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Methods of irrigation

The methods by which irrigation is applied to the land should depend, under ideal conditions, on individual land features such as the slope of the land, the crops to be irrigated, and the nature of the water-supply and the ability of the soil to absorb and hold water.

There are four general methods of applying water: 1) by flooding, thus wetting all the land surface; 2) by furrows, thus wetting only part of the ground surface; 3) by sprinkling, in which the soil is wetted with a spray; 4) by subirrigation, in which the soil is wetted only a little but in which the subsoil is saturated. The first three methods come under the general heading of surface irrigation.

Flood irrigation generally requires large streams or canals, gentle topography (ground slopes should usually be no greater than three per cent) and careful leveling of the land. In theory, it should be possible to ensure that every part of the area to be irrigated absorbs the predetermined amount of water; but in practice, although all parts usually receive an adequate amount, some receive too much. For this reason, flood irrigation is more suited to close-growing crops like rice.

Furrow irrigation is a method by which water is run in furrows, normally made by cultivating between crop rows. The earth is thrown up into ridges between the furrows and the seeds are planted in the center of the ridges. Furrow irrigation is very common because it is adaptable to a great variety of land slopes and soil textures and can be used with either large or small streams of irrigation water.

Difficulties may arise with the use of furrow irrigation on unsuitable soils. If the soil is very pervious, the water running along the furrows may sink vertically into the soil without ever reaching the center of the ridges where the seeds are sown. On the other hand, the soil may be so impervious that the water does not reach the center of the ridge and the seeds do not germinate anyhow. A more general disadvantage of furrow irrigation is to ensure that the whole of the irrigation area receives enough water, it is almost always necessary to overwater some parts.

Sprinkler or spray irrigation applies water to the surface of the soil in the form of a spray, and is a form of artificial rain. A common type of sprinkler head is the revolving one, which distributes water radially. This form of irrigation has advantages over other surface irrigation. It can be adapted for use on almost all types of soil, especially sandу soils which absorb water rapidly. It enables erosion to be controlled on steep land and can often be used on soils that are too shallow, too steep or too rolling to be irrigated by surface methods. Small streams of water can be used efficiently with this method, and it is adaptable to all the major crops with the exception of those, like rice, that require standing water. A uniform application of water is made possible, and the amount and timing of the irrigation can be easily controlled. Land is not needed for irrigation structures, and so larger areas are available for cropping. There are, however, a number of disadvantages of sprinkler systems. The water distribution is easily affected by the wind, which may disturb the pattern of
wetting so that some parts get too much water and some too little. The power requirements necessary to maintain the water pressure are usually greater than for other methods of irrigation, and the water used must be clean and free from debris. To ensure the most economical use of the equipment, a constant supply of water is needed. Most important of all, the initial costs of installing such systems are very high. It is especially popular as a form of supplemental irrigation in areas with adequate rainfall.

Subirrigation or subsoil irrigation applies water beneath the ground rather than on the surface. By means of lateral ditches or mole or tile drains, a water-table is maintained at some predetermined depth below the soil surface. From the water-table the water seeps upwards to the plant roots through capillary action. This method of irrigation requires complete control of the elevation of the water-table to ensure that the plant root zone in the soil is kept free from excess water. Lands suitable for this method of irrigation are rather limited; since it requires a special combination of natural conditions. It needs a layer of permeable soil immediately below the surface to allow the free movement of water, and a level surface which should be approximately parallel to the water-table.

Here are some things that farmers are doing to be more efficient: levelling of fields; surge flooding;capture and reuse of runoff.

Ø Levelling of fields: Flood irrigation uses gravity to transport water, and, since water flows downhill, it will miss a part of the field that is on a hill, even a small hill. Farmers are using leveling equipment, some of which is guided by a laser beam, to scrape a field flat before planting. That allows water to flow evenly throughout the fields.

Ø Surge flooding: Traditional flooding involved just releasing water onto a field. In using surge flooding, water is released at prearranged intervals, which reduces unwanted runoff.

Ø Capture and reuse of runoff: A large amount of flood-irrigation water is wasted because it runs off the edges and back of the fields. Farmers can capture the runoff in ponds and pump it back up to the front of the field where it is reused for the next cycle of irrigation.

Word List

to apply - застосовувати	to revolvе - обертатися
to depend - залежати	rapidly - швидко
land features топографічна інформація	to enable - дозволяти
crops - с/г культура	erosion - ерозія, руйнування
nature - походження, природа	shallow - невеликий
ability - здатність	steep - крутий
flooding - дощування	uniform - постійний
sprinkling - дощування	to affect - впливати
to spray - розбризкування	to disturb - порушувати
furrows - поливання по борознах	pattern - рух (струї)
subirrigation- підґрунтове зрошування	free - вільний
heading - заголовок	debris - домішки, бруд
gentle - слабо визначений	supplemental - додатковий
topography - рельєф	lateral - боковий
levelling - вирівнювання	root - коріння
to ensure - забезпечувати	mole or tile drains - to seep - просочуватися
predetermined - визначений
although - хоча	elevation - висота
adequate - відповідний	excess - надлишок
suited - підходящий	layer - шар
close-growing - вологостійкі	surge flooding - поступове зрошення
crops - рослини	capture - збір
to throw up ridges - робити насипи	reuse - повторне використання
adaptable - пристосований	to guide - направляти
textures - текстура	beam - промінь
pervious - рихлий	to scrape - очистити
to sink - всмоктуватися	flat - рівний
to reach - досягти	to release - звільняти
seeds - насіння	edge - край
to germinate - проростати	prearranged - заздалегідь підготовлений
on the other hand - з іншого боку -
overwater to - перезволожений	to waste - витрачати

Вправа 1

Визначте значення виразів за подібністю з українською мовою:

ideal conditions; land features; economical use; a popular form; normal technique of cultivation; a special combination; capillary action; natural conditions; in theory; parallel to the water-table; to sink vertically; to distribute water radially; in the center

Вправа 2

Визначте значення наступних слів виділіть слово утворюючі префікси та суфікси:

to overwater the area; to overestimate results; to underestimate the fact; subirrigation; subsoil irrigation; adaptation; an easily adaptable method; predetermined depth; approximately parallel

Вправа 3