In the Himalayan region, soil erosion by water is a significant cause of land degradation and a serious environmental threat. The complicated phenomena of soil erosion are governed by a number of natural processes, which has an impact on crop yields, water quality, and soil fertility. Due to the considerable spatial variability of soil erosion, it is important to know where it is happening when planning, for example, soil and water conservation measures. One of the main causes of soil erosion brought on by water is rainfall.
In numerous regions of India, soil erosion is a significant environmental problem. There is a need to evaluate the danger of soil loss and adopt preventive measures since the removal of fertile top soil directly affects the productivity of crops.
Introduction
Topsoil on the soil surface is carried off the ground by water or wind and moved to other surfaces during the process of soil erosion. After population expansion, it is regarded as the most significant environmental issue the world currently faces. The majority of soil from farmlands is washed away about 10–40 times faster than it is being replaced, according to Pimentel et al., 2009, who provided examples of the United States losing soil at a rate of 10–40 times faster than the average replacement rate and China and India losing soil at a rate of 30–40 times faster. The 20th century has seen a rise in the trend of soil erosion.
Soil erosion is a pertinent global issue because of its direct and indirect effects on the environment and economy. It is a slow, dynamic natural process that uses water or wind action to separate, move, and accumulate productive surface soil throughout the earth's surface (Jain et al. 2001). The erosivity of rainfall, the erodibility of soil, land cover, and topography are environmental elements that contribute to soil erosion. This natural process could become dangerous if increased anthropogenic activities including land clearing, agriculture (ploughing and irrigation), overgrazing, deforestation, construction, surface mining, and urbanization cause more soil loss than is typical. Numerous nations view soil erosion as a critical issue of concern due to the problem being exacerbated by unscientific farming techniques and poor land management (Lal 2003). A number of direct and indirect effects of soil erosion and related land degradation lead to significant environmental, economic, and social issues. The loss of soil nutrients brought on by the removal of fertile soil from the top layer of the soil profile lowers agricultural output (Lal 1998). The deposited silt in lakes, reservoirs, canals, and rivers is increased by the eroded soil particles, which lowers the water holding capacity of freshwater reservoirs. Aquatic ecosystems are impacted by an increase in suspended debris in waterbodies. Additionally, the hazardous pesticides and chemicals used on agricultural land contribute to eutrophication and river contamination through soil erosion (Wang et al. 2009). Intense soil erosion has a number of unintended consequences, such as raising the risk of flooding and causing financial losses in irrigation and hydropower projects.
According to estimates, soil erosion has a negative impact on 329 Mha, or nearly 53% of India's total geographic area, with an average yearly rate of 16 t h-1 year-1 (Jain et al. 2001Pandey et al. 2009). An estimated 5334 m tonnes of soil are removed from India each year for a variety of causes, according to estimates (Pandey et al. 2007). The Indian government has made various attempts to stop soil erosion and land degradation, but proper conservation planning and management have been hampered by a lack of accurate information. To identify places vulnerable to severe erosion and implement an effective land management program, it is crucial to quantify soil loss and estimate risk. The field-based methods for quantifying soil loss take a long time, and a deficient sampling plot could reduce the accuracy of the area actually subjected to soil erosion. Due to the time and money required by this traditional field-based method, it is very difficult to monitor and accurately map the spatial pattern of soil loss over a vast area (Kumar and Kushwaha 2013).
Soil Erosion in Historical Perspective
Land degradation due to accelerated erosion is a serious global issue because soil resources of the world are finite, non-renewable in the human-time scale, fragile to land misuse and soil mismanagement, especially in harsh environments and ecologically sensitive ecoregions, and unequally distributed geographically leading to scarcity of high quality soils in densely populated regions of the world. Accelerated soil erosion, physical displacement of soil by different agents of erosion, leads to changes in soil quality especially that of the surface horizon. The magnitude of erosion-induced change in soil quality, and its capacity to perform different functions (agronomic, engineering, environmental regulation, aesthetic, cultural, archeological etc.), depends on antecedent conditions and soil profile characteristics.
There are three possible scenarios of erosion-induced changes in soil quality. 1. In some soils of deep and uniform topsoil depth, such as soils developed on loess or alluvial parent material, moderate levels of soil erosion may have no effect on soil quality. 2. In contrast to scenario 1, erosion may cause drastic adverse changes in soil quality, especially in soils with a root-restrictive layer at shallow depth. 3. Soil erosion, in some rare circumstances, may lead to improvements in soil quality because the sub-soil has edaphologically more favorable soil quality than surface soil. In addition to on-site improvements in soil quality by erosion of some soils (e.g., paleosols), off-site improvements in soil quality may happen at depositional sites especially if the depositional material came from accelerated erosion on soils of marginal economic returns or functions of value to humans.
