Question

The discharge rate of drip emitters usually ranges from

Answer 1

Drip irrigation, also referred to as micro irrigation, trickle irrigation or localized irrigation, involves dripping water onto the soil at very low rates (2 - 20 liters/hour) from a system of small diameter plastic pipes fitted with outlets called emitters or drippers. Water is applied close to plants so that only part of the soil in which the roots grow is wetted, unlike surface and sprinkler irrigation, which involves wetting the entire soil profile. With drip irrigation water, applications are more frequent (usually every 1 - 3 days) than with other methods, thereby providing a favorable high moisture level in the soil for the plant. As long as the application rate is below the soil's infiltration capacity, the soil remains unsaturated and no free water stands or runs over the surface.

The highest coverage was recorded in the Americas (1.9 Mio. ha) followed by Europe and Asia (1.8 Mio. ha each), Africa (0.4 Mio ha), and Oceania (0.2 Mio. ha). The top ten countries in drip irrigated areas were USA, Spain, India, China, Italy, Brazil, South Africa, Russia, Mexico, and Saudi Arabia. These countries shared 77% of the total drip-irrigated area of the world. In five countries viz. Austria, Israel, Libya, Slovak Republic and United Kingdom, irrigation is accomplished solely through pressurized systems.

A typical drip irrigation system consists of the following components:

Pump unit;

Control head;

Mainlines and sub-mainlines;

Lateral lines;

Emitters or drippers.

The system may include additional features, such as reservoir tanks, filters and fertigation devices.

Design

The pump unit takes water from the source and provides the right pressure for delivery into the pipe system.

The control head consists of valves to control the discharge and pressure in the entire system. It may also have filters to clear the water. Common types of filter include screen filters and graded sand filters that remove fine material suspended in the water. Some control head units contain a fertilizer or nutrient tank. These slowly add a measured dose of fertilizer into the water during irrigation. This is one of the major advantages of drip irrigation over other methods.

Mainlines, sub-mainlines and lateral lines supply water from the control head into the fields. They are usually made from PVC or polyethylene hose and should be buried below ground because they easily degrade when exposed to direct solar radiation. Water distribution to the plants is effected through lateral lines hosting the specific drip devices or emitters. In principle, there are two types of drip irrigation:

Sub-surface drip irrigation - Water is applied below the soil surface.

Surface drip irrigation - Water is applied directly to the soil surface.

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Sub-surface Drip Irrigation

Sub-surface irrigation (SDI) is a more sophisticated and hence expensive and rare method, which employs narrow plastic tubes of about 2 cm diameter. These are buried in the soil at a depth between 20 and 50 cm, deep enough so as not to interfere with normal tillage or traffic. The tubes are either porous throughout, or are fitted with regularly spaced emitters or perforations. If porous, the tubes exude water along their entire length. If fitted with emitters, they release water only at specific points. The released water then spreads or diffuses in the soil. The pattern of wetting depends on the properties of the surrounding soil, as well as on the length of the interval between adjacent emitters and their discharge rates.