Agricultural land covers
Soils (
The processes of additions, losses, transfers and translocation, and transformations of matter and energy over centuries and millennia produce a medium – soil (Simonson, 1959), which supports plant roots and fulfils many other ecosystem functions (Lal, 2008; Nannipieri et al., 2003; Paul, 2014). These functions commonly decrease due to human activities, in particular through agricultural practices because of accelerated soil erosion, nutrient loss (despite intensive fertilization), aggregate destruction, compaction, acidification, alkalization and salinization (Homburg and Sandor, 2011; Sandor and Homburg, 2017). Accordingly, the factor humankind has nearly always been considered to be a soil-degrading entity that, by converting natural forests and grasslands to arable lands, changes the natural cycles of energy and matter. Except in very rare cases that lead to the formation of fertile soils such as Terra Preta in the Amazon Basin (Glaser et al., 2001), Plaggen in northern Europe (Pape, 1970) and Hortisols (Burghardt et al., 2018), soil degradation is the most common outcome of agricultural practices (DeLong et al., 2015; Homburg and Sandor, 2011). Soil degradation begins immediately after conversion of natural soil and involves the degradation in all physical, chemical and biological properties (Table 1). The result is a decline in ecosystem functions.
Processes and mechanisms of soil degradation by agricultural land use.
aggregate destruction
compaction by heavy machinery
ploughing at a constant depth
destruction of aggregates
removal of plant biomass via harvesting
residual burning
destruction of macroaggregates
loss of nutrients
narrowing of
removal of plant biomass via harvesting
nutrient leaching
SOM mineralization and N-P fertilization
N fertilization
cation removal by harvest
acidification and
loss of SOM
irrigation (with low-quality water and/or groundwater level rise by irrigation)
Continued.
weeding
pesticide application
monocultures or narrow crop rotations
mineral fertilization
ploughing and grubbing
pesticide application
respiration enzyme activities
recalcitrance of remaining SOM
mineral fertilization
shift in microbial community structure
Soil degradation gains importance with the rapid increase in the human population (Carozza et al., 2007) and technological progress. Increasing food demand requires either larger areas for croplands and/or intensification of crop production per area of already-cultivated land. Because the land resources suitable for agriculture are limited, most increases in food production depend on the second option: intensification (Lal, 2005). While prohibiting or reducing degradation is essential in achieving sustainable food production (Lal, 2009), many studies have addressed individual mechanisms and specific drivers of soil degradation (Table 1). Nonetheless, there is still no standard and comprehensive measure to determine soil degradation intensity and to differentiate between degradation stages.
Agricultural soils (croplands plus grasslands) cover
Humans began to modify natural soils at the onset of agriculture ca. 10–12 thousand years ago (Diamond, 2002; Richter, 2007), resulting in soil degradation. Examples of soil degradation leading to civilization collapses are well known, starting at least with Mesopotamia (18th to 6th centuries BCE; Diamond, 2002; Weiss et al., 1993). Notwithstanding all the negative impacts humans have on soils, the intention was always to increase fertility to boost crop production (Richter et al., 2011; Sandor and Homburg, 2017), reduce negative environmental consequences and achieve more stable agroecosystems. To attain these aims, humans have (i) modified soil physical and hydrological properties (for example, by removing stones and loosening soil by tillage, run-off irrigation, draining and terracing); (ii) altered soil chemical conditions through fertilization, liming and desalinization; and (iii) controlled biodiversity by sowing domesticated plant species and applying biocides (Richter et al., 2015; Richter, 2007). Although these manipulations commonly lead to soil degradation (Homburg and Sandor, 2011; Paz-González et al., 2000; Sandor et al., 2008), they are aimed at decreasing the most limiting factors (nutrient contents, soil acidity, water scarcity, etc.) for crop production regardless of the original environmental conditions in which the soil was formed (Guillaume et al., 2016b; Liu et al., 2009). Thus, agricultural land use always focused on removing limiting factors and providing optimal growth conditions for a few selected crops: 15 species make up 90 % of the world's food, and three of them – corn, wheat and rice – supply two-thirds of this amount (FAO, 2018). These crops (except rice) have similar water and nutrient requirements in contrast to the plants growing under natural conditions. Consequently, agricultural land use has always striven to narrow soil properties to uniform environmental conditions.
