Agriculture Reference
In-Depth Information
6
Soil Formation
Marty Goldhaber* and Steven A. Banwart
Essentially, all life depends upon the soil . . . There can be no life without soil and no soil
without life; they have evolved together.
USDA Yearbook of Agriculture (1938) by Charles E. Kellogg
Abstract
Soil formation reflects the complex interaction of many factors, among the most important of which
are (i) the nature of the soil parent material, (ii) regional climate, (iii) organisms, including humans,
(iv) topography and (v) time. These processes operate in Earth's critical zone; the thin veneer of our
planet where rock meets life. Understanding the operation of these soil-forming factors requires an
interdisciplinary approach and is a necessary predicate to charactering soil processes and functions,
mitigating soil degradation and adapting soil management to environmental change. In this chapter,
we discuss how these soil-forming factors operate both singly and in concert in natural and human
modified environments. We emphasize the role that soil organic matter plays in these processes to
provide context for understanding the benefits that it bestows on humanity.
Introduction
held in terrestrial vegetation. For these reasons,
the behaviour of soil organic matter during
soil formation and erosion is an important
topic at all scales, from local to global. In
this paper, soil organic carbon (C org ) will be
taken as a proxy for organic matter, unless
specified otherwise.
We approach the subject of soil formation
with a broad perspective rooted in geology.
The reason is that soil formation is a reflection
of processes occurring over a greater vertical
interval of Earth's near surface, rather than the
soil profile itself. In fact, soils are nested within
Earth's critical zone (CZ), which represents
In this paper, we examine the processes of
soil formation, emphasizing factors that in-
fluence or are influenced by the organic matter.
Soil organic matter is crucial to the func-
tioning of natural and managed ecosystems.
It is also a significant component of the glo-
bal carbon (C) budget. Excluding carbonate
rocks, it represents about 1500 Gt C in the
top 1 m, and possibly another 900 Gt C at a
depth of 1-2 m (e.g. Batjes, 1996). This mass
is approximately twice that of the carbon held
in the atmosphere and three times the amount
 
 
 
 
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