FEATURES NEWS THE RISING NEPAL (DAILY)

By Sushil Thapa

SOIL erosion is a natural process of detachment transportation and deposition of soil materials by erosion agents namely water, wind, snow and gravity. The energy from the erosion agents acts upon the soil materials, detach soil particles, entrain them in means of transport , push them away and deposit them elsewhere where the energy of transportation is counteracted.

Classification

Based on the level of human influences erosion can be broadly classified into two groups. Natural or geological soil erosion and, accelerated soil erosion.

Since the natural soil erosion is away from human reach and has slower rate than the rate of soil genesis, it is not taken as the great problem where loss of 0.5 ton of soil/ha/year take place. It removes 1 cm of topsoil in one hundred years. But accelerated soil erosion is due to the effect of human activities like clearance of forest, open grazing system, constructional works, traditional farming system etc. where loss of soil materials takes place at the rate of 60 to 100 mt/ha/year. It removes 1 cm of top soil in one year. The formation of 1cm of soil by soil genesis takes 15-100 years but the same amount of soil is lost in a year. So, soil erosion is responsible for the loss of soil fertility in Nepal.

According to the role played by the major erosion agents, accelerated soil erosion is further divided into four types: Water erosion, wind erosion, glacial erosion and mass movement.

Among them wind erosion and glacial erosion do not play significant role in soil erosion in Nepal but due to its mountainous topography running water and gravitational force work together resulting in massive soil erosion. A combined occurrence of water erosion and mass movement is a typical process of erosion in Nepal.

A mountainous country Nepal has many steep slopes and sloppy terraces where farmers cultivate the land of fulfill their socio-economic needs. Aged, unskilled and ignorant people having no other option of livelihood indulge in agriculture. Similarly, deforestation, slash and burn systems, use of marginal and sloppy land and open grazing system still existing in hills, which in turn contribute to soil erosion.

As the raindrop hitting the earth surface at a velocity of 914 cm/sec can splash the soil particle 61 cm high and 152-cm away, water appears as the main agent of soil erosion. This agent together with above-mentioned causes (wind, glacial and mass movement) results in huge loss of vegetation and bio-diversity. Due to the lack of vegetation and conservation practices water running from top to the bottom of the slopes causes high degree of soil erosion resulting in heavy loss of fertile top soil. Hence, hill agriculture is suffering with low level of input and insignificant output. The majority of the mountainous districts (i.e. 41 districts) have been asserted as food deficit zone of the country. The soil practicles detached and carried away from the hills are usually deposited into the Terai region where destruction of vegetation and productive land and degradation of soil fertility take place. Flooding from hills to Terai is the major reason for deforestation and stream bank erosion. Erosion has also been contributing to the destruction of the infrastructure like road (a terrible problem of Nepal), stream bank, bridges hydroprojects and houses and causes pollution to natural water, disturbance in hydrological cycle and environmental degradation. Ultimately, it results in great harm to human life and civilisation. In short, it can be said that water erosion is one of the major constraints in agricultural development of Nepal. Due consideration needs to be paid for its conservation.

It is highly essential to work hard to tackle with this challenge in order to boost the overall food production of the country, to meet the growing need of the rising population and to make Nepal a prosperious and healthy country. It is the fact that soil is the basis of human life and civilisation the ecosystem and the environment. Soil, water, plants, humans and animals are closely interrelated and interact with each other for their existence. Human intellect tends to understand the nature of this interaction for the conservation of these valuable natural assets without causing negative impacts on the environment. Soil is, as a precious asset naturally synthesised in the course of a long period. From the past experiences it seems that we need to concentrate our teaching research, and extention works on the field of "soil conservation practices."

Although, it is not possible to bring soil loss to zero level but the objective of the soil/water conservation should be to minimise the soil loss to the possible lowest level. To meet this goal the farmers need to be provided with practical education that include mechanical methods of conservation, biological methods of conservation and bioengineering methods of conservation.

Method

Mechanical works, include the construction of terraces, hillside ditches, soil trap, check dam, spillways and good drainage system. This method prevents erosion by decreasing the velocity of running water. Biological method includes planting of vegetation like green manuring and covers crops, mulching contour cultivation, strip cropping , agro-foresty, etc. This method prevents the water erosion by filtering the turbid water, decreasing the surface runoff, binding the soil, increasing the rate of infiltration and covering the soil surface. Similarly, bioengineering method is the integration of both mechanical and biological methods as far as practicable. In addition, the education must encourage them to apply new systems of cropping like rotational cropping, mixed cropping, inter cropping, multiple cropping etc. The new technology of agriculture should be introduced to the hills as far as possible. The existing traditional/indigenous method of farming should be improved.

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