Soil Degradation: Global Assessment

Table of Contents:

Introduction..................................................................................................199

Selim Kapur

University of Qukurova

Erhan Akga

Adiyaman University

Introduction

Background...................................................................................................199

Europe • Asia • Africa • Central and South America • North America • Australia

Conclusions...................................................................................................208

References......................................................................................................209

One of the major challenges that humanity will face in the coming decades is the need to increase food production to cope with the ever-increasing population, which is indeed the greatest threat for food/ soil security.111 The worldwide loss of 12 million hectares (ha) of agricultural land per year was reflected in the average annual loss up to €38 billion for EU25,|2) in spite of the strict laws for environmental protection enacted there. This is the unpalatable but important indicator of a steady decline in agricultural production and increase in soil damage, reflecting the “impaired productivity” in a quarter of the world’s agricultural land/3-51

Background

Soil can degrade without actually eroding. It can lose its nutrients and soil biota and can become damaged by waterlogging and compaction. Erosion is only the most visible part of degradation, where the forces of gravity, water flow, or wind actively remove soil particles.

Rather than taking the classical view that soil degradation was, is, and will remain an ongoing process, mainly found in countries of the developing world, this phenomenon should be seen as a worldwide process that occurs at different scales and different time frames in different regions. The causes of biophysical and chemical soil degradations are enhanced by socioeconomic interventions, which are the main anthropogenic components of this problem, together with agricultural mismanagement, overgrazing, deforestation, overexploitation, and pollution as reiterated by Lai,161 UNEP/ISRIC,171 Lai,181 Eswaran & Reich,191 Eswaran et al.,1101 Kapur et al.,ln| and Cangir et al.,1121 as the main reasons for erosion and chemical soil degradation.

Soil degradation, the threat to “soil security,” is ubiquitous across the globe in its various forms and at varying magnitudes, depending on the specific demands of people and the inexorably increasing pressures on land. Europe provides many telling examples of the fragile nature of soil security and the destructive consequences of a wide range of soil degradation processes. Asia, Africa, and South and

North America are not only partly affected by the nonresilient impacts of soil degradation but also experiencing more subtle destruction of soils through political developments, which seek to provide temporary relief and welfare in response to the demands of local populations.

Europe

The major problems concerning the soils of Europe are the loss of such resources owing to erosion, sealing, flooding, large mass movements as well as local and diffuse soil contamination, especially in industrial and urban areas, and soil acidification.113,141 Salinity is a minor problem in some parts of Western and Eastern Europe, but with severe effects at the northern and western parts of the Caspian Sea (with low salinity)1151 mainly because of the shift to irrigated agriculture and destruction of the natural vegetation (Figure 27.1).

Urbanization and construction of infrastructure at the expense of fertile land are widespread in Europe, particularly in the Benelux countries, France, Germany, and Switzerland, and such effects are most conspicuously destructive along the misused coasts of Spain, France, Italy, Greece, Turkey, Croatia, and Albania. The drastic increase in the rate of urbanization since the 1980s is now expected to follow the Blue Plan, which seeks to create beneficial relationships among populations, natural resources, the main elements of the environment, and the major sectors of development in the Mediterranean Basin and to work for sustainable development in the Mediterranean region. The very appropriate term “industrial desertification” remains valid for the once degraded soils of East Europe, under the pressure of mining and heavy industry, as in Ukraine where such lands occupy 3% of the total land area of the country.122,231

There are three broad zones of “natural” erosion across Europe, including Iceland: (1) the southern zone (the Mediterranean countries); (2) a northern loess zone comprising the Baltic States and part of Russia; and (3) the eastern zone of Slovenia, Croatia, Bosnia-Herzegovina, Rumania, Bulgaria, Poland, Hungary, Slovakia, the Czech Republic, and Ukraine (Figure 27.1). Seasonal rainfalls are responsible for severe erosion owing to overgrazing and the shift from traditional crops. Erosion in southern Europe is an ancient problem and still continues in many places, with marked on-site impacts and with significant decreases in soil productivity as a result of soil thinning. The northern zone of high-quality loess soils displays moderate effects of erosion with less intense precipitation on saturated soils. Local wind erosion on light textured soils is also responsible for the transportation of agricultural chemicals used in the intensive farming systems of the northern zone to adjacent water bodies, along with eroded sediments. The high erodibility of the soils of the eastern zone is exacerbated by the presence of large state-controlled farms that have introduced intensive agriculture at the expense of a decrease in the natural vegetation. Contaminated sediments are also present in this zone, particularly in the vicinity of former industrial operations/deserts, with high rates of erosion in Ukraine (33% of the total land area) and Russia (57% of the total land area), whose agricultural land has been subjected to strong water and wind erosion ever since the beginning of industrialization.

