Reviews and syntheses: Agropedogenesis – humankind as the sixth soil-forming factor and attractors of agricultural soil degradation

Abstract

Abstract. Agricultural land covers 5.1×109 ha (ca. 50 % of potentially suitable land area), and agriculture has immense effects on soil formation and degradation. Although we have an advanced mechanistic understanding of individual degradation processes of soils under agricultural use, general concepts of agropedogenesis are absent. A unifying theory of soil development under agricultural practices, of agropedogenesis, is urgently needed. We introduce a theory of anthropedogenesis – soil development under the main factor “humankind” – the sixth factor of soil formation, and deepen it to encompass agropedogenesis as the most important direction of anthropedogenesis. The developed theory of agropedogenesis consists of (1) broadening the classical concept of factors→processes→properties→functions along with their feedbacks to the processes, (2) a new concept of attractors of soil degradation, (3) selection and analysis of master soil properties, (4) analysis of phase diagrams of master soil properties to identify thresholds and stages of soil degradation, and, finally, (5) a definition of the multidimensional attractor space of agropedogenesis. The main feature of anthropedogenesis is the narrowing of soil development to only one function (e.g. crop production for agropedogenesis), and this function is becoming the main soil-forming factor. The focus on only one function and the disregard of other functions inevitably lead to soil degradation. We show that the factor humankind dominates over the effects of the five natural soil-forming factors and that agropedogenesis is therefore much faster than natural soil formation. The direction of agropedogenesis is largely opposite to that of natural soil development and is thus usually associated with soil degradation. In contrast to natural pedogenesis leading to divergence of soil properties, agropedogenesis leads to their convergence because of the efforts to optimize conditions for crop production. Agricultural practices lead soil development toward a quasi-steady state with a predefined range of measured properties – attractors (an attractor is a minimal or maximal value of a soil property toward which the property will develop via long-term intensive agricultural use from any natural state). Based on phase diagrams and expert knowledge, we define a set of “master properties” (bulk density and macroaggregates, soil organic matter content, C:N ratio, pH and electrical conductivity – EC, microbial biomass and basal respiration) as well as soil depth (A and B horizons). These master properties are especially sensitive to land use and determine the other properties during agropedogenesis. Phase diagrams of master soil properties help identify thresholds and stages of soil degradation, each of which is characterized by one dominating process. Combining individual attractors in a multidimensional attractor space enables predicting the trajectory and the final state of agrogenic soil development and developing measures to combat soil degradation. In conclusion, the suggested new theory of anthro- and agropedogenesis is a prerequisite for merging various degradation processes into a general view and for understanding the functions of humankind not only as the sixth soil-forming factor but also as an ecosystem engineer optimizing its environment to fulfil a few desired functions.

Agricultural acceleration of soil carbonate weathering

“…Our goal was to compare deep SIC storage and dynamics based on carbon isotopes under paired land uses to see whether this supposedly stable pool of carbon may respond to land‐use‐induced changes in soil water fluxes at decadal timescales, potentially forcing soils across the threshold between net carbonate accumulation and loss (Chadwick & Chorover, 2001). In this framework, anthropogenic activities such as farming act as a sixth state factor dictating soil formation (Kuzyakov & Zamanian, 2019; Richter Jr., 2007). Water flux and acid–base reactions are primary determinants of whether weathering products (in our case, dissolved carbonate) are retained or flushed (Equation 1).…”

Variations in soil nutrient dynamics and bacterial communities in long-term tea monoculture production systems

“…Another explanation is that greater nutrient availability like C and N in the soil could subsequently strengthen microbial interactions in order to enhance the efficiency of resource turnover that benefits tea growth (Shi et al, 2016;Zhao et al, 2019). Lastly, according to the topological characteristic analysis, long-term tea monoculture and agropedogenesis reduced betweeness centralization and the links of key bacterial taxa in the networks, which could partially contribute to the tightening of soil bacterial associations in tea plantation (Kuzyakov and Zamanian, 2019).…”

Soil Water Retention and Soil Compaction Assessment in a Regional-Scale Strategy to Improve Climate Change Adaptation of Agriculture in Navarre, Spain

“…At the same time, changes in soil cover and management associated to the intensification of agricultural production, and the increasing demand for natural resources, increase anthropogenic pressure affecting soil properties and leading to soil degradation processes [13]. Understanding alterations in soil properties over time of cultivation, such as the increase in the soil bulk density (BD), the disruption of soil aggregates, or alterations in pores distribution that may affect soil water dynamics [14,15], have been the object of attention for years by researchers, policymakers and farmers focusing on developing soil degradation control strategies [16,17]. These strategies should consider not only their potential impact on soil conservation, but also the need for maintaining agricultural yields and, if possible, mitigating the effects of climate change on land degradation [18].…”