By Dr. Mohammed Sa’id Berigari,
Senior Soil and Environmental Scientist, USA, 04/22/2012
The US suffered major dust storms,
causing loss of great quantities of topsoil and human lives 75 years ago when
the Soil Science Society of America was established. These catastrophic events created public
awareness that soils are essential to the well-being of the society and led to founding
Soil Conservation service. Farmers were
enticed to implement erosion control practices at a time when many soil
processes were still poorly understood.
In this paper an argument is presented that the current status of soils
worldwide parallels that of the United States 75 years ago. In spite of remarkable progress in our
understanding of soil processes during the last few decades, many aspects of
soils still remain unanswered that need refocused research. Pointing out these persistent “islands of
ignorance” would be very helpful in alerting public opinion about the
importance of soils, enticing more students to study soils, and influencing
policy –making relative to soil degradation and conservation worldwide.
1. Soils
Impacts on Society
Dust bowls also occurred in the last
decade in other parts of the world far from the US. A vivid example is the dust
bowls occurred in China in the northwestern provinces of Inner Mongolia, Gansu,
Ningxia, Qinghai, and Xinjiang that plowed great areas of marginal lands. And those provinces were additionally suffering from overplowing
and overgrazing the lands after 1994, when the Chinese Government decided to
require that all cropland used for construction be offset by land reclaimed
elsewhere(Yang and Li, 2000). Inner
Mongolia led a 22% cropland expansion.
Moreover, following economic reforms of 1978, livestock population in
the region grew rapidly, often far above the land’s carrying capacity. A direct
result of these two trends is that soils have deteriorated, wind erosion
intensified, and once seldom, seasonal dust storms became a far more common
events. In April 2001, one of the worst
dust storms hit Beijing and then moved eastward, eventually blanketing areas
from Canada to Arizona with a layer of dust. Other dust storms have continued
since. On March 20/2010 another massive
sandstorm went from arid lands of Inner Mongolia to China. The yellow dust reduced visibility and air quality
to harmful levels in Beijin, the nation’s capital, delaying flights at Beijing’s
Airport and creating a dust warning in Seoul, before reaching Taiwan and Japan.
The wide spread dust storms in Australia,
Africa, and China and other parts of Asia are clear manifestation of worldwide
soil erosion. The frequent brown plumes
at estuaries, where sediment –laden river waters enter oceans, are unmistakable
displays of grand -scale soil erosion. Yet, as Montgomery (2007) pointed out soil
erosion is far more widespread than that just mentioned above. He estimated
that we are now losing about 1% of topsoil per year to soil erosion, most of it
caused by agriculture. The evidence
exists everywhere that we are skinning the earth. We see that in the brown streams running from
construction sites and in sediments-choked rivers downstream from clear cut
forests. We see it where farmers’
tractors detour around gullies, where mountain bikes jump with deep channels carved
into dirt roads, and where new suburbs and strip malls pave fertile lands. And if it gets worse than it is now, it could
periodically interrupt air transportation, cause major health problems, or halt
navigation in many rivers.
2. Soils
Relation to World Food Security
We know very well that soils and food
production are irrevocably connected and each country strives to secure food
for its population. For example, a number of countries in Asia and the Middle
East faced with food supply problems in the coming years have in the last
decade initiated major programs to purchase vast areas of land in Africa and
Latin America. The “land grab” of unparalleled
proportions have been studied very little in the academic literature (Robertson,
and Pinstrup-Andesen, 2010).
Nevertheless,
it is clear that a number of relatively” land-rich” developing nations are
sanctioning the sale or transfer of user rights of large areas (some time
million of hectares) for foreign investments.
Smallholder farmers, without formal land titles currently occupy much of
the land leased or sold in these transactions, threaten the internal food
security of the seller state. A greater
concern is that this land grab, especially when put under intensive agriculture
practices in countries like Sudan, Algeria, Madagascar or Egypt where water
availability may be an important issue, will lead to the same type of soil
degradation that occurred in northwestern China in the past decade and that
will see more dust bowls in the future, with local starvation, population
migration, and compromised national and international security.
From a resource point view, recognizing
that water is as important to crop production if not more important than soil
material in which crops use as medium of their growth and that water will be
scarce in many parts of the world in the coming years. Therefore, it makes sense to produce food
where water is. With the exception of
few countries, like Brazil, that are blessed with abundant water supplies, in
general the requirement to go where the water is would force us to turn to the
oceans, which covers 71% of the earth’s surface and contains 97% of the planet’s
water. Roughly 66% of the world population live in coastal regions around the
world, so that obtaining food and energy from the oceans would not create
logistic problems. Furthermore, Japan has shown, for centuries, that it is
possible to derive considerable quantities of food from oceans. Various seaweed, sea vegetables, and
countless fish products often not consumed in other countries, find their way
in the daily diet of the Japanese people.
