil poor in organic matter and life, an original mother rock of the soil. We must no longer think we can move, manipulate, destroy, create soil as if it were an object and then expect it to work as a living system to render service to us.

If the purpose of conventional agriculture is to build new soils, then we need to think about building Copedons between Humipedons and Lithopedons, not destroying this historical organization. Ask us what these layers really are (studying natural references) and how they can be built in compliance with natural and biological laws. It is perhaps possible to build new Humipedons. This is what we try to do with composts or hydroponic solutions. We can try to make them better, more like existing Humipedons. The other possibility is organic farming. The right method should be very similar to the one proposed by Masanobu Fukuoka in his famous book "Natural Way of Farming" (Fukuoka, 1985) to intervene as little as possible. Understand how it works and accompany the movement, changing the cards in the game as little as possible. It is difficult and, for this reason, it is the right way, and it needs a scientific preparation of high naturalistic/biological level.

6.6. Agriculture, human health and environment

We offer the propositions that:

6.6.1.1. We offer the propositions that:

a) Intensive agriculture should be abandoned;

b) agriculture should produce enough food for an increasing number of humans.

Is it possible to produce enough food and to stay in good health all over planet Earth? For knowing this, other two parameters should be considered:

a) the need for a global management of Earth resources, like a United Nations
Organization that would decide democratically;

924
925
Organization that would decide democratically;
b) the regulation of birth rate might be achieved with a calculation of Earth's bearing capacity (shared ecological footprint) within the framework of a humanity that shares resources better than today.

## 6.7. Agroforestry

This is also an important point, not detached from the previous one. The agro-forestry use of the lands of our planet is often presented as an ecological and sustainable method of exploitation both internationally and nationally. The concept is acceptable. It is known how trees increase the volume of the ecosystem, with helpful implications in the air and soil parts of the ecosystem (Jose, 2009; Altieri et al., 2015; Marsden et al., 2019; Wang et al., 2020).

What must be avoided is that it becomes a disguised method of stealing more land from the forest. Since the part already taken (1/2) does no longer satisfy a humanity in search of food, we operate on the part that remains, transforming it into an agricultural forest. If the process is conceivable for the ecological exploitation of those parts of the forest (equatorial and otherwise) which have already been converted into cultivated fields and then abandoned, it should be banned in the still forests, whether they are treated with tall trees or coppices.

## 7. Conclusions and future insights

In this commentary paper, we presented cross-disciplinary and holistic approaches applied to agricultural soils. Converting the conventional management systems of agricultural land into more sustainable and environment-preserving systems has become urgent. Conventional vegetable and fruit production, because of the unavoidable lack of resources (particularly soil and water), is going to be economically and environmentally disadvantageous, while, on the other side, organic farming, whose benefits and costs are controversial, is not always self-sustaining and durable, and it cannot cover the enormous and increasing world demand. For avoiding this dilemma, the productive systems should be directed towards the principles of an innovative, sustainable, regeneration and conservative agriculture, which includes rationally the existing and innovative agro-technological practices, such as no- or minimum soil tillage, on-site nutrient input and recycling, adequate irrigation and rational management of crop residues. This innovative approach, aimed to keep
959 production at a high level and cultivating lastingly, can render a wide range of benefits to farmers and the environment. In addition, better understanding the role of soil fauna in such systems has a key role to adapt management strategies and mitigating GHGs emissions. Furthermore, the role of soil organisms (both microbes and animals) to ecosystem services and their close relationship with soil organic matter has been often overlooked, while it should be seriously taken into account in future land management strategies.

965 The world's soils are rapidly deteriorating because of soil erosion, nutrient depletion and other threats, but sustainable practices and technologies can reverse this trend. One key point from the new IPCC report (Shukla et al., 2020) is that conventionally tilled soils erode over 100 times faster than they form and that land degradation represents "one of the biggest and most urgent challenges" that humanity faces. Humans have degraded roughly one-third of the world's topsoil, and about 3.2 billion people - more than a third of humanity - already suffer from the effects of degraded land. Continuing down this path does not bode well for feeding a growing world population. Barriers to adopting regenerative farming systems include force of habit, lack of knowledge about new practices and real and perceived economic risk during the transition. The benefits of rebuilding healthy, fertile soil are clear. Economic benefits of land restoration average 10 times the costs. Thus, sustainable agriculture appears to have a big economic, social and political impact (Baggaley et al., 2020). We trust that sustainable agriculture will contribute to understand how important the soil as a living matrix is for both climate regulation and plant production. A better grasp of how soil organisms interact with organic matter turnover and stabilization will open novel ways for the sustainable management of soils. It is time to take soil seriously in consideration and to rethink humanity's relationship to the environment and particularly to soil. In their article, Kopnina et al. (2018) hope for change from an anthropocentric mentality based on human-centered values and things to a more comprehensive vision that includes non-human living beings and things, such as environmental life-support systems. Thus, it would be necessary to promote a general law of soil protection, as soil produces food and sustains all ecosystems, independently from human need to economically grow. People need to change agriculture and land use, and we all wish to have 'more sustainable' soils, the only basis for a healthier world.

988

989

990 References

991
992 Abhilash, P.C., Dubey, R.K., Tripathi, V., Gupta, V.K., Singh, H.B., 2016. Plant Growth-Promoting Microorganisms for Environmental Sustainability. Trends Biotechnol. https://doi.org/10.1016/j.tibtech.2016.05.005

995 Achat, D.L., Fortin, M., Landmann, G., Ringeval, B., Augusto, L., 2015. Forest soil carbon is threatened by intensive biomass harvesting. Sci. Rep. 5, 15991. https://doi.org/10.1038/srep15991

998 Adl, S.M., Coleman, D.C., Read, F., 2006. Slow recovery of soil biodiversity in sandy loam soils of Georgia after 25 years of no-tillage management. Agric. Ecosyst. Environ. 114, 323-334. https://doi.org/10.1016/j.agee.2005.11.019

1001 Afes, 2009. Référentiel Pédologique 2008, Savoir-fai. ed. Quae, Versailles.

1002 Ajayi, O.C., 2007. User acceptability of sustainable soil fertility technologies: Lessons from farmers' knowledge, attitude and practice in Southern Africa. J. Sustain. Agric. 30, 21-40. https://doi.org/10.1300/J064v30n03_04

1005 Altieri, M.A., Nicholls, C.I., Henao, A., Lana, M.A., 2015. Agroecology and the design of climate change-resilient farming systems. Agron. Sustain. Dev. https://doi.org/10.1007/s13593-015-0285-2

1008 Angelini, P., Fenoglio, S., Isaia, M., Jacomini, C., Migliorini, M., Morisi, A., 2002. Tecniche di biomonitoraggio della qualità del suolo. ARPA Piemonte. Area tematica Conservazione della natura., PINEROLO (TO).

1011 Arrouays, D., Pelissier, P., 1994. Changes in carbon storage in temperate humic loamy soils after forest clearing and continuous corn cropping in France. Plant Soil 160, 215-223. https://doi.org/10.1007/BF00010147

1014 Badagliacca, G., Petrovičová, B., Pathan, S.I., Roccotelli, A., Romeo, M., Monti, M., Gelsomino, A., 2020. Use of solid anaerobic digestate and no-tillage practice for restoring the fertility status of two Mediterranean orchard soils with contrasting properties. Agric. Ecosyst. Environ. 300, 107010. https://doi.org/10.1016/j.agee.2020.107010

1019 Baggaley, N., Lilly, A., Blackstock, K., Dobbie, K., Carson, A., Leith, F., 2020. Soil risk maps – Interpreting soils data for policy makers, agencies and industry. Soil Use Manag. 36, 19-26. https://doi.org/10.1111/sum.12541

1022 Balbo, A., Benedetti, A., Biagini, B., Bloem, J., Bouraoui, F., Bozzaro, S., Brenna, S., Cenci, R.M., Citterio, S., Cluzeau, D., Dilly, O., Ekschmitt, K., Filippi, C., Gardi, A., La Terza, A., Menta, C., Montanarella, L., Musmeci, L., Parisi, V., Peres, G., Pompili, L.,
1025 Schmuck, G., Sena, F., Gorbati, S., Viarengo, A., Zullini, A., Grasserbauer, M., 2006.

1026 Bio-Bio Project, in: Cenci, R.M., Sena, F. (Eds.), BIODIVERSITY – BIOINDICATION
1027 TO EVALUATE SOIL HEALTH - ISPRA 22 JUNE 2006. EUR 22245 EN – European
1028 Commission Directorate-General Joint Research Centre, Ispra (VA) Italy, p. 133.

1029 Baldrian, P., 2017. Forest microbiome: diversity, complexity and dynamics. FEMS Microbiol. Rev. 41, 109–130. https://doi.org/10.1093/femsre/fuw040

1031 Bampa, F., O'Sullivan, L., Madena, K., Sandén, T., Spiegel, H., Henriksen, C.B., Ghaley, B.B., Jones, A., Staes, J., Sturel, S., Trajanov, A., Creamer, R.E., Debeljak, M., 2019. Harvesting European knowledge on soil functions and land management using multi-criteria decision analysis. Soil Use Manag. 35, 6–20. https://doi.org/10.1111/sum.12506

1036 Bardgett, R.D., Van der Putten, W.H., 2014. Belowground biodiversity and ecosystem functioning. Nature 515, 505–511. https://doi.org/10.1038/nature13855

1038 Barrett, L.F., 2009. The Future of Psychology: Connecting Mind to Brain. Perspect. Psychol. Sci. 4, 326–339. https://doi.org/10.1111/j.1745-6924.2009.01134.x

1040 Bartoli, C., 1966. Études écologiques sur les associations forestières de la Haute Maurienne. Ann. des Sci. For. INRA/EDP Sci. 23, 429–751.