A vast majority of agricultural soils fall in scenario #2 of decrease in soil quality with accelerated erosion. Erosion-induced degradation in soil quality has been a problem of numerous bygone civilizations (McCracken, 1987). Siltation of irrigation canals and fields was a major problem in the ancient Mesopotamian agriculture. Silt deposition had raised the level of the fields by almost 1 m over a 500-year period. This rise in the land surface reduced the level of water available for irrigation purposes. Further, siltation of the canal bed sharply reduced its flow and head of water it could provide to its branches. The cost of desilting was enormous, and its consequences disastrous. Olson (1981) also postulated that soil erosion was the cause of the downfall of several once-thriving cultures and civilizations.
The deforestation of cedar wood from nations bordering the Mediterranean in the Middle East led to catastrophic erosion, the overthrow of the Phoenicians, and the destruction of the granaries of the Roman Empire. Accelerated erosion obliterated the productive agriculture that existed in Mesopotamia, modern-day Iraq, around 10,000 B.C. Many ancient cultures, including the Harappan-Kalibangan civilization in western India, Negev in the Middle East, the Maghreb region of northwest Africa (including Tunisia and Algeria), and the Mayan civilization in central America, perished as a result of it (Olson 1981). Our current global civilization is similarly troubled by rapid soil erosion to earlier civilizations. According to management and environmental conditions, some soils and ecoregions are more sensitive than others, and the degradative impacts are unique to those soils and ecoregions (Wolman, 1985). 1980 saw the world's food production expand at a slow rate, in part because to rapid soil erosion (Pimentel et al., 1995).
Due to rising population and deteriorating soil, the amount of cropland per person is diminishing. However, it is clear that soil-related restrictions are easier to handle than climatic, topographic, and hydrologic ones that affect erosion-induced degradation. Enhanced soil and water management techniques, genetic engineering, and biotechnology have the potential to increase agricultural productivity. However, soil deterioration negates the advantages of these technologies because more advanced agricultural technology cannot always be used on highly damaged soils (Wallace, 1994).
Global Extent of Land Degradation by Soil Erosion
There are no accurate global estimates of soil degradation brought on by erosion. 1094 million ha of land were damaged by water erosion and 548 million ha by wind erosion, according to Oldeman (1994). According to the overall area affected, Asia is more affected by water erosion than Africa, South America, Europe, Oceania, North America, and Central America combined. Asia > Africa > South America = Europe > North America > Oceania > Central America is the order in which wind erosion occurs globally.
The main determinants of the severity and degree of soil degradation are the climate and the soil. In contrast to cool and humid climates, soil erosion and the ensuing land degradation are more severe in hot and dry regions.
Effects of Soil Erosion
Depending on the type of erosion, soil erosion can have either good or negative effects. The richest alluvial soils, which have supported intensive agriculture for millennia for many ancient civilizations, were created by geologic erosion, a long process of weathering and sediment transport. The soils of the Indus valley, Indo-Gangetic plains, and Nile delta are a few examples of such fertile soils. These are some illustrations of some long-term advantageous outcomes of soil erosion. Some depositional sites' productivity can be increased by soil erosion because it enhances the depth of the roots and the soil's moisture balance. However, faster soil erosion generally has some very bad consequences.
These detrimental effects can be classified as either onsite or long-term detrimental effects on soil quality and productivity, or onsite or short-term bad effects. The direct and indirect influences on soil productivity and quality contribute to the on-site effects on crop output. There are several interrelated processes and mechanisms that contribute to the direct consequences of rapid soil erosion on crop productivity. Reduced effective rooting depth, loss of soil nutrients and soil organic carbon (SOC), loss of plant available water and available water content (AWC), loss of land area, and seedling injury are the main mechanisms that cause crop output to fall as a result of erosion. Additional costs for equipment, delayed planting or resowing, supplemental irrigation needed due to the loss of water flow, and a host of other indirect effects of increased soil erosion are also present. These effects are mostly caused by the loss of resources during the season. Globally, around 33% of the world's cropland is less productive due to the localized effects of soil erosion (Brown and Young, 1990).
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Authors
Sandip Kumar Gautam, Kautilya Chaudhary, Anil Kumar
Department of Soil Science, CSJM University, Kanpur Nagar, UP (209202)
Sandipkumar9930@gmail.com
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