Why soil — and soil science — matters. millennium essay. NATURE| VOL 407 | 21 SEPTEMBER 2000 | www.nature.com 301

Posted by Dan H. Yaalon 18 Dec 2000 11:37:40

Dan H. Yaalon
Many ancient religions recognized
the importance of soils, and their
customs evolved into a spiritual
attachment to the life-giving Earth. But
surprisingly, ancient and classical scholars
did not study the nature of soil. Early scien-tists
also ignored it. For instance, the
famous naturalist Alexander von Humboldt
(1769–1859), a founder of plant geography,
never compared the soils of the several con-tinents
on which he studied the distribution
of plant species. This attitude still crops up
frequently. The Fontana History of the Envi-ronmental
Sciences (1992) contains no men-tion
of soils as a branch of environmental
science, although other Earth sciences are
included. Is soil just dirt, too commonplace
for mention or study?
I am a pedologist — an Earth scientist
focusing on the origin and distribution of
soils in relation to the history of landscapes.
We have much to learn about non-arable
soils, and must try to integrate our knowl-edge
into a holistic view of the Earth’s
dynamics and biogeochemical transforma-tions.
Soils are economically and socially
important. They can even have beauty: the
soil scientist Hans Jenny (1899–1992) was
enchanted by the soils depicted in paintings.
To paraphrase Leonardo da Vinci: why do
we know more about distant celestial ob-jects
than we do about the ground beneath
our feet?
New ideas about the nature and origin of
soils emerged only in the second half of the
nineteenth century. V. V. Dokuchaev (1846–
1903) and E. W. Hilgard (1833–1916), both
mineralogists and chemists by training, rec-ognized
in their soil surveys that climate,
vegetation and substrate were all important,
and saw the importance of soil horizonation
— the development of different layers of
soil parallel to the surface — in representing
and elucidating a landscape’s history.
Dokuchaev had imperial backing in Russia,
and several distinguished followers; Hilgard,
although a respected university professor in
the United States, was not favoured by the
establishment. An opportunity to promote
his ideas was lost when J. W. Powell and he
failed to establish a geological–agricultural
(soil) survey in the US Geological Survey.
Language barriers hindered communication
between soil scientists, and the spread of
knowledge was painfully slow, even after the
new Russian pedogenetic ideas were present-ed
at world exhibitions and translated.
Gradually, topographical and biological
effects, and the duration of soil-formation
processes were all recognized as equally
important factors in soil evolution. It took
more than one generation before C. F. Mar-but
(1863–1935) included the concepts of
external and internal environmental effects
on pedogenesis in the influential US Depart-ment
of Agriculture soil survey, established
by Milton Whitney in 1899. When Jenny
submitted his now-classic book on the ‘five
soil-forming factors’ and the quantitative
approach to single-factor soil-forming func-tions,
it was at first rejected for publication. It
took five years before the book was eventual-ly
published in 1941.
The importance of soils as a life-support
system and in the production of food and
fibre was duly recognized. There were spec-
tacular achievements, helping to feed the
ever-growing population. Nowadays, most
of the 50,000 soil scientists work in agro-nomic
institutes, studying the composition
and dynamics of soils in ever greater detail.
Yet less than 5% of the global agricultural
research budget goes on soil research.
The use of soils in road building,
construction, ceramics and the cement and
aluminium industries is another area where
a basic knowledge of soil and landscapes is
important. Technological institutes pro-mote
this study, which is anchored in ancient
practical applications.
Soils teem with life. The Nobel laureate
Selman Waksman (1888–1973) isolated
streptomycin from soil biota, and the preser-vation
of pedodiversity and biodiversity may
aid similar research in the future. Also, it
seems plausible that biological evolution was
influenced and constrained by the properties
of the soil environment, an attractive field of
unexplored research. For Earth scientists,
ancient and buried soils are one of the better
proxies for reconstructing past climate and
the development of the landscape.
But it is as the transformer, regulator,
buffer and filter of water, nutrients and
other dissolved and dispersed compounds
that soils are most important to humankind
— a focal and connecting link between
the biogeochemical cycles of the Earth and
the dynamic atmospheric system. In the
conceptual wiring diagram of the Interna-tional
Geosphere–Biosphere Program the
soil system, especially its carbon dynamics,
is the central link between the physical
climate and biogeochemical systems. It is
therefore a major route to understanding
and predicting the effects of human actions
on the Earth.

Dan H. Yaalon is at the Institute of Earth Sciences,
Hebrew University, Givat Ram Campus,
Jerusalem 91904, Israel.

Attachment: See also Nature