Localized zones of likely soil contamination through the activities of heavy industry are common in northwestern and central Europe as well as northern Italy, together with more scattered areas of known and likely soil contamination caused by the intensive use of agricultural chemicals. Sources of contamination are especially abundant in the “hot spots” associated with urban areas and industrial enclaves in the northwestern, southern, and central parts of the continent (Figure 27.1). Acidification through deposition of windborne industrial effluents and aerosols has been a longstanding problem for the whole of Europe; however, this is not expected to increase much further, especially in western Europe, as a result of the successful implementation of emission-control policies over the recent years.131

The desertification of parts of Europe has been evident for some decades, and the parameters of the problem are now becoming clear, with current emphasis on monitoring of the environmentally sensitive areas122,201 on selected sites, seeking quality indicators for (1) soil (particularly organic carbon; (2) vegetation; (3) climate; and (4) human management throughout the Mediterranean basin. Apart from the human factor, these indicators are inherent.

Soil degradation in Europe

FIGURE 27.1 Soil degradation in Europe.

Source: Adapted from UNEP/ISRIC.P1 Kobza.l'6! USDA-NRCS,I|7-I81 Erol,l‘»l Kosmas et al.l20' Kharin et al.l2'l

Asia

The most severe aspect of soil degradation on Asian lands has been desertification owing to the historical, climatic, and topographic character of this region as well as the political and population pressures created by the conflicts of the past 500 years or so. Salinization caused by the rapid drop in the level of the Aral Sea and the water-logging of rangelands in Central Asia owing to the destruction of the vegetation cover by overgrazing and cultivation provide the most striking examples of an extreme version of degradation—desertification caused by misuse of land. Soil salinity, the second colossal threat to the Asian environment, has occurred through the accumulation of soluble salts, mainly deposited from saline irrigation water or through mismanagement of available water resources, as in the drying Aral Sea and the Turan lowlands as well as the deterioration of the oases in Turkmenistan, with excessive abstraction of water in Central Asia (Figure 27.2 ).1211

The dry lands of the Middle East have been degrading, since the Sumerian epoch, with excessive irrigation causing severe salinity and erosion-siltation problems,1211 especially in Iraq, Syria, and Saudi Arabia. Iraq has been unique in the magnitude of the historically recorded build-up of salinity levels,

with 4.81 million ha saline land, which is 74% of the total arable land surface (i.e., 90% of the land in the southern part of that country). The historical lands of Iran, Pakistan, Afghanistan, India, and China are also subject to ancient and ongoing soil degradation processes, which are subtle in some areas but evident and drastic in others (Figure 27.2).

Africa

Africa’s primary past and present concern has been the loss of soil security by nutrient depletion, that is, the decreasing NPK levels (kg/ha) along with micronutrients in cultivated soils following the exponential growth in population and the resulting starvation and migrations (Figure 27.3). Intensification

of land use to meet the increased food demands combined with the mismanagement of the land leads to the degradation of the continental soils. This poses the ultimate question of how the appropriate sustainable technologies that will permit increased productivity of soils can be identified. This problem is illustrated by the example of the Sudan, where nutrient depletion has steadily increased through more mechanized land preparation, planting, and threshing without the use of inorganic fertilizers, and legume rotations. Thus, aggregate yields have been falling as it became more difficult to expand the cultivated area without substantial public investments in infrastructure. This decline in yield has occurred at enormous rates in Vertisols of Sudan, with the mean annual sorghum yields decreasing from 1000 to 500kg/ha and the wholesale price of sorghum increased 3.7% per month since 2007.11251 In Burkina Faso, the decreased infiltration and increased runoff causing erosion are further consequences of repeated cultivation. Thus, the technological measures to be identified for these two African examples must include development of water retention technologies in Burkina Faso, while polyculture/ rotations with proper manuring and fertilization for cost-efficient provisions of N and P and preferably green manuring are all needed in Sudan to permit the balanced management of soil moisture, nutrients, and organic matter (and to enhance C-sequestration, a main goal for sustainability based on the earth sciences—to ensure the security of both the soil and global climate).125,261

Central and South America

Africa and Latin America have the highest proportion of degraded agricultural land. Water and wind erosion are the dominant soil degradation processes in Central and South America and have caused the loss of the topsoil at alarming rates because of the prevailing climatic and topographic conditions. Almost as important is the loss of nutrients from the Amazon basin (Figure 27.4).1271 These effects are mainly attributable to deforestation and overgrazing, the former being responsible for the degradation of 576 million ha out of 1,000 million ha potential agricultural land. Another important factor has been the ever-increasing introduction of inappropriate agricultural practices derived from the so-called imported technology, which have not been properly adapted to indigenous land-use procedures. The traditional methods of permitting the land to recover naturally have been almost totally abandoned and replaced by unsuitable technological measures designed to maintain production levels (temporarily) and to overcome the loss of soil resilience, thus increasing chemical inputs.

The rapid industrialization/urbanization of the limited land resources in the Caribbean region has been expelling agricultural communities to remote and marginal regions that are at present rich in biodiversity and biomass—a major global C sink. Moreover, large-scale livestock herding of Central and South America is also a major threat to soil security and has been responsible for degrading 1 million km2 of Argentinean, Bolivian, and Paraguayan pasturelands.

