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soil erosion and its type

INTRODUCTION

Soil erosion is a worldwide challenge for the sustainability of agriculture, especially in the tropical region. It is the process of detachment and transport of soil particles. Erosion can decrease rooting depth, soil fertility, organic matter in the soil and plant-available water reserves (Lal, 1987). The rates of soil erosion that exceed the generation of new topsoil are a dynamic process which may lead to a decline of soil productivity, and result in lower agricultural yield and income, at least in the long run.

The balance between soil-forming and depleting processes is of utmost importance for attaining long-term sustainability in any production system. Soil is a non-renewable resource and the basis for 97 percent of all food production (Pimentel, 1993), strategies to prevent soil depletion are critical for sustainable development. For developing suitable soil conservation strategies, knowledge of the prevailing and permissible rates of soil erosion is an essential pre-requisite. In order to adequately understand the complex issue related to land degradation, it is necessary to identify the underlying causes and gain a comprehensive understanding of the physical, economic, political, institutional and social dimensions.

The question of sustainability of agriculture mainly focuses on production over an extended scale of time and space. This essentially would mean that crop production and economic gains would flourish over a long period of time, almost infinitely and globally ( Van Loon, et al. 2004; Shah, 2006). It encompasses a range of strategies for addressing many of the problems such as loss of productivity from excessive erosion and associated plant nutrient losses; surface and groundwater pollution from pesticides, fertilisers, and sediment; impending shortage of non-renewable resources; and low farm income from depressed commodity prices and high production cost (Parr et al, 1990).

 

Moreover, agricultural sustainability implies a time dimension and the capacity of a farming system to endure indefinitely (Lockeretz, 1988). The problem of soil erosion is prevalent over 53 percent of the total land area of India (Dhruvanarayana and Ram Babu, 1983). India loses about 16.4 t of soil ha–1 yr–1, of which 29 percent is lost permanently into the sea, 10 percent gets deposited in the reservoirs reducing their capacity by 1–2 percent every year and the remaining 61 percent gets displaced from one place to another (Narayana, and Rambabu, 1983; Mandal and Sarda, 2011). The regions of high erosion include the severely eroded gullied land along the banks of the rivers the Yamuna, Chambal. In these areas decline in the growth rates of agricultural production and productivity is a serious issue considering the questions of food security, livelihood, and environment. 

Water Erosion

Water erosion results from the removal of soil material by flowing water. A part of the process is the detachment of soil material by the impact of raindrops. The soil material is suspended in runoff water and carried away. Four kinds of accelerated water erosion are commonly recognized: sheet, rill, gully, and tunnel (piping).

Sheet erosion is the more or less uniform removal of soil from an area without the development of conspicuous water channels. The channels are tiny or tortuous, exceedingly numerous, and unstable; they enlarge and straighten as the volume of runoff increases. Sheet erosion is less apparent, particularly in its early stages than other types of erosion. It can be serious on soils that have a slope gradient of only 1 or 2 percent; however, it is generally more serious as slope gradient increases.

Rill erosion is the removal of soil through the cutting of many small, but conspicuous, channels where runoff concentrates. Rill erosion is intermediate between sheet and gully erosion. The channels are shallow enough that they are easily obliterated by tillage; thus, after an eroded field has been cultivated, determining whether the soil losses resulted from sheet or rill erosion is generally impossible.

Gully erosion is the consequence of water that cuts down into the soil along the line of flow. Gullies form in exposed natural drainage-ways, in plow furrows, in animal trials, in-vehicle ruts, between rows of crop plants, and below broken man-made terraces. In contrast to rills, they cannot be obliterated by ordinary tillage. Deep gullies cannot be crossed with common types of farm equipment.

WATER EROSION IN SOIL EROSION

Soil Erodibility

Soil erodibility is an estimate of the ability of soils to resist erosion, based on the physical characteristics of each soil. Generally, soils with faster infiltration rates, higher levels of organic matter and improved soil structure have a greater resistance to erosion. Sand, sandy loam and 2 loam textured soils tend to be less erodible than silt, very fine sand, and certain clay textured soils.

Tillage and cropping practices which lower soil organic matter levels, cause poor soil structure, and the result of compacted contribute to increases in soil erodibility. Decreased infiltration and increased runoff can be a result of compacted subsurface soil layers. A decrease in infiltration can also be caused by a formation of a soil crust, which tends to "seal" the surface. On some sites, a soil crust might decrease the amount of soil loss from sheet or rain splash erosion, however, a corresponding increase in the amount of runoff water can contribute to greater rill erosion problems.

Past erosion has an effect on a soils' erodibility for a number of reasons. Many exposed subsurface soils on eroded sites tend to be more erodible than the original soils were, because of their poorer structure and lower organic matter. The lower nutrient levels often associated with subsoils contribute to lower crop yields and generally poorer crop cover, which in turn provides less crop protection for the soil.