Abstract
Soil is one of the most valuable natural resources. Despite soil importance, the pressures on soil have increased in recent decades. Soil degradation is a critical and growing problem, whereby soil erosion presents a prevailing process compared to other degradative processes. The intensity of erosion depends on the topography, climate conditions, soil characteristics, human activities, and the presence of vegetation. In this chapter, the diverse factors that cause soil erosion have been evaluated. The level of damage associated with soil erosion has been analyzed, with emphasis on the impacts they may have on the global carbon cycle, phosphorus loss, dust emissions, eutrophication, and soil biodiversity.
TopIntroduction
Soil, the biologically active medium that has been formed in the uppermost layer of Earth’s crust, plays a vital role in the functioning of terrestrial ecosystems. Soil is essential for humans because it presents the basis for food production. Besides, soil acts as a filter for contaminants, a reservoir of water and nutrients, participates in the cycling of carbon and other elements through the global ecosystem, serves as a habitat for soil organisms, as well as a landscaping and engineering medium.
Despite its importance, the pressure on soil is increasing. As an element of the land degradation process, soil degradation refers to a decline in soil productivity and quality. Several physical, chemical, and biological processes are responsible for the degradation of soil. The physical methods include deterioration of soil structure, compaction, crust formation, erosion, and desertification. Among all chemical processes, leaching, soil fertility decline, acidification, salinization and pollution are significant. The biological processes of soil degradation include carbon reduction and a decrease in soil biodiversity (Osman, 2014).
Several natural and anthropogenic causes can lead to soil degradation. Among the natural ones, the most important are frequent floods, high-velocity wind, high-intensity rains, leaching in humid regions, drought in arid areas, etc. As regards anthropogenic causes, the most significant are deforestation, overgrazing, inadequate use of agrochemicals, monocropping, shifting cultivation (Dragović & Vulević, 2020; Osman, 2014).
Many studies confirm the connection between deforestation and soil degradation. Based on research, conversion of the forest area into the pasture and the subsequent unregulated grazing have altered the erosion rate, nutrient amount and soil characteristics (Rhoades, 2011). Hajabbasi et al. (1997) were investigated deforestation effects on soil physical and chemical properties in the Lordegan region of central Zagros Mountain, Iran. Deforestation and clear-cutting of the forests resulted in lower soil quality. Namely, deforestation and subsequently tillage practices resulted in a 50% decrease in organic matter and total nitrogen, a 10 to 15% decrease in soluble ions comparing to the undisturbed forest soil. Also, the tilth index coefficient of the forest site was significantly higher (0.717) than the cultivated forest and the deforested areas (0.633 and 0.573, respectively). The consequences of deforestation vary from soil erosion and sedimentation to loss of biodiversity, climate change, flood and drought, the decline in water quality, etc.
Overgrazing is one of the most severe problems on a global scale in terms of soil degradation. Depending on grazing intensity, soil organic matter, nitrogen content, microbial activity and soil moisture vary. All the above-mentioned factors and loss of vegetation cover lead to soil erosion and desertification. The results obtained by studying a dry Mediterranean agro-forest landscape (Crete, Greece) indicate that soil erosion increases and soil moisture decrease on overgrazed land and highlight the crucial role of sustainable grazing in land degradation mitigation (Kairis et al., 2015). According to research conducted in eastern Hovsgol, Mongolia, soil fertility decreases and soil chemical properties change due to overgrazing. In overgrazed areas, soil organic matter content was 30-50% lower and exchangeable calcium 40-60% lower than non-grazing areas. Nitrogen content was also lower in overgrazed valleys. Overgrazing was also found to affect soil physical characteristics in terms of increasing topsoil temperature, decreasing moisture, and increasing bulk and particle density (Wang & Batkhishig, 2014).
Modern agriculture relies on the extensive use of agrochemicals, pesticides, fertilizers and soil conditioners, to increase crop productivity by controlling harmful pests, pathogens, and weeds (Mandal et al., 2020). Excessive applications of nitrogen and phosphorus fertilizers lead to the disruption of the natural nitrogen and phosphorus cycles. Also, the use of fertilizers introduces heavy metals and radionuclides from mineral fertilizers and pathogens, veterinary pharmaceuticals, and endocrine disrupters from organic fertilizers into the soil. Their inappropriate use hurts the soil quality and represents one of the basic forms of degradation.
Key Terms in this Chapter
Carbon Cycle: The continuous movement of carbon between different living organisms on earth and between living organisms and the environment, through natural processes like photosynthesis, respiration, and decomposition in the soil, and also the burning of fossil fuels.
Eutrophication: The process by which a body of water becomes enriched in dissolved nutrients that stimulate the growth of aquatic plant life, usually resulting in the depletion of dissolved oxygen.
Soil Erosion: Detachment and movement of topsoil or soil material from the upper part of the profile by the action of wind or running water, especially due to changes brought about by human activity (such as unsuitable or mismanaged agricultural methods).
Biodiversity: The variability among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species, and ecosystems.
Sustainable Development: The practice of maintaining productivity by replacing resources used with resources of equal or greater value without degrading or endangering natural biotic systems.
Environmental Quality: A state of ecological conditions in environmental media, expressed in terms of indicators or indices related to environmental quality standards.
Soil Degradation: Element of the land degradation process which refers to a decrease in soil’s productivity and quality.
Air Pollution: The presence in or introduction into the air of a substance with harmful or poisonous effects.