Humans can even change soil types as defined by classification systems (Fig. S1 in the Supplement) by inducing erosion, changing the thickness of horizons and their mixture, decreasing soil organic matter (SOM) content, destroying aggregates, and accumulating salts (Dazzi and Monteleone, 2007; Ellis and Newsome, 1991; Shpedt et al., 2017). A Mollisol (similar to Chernozems or Phaeozems), for example, turns into an Inceptisol (similar to Cambisols) by decreasing total SOM (Lo Papa et al., 2013; Tugel et al., 2005) and/or thinning of the mollic epipedon by tillage and erosion and destroying granular and sub-polyhedric structure (Ayoubi et al., 2012; Lo Papa et al., 2013). Accordingly, humankind can no longer be treated solely as a soil-degrading but also as a soil-forming factor (Amundson and Jenny, 1991; Dudal, 2004; Gerasimov and Fridland, 1984; Richter et al., 2015; Sandor et al., 2005). The result is the formation of anthropogenic soils (soils formed under the main factor humankind). This is well known for rice paddies, i.e. Hydragric Anthrosols (Chen et al., 2011; Cheng et al., 2009; Kölbl et al., 2014; Sedov et al., 2007), Hortic Anthrosols (long-term fertilized soils with household wastes and manure) and Irragric Anthrosols (long-term irrigated soils in dry regions; WRB, 2014). These effects have stimulated the ongoing development of soil classifications to reflect new directions of soil evolution (Bryant and Galbraith, 2003; Richter, 2007): anthropedogenesis, i.e. soil genesis under the main factor humankind, and in particular agropedogenesis, i.e. soil genesis under agricultural practices as a subcategory of anthropedogenesis.
Human impacts on soil formation have immensely accelerated in the last 50–100 years (Dudal, 2004; Gerasimov and Fridland, 1984; Richter, 2007) with the (1) introduction of heavy machinery, (2) application of high rates of mineral fertilizers, especially after discovery of N fixation by the Haber–Bosch technology, (3) application of chemical plant protection, and (4) introduction of crops with higher yield and reduced root systems. We expect that, despite various ecological measures (no-till practices, restrictions on chemical fertilizer applications and heavy machinery, etc.), the effects of humans on soil formation will increase in the Anthropocene and will be even stronger than for most other components of global change. This urgently calls for a concept and theory of soil formation under humans as the main factor.
Soil formation processes under agricultural practices.
water
salts
sediments
organic matter
plant residues
organic fertilizers
N (to
dissolved organic matter
soluble salts
acceleration of nutrient (C, N, P, etc.) cycles
formation of potassium-rich clay minerals
mineral
organic (manure and crop residues)
fine earth erosion
whole soil material
soluble salt transportation to the topsoil
humification of organic residues
organo-mineral interactions
pesticides
herbicides
nutrients leaching
cations
soil horizon mixing
homogenization
bioturbation
compaction of top- and subsoil
aggregate destruction
liming
gypsum
sand
biochar
nutrients
ballast (Si, Al, Na, etc.) elements
fungal community
Anthropedogenesis is the soil formation under the main factor “human” (Amundson and Jenny, 1991; Bidwell and Hole, 1965; Howard, 2017; Meuser, 2010; Richter, 2007; Yaalon and Yaron, 1966). Agropedogenesis is the dominant form of anthropedogenesis and includes soil formation under agricultural use – mainly cropland (Sandor et al., 2005). The other forms of anthropedogenesis are construction of completely new soils (Technosols, e.g. urban soils or mine soils). These other forms of anthropedogenesis are not treated here because they are not connected with agriculture.