1042 Bayat, O., Karimzadeh, H., Eghbal, M.K., Karimi, A., Amundson, R., 2018. Calcic soils as indicators of profound Quaternary climate change in eastern Isfahan, Iran. Geoderma 315, 220–230. https://doi.org/10.1016/j.geoderma.2017.11.007

1045 Beaudette, D.E., Roudier, P., O'Geen, A.T., 2013. Algorithms for quantitative pedology: A toolkit for soil scientists. Comput. Geosci. 52, 258–268. https://doi.org/10.1016/j.cageo.2012.10.020

1048 Berdugo, M., Delgado-Baquerizo, M., Soliveres, S., Hernández-Clemente, R., Zhao, Y., Gaitán, J.J., Gross, N., Saiz, H., Maire, V., Lehmann, A., Rillig, M.C., Solé, R. V., Maestre, F.T., 2020. Global ecosystem thresholds driven by aridity. Science (80–). 367, 787–790. https://doi.org/10.1126/science.aay5958

1052 Bernier, N., 2018. Hotspots of biodiversity in the underground: A matter of humus form? Appl. Soil Ecol. 123, 305–312. https://doi.org/10.1016/j.apsoil.2017.09.002

1054 Bernier, N., Ponge, J.F., 1994. Humus form dynamics during the sylvogenetic cycle in a mountain spruce forest. Soil Biol. Biochem. 26, 183–220. https://doi.org/10.1016/0038-0717(94)90161-9

1057 Birkeland, P.J., 1999. Soils and geomorphology, 3 edition. ed, null. Oxford University Press.
1058 Bispo, A., Bougon, N., Eglin, T., Gascuel, C., Gelin, S., Jaillard, B., Ranjard, L., Schnebelen, N., (EDITORS), 2018. Carrefour de l'innovation agronomique - 18 octobre 2018 Conseil Régional Bourgogn-Franche Comté - Dijon - INRA, in: Bispo, A., Bougon, N., Eglin, T., Gascuel, C., Gelin, S., Jaillard, B., Ranjard, L., Schnebelen, N. (Eds.), De La Connaissance de La Biologie Des Sols et de Ses Fonctions, À Son Pilotage. Creative Common CC BY-NC-ND 3.0, p. 106.

1064 Blouin, M., 2018. Chemical communication: An evidence for co-evolution between plants and soil organisms. Appl. Soil Ecol. 123, 409-415. https://doi.org/10.1016/j.apsoil.2017.10.028

1067 Blouin, M., Zuily-Fodil, Y., Pham-Thi, A.-T., Laffray, D., Reversat, G., Pando, A., Tondoh, J., Lavelle, P., 2005. Belowground organism activities affect plant aboveground phenotype, inducing plant tolerance to parasites. Ecol. Lett. 8, 202-208. https://doi.org/10.1111/j.1461-0248.2004.00711.x

1071 Blum, W., Schad, P., Nortclif, S., 2018. Essentials of Soil Science Soil formation, functions, use and classification (World Reference Base, WRB).

1073 Bolan, N.S., 1991. A critical review on the role of mycorrhizal fungi in the uptake of phosphorus by plants. Plant Soil. https://doi.org/10.1007/BF00012037

1075 Bonanomi, G., D'Ascoli, R., Antignani, V., Capodilupo, M., Cozzolino, L., Marzaioli, R., Puopolo, G., Rutigliano, F.A., Scelza, R., Scotti, R., Rao, M.A., Zoina, A., 2011. Assessing soil quality under intensive cultivation and tree orchards in Southern Italy. Appl. Soil Ecol. 47, 184-194. https://doi.org/10.1016/j.apsoil.2010.12.007

1079 Braun-Blanquet, J., 1964. Pflanzensoziologie. Wien, Austria.

1080 Brenna, S., Tabaglio, V., 2013. Guidelines for Conservation Agriculture application and dissemination. STUDIO CHIESA For information on the project and the guidelines: www.lifehelpsoil.eu - info@lifehelpsoil.eu.

1083 Brussaard, L., De Ruiter, P.C., Brown, G.G., 2007. Soil biodiversity for agricultural sustainability. Agric. Ecosyst. Environ. 121, 233-244.

1085 Bünemann, E.K., Bongiorno, G., Bai, Z., Creamer, R.E., De Deyn, G., de Goede, R., Fleskens, L., Geissen, V., Kuyper, T.W., Mäder, P., Pulleman, M., Sukkel, W., van Groenigen, J.W., Brussaard, L., 2018. Soil quality – A critical review. Soil Biol. Biochem. 120, 105-125. https://doi.org/10.1016/j.soilbio.2018.01.030

1089 Camaret, S., Bernier, N., Eynard-Machet, R., Dobremez, J.-F., Fay, J., Gauquelin, X., Khelifa, J., Lancon, M.F., Leclerc, D., Marrouche, A., Zanella, A., 2000. Distribution spatiale et
1091 évolution temporelle de la végétation et de sa diversité : relations avec l'hétérogénéité des structures des peuplements en pessière d'altitude. Université de Chambery (France);
1092 laboratoire de Dynamique des Ecosystèmes d'Altitude: 285 p.
1093

1094 Charzyński, P., Galbraith, J.M., Kabała, C., Kühn, D., Prokofeva, T.V., V.I., V., 2017. Classification of urban soils, in: Maxine J., L., John Kim, K.-H., Jean Louis, M., Wolfgang, B., Przemyslaw, C., Ahaw K., R., IUSS Working Group SUITMA 2017 (Eds.), Soils within Cities.

1098 Chaussod, R., 1996. La qualité biologique des sols : Évaluation et implications. Forum « Le sol, un patrimoine menacé ? » Paris, 24 octobre 1996. Etude Gest. des Sols 3, 261-278.

1100 Cheik, S., Jouquet, P., 2020. Integrating local knowledge into soil science to improve soil fertility. Soil Use Manag. 36, 561-564. https://doi.org/10.1111/sum.12656

1102 Clements, F.E., 1936. Nature and Structure of the Climax. J. Ecol. 24, 252-284.

1103 Crecchio, C., Gelsomino, A., Ambrosoli, R., Minati, J.L., Ruggiero, P., 2004. Functional and molecular responses of soil microbial communities under differing soil management practices. Soil Biol. Biochem. 36, 1873-1883.
1106 https://doi.org/10.1016/j.soilbio.2004.05.008

1107 Cremeens, D.L., Brown, R.B., Huddleston, J.H. (Eds.), 1994. Whole Regolith Pedology, SSSA Special Publications. Soil Science Society of America, Madison, WI, USA.
1109 https://doi.org/10.2136/sssaspecpub34

1110 Dale, V.H., 1997. The relationship between land-use change and climate change. Ecol. Appl.
1111 https://doi.org/10.1890/1051-0761(1997)007[0753:TRBLUC]2.0.CO;2

1112 Dastgerdi, A.S., Sargolini, M., Pierantoni, I., Stimilli, F., 2020. Toward An Innovative Strategic Approach For Sustainable Management Of Natural Protected Areas In Italy. Geogr. Environ. Sustain. 13, 68-75. https://doi.org/10.24057/2071-9388-2019-143

1115 de Vries, F.T., Shade, A., 2013. Controls on soil microbial community stability under climate change. Front. Microbiol. 4, 1-16. https://doi.org/10.3389/fmicb.2013.00265

1117 de Vries, F.T., Wallenstein, M.D., 2017. Below-ground connections underlying above-ground food production: a framework for optimising ecological connections in the rhizosphere.
1119 J. Ecol. 105, 913-920. https://doi.org/10.1111/1365-2745.12783

1120 Diacono, M., Montemurro, F., 2010. Long-term effects of organic amendments on soil fertility. A review. Agron. Sustain. Dev. 30, 401-422.
1122 https://doi.org/10.1051/agro/2009040

1123 Didden, W.A.M., Marinissen, J.C.Y., Vreeken-Buijs, M.J., Burgers, S.L.G.E., de Fluiter, R.,
1124 Geurs, M., Brussaard, L., 1994. Soil meso- and macrofauna in two agricultural systems: factors affecting population dynamics and evaluation of their role in carbon and nitrogen dynamics. Agric. Ecosyst. Environ. 51, 171–186. https://doi.org/10.1016/0167-8809(94)90042-6

1128 Dokuchaev, V. V., 1900. Zones verticales des sols, zones agricoles, sols du Caucase. Collection pédologique, Exposition Universelle, Ed. Ministère des Finances de St-Péterbourg.

1131 Doran, J.W., Zeiss, M.R., 2000. Soil health and sustainability: managing the biotic component of soil quality. Appl. Soil Ecol. 15, 3–11. https://doi.org/10.1016/S0929-1393(00)00067-6

1134 Drosos, M., Nebbioso, A., Piccolo, A., 2018. Humeomics: A key to unravel the humusic pentagram. Appl. Soil Ecol. 123, 513–516. https://doi.org/10.1016/j.apsoil.2017.07.027

1136 Duru, M., Therond, O., Martin, G., Martin-Clouaire, R., Magne, M.-A., Justes, E., Journet, E.-P., Aubertot, J.-N., Savary, S., Bergez, J.-E., Sarthou, J.P., 2015. How to implement biodiversity-based agriculture to enhance ecosystem services: a review. Agron. Sustain. Dev. 35, 1259–1281. https://doi.org/10.1007/s13593-015-0306-1

1140 EASAC - European Academies Science Advisory Council, 2018. Opportunities for soil sustainability in Europe. EASAC policy report 36. German National Academy of Sciences Leopoldina 2018.

