Boom irrigation

One of the best technology developments in the last 20 years is the irrigation boom. It works best with plug or cell trays, pot to pot spaced plants or cuttings in beds. It provides precise watering with a minimum of wasted water. The system is easy to install in new or existing greenhouses.

System components
A boom system consists of one or more supply pipes containing nozzles that apply water as the system moves over the plants. It is usually suspended from a single or double overhead rail system attached to the trusses or greenhouse frame. An alternate method is a rail-supported gantry across the width of the greenhouse or bay. Water is supplied by a suspended trailing hose and the unit powered by an electric supply cable.

The least expensive units cost about $4,000. Boom widths to 70 feet are available. Bench or bed lengths to 400 feet can be watered with one setting. Some systems allow the boom to be moved from one bay or greenhouse to another.

A fixed or variable-speed gear motor is commonly used to power the boom. Manufacturers use fractional-horsepower DC motors to allow varying speed of travel. Speeds of 25 to 250 feet per minute are available, allowing a light mist or a thorough soaking.

Adequate water required
As with any automatic watering system, an adequate water supply is necessary. The wide selection of nozzle capacities available allows booms to be designed to fit most water supplies.

Stainless-steel fan or cone-spray nozzles are used to give good coverage. Generally, 12- to 20-inch spacing is used with a nozzle capacity of from 0.067 to 0.8 gallons per minute. Turret head nozzles allow selection of irrigation rate. Height of the nozzles above the plants is a critical dimension to provide that overlap. Additional nozzles may be placed at the ends of the boom to provide extra water for plants near the sidewall or aisles.

Clean water, free of particulate matter, is essential to prevent clogging of the nozzles. One or more filters with a 150 to 200 mesh should be placed in the supply line.

Methods of boom control
The most flexible systems use programmable controllers that allow speed changes, skipping of empty bench areas, selection of boom sections to activate and multiple passes over the same area. Magnets attached to the rail determine where to turn the irrigation water on. If connected to a PC, monitoring and changes in control can be done from off site. Some control systems retain a log of operation.

Safety and reliability are addressed in a number of ways. A variety of sensors may be employed to detect bloom obstructions, mechanical problems, low water pressure or power failure. An alarm can be activated if a problem occurs.

Boom advantages
In addition to the greater uniformity of water application, there are other advantages to a boom system. Less water is needed because the system can be operated to provide the optimum amount of water for the crop. Less aisle space is needed for watering. Labor is reduced as irrigation can be done while doing other chores.

Because of the large number of options, careful selection of a boom system is required. Factors affecting your selection include type and style of greenhouses, cropping system, water quantity and quality and the amount of automation you desire. You should shop around to find a system that is most economical for your growing needs.