North America

The most prominent outcome of soil degradation (or more correctly desertification) in United States is exemplified by the accelerated dust storm episodes of the 1930s—the Dust Bowl years, marked by the “Black Blizzards,” which were caused by persistent strong winds, droughts, and overuse of the soils. These resulted in the destruction of large tracts of farmland in the south and central United States. Recently, salinization has become an equally severe problem in the western part of the country (Figure 27.5) through artificial elevation of water tables by extensive irrigation, with associated acute drainage problems. An area of about 10 million ha in the west of United States has been suffering from salinity-related reductions in yields, coupled with very high costs in both the Colorado River basin and the San Joaquin Valley.1281 Unfortunately, new irrigation technologies, such as the center pivot irrigation system (developed as an alternative to the conventional irrigation systems causing the salinity problems), have caused a decline of the water-table levels in areas north of Lubbock, Texas, by around 30-50 m, leading to a dramatic decrease in the thickness of the well-known Ogallala aquifer by 11% decrease between 2003

Soil degradation in Central and South America

FIGURE 27.4 Soil degradation in Central and South America.

Source: Adapted from UNEP/ISRIC.171 Kharin et alJ2'1

and 2011 only. In some areas, this has been followed by ground subsidence, which is an extreme form of soil structure degradation, that is, loss of the physical integrity of the soil.

Loss of topsoil, as a result of more than 200 years of intensive farming in United States, is estimated to vary between 25% and 75% and exceeds the upper limit in some parts of the country.118,19! United States provides good examples of the difficulties involved in erosion control, with its large-scale intensive agriculture—deteriorating soil structure and increasing erosion of its susceptible soils. This problem could be overcome primarily by the strict introduction of the no-till system. No-till areas have increased from 4 million ha in 1989 to 25.3 million ha in 2004, and they are forecast to follow a linear extrapolation until 48 million ha out of the total 81 million ha of cultivated land will be attained.1291 Conservation farming is practiced in only about half of all U.S. agricultural land and on less than half of the country’s most erodible cropland. Conservation farmers are encouraged to use only the basic types of organic

Soil degradation in North America

FIGURE 27.5 Soil degradation in North America.

Source: Adapted from UNEP/ISRIC.171 Kharin et al.12'1

fertilizers, such as animal and green manure together with compost, mulch farming, improved pasture management, and crop rotation, to conserve soil nutrients.

Canada is a large country where 68 million ha of available land is cultivated, which is only the 7.4% of the territorial of the country with an average farm size of 450 ha. It is reported that Canada has experienced annual soil losses on the prairies, through wind and water erosions, that are similar to the Asian steppes, amounting, respectively, to 60 and 117 million tons. These annual rates are much higher than the rate of soil formation, resulting in an annual potential grain production loss of 4.6 million tons of wheat. With regard to primary soil salinity, during historic times, the prairies have experienced steady increases related partially to increasing groundwater levels. Major problems of secondary salinity are estimated to affect 2.2 million ha of land in Alberta, Saskatchewan, and parts of Manitoba, with an immense economic impact each year.

Australia

The Australian agricultural/soil resource base has been endangered, as the “business as usual” concept was adopted on the continent to achieve temporary economic betterment. Identification of different types of soil degradation in Australia reveals that erosion has been the main component, primarily via dust storms, which are still a serious problem, especially where cropping practices do not include retention of cover and minimum tillage methods. Water erosion effects are also particularly severe in areas of summer rainfall and topographic extremities (Figure 27.6). Although water is a scarce resource in Australia, about 14 million tons of soil is lost in Australia by water erosion. Remedial actions for this include the well-known measures of maintaining adequate cover and changing prevailing attitudes toward stock management, storage feed, redesign of watering sites, and management of riparian areas.

Part of the excess salinity in Australia is of primary origin and was retained in the subsoil by trees, which have now been cleared to create soil surfaces for cropping and pastures, allowing penetration of water to the saline subsoil, then followed by abstraction from the water table, thus leading to the ultimate disaster. About 30% of Australia’s agricultural land is sodic, creating poor physical conditions and impeded productivity. This problem can only be alleviated by massive revegetation programs and by taking extra care of the water table and plant cover. Despite the introduction of costly conventional measures for reclamation, salinity levels continue to increase across Australia in the dry and irrigated

soils. The dryland salinity in the continent affects about 5 million ha of farmland and is expanding at a rate of 3-5% per year.1301

The retardation of organic matter levels also requires remediation measures, with economically justified fertilizer use strategies to be utilized throughout the continent. Moreover, overgrazing has resulted in the impoverishment of plant communities and loss of habitats as well as the decline in the chemical fertility of the soil by progressive depletion of organic matter in the topsoil, followed by deterioration in the soil structure.

Acidification caused by legume-based mixed farming plus use of ammonia-based fertilizers threatens 55 million ha of Australian land. Liming seems to be the most effective present remedy, but is costly, does not lead to rapid recovery, and is impractical for subsoil acidity. Thus, the precise remedies are yet to be developed for the conditions on this continent, utilizing careful, long-term monitoring and the experience of farmers to devise specific treatment and conservation procedures.

 
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