1143 El-Tarabily, K.A., Sivasithamparam, K., 2006. Non-streptomycete actinomycetes as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Soil Biol. Biochem. 38, 1505–1520. https://doi.org/10.1016/j.soilbio.2005.12.017

1146 Enwall, K., Nyberg, K., Bertilsson, S., Cederlund, H., Stenström, J., Hallin, S., 2007. Long-term impact of fertilization on activity and composition of bacterial communities and metabolic guilds in agricultural soil. Soil Biol. Biochem. 39, 106–115. https://doi.org/10.1016/j.soilbio.2006.06.015

1150 FAO-UNESCO, 1974. Soil map of the world 1:5 000 000. Vol. 1. UNESCO, Paris.

1151 FAO, 2020. Technical specifications and country guidelines for Global Soil Organic Carbon Sequestration Potential Map GSOCseq. Rome, Italy.

1153 FAO and ITPS, 2015. Status of the World's Soil Resources (SWSR) – Technical Summary. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils, FAO. ed. Rome, Italy.

1156 Fausto, C., Mininni, A.N., Sofo, A., Crecchio, C., Scagliola, M., Dichio, B., Xiloyannis, C.,
1157 2018. Olive orchard microbiome: characterisation of bacterial communities in soil-plant compartments and their comparison between sustainable and conventional soil management systems. Plant Ecol. Divers. 11, 597-610.
1158
1159
1160 https://doi.org/10.1080/17550874.2019.1596172

1161 Fierer, N., 2017. Embracing the unknown: Disentangling the complexities of the soil microbiome. Nat. Rev. Microbiol. https://doi.org/10.1038/nrmicro.2017.87

1163 Filip, Z., 2002. International approach to assessing soil quality by ecologically-related biological parameters, in: Agriculture, Ecosystems and Environment. Elsevier, pp. 169–174. https://doi.org/10.1016/S0167-8809(01)00254-7

1166 Filser, J., Faber, J.H., Tiunov, A. V., Brussaard, L., Frouz, J., De Deyn, G., Uvarov, A. V., Berg, M.P., Lavelle, P., Loreau, M., Wall, D.H., Querner, P., Eijsackers, H., Jiménez, J.J., 2016. Soil fauna: key to new carbon models. SOIL 2, 565–582.
1169 https://doi.org/10.5194/soil-2-565-2016

1170 Friberg, H., Lagerlöf, J., Rämert, B., 2005. Influence of soil fauna on fungal plant pathogens in agricultural and horticultural systems. Biocontrol Sci. Technol.
1171
1172 https://doi.org/10.1080/09583150500086979

1173 Fukuoka, M., 1985. The naturam way of farming. The theory and practice of green philosophy, Reprint 20. ed. Madras, India.

1175 Fusaro, S., 2015. Evaluation, maintenance and improvement of biodiversity for environmental protection and crop, in: Squartini, A., Paoletti, G.M. (Eds.), Doctorate Thesis. Università degli Studi di Padova (Italia), p. 255.

1178 Gil-Sotres, F., Trasar-Cepeda, C., Leirós, M.C., Seoane, S., 2005. Different approaches to evaluating soil quality using biochemical properties. Soil Biol. Biochem. 37, 877–887.
1179
1180 https://doi.org/10.1016/j.soilbio.2004.10.003

1181 Giller, K.E., Beare, M.H., Lavelle, P., Izac, A.M.N., Swift, M.J., 1997. Agricultural intensification, soil biodiversity and agroecosystem function. Appl. Soil Ecol. 6, 3–16.
1182
1183 https://doi.org/10.1016/S0929-1393(96)00149-7

1184 Gupta, R.K., Abrol, I.P., Finkl, C.W., 2008. Encyclopedia of Soil Science, Encyclopedia of Earth Sciences Series. Springer Netherlands, Dordrecht. https://doi.org/10.1007/978-1-4020-3995-9

1187 Gupta, V.V.S.R., Germida, J.J., 2015. Soil aggregation: Influence on microbial biomass and implications for biological processes. Soil Biol. Biochem.
1188
1189 https://doi.org/10.1016/j.soilbio.2014.09.002
1190 Hartmann, F., 1965. Waldhumusdiagnose auf Biomorphologischer Grundlage, Auflage: S. ed.

1191 Springer - Verlag, Wien, Austria.

1192 Hartmann, F., Marcuzzi, G., 1970. Diagnosi degli humus forestali su basi biomorfologiche.

1193 CEDAM Padova (Italy), Padova.

1194 Hasan, H.M.M., Jochheim, H., Schultz, A., 2017. Optimization of selected parameters of the

1195 forest growth model Biome-BGC (version ZALF) using HOPSPACK, in: 2017 20th

1196 International Conference of Computer and Information Technology (ICCIT). IEEE, pp.

1197 1-7. https://doi.org/10.1109/ICCITECHN.2017.8281845

1198 Heemsbergen, D.A., Berg, M.P., Loreau, M., Van Hal, J.R., Faber, J.H., Verhoef, H.A., 2004.

1199 Biodiversity effects on soil processes explained by interspecific functional dissimilarity.

1200 Science (80-. ). 306, 1019-1020. https://doi.org/10.1126/science.1101865

1201 Hoang, D.T.T., Pausch, J., Razavi, B.S., Kuzyakova, I., Banfield, C.C., Kuzyakov, Y., 2016.

1202 Hotspots of microbial activity induced by earthworm burrows, old root channels, and

1203 their combination in subsoil. Biol. Fertil. Soils 52, 1105-1119.

1204 https://doi.org/10.1007/s00374-016-1148-y

1205 Hobbs, P.R., Sayre, K., Gupta, R., 2008. The role of conservation agriculture in sustainable

1206 agriculture. Philos. Trans. R. Soc. B Biol. Sci. 363, 543-555.

1207 https://doi.org/10.1098/rstb.2007.2169

1208 Hopkin, S., 2008. Biological Indicators of Soil Health. Ed. by C. E. PANKHURST, B. M.

1209 DOUBE and V. V. S. R. GUPTA. 23x15 cm. Pp. xii+451 with 70 text-figures.

1210 Wallingford, U.K.: CAB International, 1997. Price h/b: £60.00, ISBN 0 85199 158 0.

1211 New Phytol. 139, 389-392. https://doi.org/10.1111/j.1469-8137.1998.194-3.x

1212 IUSS Working Group WRB, 2015. World Reference Base for Soil Resources 2014, update

1213 2015 International soil classification system for naming soils and creating legends for

1214 soil maps., World Soil Resources Reports No. 106. Food and Agriculture Organization

1215 of the United Nations, Rome, Italy. https://doi.org/10.1017/S0014479706394902

1216 IUSS Working Group WRB 2007, 2007. World Reference Base for Soil Resources 2006,

1217 First Update 2007. FAO, Rome.

1218 IUSS Working Group WRB 2010, 2010. Guidelines for constructing small-scale map legends

1219 using the WRB. Rome.

1220 Jabiol, B., Feller, C., Grève, M.H., 2005. Quand l'humus est à 1 ' origine de la pédologie. 2.

1221 Avant et après P.E. Müller: évolution des conceptions sur la description et la typologie

1222 « des humus ». Etudes Gest. des Sols 12, 123-134.
1223 Jahn, R., Blume, H.-P., Asio, V.B., Spaargaren, O., Schad, P., Langohr, R., Brinkman, R., Nachtergaele, F.O., Pavel Krasilnikov, R., 2006. Guidelines for Soil Description - Fourth Edition, FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS. FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS, Rome, Italy.

1228 Jansson, J.K., Hofmockel, K.S., 2018. The soil microbiome — from metagenomics to metaphenomics. Curr. Opin. Microbiol. https://doi.org/10.1016/j.mib.2018.01.013

1230 Jeanbille, M., Buée, M., Bach, C., Cébron, A., Frey-Klett, P., Turpault, M.P., Uroz, S., 2016. Soil Parameters Drive the Structure, Diversity and Metabolic Potentials of the Bacterial Communities Across Temperate Beech Forest Soil Sequences. Microb. Ecol. 71, 482–493. https://doi.org/10.1007/s00248-015-0669-5

1234 Jenny, H., 1980. The Soil Resource, Origin and Behaviour. Springer-Verlag, New-York.

1235 Jenny, H., 1941. Factors of Soil Formation : A System of Quantitative Pedology, null. Dover Publications Inc., New York, United States.

1237 Jiang, N., Tang, C., Hata, T., Courcelles, B., Dawoud, O., Singh, D.N., 2020. Bio- mediated soil improvement: The way forward. Soil Use Manag. 36, 185–188. https://doi.org/10.1111/sum.12571

1240 Jose, S., 2009. Agroforestry for ecosystem services and environmental benefits: an overview. Agrofor. Syst. 76, 1–10. https://doi.org/10.1007/s10457-009-9229-7

1242 Juilleret, J., Dondeyne, S., Hissler, C., 2014. What about the regolith, the saprolite and the bedrock? Proposals for classifying the subsolum in WRB, in: Conference: European Geosciences Union 2014. Volume: Geophysical Research Abstract 16. Vienna Austria.

