Soil erosion involves the shedding away of the topsoil due to the influence of various factors. Soil erosion irrespective of whether it is due to water, wind or tillage, involves three discrete actions. They are soil detachment, movement and deposition. Topsoil, the visible portion of the surface of the soil has rich organic matter and highly fertile is relocated elsewhere. This results in the abnormal build-up of mass in an uneven manner over time. Soil erosion reduces cropland productivity and contributes to the pollution of adjacent watercourses, wetlands and lakes. Furthermore, the earth is constantly under the influence of both man-made and natural forces that can seriously impact its surface over the long run. The surface of the earth contains a mix of hills, terrains, water, valleys and rocky fountains instead of being constantly flat and firm which can result in landslide and erosion. Adding to this, much of soil erosion in India is due to the faulty farming practices with no long-term vision to save the fertility and composition of the soil. Practices such as faulty ploughing, lack of mulching and the shifting cultivation can result in steep slopes across farming fields. One of the problems in managing soil erosion is that people take it for granted as they feel that soil erosion is not so harmful when compared to the air and water pollution.
Types of soil and soil erosion
The degree of soil erosion varies in many ways on different landforms. The type and structure of soil depend upon compaction, type of cultivation under practice, removal of vegetation, uncontrolled moving or handling of soil, and excessive sodium in the soil are among many other factors. However, soil erosivity is fundamentally determined by the composition, moisture, and compaction of a given soil. Based on these factors, the soil is classified into granular, dusty, clay-filled, and mixed. The degree of erosion impacts differently in each case. Let us discuss some of the factors contributing to soil erosion.
Classification of Soil Erosion
One of the best things to assure the soil fertility is the control of soil erosion but it is important to understand what causes erosion and how it is related to the classification through which remedies can be planned. The different types of soil erosion types are as follows.
Rain Drop or Splash Erosion isthe erosion due to the impact of the force and angle of falling raindrops on the soil surface which we will be discussed below again. Sheet erosion is the uniform removal of thin layers of soil due to to the forceful wind. It is commonly seen in the land areas with loose, shallow topsoil overlie compact soil. Rill Erosion is a kind of water erosion in which the erosion takes places through narrow and straight channels called head cuts and rills can be seen commonly during heavy rain. Gully Erosion occurs due to the runoff of surface water causing the removal of soil with drainage lines. Finally, stream bank erosion occurs due to washing up away from banks of a stream or a river.
Factors determining soil erosion
Type of soil
Soil sediments containing excessive clay and the land built up with rocky mountains tend to be more resistant to erosion than any other soil. On the other hand, fine and dusky soil mixtures are more vulnerable to soil erosion because of their loosely arranged particulate structure. Similarly, soil with sandy or silt based mixtures are also prone for the loss of topsoil.
Organic material in the soil
A soil containing excessive organic materials form strong layers which can resist the erosion. This is due to the fact that organic materials tend make soil colloidal, coagulated, sticky which altogether provides a great degree of compaction.
The ratio of moisture
A moisture soil is formed when the water content drips through the loosely organized granular and dusky layers. The ratio between solid and liquid content in the soil sets limits on the amount of water that can be absorbed by the soil. A soil that is slightly moist and sticky tends to be resistant while the free and dried layers can emaciate the top layer easily. In addition, mass vegetation with the firmly spread roots on the topsoil can hold the soil strong along with the moisture.
The topography refers to the physical arrangement of the surfaces of land. Soil erosion is intensive and faster on the longer and steeper slopes with no proper vegetative cover when compared to the lands built-up by the shorter, less steep slopes.
The duration and the force of the rainfall along with its direction determine the degree of soil erosion. The raindrops that hit the surface of the soil in a slanty manner takes away more soil than the ones that hit straight. Furthermore, in the areas where rainfall is windy and stormy, the soil is highly susceptible to soil erosion when compared to those areas that receive a cyclic but slow and continued rain pattern.
The geographic location of the land
Naturally, the proximity to the rivers, oceans, canals and other major water sources are some of the high-risk factors predisposing the soil to erosion. This is due to the mechanical force of the strong waves that hits the shores. Sch forces not only cause erosion, but they can be a reason for the landslide.
Tillage and farming Practices
The degree of soil erosion by water is linked with tillage operations. Based on the depth, direction and timing of plowing along with the type of tillage equipment the farmers use, soil undergoes different levels of erosions. Lesser the disturbance of vegetation or residue cover at or near the surface, the more effective is the tillage practice. Therefore, it is recommended that the tillage practices should be highly scientific. Moreover, unsustainable agricultural practices can set the farmers at risk of loss due to erosion. The tillage of agricultural lands crushes the soil into finer particles making them freely move with the influence of rain and wind is one of the major contributing factors for soil erosion. Practices such as frequent plowing, or ploughing from steeps towards the deeper areas, mono-cropping,and farming on steep slopes can further increase the chances of soil erosion
Types of soil and their permeability
Structure of soil is determined by the shape of its contents, size of peds, and grade or the ability to create cohesion of aggregates. All these factors together help in providing the soil with a specific size, smoothness, shape, the pore structure. The pore structure of a soil mass helps to assess how easily air, water, and roots can penetrate through the soil making it more vulnerable for soil-loss. The granular structure of the soil is the most common type of topsoil that reasonably offers a high pore space than any other types, while the columnar structure is frequently found in soils that have high sodium. The acidity provided by the sodium determines the dispersing levels of soil. On the other hand, the platy structure holds a minimal pore space supporting the soil to build itself into a compact mass. On the contrary, few soils lack a specific structure which can make them vulnerable for erosion, however, since the mixed soil contains 2 or more types of soil, they are good for cultivation. Massive soil has large granular pores which can sometimes be eroded due to harsh rain.
Management of soil erosion
Mass vegetation: Soil erosion management varies as a practice can be well-fit in sloppy land may not be suitable for a flat area. However, one of the effective methods to prevent erosion prevention is to increase vegetative cover on the land. Mass vegetation helps prevent both wind and water erosion.
Terracing: It is a practice of planting small shrubs and plants against the sloppy farmlands to create barrier against the free flow of topsoil. It has been practised for people all over the world from many centuries. Terracing is a measure to enable windbreaks also.
Crop residues: Theyplay an important role in the mitigation of erosion as they can reduce the impact of forceful raindrops breaking up the soil particles.
Crop selection; Crop selection can help to decide which crops suit a suitable soil type. There is a higher potential for erosion when producing potatoes than, cultivating cereals, or oilseed crops. Plants with fibrous root system aids in combatting soil erosion in a better way than the non-fibrous ones
Mechanical measures: Some of the manual methods can prevent easy cast-off of topsoil. Some of them are building small obstructive canals against the sloppy land, ploughing in a certain direction that doesn’t allow easy flow of water.