Get Watered Down!

Trends and techniques for drip and drench irrigation
By Curt Harler

Drip irrigation is no longer news. Yet the changeover to drip systems in the Northeast shows how solidly irrigation systems are built and how long they last. The move to drip irrigation, especially for vegetable growers, has been slow and steady over the past 10 years. That does not mean, however, that systems are slow to pay back the investment.

Commercial produce farmers find drip irrigation and plastic are an ideal combination.
Photos by Armando Suárez-Romero.

"In general, you should get your investment returned the first year," says John W. Zimmerman, president of Rain-Flo Irrigation, East Earl, Pa. While he notes that breakeven will depend on the season and the crop's value, he maintains that most growers will pay for their systems and have a bit more after one solid season.

"For commercial produce farmers, drip irrigation and plastic are ideal," he adds.

Jim Peeler, owner of Charles Harris Irrigation, Monson, Mass., encourages growers to look beyond the initial cost of the irrigation system.

"A grower using drip tape will need to replace the drip tape annually in most cases. Each year's tape must be pulled up and disposed of. Labor hours need to be considered. A grower using aluminum pipe and sprinklers or a hard hose traveler will have very different labor costs from the one using drip tape," Peeler says.

Fuel or electricity costs also must be considered. "All of this must be balanced against the increase in value of the crop," Peeler says. A grower should look at a typical five-year period. Keeping in mind the farm's soil, the crops on the farm and the unpredictable nature of rainfall, a grower should compute how many years out of five there will be a benefit to irrigation.

"If there is a significant benefit in two or more years, it's generally worth investing in irrigation," Peeler says. "Many growers would argue that even one dry year in five more than justifies the investment."

It's not just dollars and drought that need to be factored in. "Drip irrigation systems can be used to apply fertilizer where it would be impractical or impossible to get a tractor," notes Armando Su<0x00E1>rez-Romero with Netafim USA. Some likely spots are wet fields, those with high slopes or with tall, established crops.

That helps explain the popularity of irrigation use in high-precipitation areas like New England, New York or Pennsylvania, he adds.

Peeler says there are no earthshaking changes in irrigation technology. "It's more like constant gradual improvement on all fronts, so regardless of the method a grower uses to irrigate, there is always a way to improve," he says.

Zimmerman notes that many growers are learning techniques and technology from neighbors and friends. Any good dealer, however, will walk a grower through the math. It's not all that hard, especially with a small calculator at hand.

Water requirements

"The rain doesn't always fall when we need it," Peeler says, adding that vegetable and fruit growers in the Northeast strive to maximize quality in what they grow and sell. "Having appropriate soil moisture is key," he adds. That means computing the water rate properly.

The standard flow drip tape is .45 GPM at 8 PSI. This flow is per 100 feet of row. Multiply linear feet of drip tape by flow rate to calculate pump requirements. A quick calculation shows 5,000 feet of drip tape X .0045 flow = 22.5 GPM pump flow requirement. That low number will surprise those using over-the-top irrigation.

"Drip tape requires low pressure," Zimmerman says. "Only 8 to 15 PSI at the head lines will give approximately 10 PSI in the drip lines."

"Drip irrigation requires much less pressure than traditional overhead irrigation," Peeler agrees. As a rule of thumb, he says the typical power requirements might be 75 percent less. "In extreme situations, with a well-designed drip irrigation system the power requirement may be 95 percent down. This makes a huge difference in energy consumption, especially with the energy costs we see today," he points out.

One of the first questions to resolve when considering an irrigation system is the water source. Is there water? Is there sufficient flow? Are there local restrictions on drawing from a well or creek?

For operations irrigating plots under 1 acre in size, Zimmerman says any residential-quality well will suffice. The grower can control which rows are watered with a pressure gauge.

"Bigger areas need a 20 to 30 GPM water flow at a minimum," he advises. The alternative is a pond or stream. One advantage of a well is that it requires only a screen filter. A stream or lake requires a more robust back-flush filter or similar.