Other countries can do the same as
Japan in harvesting the oceans, if not for human food, at least for animal
feeds or sea crops that could be converted to biofuels. If this trend toward seafarming materializes
then soils that are subject to erosion and degradation worldwide could be
reforested to a far greater extent than at present or could be put under
natural vegetation. When soil
degradation is significantly reduced that would alleviate some of the problems
discussed earlier including to a large extent (except permafrost soils) the
possible positive feedback of soils to climate change.
3. Soils
Significance in the Climate Change
Another area by which soils profoundly can affect society is related to
global climate change where they play major roles in the carbon cycles. Worldwide soils contain more than 1,550 Pg
(Peta gram) carbon in the top one meter alone (Baveye, 2007) which is more than
twice the quantity of carbon in the atmosphere.
That is soils contain 300 times the amount of carbon currently released globally
per year from burning fossil fuels. Additionally,
in many soils, soil organic matter contains large quantities of nitrogen that
are metabolized by microorganisms, thus, can also contribute significantly to
emissions of greenhouse gases. Therefore,
even small changes < 1% in the amount of soil carbon may lead to sources of
greenhouse gases that could be significant relative to those emitted by fossil
fuel combustion ( Rostand et al., 2000).
Enhanced release of carbon by world soils could drastically exacerbate
CO2 levels in the atmosphere leading to fast global warming and
ultimately to a positive feedback mechanism that might cause climate change to
get out of hand (Baveye, 2007).
It is uncertain whether soils in
temperate and tropical regions are likely to be net sources of greenhouse
gases. Only in the high latitude
permafrost, especially in Siberia, where the picture is clearly in favor of
positive feedback to climate warming.
Siberia with an area of 106 km2 has deep up to 90
m deposits of organic-rich frozen loess that accumulated during the
Pleistocene. That large organic carbon
pool (about 450 Pg, more than half the amount of carbon in the atmosphere) has
not been considered generally in most global carbon inventories (Zimov et al.,
2006). Similar less extensive deposits exist
in Alaska, where recent evidence indicates that permafrost is thawing at a much
faster rate than previously expected.
The organic carbon in these soils decomposes rapidly upon thawing and
releases CO2 gas to the atmosphere. Concurrently methane gas
entrapped as large bubbles in the permafrost is released so fast that it
prevents the surface from freezing, even during middle of winter (Walter et
al., 2006). Methane is 18 to 25 times
more potent as a gas than CO2, thus, its release by permafrost is
significant at least in short terms until CH4 is transformed into CO2
upon oxidation.
4. Soil
Pollution in Urban Areas
The world population has become
increasingly urbanized. On the average
more than 50% of people live in urban and suburban areas and this number is
constantly increasing. In many cases, a
consequence of this trend is that cities are expanding into their
industrialized outskirts, where researchers have found soils are routinely
contaminated with various organic and inorganic compounds. Even in the traditional city centers, soils
are contaminated often significantly with pollutants such as lead from paint
and gasoline or polyaromatic hydrocarbons from vehicle exhausts or coal-fired
power plant emissions (Belluk et al., 2003; Morillo et al., 2007). Recently the public in general has become
more aware of potential problems associated with contaminant levels in urban
soils, partly because they are likely to affect children more directly, given
the tendency of toddlers and infants to ingest considerable amounts of soils through
hand-to-mouth transfer when playing in public parks. In a number of cities in the US and Europe ,
parent associations have voiced serious concerns about financially motivated
construction of day- care facilities and schools on former brownfields. Even though soils at these sites may have
been considered “clean” (i.e., with contaminant concentrations less than
regularity limits) at the time when the building were erected, reports of
noticeable emanations of volatile organic chemicals are causing parental
concerns over their children’s exposure to chemicals that could affect their
well-being and cognitive development (Weber, 2011).
5. Soil
Biota Metabolism Underestimation
The best example for how ignorant we
still are about many soil processes is the failure of the Biosphere II
experiment in Arizona, USA, more than 18 years ago. Initially planned as an attempt to create a
balanced and self-sustaining replica of Earth’s ecosystems, however, by September 26,
1993 it became clear that the $200 million experiment failed to meet many of its
objectives. Particularly, the 25 small
vertebrates with which the project started, only six did not die out by the end
of the mission. Almost all the insect
species became instinct, including those that had been selected for pollinating
plants.
What
really led to the failure of the project was the fact that oxygen levels in the
air could not be sustained at appropriate concentrations. There were several reasons for that, but the
key ones, was the O2 consumption by soil microorganisms had been
grossly underestimated by the scientists involved. Specifically, in the
rainforest and savanna areas of Biosphere II, soils were rich in organic matte
(O.M.). Microbes metabolized O.M. at an unexpectedly
high rate, in the process using up a lot of O2 and producing
significant quantities of CO2. Before 18 months into the experiment, the O2
levels dropped to the point where the crew could hardly function, oxygen had to
be pumped into the system so that crew members could complete the two-year
mission as planned.
