Irrigation Necessity and Types Questions and Answers

Answer: D

The difference is the intake opportunity time.

In surface irrigation the advance curve records when water first reaches each point along the field, and the recession curve records when water disappears from it. The time between the two at any point is how long water stands there and can infiltrate: the intake (infiltration) opportunity time. Its variation along the field governs how uniformly the water is applied.

Time of concentration, lag time and time to peak are watershed runoff terms describing a hydrograph, not the wetting interval in an irrigation event.

Answer: C

The answer keyed is that sub-irrigation is useful where there is capillary movement in the root zone.

In sub-irrigation, water is applied below the surface, by raising the water table or through buried pipes, and reaches the roots by capillary rise. It works where the soil has good capillary movement into the root zone, a fairly permeable surface layer and an impervious layer below to hold the water table up.

Saline water is unsuitable, because water rising by capillarity and evaporating leaves salt at the surface. A heavy clay transmits water too slowly. And the absence of a hard pan is a drawback, since a hard pan below the root zone is what keeps the raised water table from draining away.

Answer: D

Conjunctive use means the combined use of surface and ground water resources.

Conjunctive use plans the use of canal (surface) water and well (ground) water together, so that each makes up for the other's weaknesses. Groundwater can be pumped in dry years or at times when canal supplies fail, and surface water can recharge aquifers in wet years. It also helps control waterlogging in canal commands by pumping out the rising groundwater.

Combining irrigation with hydropower is multipurpose use, use by cooperative farmers is a form of management, and use in both kharif and rabi is a cropping matter. None is conjunctive use.

Answer: C

The method is Furrow irrigation.

In furrow irrigation, water flows in small narrow channels (furrows) between rows of crops such as maize, cotton, sugarcane and vegetables. Only part of the ground surface is wetted, so less water is lost to evaporation and the consumption of water is lower than in methods that flood the whole field.

Basin and flood irrigation both cover the entire area with water. Perennial irrigation refers to supplying water throughout the crop period from a reliable source, not to the way water is applied to the field.

Answer: C

The true statement is that basin irrigation is used for crops that are not affected by standing water for 12-24 hours.

In basin irrigation the field is divided into level plots surrounded by low bunds, and each basin is filled with water that stands until it soaks in. It suits crops that tolerate standing water for a day or so, such as rice, wheat, fodder and orchard trees.

Long parallel strips separated by low ridges describe border irrigation, not basins. Row crops such as maize and sorghum are usually irrigated by furrows. Basin irrigation uses relatively large quantities of water, so 'less time and less water' is wrong.

Answer: B

The correct match is a-I, b-III, c-IV, d-II.

• Flooding the whole field (a level plot surrounded by bunds) is basin irrigation (I).
• Feeding water into small channels between crop rows is furrow irrigation (III).
• Applying water to long strips of land separated by low ridges is border irrigation (IV).
• Spraying water through the air so that it falls like rain is sprinkler irrigation (II).

Every other option pairs at least one method with the wrong description.