Backwash filters, rather than the traditional sand filters, are gaining popularity. They are simple to use and, in general, can be installed anywhere near the pump - anywhere there is good pressure in the system.

Drip irrigation systems can be used to apply fertilizer where it would be impractical or impossible to get a tractor.

What fits?

Peeler, and many others, use the terms "drip" and "trickle" interchangeably to refer to any irrigation where the water drips rather than sprays. Micro irrigation includes everything that drips and also small sprayers, sprinklers and misters.

Figuring exactly what will work on any particular farm requires a partnership between the grower and the irrigation firm. "Usually, we walk the fields and look at field maps with the grower to get a full understanding of the grower's needs," Peeler says. He then works up a design and presents it to the grower, and, if necessary, they will fine-tune the design.

One consideration is the size of tape used. Zimmerman recommends 6-mil drip tape for experienced growers only. "It should be used for short-season crops that are not under plastic mulch," he recommends. It offers minimal insect resistance. An 8-mil drip tape is more commonly used throughout the Northeast for most vegetable crops, either under plastic mulch or along rows.

The 10-mil drip tape works best in heavy, rocky soils and where insects and wireworms are a problem. "It is also good for overwinter crops like strawberries," Zimmerman says.

Tuning techniques

For growers who have gone to plastic culture, drip irrigation is ideal. Plastic mulch keeps heat in the soil, controls weeds and helps the soil retain moisture.

"You can harvest while you are irrigating, since the irrigation tape is under the mulch film," Zimmerman points out. Even tall crop producers, like sweet corn growers, can use drip successfully. The secret for sweet corn is to go to tight double rows.

Basically, the idea is to have a single row of drip line run between two narrow rows. These rows might be anywhere between 16 and 20 inches apart. On either side of the double row is a more typical 30 or 36-inch spacing that allows harvesting.

Whether the grower chooses a tight 16-inch space or a wider 20-inch double row will depend on local conditions.

"The latest thing in drip irrigation has been the adoption of it in places like Kansas or Nebraska to replace pivots in very large commodity crop operations with buried systems," says Su<0x00E1>rez-Romero. That trend likely will be seen on the East Coast soon.

Moving away from overhead irrigation spells a lot of savings. For one thing, overhead irrigation takes twice the flow rate. Overhead requires greater pressure and sturdier valves.

Not everything will mesh nicely with drip. Lettuce, for one, still seems to do better with an overhead system.

Center-pivot systems still rule on larger sweet corn operations and for alfalfa.

Life cycle

Most drip irrigation components will last many years. The exception, Zimmerman notes, is the actual tape.

"Small growers with good labor and iron-free water can roll it up and reuse it," he says. However, having iron-free water is a key. Iron will clog the drip lines the following year, rendering it useless.

On any system, Zimmerman recommends producers chlorinate their surface water-using systems every two weeks. "Inject approximately a half-gallon of chlorine bleach per acre," he says. "Run the system for about 20 minutes, then let it set for a half-day before irrigating again."

In addition, pumps and pipes should be drained, says Peeler. Filters should be cleaned. Aluminum pipe gaskets should be checked. Damaged components should be repaired or replaced. Pump primers should be rebuilt, he says.

"In a dry year, irrigation saves crops all over New England," Peeler says. He notes that the typical situation is not as drastic as being a matter of having a crop to harvest versus not having one, but rather having a profitable, high-quality and abundant harvest versus one that is none of those things.

"Growers often look at using sprinklers for frost protection as 'saving' the crop because, without them, they may have little to no crop to harvest. Strawberry, blueberry and cranberry growers do a lot of this," Peeler explains.

Whatever the reason - drought insurance, spoon-feeding fertilizer, frost protection - growers with high-value crops can expect a quick payback on their irrigation investment. It's worth checking into.

Curt Harler is a freelance writer from Strongsville, Ohio.