Greenhouse Watering Systems Boom Irrigation – Apply Water/Chemicals Solutions More Efficiently


The effective, efficient delivery of water/chemical solutions to greenhouse crops is of paramount importance in successfully producing a greenhouse crop.

Water is effectively delivered when it is applied in a timely fashion and uniformly applied in proper amounts. Compromising on any of the above could unnecessarily stress the greenhouse crop and result in reduced plant vigor, increased mortality and lower a crops marketability.

One of the most efficient methods of effectively delivering water to plants is via an overhead boom irrigator. With. a series of nozzles spaced across a length of pipe, the resulting band of water these nozzles apply is remarkably uniform.

Due to this uniformity, booms are able to apply water/chemical solutions far more efficiently than fixed sprinkler systems. When coupled to a motorized carrier riding on some form of track system, it truly becomes a low cost means of irrigating large areas in a relatively short time period. Booms that have been in operation for over 10 years are not uncommon.

There are two types of watering booms: Wet and Dry

A boom is considered a wet boom if the pipe span is not only used as a support mechanism for the spray nozzles but delivers the water to them as well, hence the name WET BOOM.

A boom that is used merely as a span along which to space the nozzles, but not deliver any water, is considered a DRY BOOM.

The water/chemical solution is delivered to the nozzles via a separate hose line which runs along the boom span using it as a support mechanism by which to feed each nozzle. The Agronomic industry typically uses Dry Booms because the nozzle spacing can be altered to accommodate varying row crop spacing.

Since greenhouse space comes at a premium price, row cropping is not economically feasible. Therefore most booms used in the greenhouse are typically Wet booms and the following discussion will focus on such a boom style.

In comparison to other watering methods, Boom irrigation may place a greater demand on your plumbing system. Booms typically span the width of the greenhouse and are capable of irrigating the entire width simultaneously or in portions depending upon how many valves the boom is equipped with.

Determining water flow requirements for a boom is a function of the # of nozzles the boom is to be equipped with, their G.P.M. output and the inner diameter of the pipe used to supply them. Typical spacing for nozzles is 14″ to 20″ inches.

Outputs run from 0.067gpm* for misting to 0.8 gpm for watering bedding plants or potted crops. *Nozzle outputs are based upon 40 psi operating pressure. The standard pipe size is 1″ id.

Nozzle count is determined as follows:

(Boom length (in feet) x 12) minus aisle widths in inches (divided by nozzle spacing + 1) + edge Count* = nozzle count. *Properly designed booms take into account edge drying by doubling up the nozzles along edges of growing areas.

In some cases these nozzles are mounted on swivels so that a directional spray can be achieved along the edges. With the following information we can determine the maximum load a boom will place upon a plumbing system.

Example:

We have a 3 bay gutter connected greenhouse with bays 30′ wide and a center aisle 24″ wide down each bay. One bay is used to root cuttings, another for bedding plants and the third for potted crops.

We will equip our boom with a special three headed nozzle body, with a nozzle tip appropriate for each particular crop. Our tip sizes will be 0.067, 0.4 and 0.8 gpm. Since we are concerned with maximum loads the boom will place upon our plumbing system we only need to focus on the 0.8 gpm tips.

Our nozzle count is figured thusly: (30 x 12) – 24"aisle width (divided by 14" nozzle spacing + 1) + 4 edges. The result is a boom requiring a total of 29 nozzles. 29 x 0.8 =23.2 gpm demand on our plumbing system. 23.2 gallons per minute is well within the flow rate a 1 " id pipe is capable of supplying so we know that, should we choose, we can irrigate the entire greenhouse width simultaneously.

Controlling nozzle output is only one means by which a boom irrigator can control the amount of moisture it applies. A very important second feature of boom irrigators is their ability to move. A well designed boom irrigator will have a D.C. motor affording variable speed adjustment.

By controlling the travel speed, a grower can deliver precisely the amount of moisture a crop requires and to whatever particular depth desired. Typical speeds range from 3.5 to 70 feet per minute.

Knowing how much water a boom can apply and at what speeds it is capable of moving provides the foundation necessary to answer the following question.

The question is: How much square footage can we expect a boom to irrigate?

This requires knowing the daily moisture requirements of the greenhouse crop. With geographical differences (solar and thermal differences), microclimate differences ranging from the amount of horizontal air flow to soilless mix used, not to mention differences between crops, it becomes a question with as many answers as there are different greenhouses. Typical ranges are anywhere from 10,000 to 20,000 square feet per boom irrigator.

Naturally most greenhouses do not contain 20,000 sq. ft. under a single roof. To irrigate this much area requires a boom designed with an ability to be transferred. Depending on the design of the boom irrigator, this transfer can be from bay to bay or house to house. This is accomplished by means of overhead track systems which allow the machine to be moved to the next area in need of irrigation.

These types of overhead track systems are very similar to ones seen in the dry cleaning industry. With gutter connected houses the machine is usually moved from bay to bay along the end wall.

At each bay a switch is provided to allow the machine to move off the transfer track and down into the bay or continue down the transfer track to the next bay. With free standing quonsets, the machine is moved out the end wall door onto an overhead track running along the outside from house to house. Some boom manufacturers provide booms that pivot allowing them to exit through normal size door widths.

The level of control features now available in boom irrigators runs from simplistic to state of the art. The basic package includes a boom drive system equipped with variable speed and a simple timing mechanism to start the boom irrigator at a particular time of day. More sophisticated controls allow a machine to hold many watering programs each with their own start, stop, multiple pass and repeat time intervals.

Where crop changes occur on the bench they can speed up or slow down to change the water output. The booms can turn the water off where aisles or blank spots on the bench occur and turn the water back on where the bench is full. Some are able to be remote started via environmental computers or devices that measure solar load.

Although booms are capable of watering a crop more effectively and efficiently than most other methods and do so year in and year out with only one paycheck, it is just as important to have a system you can depend upon. Well designed boom irrigators have safety features built in to insure no damage occurs to the crop they are entrusted to irrigate. Several common safety features are:


  • A collision feature that turns the machine travel and water off if it should collide with some obstruction.
  • A low water pressure shutoff feature that stops the machine and turns the water off if it drops below a substandard pressure level. It then waits until the pressure is regained before resuming.
  • A water shut-off feature should a power loss occur
  • Some booms are able to utilize the phone line to call you during off hours should some problem occur. Additionally well designed booms will incorporate modular construction to afford easy change out of parts in the field.

Booms provide growers with a means of increasing their profit margin. Typical boom systems purchased provide a payback period for their new owners within the first year of use. This is accomplished in many ways.

Their more efficient use of water/chemical solutions compared to hand watering or fixed sprinkler systems.

  • The consistent uniformity of application.
  • The timeliness of applying the solution.
  • Enhanced rooting of cuttings and germination of plugs.
  • The ability to reduce or eliminate access aisles formerly needed to hand water and replace with income generating crop.
  • The fact that booms work without requiring a paycheck.

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