Agropedogenesis should be clearly separated from the natural pedogenesis because of (1) strong dominance of the factor “human” over the other five factors of soil formation, (2) new processes and mechanisms that are absent under natural soil development (Table 2), (3) new directions of soil developments compared to natural processes (Table 2), (4) frequent development of processes in the reverse direction compared to natural pedogenesis, and (5) much higher intensity of many specific processes compared to natural developments and consequently faster rates of all changes.
Conceptual scheme of soil development, i.e. pedogenesis,
under natural conditions (green lines) and agropedogenesis due to long-term
agricultural practices (red lines). Green area: the increasing variability
in natural soils during pedogenesis. Yellow area: decrease in the
variability in soil properties by agricultural use. Double-line vertical arrow:
the start of cultivation.
Agropedogenesis and natural pedogenesis are partially opposite. Natural soil formation involves the development of soils from parent materials under the effects of climate, organisms, relief and time (Dokuchaev, 1883; Jenny, 1941; Zakharov, 1927; Supplement). Here, soil formation will reach the quasi-steady state typical for the combination of the five soil-forming factors (Targulian and Goryachkin, 2004) (Fig. 1). Agropedogenesis, in most cases, is a process involving the loss of soil fertility, i.e. degradation because of intensive agriculture and narrowing of soil properties. Agropedogenesis is partially the reverse of soil formation, but the final stage is not the parent material (except in a few cases of extreme erosion). Agropedogenesis also leads to a quasi-steady state of soils (Fig. 1; Eleftheriadis et al., 2018; Wei et al., 2014). The time needed to reach this quasi-steady state, however, is much shorter (in the range of a few centuries, decades or an even shorter time period) than for natural pedogenesis, which involves millennia (Tugel et al., 2005). The range of soil properties at this quasi-steady state will show the end limit of agricultural effects on soil development.
Our theory of agropedogenesis is based on five components: the (1) concept of
“
The original concept of “
Soil genesis based on the five natural factors of
soil formation and the sixth factor: human. Natural processes are
presented in green, and human processes are presented in red.
The concept factors
Considering the recent development of functional approaches and ecosystem
perspectives, this triad is insufficient. We therefore introduce the
concept
One function – plant growth – is crucial for agropedogenesis (Fig. 2)
because humans change this natural function to an anthropogenic function –
crop growth – thus adapting and modifying natural soils to maximize
productivity and crop yields. As it is not possible to simultaneously
maximize all functions, the functions other than “crop growth” decrease or
even disappear. Accordingly, agropedogenesis is driven by processes pursuing the maximization of only one function – crop growth. The consequence is that all other soil
functions are reduced. We define
Examples for attractors of soil properties by
anthropogenic degradation:
Agropedogenesis clearly shows that the natural sequence
Despite a very broad range of individual properties of natural soils,
long-term intensive agricultural land use strongly narrows their range
(Homburg and
Sandor, 2011; Kozlovskii, 1999; Sandor et al., 2008) and ultimately brings
individual properties to the so-called attractors of degradation
(Kozlovskii, 1999):
An attractor of a soil property is a numerical value toward which
the property develops from a wide variety of initial or intermediate states
of pedogenesis. An attractor of agricultural soil degradation is a minimal or
maximal value, toward which the property tends to develop by long-term
intensive agricultural use from a wide variety of initial conditions common
for natural soils.
Attractors of soil properties are common for natural pedogenesis and
anthropedogenesis (Fig. 1). The well-known examples of natural pedogenic
attractors are the maximal SOM accumulation (
Natural pedogenesis leads to a divergence of pedogenic properties and consequently to the broadening of the multidimensional attractor space (see below) because various soils develop to steady state from the same parent materials depending on climate, organisms and relief (Fig. 1). The time necessary for natural processes to reach these attractors is at least 1–2 orders of magnitude longer than the periods to reach the attractors of agropedogenesis (see below).
