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.
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.