6. Soils
Remarkable Biodiversity
Soils in general contain huge and
diverse populations of microorganisms, thus, constitute a formidable challenge
to anyone trying to understand soil
processes, many of which one way or another are mediated by, or at the very least
involve microorganisms. The identity of
most of these microorganisms, however, remains a challenging frontier. It is estimated that 99.5% of organisms in
soils have not been cultivated. Some experts in the field admit that it will be
necessary in the near future to “develop and apply new approaches to cultivate
the previously uncultivated and rare members of the soil community to assign
functions to the vast number of unknown or hypothetical genes that will
undoubtedly be found”. Soils will remain most extensive natural
biological laboratories where they host an immense number of microbes that
carry out an array of degradations including some of most complex compounds
added to soils. The soil biodiversity challenge, therefore,
still remains intact and in certain ways has grown.
7. Soils
Contribution to Carbon Sequestration.
Considerable uncertainty persists
regarding the practical conditions under which carbon sequestration in soils
could be feasible. Sequestration of carbon in soils is often seen as “win win”
situation to offset a substantial portion of anthropic CO2
emissions. However, over the last decade, many studies have demonstrated, time
and again, that the simple addition of easily biodegradable carbon sources, or
even some plant litter to soils as a way
to enhance sequestration, could seriously backfire and actually lead to decreases
in soil carbon.
The initial O.M. and moisture contents of the
soil within plow layer, soil texture, the C:N ratio of the added organic
substance, and the soil and air temperatures are important parameters in biodegradation of any organic material added
to soils, consequently a net gain or
loss of soil carbon. Soil organic matter
is more likely to accumulates (carbon sequestration) in heavy textured soils
with grass cover in wet, and cool environment.
For some time the adoption of
no-tillage agriculture was thought to be a realistic practice for sequestration
of carbon in soils. However, the
effectiveness of such practice depends heavily on how deep one is willing to
monitor soil organic matter changes. When
one samples deeper in the soil profile than the traditional 30-40 cm, the
alleged advantage of no-tillage over conventional tillage relative to carbon
sequestration disappears or even reversed in some cases.
8. Soil Micro- Hetero geniety Properties
Researchers in the last few years
recognized that the physical and chemical microenvironment in which
microorganisms proliferate and actively function in soils are extremely
heterogeneous at all spatial scales, in particular at the micrometric scale
typical of many microorganisms.
Recent technological progresses have
provided researchers with sophisticated equipment to observe the geometry of
pores and solids in soils at resolutions as small as 0.5 µm and to observations
of sharp differences in accumulation of trace metals and chemical composition
of organic matter in soils over minute distances in the order of nanometers to
micrometers respectively. Further
advances in thin sections of soils has led to comparisons between explicit pore
scale simulations and macroscopic continuum approximations that revealed
inhomogeneous solute distribution within soil pores which markedly affect
macroscopic estimates of elemental turnover rates and that the error associated
with large-scale rate estimates to depend on the type of reaction, pore
geometry, reaction kinetics, and macroscopic concentration gradient.
These experimental and modeling results
pose a number of questions about the validity of the bulk-averaged measurements
of soil chemical and biochemical properties, that are routinely carried out in
wet-chemistry or microbiological laboratories worldwide and on which current
models of C and N dynamics in soil are based.
Other questions that wait adequate answers relate to the type of
measurement that should be performed, beside macroscopic averages and to the
proper way of reflecting the macroscopic emergence of microscale
heterogeneities of soil dynamics.
9. Soils Are Still a Crucial Frontier of Applied Science: Why not?
The ample examples presented in the
previous sections demonstrated that soils continue to be critical to the
survival of human societies. Even if
floating cities ever develop, as some architects envision, most human
population will still be in close contact with soils on a daily basis. Soils also, remain, for the most part, very
poorly understood, and research to improve
that picture will be challenging in the foreseeable future. As Montgomery (2007) put it” soils are our
most underappreciated, least valued and yet essential natural resource”
Another reason for arguing the case
that soils are a critical frontier of science is that to do so will require
researchers to publicize the fact that there are still many aspects of soils
that remain extremely controversial. The soil science community in the past has
not been keen to advertize its case to the public in large about vast areas of
soils that need intensive research to unravel their mysteries as they still
exist in the 21 st Century.
Soils will remain the backbone of human
survival as they did at the dawn of land cultivation to this day and beyond.
Note:
This article is extracted in a condensed form from its modified version
in the reference listed below. The details of cited references appeared only in
the original paper consisting of five page- list when published in 2011 in the
Soil Sci.Soc.Amer.J. 75(6): 2037-2048 and could be viewed at: www.soils.org/publications/sssa/tocs/75/6.
Reference
Baveye, P.C.; D.Rangel; A.R.Jacobson;
M. Laba; C. Darnault; W.Otten; R.Radulovich; and F.A.O.Camargo. 2011. From dust bowl to dust bowl: Soils still a frontier of science. CSA (Crops, Soils, Agronomy) news of Crop
Sci.Soc. Amer., Soil Sci.Soc.Amer. and Amer.Soc. Agron: 5-11.
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