In contrast to natural pedogenesis, agropedogenesis narrows the soil
properties by optimizing environmental conditions for agricultural crops
with similar requirements (Lo Papa et
al., 2011, 2013). Consequently, each soil property follows a trajectory from
a specific natural level toward the unified agrogenic attractor (Fig. 1).
Therefore, in contrast to natural pedogenesis resulting in divergence of soil properties,
The convergence in soil properties (and thus reaching an attractor) after starting in various initial states is evident by comparing soils under long-term (e.g. decades and centuries) cultivation (Sandor and Homburg, 2017). The challenges that ancient farmers faced were fundamentally the same as today, although recent decades are characterized by a major intensification of chemical impacts (fertilization and pesticides) and heavy machinery (Dudal, 2004; Sandor and Homburg, 2017). The main difference between soil degradation in the past and in the modern era is the rates and extent but not the processes or mechanisms themselves. The dynamics of soil properties in long-term cultivations have revealed a narrowing in the measured values of a given property over time, i.e. a tendency toward the attractor of that property (Alletto and Coquet, 2009; Dalal and Mayer, 1986a, c; Haas et al., 1957; Nyberg et al., 2012; Figs. 3, 4, 5, and S2).
Example of the divergence of soil properties of abandoned
agriculturally used Chernozem (under steppe) and Phaeozem (under forest)
after termination of cultivation (Ovsepyan et al., 2019, modified). The soil
properties were analysed by principal component analysis (PCA). The soils
had very similar properties due to long-term (
Overview on rates of key processes of agropedogenesis and
their trajectory in reaching their attractors. Curves start from 0 or 1
(relative values) at the onset of cultivation and go to 1 or 0 for the
specific attractors. Each curve is labelled with the specific property. Small
arrows after each parameter title show the estimated level of attractor in
absolute values. After approaching its attractor, each process slows down and
finally stops. The timescale is logarithmic. Curve shape, time to reach
attractor and attractor levels are only estimates and require future
adjustment based on experimental data. pH
Effects of duration of forest conversion to cropland on
decreasing soil organic carbon (SOC)
In reaching the attractor values, however, the process rates and dynamics
differ among various soil properties (Figs. 5 and 6), in various geo-climatological
regions
(Chen
et al., 2011, p. 29 011; Guillaume et al., 2016b; Hartemink, 2006) and
according to land-use intensity. For example, microbial biomass carbon (C)
(Henrot and Robertson, 1994) and
aggregate stability
(Wei et al., 2014)
respond faster than SOM and total N to cultivation. Cultivation affects
total N and P content less than organic C because of N and P fertilization
(Guillaume et al., 2016a), whereby a strong decrease in C input is inferred
by the decreasing
Soils and their functions are characterized by and are dependent on the full
range of physical, chemical and biological properties. A few of them – the
master soil properties – however, are responsible for a very broad range of
functions and define other properties
(Lincoln et al.,
2014; Lisetskii et al., 2013; Seybold et al., 1997). We define a soil property as being a master property if it has a strong effect on a broad range of other properties and functions and if it cannot be easily assessed based on the other properties. For natural
pedogenesis, such master properties – inherited partially from the parent
material – are clay mineralogy and
Soil properties suggested in the literature and in agropedogenesis theory as being master properties
The master properties of agropedogenesis may differ from those of natural
soil development. The crucial difference is that the
Master soil properties have an additional important function: they are responsible or co-responsible for the changes in other properties. Changes in a master property over time may therefore intensify or dampen changes in other (secondary) properties. The stability of macroaggregates, for example, increases with the content and quality of SOM (Boix-Fayos et al., 2001; Celik, 2005). The infiltration rate and water-holding capacity decrease with increasing bulk density (Rasa and Horn, 2013; Raty et al., 2010), promoting erosion. These relations between soil properties, however, seem to be significant only within certain ranges, i.e. until thresholds are reached. Beyond such thresholds, new relations or new master properties may govern. For example, an increasing effect of SOM content on aggregate stability in extremely arid regions of the Mediterranean was recorded at above the 5 % SOM content threshold (Boix-Fayos et al., 2001). Increasing organic matter contents up to this 5 % threshold had no effect on aggregate stability: instead, the carbonate content was the main regulator (Boix-Fayos et al., 2001). Microbial biomass and respiration in well-drained Acrisols in Indonesia are resistant to decreasing SOM down to 2.7 % of SOM but strongly dropped beyond that value (Guillaume et al., 2016a). While the amounts of SOM and total N in sand and silt fractions may continuously decrease with cultivation duration, those values in the clay fraction remain stable (Eleftheriadis et al., 2018; Fig. 3e). Bulk density increases non-linearly with SOM decrease, and the rates depend on SOM content (Fig. 6). Phase diagrams are very useful in identifying such thresholds (see below).