1245 Kaneda, S., Kaneko, N., 2008. Collembolans feeding on soil affect carbon and nitrogen mineralization by their influence on microbial and nematode activities. Biol. Fertil. Soils 44, 435–442. https://doi.org/10.1007/s00374-007-0222-x

1248 Karimi, B., Dequiedt, S., Terrat, S., Jolivet, C., Arrouays, D., Wincker, P., Cruaud, C., Bispo, A., Chemidlin Prévost-Bouré, N., Ranjard, L., 2019. Biogeography of Soil Bacterial Networks along a Gradient of Cropping Intensity. Sci. Rep. 9, 3812. https://doi.org/10.1038/s41598-019-40422-y

1252 Karimi, B., Terrat, S., Dequiedt, S., Saby, N.P.A., Horrigue, W., Lelièvre, M., Nowak, V., Jolivet, C., Arrouays, D., Wincker, P., Cruaud, C., Bispo, A., Maron, P.-A., Bouré, N.C.P., Ranjard, L., 2018. Biogeography of soil bacteria and archaea across France. Sci. Adv. 4, eaat1808. https://doi.org/10.1126/sciadv.aat1808
1256 Kassie, M., Jaleta, M., Shiferaw, B., Mmbando, F., Mekuria, M., 2013. Adoption of interrelated sustainable agricultural practices in smallholder systems: Evidence from rural Tanzania. Technol. Forecast. Soc. Change 80, 525-540.
https://doi.org/10.1016/j.techfore.2012.08.007

1260 Klinka, K., Green, R.N., Trowbridge R.L., L.E., L., 1981. Taxonomic classification of humus forms in ecosystems of British Columbia. First approximation., Report 8. ed, Land and Management. Ministry of Forests, Province of British Columbia.

1263 Kopnina, H., Washington, H., Taylor, B., J Piccolo, J., 2018. Anthropocentrism: More than Just a Misunderstood Problem. J. Agric. Environ. Ethics 31, 109-127.
https://doi.org/10.1007/s10806-018-9711-1

1266 Korkina, I.N., Vorobeichik, E.L., 2018. Humus Index as an indicator of the topsoil response to the impacts of industrial pollution. Appl. Soil Ecol. 123, 455-463.
https://doi.org/10.1016/j.apsoil.2017.09.025

1269 Lago, M. del C.F., Barreal, M.E., Gallego, P.P., Briones, M.J.I., 2020. Legacy Effects of Agricultural Practices Override Earthworm Control on C Dynamics in Kiwifruit Orchards. Front. Environ. Sci. 8, 545609. https://doi.org/10.3389/fenvs.2020.545609

1272 Lal, R., 2015. Restoring Soil Quality to Mitigate Soil Degradation. Sustainability 7, 5875-5895. https://doi.org/10.3390/su7055875

1274 Lavelle, P., 2002. Functional domains in soils. Ecol. Res. 17, 441-450.
https://doi.org/10.1046/j.1440-1703.2002.00509.x

1276 Lavelle, P., Moreira, F., Spain, A., 2014. Biodiversity: Conserving Biodiversity in Agroecosystems, in: Encyclopedia of Agriculture and Food Systems. Elsevier, pp. 41-60. https://doi.org/10.1016/B978-0-444-52512-3.00019-X

1279 Lavelle, P., Spain, A., Fonte, S., Bedano, J.C., Blanchart, E., Galindo, V., Grimaldi, M., Jimenez, J.J., Velasquez, E., Zangerlé, A., 2020. Soil aggregation, ecosystem engineers and the C cycle. Acta Oecologica 105, 103561.
https://doi.org/10.1016/j.actao.2020.103561

1283 Legros, J.-P., 2019. A l'aube de la Science du sol. Bull. l'Academie des Sci. Lettres Montpellier 42, 381-383.

1285 Lehmann, J., Kleber, M., 2015. The contentious nature of soil organic matter. Nature 528, 60-68. https://doi.org/10.1038/nature16069

1287 Lenton, T.M., Dahl, T.W., Daines, S.J., Mills, B.J.W., Ozaki, K., Saltzman, M.R., Porada, P., 2016. Earliest land plants created modern levels of atmospheric oxygen. Proc. Natl. Acad. Sci. U.S.A. 113, 10217-10222.
1289 Acad. Sci. 113, 9704-9709. https://doi.org/10.1073/pnas.1604787113

1290 Li, Z., Zhao, B., Olk, D.C., Jia, Z., Mao, J., Cai, Y., Zhang, J., 2018. Contributions of residue-
1291 C and -N to plant growth and soil organic matter pools under planted and unplanted
1292 conditions. Soil Biol. Biochem. 120, 91-104.
1293 https://doi.org/https://doi.org/10.1016/j.soilbio.2018.02.005

1294 Liang, C., Amelung, W., Lehmann, J., Kästner, M., 2019. Quantitative assessment of
1295 microbial necromass contribution to soil organic matter. Glob. Chang. Biol. 25, 3578-
1296 3590. https://doi.org/10.1111/gcb.14781

1297 Longo, S., Cofré, N., Soteras, F., Grilli, G., Lugo, M., Urcelay, C., 2016. Taxonomic and
1298 Functional Response of Arbuscular Mycorrhizal Fungi to Land Use Change in Central
1299 Argentina. pp. 81-90. https://doi.org/10.1007/978-3-319-24355-9_7

1300 Lorenz, E.N., 1963. Deterministic Nonperiodic Flow. J. Atmos. Sci. 20, 130-141.
1301 https://doi.org/10.1175/1520-0469(1963)020<0130:DNF>2.0.CO;2

1302 Lowenfels, J., 2017. Teaming with Fungi: The Organic Grower's Guide to Mycorrhizae.
1303 Timber Press portland London.

1304 Lupatini, M., Korthals, G.W., de Hollander, M., Janssens, T.K.S., Kuramae, E.E., 2017. Soil
1305 Microbiome Is More Heterogeneous in Organic Than in Conventional Farming System.
1306 Front. Microbiol. 7, 2064. https://doi.org/10.3389/fmicb.2016.02064

1307 Magdoff, F., Weil, R.R., 2004. Soil Organic Matter in Sustainable Agriculture. CRC Press.

1308 Mahdavi, A., Wunder, S., Mirzaeizadeh, V., Omidi, M., 2019. A hidden harvest from semi-arid forests: landscape-level livelihood contributions in Zagros, Iran. For. Trees
1309 Livelihoods 1-18. https://doi.org/10.1080/14728028.2019.1571447
1310

1311 Marinari, S., Masciandaro, G., Ceccanti, B., Grego, S., 2000. Influence of organic and mineral
1312 fertilisers on soil biological and physical properties. Bioresour. Technol. 72, 9-17.
1313 https://doi.org/10.1016/S0960-8524(99)00094-2

1314 Marsden, C., Martin-Chave, A., Cortet, J., Hedde, M., Capowiez, Y., 2019. How agroforestry
1315 systems influence soil fauna and their functions - a review. Plant Soil
1316 https://doi.org/10.1007/s11104-019-04322-4. https://doi.org/10.1007/s11104-019-04322-4

1318 Matson, P.A., Parton, W.J., Power, A.G., Swift, M.J., 1997. Agricultural intensification and
1319 ecosystem properties. Science (80-. ). 277, 504-509.
1320 https://doi.org/10.1126/science.277.5325.504

1321 Mayr, E., 1942. Systematics and the origin of species from the viewpoint of a zoologist,
1322 Harvard Un. ed. Columbia University Press., New York, NY.

1323 Mechri, A., Lys, P., Cachia, F., 2017. Productivity and Efficiency Measurement in Agriculture. Literature Review and Gaps Analysis. Publication prepared in the framework of the Global Strategy to improve Agricultural and Rural Statistics. FAO.

1326 Mooshammer, M., Wanek, W., Hämmerle, I., Fuchslueger, L., Hofhansl, F., Knoltsch, A., Schnecker, J., Takriti, M., Watzka, M., Wild, B., Keiblinger, K.M., Zechmeister-Boltenstern, S., Richter, A., 2014. Adjustment of microbial nitrogen use efficiency to carbon:nitrogen imbalances regulates soil nitrogen cycling. Nat. Commun. 5, 3694. https://doi.org/10.1038/ncomms4694

1331 Moragues-Quiroga, C., Juilleret, J., Gourdol, L., Pelt, E., Perrone, T., Aubert, A., Morvan, G., Chabaux, F., Legout, A., Stille, P., Hissler, C., 2017. Genesis and evolution of regoliths: Evidence from trace and major elements and Sr-Nd-Pb-U isotopes. Catena 149, 185-198. https://doi.org/10.1016/j.catena.2016.09.015

1335 Muscolo, A., Panuccio, M.R., Abenavoli, M.R., Concheri, G., Nardi, S., 1996. Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase, glutamine synthetase, and phosphoenolpyruvate carboxylase in Daucus carota α II cells. Biol. Fertil. Soils 22, 83-88. https://doi.org/10.1007/BF00384437

1339 Muscolo, A., Settineri, G., Attinà, E., 2015. Early warning indicators of changes in soil ecosystem functioning. Ecol. Indic. 48, 542-549. https://doi.org/10.1016/j.ecolind.2014.09.017

1342 Mutuo, P.K., Cadisch, G., Albrecht, A., Palm, C.A., Verchot, L., 2005. Potential of agroforestry for carbon sequestration and mitigation of greenhouse gas emissions from soils in the tropics. Nutr. Cycl. Agroecosystems 71, 43-54. https://doi.org/10.1007/s10705-004-5285-6

