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2.5. Read the text and carry out the following assignments:

1) find the sentences related to the principles involved in subirrigation;

2) read the sentences concerning the efficiency of subsoil irrigation;

3) find the paragraph mentioning the methods of irrigation used in recent years;

4) find the sentences describing the ways of water percolation into the soil profile;

5) translate the text into Ukrainian.

Text a. Principles of subirrigation.

1. Subirrigation is a method of applying water beneath the ground surface. Moisture reaches the plant roots through capillary movement.

2. Within recent years this method of irrigation has become one of the most wide-spread in the agriculture. Its application efficiency varies from 30-50 per cent in some areas up to 70-80 per cent under favourable conditions.

3. Subirrigation requires permeable soils. For successful subirrigation an adequate supply of water of good quality must be available throughout the growing season. The topography must be nearly level and smooth.

4. A barrier against excessive losses through deep percolation must exist in the soil profile. The barrier may be a relatively impervious layer in the substratum.

5. The distribution system must consist of a well planned system of main ditches, field laterals and structures which will permit the water table to be raised to a uniform depth below entire area. An adequate outlet for the drainage of the irrigated area must be provided for, particularly in humid areas.

6. The principles involved in subirrigation are practically the same in all areas, although the means of introducing water into the soil profile may differ. Lately one of them has found a wide application: an artificial water table is created over a natural barrier that prevents deep percolation of the water.

7. Water may be introduced into the soil profile through open ditches, through mole drains or through tile drains. Up to the present the first way has proved to be the most efficacious, and it will likely have become prevalent by the nearest time because it is relatively inexpensive and is adaptable to all the soil types that can be subirrigated. Mole and tile drains can be used in organic soils.

8. The main crops so irrigated are potatoes, beets, onion and corn. Under limited situations subsoil irrigation had always been a very desirable system of irrigation. In general, however, it must be used with great caution. Danger from waterlogging and salt accumulation is great.

9. Mole drains are formed by drawing a bullet-shaped cylinder through the soil to make a hole about four and a half inches in diameter. In suitable soils, moles may last for 5 years and be redrawn at low cost.

10. The extensive use of drip irrigation, impulse sprinkling and mist irrigation has in recent years enabled farmers to expand the total area of irrigated lands. These methods are designed both to meet the plants’ biological requirements and to save irrigation water.

III. Vocabulary study

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