Soil Carbon Transition Curves: Reversal of Land Degradation through Management of Soil Organic Matter for Multiple Benefits - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 27

Introduction

that the interactions that may occur can re-
sult in synergies or trade-offs. There are
many examples of good carbon manage-
ment at the local scale for food, fibre and
energy production (Chapters 22 and 23, this
volume). However, in order to improve land
management for greater carbon storage, we
need to know better how these processes
leading to benefits are aligned.
Our hypothesis is that there is a general
set of local-global feedback processes that
influence and depend on soil carbon stocks
and that occur along a chain of impact be-
tween local and global scales. We argue that
there is an evolutionary pathway of soil
utilization by humanity at local scales that -
although differing in detail from place to
place - has had a commonality over much
of our history since the dawn of agriculture.
This pathway, driven by increasing biomass
production and intensity of land use, has re-
sulted in a loss of soil organic matter, nutri-
ent and water retention and decreases in
productivity. This pathway of soil degrad-
ation has global implications for food secur-
ity, climate change, biodiversity, water qual-
ity and biofuel production for energy security
for the entire planet, and is a common thread
that links soil processes at all scales. The
variable that is a dominant control and inte-
grates the impacts of environmental change
across all of the soil functions is the organic
carbon content in the soil. We now know
how to manipulate the delivery of soil func-
tions through improved agroecological prac-
tices. Manipulation occurs through methods
that will enhance soil carbon and the result-
ing benefits it accrues. These benefits
include greater food production, due to in-
creased nutrient availability in soil organic
matter, and buffering of water and nutrients,
which generally supports terrestrial ecosys-
tem productivity, increased organic carbon
sequestration and greenhouse gas mitiga-
tion (Minasny et al ., 2011; Chapter 1, this
volume).
We explain the evolutionary pathways
of local land management as a series of soil
carbon transition curves showing local and
global implications for soil functions and
ecosystem services. The local and global de-
cisions and consequences are subsequently

Soils are - literally and figuratively - the
foundation of civilization (Janzen et al .,
2011). We derive benefits from soils that are
essential for humankind and human devel-
opment (Chapter 14, this volume). One of
these benefits is the production of food of
the type, quality and quantity to feed a glo-
bal population that will exceed 9 billion by
2050 (UN, 2011). A key question facing hu-
manity is whether the quality and health of
our planet's soils can be preserved while
providing adequate food for this growing
population (Lal and Stewart, 2012). Food
production through crops and livestock can
(but does not have to) lead to soil degrad-
ation, such as compaction, erosion, loss of
nutrients and organic matter - depending
on soil type and management (Chapters 10,
17 and 21, this volume). In addition, there
are growing demands for land for various
non-agricultural uses, such as urban expan-
sion and soil sealing associated with infra-
structure development. Moreover, biofuel
demands will compete with food produc-
tion for the most productive lands, espe-
cially with potential incentives for substi-
tuting fossil fuels by biofuels as a policy
measure to mitigate climate change and ease
energy security risks (Rajagopal et al ., 2007;
Reilly et al ., 2013).
Soil formation involves the accumula-
tion, over long periods, of organic carbon,
which can be depleted rapidly by various
processes (Victoria et al ., 2012). It can be re-
leased in the atmosphere as gaseous carbon
dioxide (CO 2 ), leaching of soluble organic
compounds and lost by wind or water ero-
sion (Amundson, 2001; Chapters 6 and 13,
this volume). These mass transformation
and transport processes occur at field and
watershed scales, but are also key compo-
nents of the global cycling of carbon and nu-
trients. Benefits, such as food production
and food security, that are linked both lo-
cally and globally to soil processes, include
supporting biodiversity, maintaining water
quality and contributing to (bio)energy se-
curity (Chapter 23, this volume). They illus-
trate not only the connection between local
processes and global mass fluxes but also