1346 Nesme, J., Achouak, W., Agathos, S.N., Bailey, M., Baldrian, P., Brunel, D., Frostegård, Å., Heulin, T., Jansson, J.K., Jurkevitch, E., Kruus, K.L., Kowalchuk, G.A., Lagares, A., Lappin-Scott, H.M., Lemanceau, P., Le Paslier, D., Mandic-Mulec, I., Murrell, J.C., Myrold, D.D., Nalin, R., Nannipieri, P., Neufeld, J.D., O'Gara, F., Parnell, J.J., Pühler, A., Pylro, V., Ramos, J.L., Roesch, L.F.W., Schloter, M., Schleper, C., Sczyrba, A., Sessitsch, A., Sjöling, S., Sørensen, J., Sørensen, S.J., Tebbe, C.C., Topp, E., Tsiamis, G., van Elsas, J.D., van Keulen, G., Widmer, F., Wagner, M., Zhang, T., Zhang, X., Zhao, L., Zhu, Y.-G., Vogel, T.M., Simonet, P., 2016. Back to the Future of Soil Metagenomics. Front. Microbiol. 7. https://doi.org/10.3389/fmicb.2016.00073
1355 Newell, K., 1984. Interaction between two decomposer basidiomycetes and a collembolan
1356 under Sitka spruce: Distribution, abundance and selective grazing. Soil Biol. Biochem.
1357 16, 227-233. https://doi.org/10.1016/0038-0717(84)90006-3

1358 Nuria, R., Jérôme, M., Léonide, C., Christine, R., Gérard, H., Etienne, I., Patrick, L., 2011.
1359 IBQS: A synthetic index of soil quality based on soil macro-invertebrate communities.
1360 Soil Biol. Biochem. 43, 2023-2045. https://doi.org/10.1016/j.soilbio.2011.05.019

1361 Oldeman, R.A.A.A., 2012. Forests: Elements of Silvology, illustrate. ed. Springer Verlag.
1362 https://doi.org/10.1007/978-3-642-75211-7

1363 Orgiazzi, A., Dunbar, M.B., Panagos, P., de Groot, G.A., Lemanceau, P., 2015. Soil
1364 biodiversity and DNA barcodes: opportunities and challenges. Soil Biol. Biochem. 80,
1365 244-250. https://doi.org/10.1016/j.soilbio.2014.10.014

1366 Osman, K.T., 2013. Nutrient Dynamics in Forest Soil, in: Forest Soils. Springer International
1367 Publishing, Cham, pp. 97-121. https://doi.org/10.1007/978-3-319-02541-4_6

1368 Pagenkemper, S.K., Athmann, M., Uteau, D., Kautz, T., Peth, S., Horn, R., 2015. The effect
1369 of earthworm activity on soil bioporosity - Investigated with X-ray computed
1370 tomography and endoscopy. SOIL TILLAGE Res. 146, 79-88.

1371 Palm, C., Blanco-Canqui, H., DeClerck, F., Gatere, L., Grace, P., 2014. Conservation
1372 agriculture and ecosystem services: An overview. Agric. Ecosyst. Environ. 187, 87-105.
1373 https://doi.org/10.1016/j.agee.2013.10.010

1374 Pan, Y., Birdsey, R.A., Fang, J., Houghton, R., Kauppi, P.E., Kurz, W.A., Phillips, O.L.,
1375 Shvidenko, A., Lewis, S.L., Canadell, J.G., Ciais, P., Jackson, R.B., Pacala, S.W.,
1376 McGuire, A.D., Piao, S., Rautiainen, A., Sitch, S., Hayes, D., 2011. A Large and
1377 Persistent Carbon Sink in the World's Forests. Science (80-). 333, 988-993.
1378 https://doi.org/10.1126/science.1201609

1379 Parisi, V., 2001. La qualità biologica del suolo. Un metodo basato sui microartropodi, Acta
1380 Naturalia de l'Ateneo Parmense.

1381 Parisi, V., 1974. Biologie e ecologia del suolo - Tecniche di ricerca. Manuale del Laboratorio
di Biologia. Boringhieri, Istituto di Biologia del Mare, Venezia.

1383 Pelosi, C., Römbke, J., 2018. Enchytraeids as bioindicators of land use and management.
1384 Appl. Soil Ecol. 123, 775-779. https://doi.org/10.1016/j.apsoil.2017.05.014

1385 Pérès, G., Cluzeau, D., Curmi, P., Hallaire, V., 1998. Earthworm activity and soil structure
1386 changes due to organic enrichments in vineyard systems. Biol. Fertil. Soils 27, 417-424.
1387 https://doi.org/10.1007/s003740050452
1388 Phillips, O.L., Baker, T.R., Arroyo, L., Higuchi, N., Killeen, T.J., Laurance, W.F., Lewis, S.L., Lloyd, J., Malhi, Y., Monteagudo, A., Neill, D.A., Núñez Vargas, P., Silva, J.N.M., Terborgh, J., Vásquez Martínez, R., Alexiades, M., Almeida, S., Brown, S., Chave, J., Comiskey, J.A., Czimczik, C.I., Di Fiore, A., Erwin, T., Kuebler, C., Laurance, S.G., Nascimento, H.E.M., Olivier, J., Palacios, W., Patiño, S., Pitman, N.C.A., Quesada, C.A., Saldias, M., Torres Lezama, A., Vinceti, B., 2004. Pattern and process in Amazon tree turnover, 1976–2001. Philos. Trans. R. Soc. London. Ser. B Biol. Sci. 359, 381–407. https://doi.org/10.1098/rstb.2003.1438

1396 Piccolo, A., 2002. The supramolecular structure of humic substances: A novel understanding of humus chemistry and implications in soil science 75, 57–134. https://doi.org/10.1016/S0065-2113(02)75003-7

1399 Piccolo, A., Spaccini, R., Savy, D., Drosos, M., Cozzolino, V., 2019. The Soil Humeome: Chemical Structure, Functions and Technological Perspectives. Chapter 7., in: S. Vaz. Jr (Ed.), Sustainable Agrochemistry. Springer International Publishing, Cham, pp. 183–222. https://doi.org/10.1007/978-3-030-17891-8_7

1403 Pinstrup-Andersen, P., Pandya-Lorch, R., 1998. Food security and sustainable use of natural resources: A 2020 vision. Ecol. Econ. 26, 1–10. https://doi.org/10.1016/S0921-8009(97)00067-0

1406 Pinton, R., Varanini, Z., Nannipieri, P., 2007. The Rhizosphere: Biochemistry and Organic Substances at the Soil-Plant Interface, Second Edition, Books in Soils, Plants, and the Environment. CRC Press.

1409 Pla, C., Cuezva, S., Martinez-Martinez, J., Fernandez-Cortes, A., Garcia-Anton, E., Fusi, N., Crosta, G.B., Cuevas-Gonzalez, J., Cañaveras, J.C., Sanchez-Moral, S., Benavente, D., 2017. Role of soil pore structure in water infiltration and CO2 exchange between the atmosphere and underground air in the vadose zone: A combined laboratory and field approach. Catena 149, 402–416. https://doi.org/10.1016/j.catena.2016.10.018

1414 Poeplau, C., Sigurðsson, P., Sigurdsson, B.D., 2020. Depletion of soil carbon and aggregation after strong warming of a subarctic Andosol under forest and grassland cover. SOIL 6, 115–129. https://doi.org/10.5194/soil-6-115-2020

1417 Pollierer, M.M., Larsen, T., Potapov, A., Brückner, A., Heethoff, M., Dyckmans, J., Scheu, S., 2019. Compound- specific isotope analysis of amino acids as a new tool to uncover trophic chains in soil food webs. Ecol. Monogr. 89. https://doi.org/10.1002/ecm.1384

1420 Ponge, J.-F., 2009. Effets des amendements sur le fonctionnement biologique des sols
1421 forestiers: mieux comprendre le rôle de la méso- et de la macrofaune dans l'évolution des humus (in French, with English summary). Rev. For. Française 61, 217-222.
1422 https://doi.org/10.4267/2042/30098
1423

1424 Ponge, J.-F.F., 2013. Plant-soil feedbacks mediated by humus forms: A review. Soil Biol. Biochem. 57, 1048-1060. https://doi.org/10.1016/j.soilbio.2012.07.019

1425 Ponge, J.-F.J.F., Pérès, G., Guernion, M., Ruiz-Camacho, N., Cortet, J., Pernin, C., Villenave, C., Chaussod, R., Martin-Laurent, F., Bispo, A., Cluzeau, D., 2013. The impact of agricultural practices on soil biota: A regional study. Soil Biol. Biochem. 67, 271-284.
1426 https://doi.org/10.1016/j.soilbio.2013.08.026
1427
1428
1429

1430 Ponge, J.F., 2003. Humus forms in terrestrial ecosystems: A framework to biodiversity. Soil Biol. Biochem. 35, 935-945. https://doi.org/10.1016/S0038-0717(03)00149-4
1431

1432 Pulleman, M.M., Marinissen, J.C.Y., 2004. Physical protection of mineralizable C in aggregates from long-term pasture and arable soil. Geoderma 120, 273-282.
1433
1434 https://doi.org/10.1016/j.geoderma.2003.09.009

1435 Ramirez, K.S., Döring, M., Eisenhauer, N., Gardi, C., Ladau, J., Leff, J.W., Lentendu, G., Lindo, Z., Rillig, M.C., Russell, D., Scheu, S., St. John, M.G., de Vries, F.T., Wubet, T., van der Putten, W.H., Wall, D.H., 2015. Toward a global platform for linking soil biodiversity data. Front. Ecol. Evol. 3, 91. https://doi.org/10.3389/fevo.2015.00091
1436
1437
1438

