Protection of the soil against erosion

Soil erosion is the destruction and wearing away of the soil by water or wind. A layer of soil formed in the source of 100 or 200 years may be destroyed in a few days by heavy rain or dust storms. The soil is rapidly destroyed but forms only over a very lengthy period. That is why it is so vitally important to protect the soil.

Soil erosion by water is widespread and most destructive. It occurs on slopes and is due to improper working of the land.

Soil erosion by water is bad for agriculture in all respects. Grain harvests on strongly eroded soils are half those on uneroded soils.

Fighting any kind of soil erosion always requires a set of anti-erosion measures. No one measure alone is effective.

Soil erosion by wind is characteristic mostly of open, dry, diffused soils. It may arise on any field with sparse vegetation.

In wind erosion, the wind usually blows small bits of soil over the surface. When the wind grows stronger, these bits not roll over the surface of the field but are even thrown into the air for distances of 3 to 4 metres.

A cloud of dust raised and driven over a field where the soil is destroyed by the wind is called a dust storm. Sometimes, the wind may erode 1 to 5 cm of soil from a field. In natural conditions, it takes 250 to 300 years to restore one cm of soil. Soil loss is thus irretrievable.

Measures against wind erosion include: firstly, protection of fields against the wind; and secondly, retention of moisture in the soil, because moist soil is firmer, plants grow quicker and more thickly on it, preventing the wind from destroying the soil.

Mud and stone streams (avalanches) in the mountains are a form of soil erosion which occurs at great speed due to steep slopes and narrow gorges. Beginning unexpectedly in small mountain streams, the streams of foaming water, mud and stone move down with the speed of a train bringing death and destruction. They bury sections of railways and motor roads, houses, entire towns, and fertile lands, turning the latter into heaps of dried mud.

Mud and stone streams inflict great damage on people and the economy in mountain areas. The people living in the countries of Europe adjacent to the Alps have always suffered from them and they occur in the mountains west of North and South America.

Mud and stone streams caused by human activities occur when the latter are incorrectly conducted in the mountains, such as mining enterprises dumping waste on steep slopes. Strong rain erodes these waste piles and disrupts the unstable balance of the loose waste masses. Dozens or even hundreds of thousands of cubic metres of soil and stones are driven by the water down mountain rivers. It is not surprising that avalanches due to human activities occur much more often than natural ones.

The second cause of mud and stone streams of human origin is uncorrect exploitation of plant resources and excessive cattle grazing in the mountains. If forests are cut down in the mountains or cattle graze for too long on denuded slopes, the soil becomes unstable.

The best way of fighting mud and stone streams is to plant forests in river valleys where they occur, prohibit the random felling of trees on mountain slopes, the disorderly dumping of refuse ore by mining enterprises, and the destruction of rock by explosions. Cattle grazing should be strictly regulated in the mountains, and banned completely in places where the danger of mud and stone streams is particularly great. At the same time, permanent hydraulic works – drainage canals, check dams and so on should be set up in river valleys.

The process of bank erosion is of particular interest in terms of soil conservation as is the washing away of soil during floods in the flood land and depositing of sand and silt in the flood land and river bed.

It is most important to preserve the rich flood land soils. Foodland meadows are the most fertile soil.

Protective forestation. There are two main types of protective forest belts: water regulating and wind breaking. The first type is intended to protect the soil from water erosion. These belts are planted across slopes.

Wind-breaking forest belts are quite different. Their purpose is to reduce wind speed on the fields between the belts.

None of the anti-erosion measures and hydraulic works can be effective without protective forest belts. In the places where the forest belt system has been created with due account for the direction of the most harmful winds, crops and soil are not harmed by the wind and harvests are higher, as a rule.

These belts should also be considered as the habitat of wild animals, recreation sites and in terms of their aesthetic value.

Ex.6 Give the definitions of the following notions:

soil erosion, wind erosion, mud and stone streams, bank erosion, protective forestation, water regulating forest belts, wind breaking forest belts.

Date: 2015-09-02; view: 1216; Нарушение авторских прав