Phase diagrams of various properties of agricultural
soils. Small arrows at the start or end of the axes show the increase in the
corresponding soil property.
Summarizing, we define master properties as a group of soil-fertility-related parameters that (1) are directly affected by management, i.e. are sensitive to agricultural use and soil degradation, (2) determine the state of many other (non-master) parameters and soil fertility indicators during agropedogenesis, and (3) should be orthogonal to each other, i.e. independent (or minimally dependent) of one other (Kozlovskii, 1999). Note that, in reality, all soil properties are at least partially dependent on each other. Nonetheless, the last prerequisite – orthogonality – ensures the best separation of soils in multidimensional space (see below) and reduces the redundancy of the properties.
Considering the three prerequisites and based on expert knowledge, as well
as on phase diagrams (see below), we suggest soil depth (A and B horizons) and
eight properties as being master properties (Table 3): density, macroaggregates, SOM, the
The combination of master properties provides a minimum dataset to determine soil development stages with cultivation duration (Andrews et al., 2002). Organic C content is the most important and universally accepted master property that directly and indirectly determines the state of many physical (soil structure, density, porosity, water-holding capacity, percolation rate and erodibility; Andrews et al., 2003; Nabiollahi et al., 2017; Seybold et al., 1997; Shpedt et al., 2017), chemical (nutrient availability, sorption capacity and pH; Lal, 2006; Minasny and Hartemink, 2011) and biological (biodiversity, microbial biomass and basal respiration; Raiesi, 2017) properties. The values of the mentioned secondary properties can be estimated with an acceptable uncertainty based on robust data on SOM content (Gharahi Ghehi et al., 2012). Finding additional soil properties beyond SOM to form the set of master properties is, however, not straightforward (Homburg et al., 2005) because it depends on the desired soil functions (Andrews et al., 2003) such as nutrient availability, water permeability and holding capacity, crop yield quantity and quality, etc. (Andrews et al., 2002). Therefore, various types of master properties, depending on geo-climatological conditions (Cannell and Hawes, 1994), have already been suggested (Table 3). Nonetheless, the dynamics, sensitivity and resistance of such properties to degradation and with cultivation duration remain unknown (Guillaume et al., 2016a).
All the properties described above move toward their attractors over the
course of soil degradation with time (Figs. 3 and 6). The duration, however,
is difficult to compare between soils because the process rates depend on
climatic conditions and land-use intensity. One option for understanding and
analysing soil degradation independent of time is to use phase diagrams. Generally, a phase
diagram is a type of chart for showing the state and simultaneous development of
two or more parameters of a matter Note that in chemistry,
mineralogy and materials sciences, a phase diagram is a type of chart used
to show conditions (pressure, temperature, volume, etc.) at which
thermodynamically distinct phases (e.g. solid, liquid or gaseous states) are
at equilibrium.
Examples of conceptual 2-D and 3-D phase diagrams linking
soil erosion intensity with
Conceptual schema of convergence of soil properties by agropedogenesis. The very broad range of natural soils and their properties will be tailored for crop production by agricultural use, resulting in Anthrosols with a very narrow range of properties. Note that the soils within the funnel are mentioned exemplarily, and not all World Reference Base (WRB) soil groups are presented. The sequence of soils within the funnel does not reflect their transformations during agropedogenesis to Anthrosols. (The extended version of this figure, reflecting multiple pathways to Anthrosols, e.g. formed and used under completely different climate and management conditions, is presented in Fig. S3.)