1439 Reinmann, A.B., Hutyra, L.R., 2017. Edge effects enhance carbon uptake and its vulnerability to climate change in temperate broadleaf forests. Proc. Natl. Acad. Sci. 114, 107-112.
1440
1441 https://doi.org/10.1073/pnas.1612369114

1442 Ruiz-Camacho, N., 2011. INDICE BIOLOGIQUE DE LA QUALITE DES SOLS (IBQS) Bio-indicateur de la qualité des sols basés sur l'étude des peuplements de macro-invertébrés [WWW Document]. https://horizon/documentation.ird.fr/exl-doc/pleins_textes/divers12-11/010057480.pdf. URL
1443
1444
1445
1446 https://horizon/documentation.ird.fr/exl-doc/pleins_textes/divers12-11/010057480.pdf

1447 Scheuerell, S., Mahaffee, W., 2002. Compost Tea: Principles and Prospects For Plant Disease Control. Compost Sci. Util. 10, 313-338.
1448
1449 https://doi.org/10.1080/1065657X.2002.10702095

1450 Schloter, M., Nannipieri, P., Sørensen, S.J., van Elsas, J.D., 2018. Microbial indicators for soil quality. Biol. Fertil. Soils 54. https://doi.org/10.1007/s00374-017-1248-3
1451

1452 Scotti, R., Bonanomi, G., Scelza, R., Zoina, A., Rao, M.A., 2015. Organic amendments as sustainable tool to recovery fertility in intensive agricultural systems. J. Soil Sci. Plant
1453
1454 Nutr. https://doi.org/10.4067/s0718-95162015005000031

1455 Shaffer, M.J., Ma, L., Hansen, S., Ma, L., Hansen, S., 2001. Modeling Carbon and Nitrogen Dynamics for Soil Management. https://doi.org/10.1201/9780367801373

1457 Shukla, P.R., Skea, J., Calvo Buendia, E., Masson-Delmotte, V., Pörtner, H.-O., Roberts, D.C., Zhai, P., Slade, R., Connors, S., R. van, D., Ferrat, M., Haughey, E., Luz, S., Neogi, S., Pathak, M., Petzold, J., Portugal Pereira, J., Vyas, P., Huntley, E., Kissick, K., Belkacemi, M., Malley, J., 2020. IPCC - Summary for Policymakers. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems. Revised by the IPCC. © 2020 Intergovernmental Panel on Climate Change. Electronic copies of this Summary for Policymakers are available from the IPCC website www.ipcc.ch.

1466 Silva, V., Mol, H.G.J., Zomer, P., Tienstra, M., Ritsema, C.J., Geissen, V., 2019. Pesticide residues in European agricultural soils – A hidden reality unfolded. Sci. Total Environ. 653, 1532–1545. https://doi.org/10.1016/j.scitotenv.2018.10.441

1469 Silva, V., Montanarella, L., Jones, A., Fernández-Ugalde, O., Mol, H.G.J., Ritsema, C.J., Geissen, V., 2018. Distribution of glyphosate and aminomethylphosphonic acid (AMPA) in agricultural topsoils of the European Union. Sci. Total Environ. 621, 1352–1359. https://doi.org/10.1016/j.scitotenv.2017.10.093

1473 Six, J., Bossuyt, H., Degryze, S., Denef, K., 2004. A history of research on the link between (micro)aggregates, soil biota, and soil organic matter dynamics. Soil Tillage Res. 79, 7–31. https://doi.org/10.1016/j.still.2004.03.008

1476 Sofo, A., Ciarfaglia, A., Scopa, A., Camele, I., Curci, M., Crecchio, C., Xiloyannis, C., Palese, A.M., 2014. Soil microbial diversity and activity in a Mediterranean olive orchard using sustainable agricultural practices. Soil Use Manag. 30, 160–167. https://doi.org/10.1111/sum.12097

1480 Sofo, A., Milella, L., Tataranni, G., 2010. Effects of Trichoderma harzianum strain T-22 on the growth of two Prunus rootstocks during the rooting phase. J. Hortic. Sci. Biotechnol. 85, 497–502. https://doi.org/10.1080/14620316.2010.11512704

1483 Sofo, A., Mininni, A.N., Ricciuti, P., 2020a. Soil Macrofauna: A key Factor for Increasing Soil Fertility and Promoting Sustainable Soil Use in Fruit Orchard Agrosystems. Agronomy 10, 456. https://doi.org/10.3390/agronomy10040456

1486 Sofo, A., Nicoletta Mininni, A., Ricciuti, P., 2020b. Comparing the effects of soil fauna on
1487 litter decomposition and organic matter turnover in sustainably and conventionally managed olive orchards. Geoderma. https://doi.org/10.1016/j.geoderma.2020.114393

1489 Sofo, A., Ricciuti, P., Fausto, C., Mininni, A.N., Crecchio, C., Scagliola, M., Malerba, A.D., Xiloyannis, C., Dichio, B., 2019a. The metabolic and genetic diversity of soil bacterial communities depends on the soil management system and C/N dynamics: The case of sustainable and conventional olive groves. Appl. Soil Ecol. 137, 21–28. https://doi.org/10.1016/j.apsoil.2018.12.022

1494 Sofo, A., Ricciuti, P., Fausto, C., Mininni, A.N., Crecchio, C., Scagliola, M., Malerba, A.D., Xiloyannis, C., Dichio, B., 2019b. The metabolic and genetic diversity of soil bacterial communities depends on the soil management system and C/N dynamics: The case of sustainable and conventional olive groves. Appl. Soil Ecol. 1–8. https://doi.org/10.1016/j.apsoil.2018.12.022

1499 Soil Science Division Staff, 2017. Soil Survey Manual Updated. Agriculture Handbook No. 18. United States Department of Agriculture.

1501 Soil Survey Staff, 2015. Illustrated guide to soil taxanomy, version 2. U.S. Department of Agriculture, natural resources Conservation Service, National Soil Survey Center, Luncorn, Nebraska. https://doi.org/https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/taxon

1505 Soil Survey Staff, 2014. Keys to Soil Taxonomy by Soil Survey Staff, 12th edition., 12th ed, Soil Conservation Service. United States Department of Agriculture, Natural Resources Conservation Service, Washington, DC.

1509 Soil Survey Staff, 2010. Keys to soil taxonomy. 11th Edition. Natural Resources Conservation Service; United States Department of Agriculture.

1511 Soil Survey Staff, 2003. Keys to soil taxonomy. 9th edition. Natural Resources Conservation Service, USDA, Washington, DC.

1513 Soil Survey Staff, 1999. Soil Taxonomy. A basic system of soil classification for making and interpreting soil surveys, 2nd edition. Natural Resources Conservation Service, USDA, Washington DC, USA.

1516 Soil Survey Staff, 1975. Soil taxonomy. Agricultural Handbook No. 436. United States Department of Agriculture (USDA), Washington, DC.

1518 Soussana, J.-F., Lutfalla, S., Ehrhardt, F., Rosenstock, T., Lamanna, C., Havlík, P., Richards, M., Wollenberg, E. (Lini), Chotte, J.-L., Torquebiau, E., Ciais, P., Smith, P., Lal, R.,
1520 2019. Matching policy and science: Rationale for the '4 per 1000 - soils for food security and climate' initiative. Soil Tillage Res. 188, 3-15.
1521 https://doi.org/10.1016/j.still.2017.12.002

1522 St. Martin, C.C.G., Rouse-Miller, J., Barry, G.T., Vilpigue, P., 2020. Compost and Compost Tea Microbiology: The "-Omics" Era. Springer, Cham, pp. 3-30.
1523 https://doi.org/10.1007/978-3-030-39173-7_1

1524 Staff Soil Survey, 2015. Ilustrated Guide to Soil Taxonomy, version 2. U.S. Department of Agriculture, Natural Resources Conservation Service, National Soil Survey Center, Lincoln, Nebraska, USA.
1525

1526 State of the World's Plants and Fungi | Kew [WWW Document], n.d.

1527 Stevenson, F.J., 1994. Humus chemistry: Genesis, composition, reactions, Organic Geochemistry. John Wiley & Sons, 1994.
1528

1529 Stevenson, P.C., Bidartondo, M.I., Blackhall- Miles, R., Cavagnaro, T.R., Cooper, A., Geslin, B., Koch, H., Lee, M.A., Moat, J., O'Hanlon, R., Sjöman, H., Sofo, A., Stara, K., Suz, L.M., 2020. The state of the world's urban ecosystems: What can we learn from trees, fungi, and bees? PLANTS, PEOPLE, PLANET 2, 482-498.
1530 https://doi.org/10.1002/ppp3.10143

1531 Susmel, L., 1980. Normalizzazione delle foreste Alpine: basi ecosistemiche, equilibrio, modelli colturali, produttività: con applicazione alle foreste del Trentino. Liviana, Padova, Italy.
1532

1533 Susmel, L., 1959. Saggio critico-sperimentale sulla applicabilita del metodo fitosociologico in selvicoltura. Ann. del Cent. di Econ. Mont. delle Venezie. Padova. 1, 3-137.
1534

1535 Sweeney, C.J., de Vries, F.T., van Dongen, B.E., Bardgett, R.D., 2020. Root traits explain rhizosphere fungal community composition among temperate grassland plant species. New Phytol. nph.16976. https://doi.org/10.1111/nph.16976

