Marginality Principle - Principles of Sustainable Soil Management in Agroecosystems - page 23

decreases by 10% and leaching or runoff increases, is that sufficient to consider this soil
as marginal? These are very complex questions that need to be addressed as we consider
how to best manage soil, address issues of marginality, and increase soils' functional
value to society.
One dilemma we face is that agricultural productivity in many areas of the world con-
tinues to increase, and we assume that soil function has continued to improve. However,
we suggest that although our crop production has increased, this has come at the expense
of a degraded soil resource. We are at the tipping point of being unable to sustain these
increases unless we recognize that human activities can create marginal soils and, more
importantly, have the capacity to reverse the trend of soil degradation. In this chapter, we
first discuss the second question, what constitutes the loss of optimal functioning, and
what criteria move a quality soil into marginality. Our findings are then used to address
the first question, how society values soil functions, and how it influences land manag-
ers' and public policy makers' definition of marginality and willingness and capacities to
protect soil quality. Future ability of agriculture to provide multifunctional roles—pro-
duction of food, fuel, fiber, and livelihoods as well as a suite of ecosystem services—
depends upon the quality of the soil resource (Hatfield 2006).
2.2 DIMENSIONS OF MARGINALITY
Marginality is an integrative principle that implies a transition from an optimum state
to a less optimum state. However, values of marginality depend upon the potential
use of the soil resource. If we consider marginality from a scientific viewpoint, then
the capability classification provides a structure for assigning a value to marginality
because there would be less productivity from a soil that moved from an optimal to
less than optimal state. The classification definitions in Table 2.1 reveal a coupling of
different soils with human use and practices reflecting the meaning of marginality
as socially constructed based on societal values for the different functions of soil.
This is particularly important since it also implies that human intervention to better
manage soil to accomplish preferred uses can be successful and is a reminder that the
norms of which soil functions are valued can shift over time.
The path a specific soil has in moving between capability classes and soil degra-
dation offers a framework from which to assess changes in the soil and movement
toward or away from marginality. Evaluation of soil traits and functions associated
with optimum states provides an experimental structure for quantifying soil degra-
dation or soil aggradation.
2.3 SOIL DEGRADATION AND LOSS OF SOIL FUNCTION
Soil degradation represents the changes in soil that reduce its capability to function.
Lal et al. (2004) documented the degradation process and how this is set in motion by
a combination of human and natural perturbations. Conceptually, soil degradation is
the shifting of soil functionality from an optimal state to a less optimal state based on
soil water holding capacity as a function of soil organic matter (SOM), as described by
Hudson (1994). This can be seen as we look across the landscape and view soils of dif-
ferent colors, indicative of a reduced SOM content in the surface ( Figure 2.3 ).