Phase diagrams have two advantages: (1) they help evaluate the dependence of properties on each other – independent of time, climate or management intensity. They represent generalized connection between the properties. This greatly simplifies comparing the trajectory of soil degradation under various climatic conditions, management intensity levels and even various land uses. (2) Such diagrams enable identifying the thresholds and stages of soil development and degradation.
We define these terms as follows.
Thresholds of soil development and degradation are
relatively abrupt changes in process rates or process directions leading to
a switch in the dominating mechanism of soil degradation. Stages of soil degradation are periods confined by
two thresholds and characterized by one dominating degradation mechanism
(Fig. 6c).
Importantly, soil degradation does not always follow a linear or exponential
trajectory (Kozlovskii, 1999; Kozlovskii and Goryachkin, 1996). This means that changes (absolute
for linear or relative for exponential) are not proportional to time or
management intensity (Kozlovskii and Goryachkin, 1996; Matus and Egli, 2019). Soil degradation proceeds in stages of various
levels of duration and intensity. The key consideration, however, is that each stage
is characterized by the dominance of one (group) of degradation processes,
whose prerequisites are formed in the previous phase.
We conclude that phase diagrams (1) enable tracing the trajectory of various soil properties as they reach their attractors, independent of time, land-use or management intensity, and (2) are useful for analysing not only the dependence (or at least correlation) between individual properties but also for identifying the thresholds of soil degradation. The thresholds clearly show that soil degradation proceeds in stages (Figs. 6c, 7 and 8), each of which is characterized by the dominance of one specific degradation process with its specific rates (and affecting the degradation of related soil properties).
The phase diagrams described above were presented in 2-D or 3-D space (Figs. 7 and 8) and help in evaluating the connections between the properties and the stages of soil degradation. The suggested nine master soil properties are orthogonal, and the phase diagrams can therefore be built in multidimensional attractor space – the space defining the soil degradation trajectory based on the master soil properties (Fig. 8g and h). Therefore, development of master soil properties during long-term agricultural land use and degradation forms a multidimensional space of properties (multidimensional space) toward which the soil will develop (trajectory) during agropedogenesis and will then remain unchanged within this equilibrium field. Accordingly, the multidimensional space of attractors defines the final stage of agropedogenesis.
The degraded soil will remain within this multidimensional space even if subsequently slightly disturbed (or reclaimed). This explains why long-term agricultural fields that have been abandoned for centuries or even millennia still show evidence of soil degradation (Hall et al., 2013; Jangid et al., 2011; Kalinina et al., 2013; Lisetskii et al., 2013; Ovsepyan et al., 2019; Sandor et al., 2008). For example, abandoned soils under succession of local vegetation such as grassland and forest show similar physicochemical and biological properties as a result of similarities in their history, i.e. agricultural land use (Jangid et al., 2011; Kalinina et al., 2019; Kurganova et al., 2019; Ovsepyan et al., 2019). The flood-irrigated soils in Cave Creek, Arizona, support only the growth of the creosote bush even about 700 years after abandonment. This contrasts with the presence of seven species of shrubs and cacti in areas between such soils. The reason is substantial changes in soil texture, i.e. via siltation, thus reducing the water-holding capacity in the flood-irrigated soils and leading to a shift in the vegetation community toward more drought-resistant species, in this case the creosote bush (Hall et al., 2013). Whereas establishing a no-till system on former pasture-land leads to a decrease in SOM, changing a formerly ploughed land to no-till had no such effect (Francis and Knight, 1993). The amidase activity in Colca soils, Peru, is still high 400 years after land abandonment due to the remaining effect of applied organic amendments on microorganisms (Dick et al., 1994). We argue that during agropedogenesis the multidimensional space of master soil properties will continuously narrow when approaching the attractors. This multidimensional space resembles a funnel (Fig. 9), meaning that the broad range of all properties in initial natural soils will be narrowed and unified to a (very) small range in agricultural and subsequently degraded soils. Identifying the attractors of master properties and the relations among them in this multidimensional space yields diagnostic characteristics for identifying and classifying agrogenic soils (Gerasimov, 1984; Kozlovskii, 1999).