1536 Takahashi, M., Hirai, K., Marod, D., Anusontpornperm, S., Limtong, P., Leaungvutivirog, C., Panuthai, S., 2019. Atypical Pattern of Soil Carbon Stocks along the Slope Position in a Seasonally Dry Tropical Forest in Thailand. Forests 10, 106.
1537 https://doi.org/10.3390/f10020106

1538 Tansley, A.G., 1935. The use and abuse of vegetational terms and concepts. Ecology 16, 284-307. https://doi.org/10.2307/1930070

1539 Torsvik, V., Øvreås, L., 2002. Microbial diversity and function in soil: from genes to ecosystems. Curr. Opin. Microbiol. 5, 240-245.
1540
1553 https://doi.org/http://dx.doi.org/10.1016/S1369-5274(02)00324-7

1554 Toutain, F., 1981. Les humus forestiers. R.F.F. 6, 449-477.

1555 Tsiafouli, M.A., Thébault, E., Sgardelis, S.P., de Ruiter, P.C., van der Putten, W.H.,
1556 Birkhofer, K., Hemerik, L., de Vries, F.T., Bardgett, R.D., Brady, M.V., Bjornlund, L.,
1557 Jørgensen, H.B., Christensen, S., Hertefeldt, T.D., Hotes, S., Gera Hol, W.H., Frouz, J.,
1558 Liiri, M., Mortimer, S.R., Setälä, H., Tzanopoulos, J., Uteseny, K., Pižl, V., Stary, J.,
1559 Wolters, V., Hedlund, K., 2015. Intensive agriculture reduces soil biodiversity across
1560 Europe. Glob. Chang. Biol. 21, 973-985. https://doi.org/10.1111/gcb.12752

1561 Van Groenigen, J.W., Van Groenigen, K.J., Koopmans, G.F., Stokkermans, L., Vos, H.M.J.,
1562 Lubbers, I.M., 2019. How fertile are earthworm casts? A meta-analysis. Geoderma.
1563 https://doi.org/10.1016/j.geoderma.2018.11.001

1564 Veen, G.F., Jasper Wubs, E.R., Bardgett, R.D., Barrios, E., Bradford, M.A., Carvalho, S., De
1565 Deyn, G.B., de Vries, F.T., Giller, K.E., Kleijn, D., Landis, D.A., Rossing, W.A.H.,
1566 Schrama, M., Six, J., Struik, P.C., van Gils, S., Wiskerke, J.S.C., van der Putten, W.H.,
1567 Vet, L.E.M., 2019. Applying the aboveground-belowground interaction concept in
1568 agriculture: Spatio-temporal scales matter. Front. Ecol. Evol. 7.
1569 https://doi.org/10.3389/fevo.2019.00300

1570 Verbruggen, E., Röling, W.F.M., Gamper, H.A., Kowalchuk, G.A., Verhoef, H.A., van der
1571 Heijden, M.G.A., 2010. Positive effects of organic farming on below-ground mutualists:
1572 Large-scale comparison of mycorrhizal fungal communities in agricultural soils. New
1573 Phytol. 186, 968-979. https://doi.org/10.1111/j.1469-8137.2010.03230.x

1574 Villecco, D., Pane, C., Ronga, D., Zaccardelli, M., 2020. Enhancing Sustainability of Tomato,
1575 Pepper and Melon Nursery Production Systems by Using Compost Tea Spray
1576 Applications. Agronomy 10, 1336. https://doi.org/10.3390/agronomy10091336

1577 Vitti, A., La Monaca, E., Sofo, A., Scopa, A., Cuypers, A., Nuzzaci, M., 2015. Beneficial
1578 effects of Trichoderma harzianum T-22 in tomato seedlings infected by Cucumber
1579 mosaic virus (CMV). BioControl 60, 135-147. https://doi.org/10.1007/s10526-014-9626-3

1581 Vitti, A., Pellegrini, E., Nali, C., Lovelli, S., Sofo, A., Valerio, M., Scopa, A., Nuzzaci, M.,
1582 2016. Trichoderma harzianum T-22 Induces Systemic Resistance in Tomato Infected by
1583 Cucumber mosaic virus. Front. Plant Sci. 7, 1520.
1584 https://doi.org/10.3389/fpls.2016.01520

1585 Vogel, H.-J., Bartke, S., Daedlow, K., Helming, K., Kögel-Knabner, I., Lang, B., Rabot, E.,
1586 Russell, D., Stößel, B., Weller, U., Wiesmeier, M., Wollschläger, U., 2018. A systemic approach for modeling soil functions. SOIL 4, 83–92. https://doi.org/10.5194/soil-4-83-2018

1587
1588 2018
1589 Wagg, C., Bender, S.F., Widmer, F., van der Heijden, M.G.A., 2014. Soil biodiversity and soil community composition determine ecosystem multifunctionality. Proc. Natl. Acad. Sci. 111, 5266–5270. https://doi.org/10.1073/pnas.1320054111

1592 Waksman, S.A., 1936. HUMUS. Origin, chemical composition and importance in nature. The Williams & Wilkins Company, Baltimore, USA.

1594 Wall, D.H., Bardgett, R.D., Kelly, E., 2010. Biodiversity in the dark. Nat. Geosci. https://doi.org/10.1038/ngeo860

1596 Wall, D.H., Nielsen, U.N., Six, J., 2015. Soil biodiversity and human health. Nature 528, 69–76. https://doi.org/10.1038/nature15744

1598 Wallenstein, M.D., Vilgalys, R.J., 2005. Quantitative analyses of nitrogen cycling genes in soils, in: Pedobiologia. Elsevier GmbH, pp. 665–672. https://doi.org/10.1016/j.pedobi.2005.05.005

1601 Wander, M.M., Cihacek, L.J., Coyne, M., Drijber, R.A., Grossman, J.M., Gutknecht, J.L.M., Horwath, W.R., Jagadamma, S., Olk, D.C., Ruark, M., Snapp, S.S., Tiemann, L.K., Weil, R., Turco, R.F., 2019. Developments in Agricultural Soil Quality and Health: Reflections by the Research Committee on Soil Organic Matter Management. Front. Environ. Sci. 7. https://doi.org/10.3389/fenvs.2019.00109

1606 Wang, S. Bin, Li, Q., Liang, W.J., Jiang, Y., Jiang, S.W., 2008. PCR-DGGE Analysis of Nematode Diversity in Cu-Contaminated Soil Project supported by the National Natural Science Foundation of China (No. 30600087) and the Knowledge Innovation Program of Institute of Applied Ecology, Chinese Academy of Sciences (No. 06L. Pedosphere 18, 621–627. https://doi.org/10.1016/S1002-0160(08)60056-9

1611 Wang, J., Zou, Y., Di Gioia, D., Singh, B.K., Li, Q., 2020. Impacts of forest conversion to plantations on the soil carbon and nitrogen dynamics, and microbial communities. Soil Biol. Biochem. 147, 107849. https://doi.org/10.1016/j.soilbio.2020.107849

1614 Whelan, A., Kechavarzi, C., Coulon, F., Sakrabani, R., Lord, R., 2013. Influence of compost amendments on the hydraulic functioning of brownfield soils. Soil Use Manag. 29, 260–270. https://doi.org/10.1111/sum.12028

1617 Williamson, K.E., Fuhrmann, J.J., Wommack, K.E., Radosevich, M., 2017. Viruses in Soil Ecosystems: An Unknown Quantity Within an Unexplored Territory. Annu. Rev. Virol. 1618
1619 4, 201-219. https://doi.org/10.1146/annurev-virology-101416-041639

1620 Wilpiszeski, R.L., Aufrecht, J.A., Retterer, S.T., Sullivan, M.B., Graham, D.E., Pierce, E.M.,

1621 Zablocki, O.D., Palumbo, A. V., Elias, D.A., 2019. Soil Aggregate Microbial

1622 Communities: Towards Understanding Microbiome Interactions at Biologically Relevant

1623 Scales. Appl. Environ. Microbiol. 85. https://doi.org/10.1128/AEM.00324-19

1624 WRB, I.W.G., 2006. World Reference Base for Soil Resources 2006. World Soil Resources

1625 Report No. 103. FAO, Rome.

1626 Yakovchenko, V., Sikora, L.J., Kaufman, D.D., 1996. A biologically based indicator of soil

1627 quality. Biol. Fertil. Soils 21, 245-251. https://doi.org/10.1007/BF00334899

1628 Yin, R., Kardol, P., Thakur, M.P., Gruss, I., Wu, G.-L., Eisenhauer, N., Schädler, M., 2020.

1629 Soil functional biodiversity and biological quality under threat: Intensive land use

1630 outweighs climate change. Soil Biol. Biochem. 147, 107847.

1631 https://doi.org/10.1016/j.soilbio.2020.107847

1632 Zanella, A., Ascher-Jenull, J., 2018a. Editorial. Humusica 1 - Terrestrial Natural Humipedons.

1633 Appl. Soil Ecol. 122, 1-9. https://doi.org/10.1016/J.APSOIL.2017.11.029

1634 Zanella, A., Ascher-Jenull, J., 2018b. Editorial. Humusica 2 - Histic, Para, Techno, Agro

1635 Humipedons. Appl. Soil Ecol. 122, 139-147.

1636 https://doi.org/10.1016/j.apsoil.2017.12.006

1637 Zanella, A., Ascher-Jenull, J., 2018c. Editorial. Humusica 3 - Reviews, Applications, Tools.

1638 Appl. Soil Ecol. 123, 297-298. https://doi.org/10.1016/j.apsoil.2018.05.016

1639 Zanella, A., Berg, B., Ponge, J.-F., Kemmers, R.H., 2018a. Humusica 1, article 2: Essential

1640 bases - Functional considerations. Appl. Soil Ecol. 122, 22-41.

