The technical term foris IRRIGATION. It is the application of water to plants either outside or under glass. Of course it is especially important under glass because there is no natural rainfall inside a . The most specialized methods of irrigation have evolved under glass where the application needs to be both efficient, accurate, and often automatic to save on labour.
WATER OF GREENHOUSE CROPS
1. WATERING CAN. Can be used for both watering and. It is a reasonably accurate and flexible method, but is also slow and costly on a large scale.
HOSE PIPE. This also can be used for watering and feeding, and is a flexible and accurate method in skilled hands. On the other hand it is costly in terms of manpower and can damage the soil structure unless the pressure is controlled.
SPRAYLINES. These can be either low level at the height of the crop, or slung above the crop on supports hanging from the greenhouse roof. Overhead spraylines have a wider throw than low level spraylines, and so fewer nozzles are required. Both systems can be used for watering or feeding. Overhead spraylines tend to overlap, thus producing variations in the application rate. High pressure, and high flow rates are required.
Low-level spraylines are useful because they can be set up to water the whole bed by using a larger nozzle size. The throw can be variable because nozzle delivery overlaps; this tends to produce a variable application rate over the whole area; this problem is also noted above for overhead spraylines.
Types of sprayline NOZZLE I) Anvil mist nozzle ii) Pin-jet iii) Rotary sprinkler
The watering equipment mentioned above can be used on outdoor crops as well; where nozzles such as the pin-jet and anvil mist nozzle are used outside, there may be problems with excessive drift due to the wind blowing the fine water droplets, so it would be advisable to use a nozzle type which produces larger coarser droplets which are not moved so easily in the wind. The rotary sprinkler would be useful here (see iii above).
SOME OTHER WATERING EQUIPMENT
1. A small oscillating spray unit for use on a lawn or vegetables e.g ‘The Lawn Queen.
2. Static spraylines with the nozzles arranged to give a cover either side of the pipes in the shape of a rectangle.
3. A pressure operated oscillating sprayline operated by a double action piston mechanism.
The area covered is rectangle shaped; this system usually operates off 25 mm (1 inch) pipe, and is a low pressure high volume system.
4. ROTARY SPRINKLER HEAD. Water is forced out from the nozzle and hits the breaker plate. This breaks up the water droplets and deflects the plate. The plate rebounds against the spring thus rotating the head in a series of short jerky movements. The spray pattern is circular.
5. LAYFLAT TUBING: Can be used outside or under protection. Consists of 50mm (2in) polythene tubing. Water passes out through pin-pricks in the tube.
6. SEEPHOSE. This consists of stitched polythene pipe. Water passes out through the stitching. With these two systems, the area covered is a long narrow strip or row. These two techniques are called trickle irrigation.
ADVANTAGES OF TRICKLE IRRIGATION
1. Useful for tunnels, propagating frames or beds.
2. Slow and accurate application of water.
3. Soil structure is not damaged.