Despite the principle of attractors – the convergence of a property of various soils to one value by degradation – we assume that these attractors may differ slightly depending on climate, parent material and management (Fig. S3). This means that the multidimensional attractor space can exhibit some local minima – metastable states (Kozlovskii, 1999). If the initial natural soil is close to such a minimum, or the management pushes the trajectory in such a direction, then agropedogenesis may stop at local minima. Thus, the global minimum will not be reached.
Nine years of continuous cropping and conventional
tillage
For example, no-till farming may increase SOM in the Ap horizon (Lal, 1997) and cause SOM contents to level off at higher values compared to tillage practices (Fig. 10). However, periodically tilling the soil to simplify weed control quickly destroys the improvements in soil properties during the no-till period (Cannell and Hawes, 1994). This results in degradation stages similar to soils under conventional tillage. The ultimate effect of irrigation on soil degradation is expected to be similar to that of dry-land farming. Despite more organic C input into irrigated systems, the SOM content remains unchanged (Trost et al., 2014) due to accelerated decomposition (Denef et al., 2008). The state of soil properties in the tropics is predictable based on pedotransfer functions commonly used in temperate regions, which, even though tropical soils are usually more clayey, have a lower available water capacity and exhibit a higher bulk density. The explanation lies in the similarities in relations among soil properties under various climatic conditions (Minasny and Hartemink, 2011). This makes the concept of attractors generalizable to all cultivated soils (Kozlovskii, 1999), although geo-climatic conditions and specific management may modify the attractor values and affect the rates of soil degradation following cultivation (Tiessen et al., 1994).
We state that (1) human activities are stronger in intensity and rates than all other soil-forming factors (Liu et al., 2009; Richter et al., 2015). Because humans exploit mainly one soil function – crop production – they optimize all soil processes and properties toward a higher yield of a few agricultural crops. Because most crops have similar requirements, the range of measured values for any soil property becomes narrower during agropedogenesis. Therefore, human activities for crop production lead to the formation of a special group of agrogenic soils with a defined and narrow range of properties – Anthrosols. The range of properties moves toward the attractor: specific for each property but similar for various soils. (2) Analysing the properties of soils from various geo-climatological conditions and types of management in relation to cultivation periods reveals (i) the dynamics of soil properties by agropedogenesis and (ii) demonstrates the final stage of agrogenic degradation when the values of various soil properties reach the attractor.
By analysing the soil development and the properties' dynamics under
agricultural use, we develop for the first time the basic theory of
agropedogenesis. This theory is based on (1) the modified classical concept
of
We developed a new unifying theory of agropedogenesis based on the long
observation of soil degradation under agricultural use and on experiments
with agricultural soils under various land-use intensity under a broad
range of climatic conditions. The presented examples of soil degradation
trajectories and of attractors of soil properties clearly do not reflect
the full range of situations. This theory therefore needs to be filled with
more observational and experimental data. Various emerging topics can be
highlighted.
No data sets were used in this article.
The supplement related to this article is available online at:
YK and KZ contributed equally to writing the paper.
The authors declare that they have no conflict of interest.
This paper is devoted to the 90th anniversary of Felix I. Kozlovskii – eminent pedologist and geo-ecologist, who introduced the theory of agropedogenesis more than 30 years ago and was the first to suggest the concept of attractors of soil degradation. We are very thankful to Sergey Goryachkin for very helpful critical suggestions to the first version of the concept.
This open-access publication was funded by the University of Göttingen.
This paper was edited by Jianming Xu and reviewed by Rouholla Taghizade and one anonymous referee.