1641 https://doi.org/10.1016/j.apsoil.2017.07.010

1642 Zanella, A., Géhu, J.-M., 1994. Proposition por une typologie forestière intégrée. Exemples

1643 d'application aux forêts de la Flandre française intérieure / Proposal for an integrated

1644 forest typology. Application examples in French Flanders inland forests. Université de

1645 Paris Sud (11), Orsay, France.

1646 Zanella, A., Ponge, J.-F., Briones, M.J.I., 2018b. Humusica 1, article 8: Terrestrial humus

1647 systems and forms - Biological activity and soil aggregates, space-time dynamics. Appl.

1648 Soil Ecol. 122, 103-137. https://doi.org/10.1016/j.apsoil.2017.07.020

1649 Zanella, A., Ponge, J.-F., Fritz, I., Pietrasiak, N., Matteodo, M., Nadporozhskaya, M.,

1650 Juilleret, J., Tatti, D., Le Bayon, R.-C., Rothschild, L., Mancinelli, R., 2018c. Humusica

1651 2, article 13: Para humus systems and forms. Appl. Soil Ecol. 122, 181-199.
1652 https://doi.org/10.1016/j.apsoil.2017.09.043

1653 Zanella, A., Ponge, J.-F., Gobat, J.-M., Juilleret, J., Blouin, M., Aubert, M., Chertov, O., Rubio, J.L., 2018d. Humusica 1, article 1: Essential bases – Vocabulary. Appl. Soil Ecol. 122, 10–21. https://doi.org/10.1016/j.apsoil.2017.07.004

1654
1655 Zanella, A., Ponge, J.-F., Matteodo, M., 2018e. Humusica 1, article 7: Terrestrial humus systems and forms – Field practice and sampling problems. Appl. Soil Ecol. 122, 92–102. https://doi.org/10.1016/j.apsoil.2017.05.028

1659 Zanella, A., Ponge, J.-F., Topoliantz, S., Bernier, N., Juilleret, J., 2018f. Humusica 2, article 15: Agro humus systems and forms. Appl. Soil Ecol. 122, 204–219. https://doi.org/10.1016/j.apsoil.2017.10.011

1662 Zanella, A., Tomasi, M., Cesare, D.S., Frizzera, L., Jabiol, B., Nicolini, G., Sartori, G., Calabrese, M.S., Manacabelli, A., Nardi, S., Pizzeghello, D., Maurizio, O., 2001. Humus Forestali - Manuale di ecologia per il riconoscimento e l'interpretazione - Applicazione alle faggete, CEA. ed. Centro Ecologia Alpina, Fondazione Edmund Mach, San Michele all'Adige, Trento (Italia): 321 p.

1667

1668

1669

1670

1671

1672

1673

1674

1675

1676 Tables

1677

<table><caption>1678 **Table 1. Historical legacies.**</caption>
  <thead>
    <tr>
      <th colspan="2">Historical legacies</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td rowspan="3">Dokuchaev (1900)</td>
      <td>Climate, biological agents, rock, topography and duration are the factors of soil differentiation, or the factors of pedogenesis.</td>
    </tr>
    <tr>
      <td>Climate and corresponding vegetation are the main ones responsible for the organization of soils on a global scale.</td>
    </tr>
    <tr>
      <td>At the field scale, climatic variability does not have to be considered while topography and variability of the geological substrate can still modify soils.</td>
    </tr>
  </tbody>
</table>
<table><tr><td></td><td>There were exceptions to the climate zonality. Locally, this or that environmental factor plays a preponderant role and masks the role of climate. "Zonal" soils, that are part of the climatic zonality; "azonal" soils, whenever the rock outcrops directly; and "intra-zonal" soils, whose characteristics are linked to special conditions, such as excess water or salt.</td></tr><tr><td rowspan="3">Jenny (1941)</td><td>The soil system is an open system.</td></tr><tr><td>The initial state of the soil system has been designated as parent material.</td></tr><tr><td>In selecting climate (cl), biological agents (o), rock (r), topography (p) and duration (t) as the independent variables of the soil system, we do not assert that these factors never enter functional relationships among themselves.</td></tr><tr><td rowspan="5">Soil and vegetation</td><td>Soil and vegetation correspond to a continuous layer that shows changes inside and outside perceptible to the human eye.</td></tr><tr><td>Both soil and vegetation covers can be broken down into sub-layers.</td></tr><tr><td>Circumscribing spatial sub-units (horizontal or vertical soil and vegetation sub-units) is not so simple, because the transition from one to the other unit is rarely abrupt; very often it is gradual and nuanced.</td></tr><tr><td>We know that using the characteristic species of the phytosociological units to map the forest vegetation, the part of the forest occupied by undefined vegetation types becomes larger than that occupied by known vegetation types.</td></tr><tr><td>It is crucial to choose carefully the environment in which you are taking the survey, it must be as homogeneous as possible considering the purposes of your work; work objectives define the size of your survey.</td></tr><tr><td rowspan="6">Need of unification</td><td>The need for unification is necessary when international organizations wanted to map soils at planet level.</td></tr><tr><td>The number of soil units which compose the legend of the Soil Map of the World is 106. The legend sheets present these soil units in an order which reflects the general processes of soil formation. The basic principles which underlie the separation of these soil units and their definitions are discussed in Chapter 3. Areas of "non soil" are shown on the map as miscellaneous land units.</td></tr><tr><td>The disagreement among soil scientists produced a scientific impasse.</td></tr><tr><td>When there are over three variables interacting, and in the soil there are dozens, a natural system end up in a chaotic and unpredictable movement.</td></tr><tr><td>Illustrated Guide to Soil Taxonomy (2015). USDA attempt to approach a larger audience (ecologists, environmental scientists, etc.).</td></tr><tr><td>Essentials of Soil Science - Soil formation, functions, use and classification (2018). WRB attempt to open to other disciplines.</td></tr><tr><td rowspan="3">Soil as living system</td><td>Living organisms organize the superficial part of the Earth's crust into layers that are visible to the naked eye.</td></tr><tr><td>Each soil horizon gets its own relative independence: since it is built by living beings and develops by its-own, it can also be considered a subsystem contained in a larger complete soil system.</td></tr><tr><td>To classify the soil means to circumscribe a surface volume of the earth's crust that grows over time and evolves as a system (called pedogenetic processes by soil scientists), dependent on those same soil forming-factors.</td></tr></table>
<table><tr><td></td><td>Topsoils are directly linked to particular groups of soil animals. This connection could have very important consequences on the management of forest and agricultural soils to stop climate from warming.</td></tr><tr><td>Jenny (1980)</td><td>Because of a possible climatic warm-up, we do not wish accelerate humus oxidation and the concomitant flux of carbon dioxide from soil into the atmosphere... The humus capital, which is substantial, deserves to be maintained because good soils are a national asset.</td></tr><tr><td>Solution?</td><td>A biological classification of the soil on a DNA basis could probably clarify the living essence of the soil.</td></tr></table>

1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696

Figure legends

1697
1698
1699
1700
1701
1702
1703
1704
1705

**Figure 1.** The three key attributes of soil, considered as a living system.

**Figure 2.** From “The contentious nature of soil organic matter”. Figure entitled: Reconciliation of current conceptual models for the fate of organic debris into a consolidated view of organic matter cycles and ecosystem controls in soil (Lehmann and Kleber, 2015).
**Figure 3.** The FAO-Unesco Soil Map of the World, a first immense effort to synthetize the distribution of the soil on our planet. On the right the cover of Volume I, which is identical in the other volumes, only changes the squared that frame the described section. Notice the design, which recalls the horizons of the soil, but also soil, vegetation and atmosphere, or an interlocking of concentric circles typical of a modern ecological vision. Just beautiful, with the maps scattered as if in a vacuum.

**Figure 4.** The 20 humus systems of the classification published by the Humus Group are divided into: 6 young or very particular natural systems (Para); 2 systems closely linked to man, one semi-natural (Agro) and one completely built by man (Techno); 5 terrestrial systems containing 17 humus forms; 5 Histic systems containing 16 humus forms; 2 Aqueous systems containing 3 humus forms. In total, the forms of humus described are 36 (not reported in the figure).

**Figure 5.** On the left, the "layers" that can be identified in the soil profile. On the right, the phases of formation of the soil profile.

**Figure 6.** Soil is more complex than we think. It is almost as if it were an underground forest, much more concentrated and with less air than that which lives above the ground. We can imagine it composed of three layers in which it evolves without being perceptible in its dynamic state. Perhaps the blue arrows can represent the real processes of soil forming generating the large groups of soils (corresponding to theoretical main pedogenetic processes) described by the modern IUSS Working Group.

**Figure 7.** Major benefits of the adoption of sustainable agricultural practices. Examples of the sustainable agricultural practices explained in the text.

## Appendices

**Appendix 1.** Quotation from Waksman, S. A. (1936). *HUMUS. Origin, chemical composition and importance in nature*. The Williams & Wilkins Company. The whole "outlook" of the authors can be found here: https://soilcarboncoalition.org/files/Waksman-Humus.pdf,
1739 particularly at pages 397-398.