Winston Churchill
1
Democracy is messy—parties battle for control, and who wins shifts over time
and location. Different parties may dominate at local, regional, and national scales
and on different issues. Yet, coherent patterns can sometimes emerge from the chaos.
Democracy, then, is a lot like soil.
In soil, coherent patterns emerge from the interchange among the “parties,” but
soil doesn’t have two parties, but three: microbes, minerals, and organic molecules;
these battle for control over the biogeochemical functioning of the overall system.
Each will dominate in some situations, be irrelevant in others, and work in concert
with one or both of the others in yet other situations and on particular processes.
The final element of the “political” system that drives our Democracy of Dirt is
the media,
2 which regulate interactions among the components—the flows of material and information. In soil, the essential medium, however, is not newspapers or the
Internet, but moisture (Kleber et al. 2015). Water carries materials as it flows through
soil and, even when static, allows dissolved materials to diffuse. As a solvent, water
regulates dissolution and precipitation and so controls mineral weathering and soil
development (e.g., Slessarev et al. 2016). Water is also an essential resource that
controls the activity of microbes (Schimel 2018). Additionally, while metabolic
waste products are small and often volatile (e.g., CO 2 , CH 4 , N 2 O, NH 3 , ethanol,
etc.), most substrate molecules are larger and often more complex; they are usually
nonvolatile and rely on water to make them accessible to microbes—solubility is a
key control over a chemical’s availability (Schimel and Schaeffer 2012).
Soil science, as an academic discipline, is about understanding these complex,
intertwined, dynamics. Yet, just as political scientists may focus their attention on
only one aspect of the overall political system, becoming expert in local politics or
the history of a single political party, so too, is it with soil scientists. Although our
ultimate goal may be to understand the integrated system that is soil, most scholars
specialize, focusing on specific components (e.g., soil biology or chemistry). As a
result, we struggle to understand the integrated system and how components shift in
their role at particular levels of organization and scales of time. For example,
microbial community composition may drive the short-term decomposition of litter
and its conversion into soil organic matter (SOM), but over millennia the fate of that
SOM is largely a function of mineral interactions that stabilize the molecules by
making it inaccessible to microbial attack (Grandy and Neff 2008; Falconer et al.
2015; Schmidt et al. 2011).
The final thing to consider in developing an integrated understanding of soil
function is the tools we use to represent, integrate, and portray that understanding—
how do we model soils? The Oxford English Dictionary includes this definition of a
model: “A simplified or idealized description or conception of a particular system.”
1 Churchill offered this famous quote in the House of Commons in 1947, but he ascribed to others:
“It has been said. . .”
2 OED: II. A person or thing which acts as an intermediary. a. An intermediate agency, instrument,
or channel; a means; esp. a means or channel of communication or expression.
90
J. Schimel
1
Democracy is messy—parties battle for control, and who wins shifts over time
and location. Different parties may dominate at local, regional, and national scales
and on different issues. Yet, coherent patterns can sometimes emerge from the chaos.
Democracy, then, is a lot like soil.
In soil, coherent patterns emerge from the interchange among the “parties,” but
soil doesn’t have two parties, but three: microbes, minerals, and organic molecules;
these battle for control over the biogeochemical functioning of the overall system.
Each will dominate in some situations, be irrelevant in others, and work in concert
with one or both of the others in yet other situations and on particular processes.
The final element of the “political” system that drives our Democracy of Dirt is
the media,
2 which regulate interactions among the components—the flows of material and information. In soil, the essential medium, however, is not newspapers or the
Internet, but moisture (Kleber et al. 2015). Water carries materials as it flows through
soil and, even when static, allows dissolved materials to diffuse. As a solvent, water
regulates dissolution and precipitation and so controls mineral weathering and soil
development (e.g., Slessarev et al. 2016). Water is also an essential resource that
controls the activity of microbes (Schimel 2018). Additionally, while metabolic
waste products are small and often volatile (e.g., CO 2 , CH 4 , N 2 O, NH 3 , ethanol,
etc.), most substrate molecules are larger and often more complex; they are usually
nonvolatile and rely on water to make them accessible to microbes—solubility is a
key control over a chemical’s availability (Schimel and Schaeffer 2012).
Soil science, as an academic discipline, is about understanding these complex,
intertwined, dynamics. Yet, just as political scientists may focus their attention on
only one aspect of the overall political system, becoming expert in local politics or
the history of a single political party, so too, is it with soil scientists. Although our
ultimate goal may be to understand the integrated system that is soil, most scholars
specialize, focusing on specific components (e.g., soil biology or chemistry). As a
result, we struggle to understand the integrated system and how components shift in
their role at particular levels of organization and scales of time. For example,
microbial community composition may drive the short-term decomposition of litter
and its conversion into soil organic matter (SOM), but over millennia the fate of that
SOM is largely a function of mineral interactions that stabilize the molecules by
making it inaccessible to microbial attack (Grandy and Neff 2008; Falconer et al.
2015; Schmidt et al. 2011).
The final thing to consider in developing an integrated understanding of soil
function is the tools we use to represent, integrate, and portray that understanding—
how do we model soils? The Oxford English Dictionary includes this definition of a
model: “A simplified or idealized description or conception of a particular system.”
1 Churchill offered this famous quote in the House of Commons in 1947, but he ascribed to others:
“It has been said. . .”
2 OED: II. A person or thing which acts as an intermediary. a. An intermediate agency, instrument,
or channel; a means; esp. a means or channel of communication or expression.
90
J. Schimel