Computer Technology Replaces Farmers’ Feel for Watering Crops : Drought: Four growers who use ‘evapotranspiration’ irrigation method are singled out by county officials as models to follow.

David Pommer no longer irrigates the Newman Ranch in Oxnard by pinching the soil to check its moisture and then watering until the ground is sufficiently soaked.

Pommer, manager of the 840-acre ranch, waters the lemon groves based on a computer-generated reading of the amount of moisture lost due to plant usage, temperature, relative humidity, day length, solar radiation and wind speed and direction.

“If you can meet the trees’ needs as closely as possible, you get the healthiest trees and the biggest crop of lemons,” Pommer said. “It’s a new technology that a lot of growers don’t want to get involved with because they don’t trust leaving so much to computers.”

As a conservation-minded grower in an industry that consumes nearly 85% of California’s water, Pommer is one of four agricultural innovators being singled out by county water resource officials as models to follow. The others are Camarillo lemon grower Will Gerry, Ojai orange and avocado grower Roger Essick, and Darrell H. Nelson, president of Fruit Growers Laboratory Inc. in Santa Paula.

Their common practice: irrigating based on “evapotranspiration,” the measurement of total water loss from the soil through evaporation and from the plant through transpiration through leaf pores.

“What a grower is ideally doing is putting on exactly what a plant needs,” said Ben Faber, a farm adviser with the UC Cooperative Extension. “The point is to optimize crop yield. Irrigate too much and you’re wasting water. Too little, and you get reduced yield.”

The six-year drought has broadened interest in irrigation by “ET,” although avid practitioners said they would use the method regardless of the availability of water. About 80% of all plant problems are water-related, Faber said, because the severity of insect damage or disease is heightened in trees stressed by too little or too much water.

The method stands to become far more widely used as growers facing mandatory water reductions must convince suppliers that they are being as responsible as possible. Some growers employing the system may find that they actually use more water, but to a more productive end.

Nelson said he used twice the amount of water per acre on his 54-acre avocado farm as his neighbor last year, but he harvested more than three times the total tonnage of fruit.

“I’m of the opinion that people should be penalized for under-irrigating as well as over-irrigating,” Nelson said.

While irrigating based on a meteorological formula has been practiced for several years in the Central Valley, it is only beginning to catch on in Ventura County, Faber said.

Essick said its shortcoming is that individual plants are assigned a coefficient that is multiplied by the “ET” reading to determine the amount of needed replacement water, and the coefficients may need more fine-tuning.

Convincing growers of the general wisdom of the practice is proving difficult, Nelson said.

“One thing every farmer knows how to do is irrigate . . . but it’s one of the most difficult things we do,” Nelson said. “I’m convinced that this is the way to go, but it will certainly take a while to correct old habits.”

The state Department of Water Resources provides “ET” readings from several Ventura County monitoring stations, but they tend to be less reliable for individual growers because they cover broad geographic areas.

Fewer than half a dozen Ventura County growers have installed evapotranspiration monitoring stations on their properties, Faber said. The systems cost $4,000 to $15,000.

“The advantage is that there are a lot of microclimates in any area, particularly up here in the Ojai Valley,” said Essick, who manages 400 acres for the Ojai Land Co. and a 35-acre family grove.

Nelson also advises his clients on ET irrigation, based on monitoring stations that his company maintains in Piru, Santa Paula, Somis and Moorpark. Within the last two years, the number of customers who consult the readings has grown from about 60 to 160, he said.

“The way most of us are looking at it is it’s not how much water we can save, but how efficiently do we use it,” said Gerry, whose family bought his property in 1937. “It doesn’t help us to save if we get a small crop.”

Gerry irrigates his 76 cultivated acres with a system whose four weather reporting stations relay information to his home computer via infrared beams.

He also is experimenting with a subterranean irrigation system that uses porous, underground hoses made from recycled tires. The hoses, which irrigate about 30 acres, deliver water nearer root level without the inevitable evaporation loss of above-ground systems. Teething coyotes also cannot get at the line, nor can spiders lay eggs in drip dispensers and clog them.

“The difficult thing is that this goes against a farmer’s nature,” Gerry said. “You’re used to seeing water being put out and feeling like you’re doing the trees some good.”

Gerry said he has been toying with different innovations to put his intellectual curiosity to the test. “I have a scientific bent, so this is exciting to me,” said Gerry, who did doctoral work in plant pathology at Iowa State University.

Both Gerry and Pommer said they appreciate the reluctance on other growers’ parts to fully embrace the new technology.

“When you experiment, you run the risk of having to replace the whole system,” Gerry said. “Practical sense is to stick with what’s working.”

“There is always that apprehension that you can pick the wrong irrigation system and jeopardize the financial stability of your ranch instantly,” Pommer said.

For the method to work properly, irrigation systems must distribute water uniformly. Pommer recently spent $300,000 to replace furrows running through 400 acres of his groves with a drip irrigation system that he expects will pay for itself through water and maintenance cost savings within three years.

Pommer said he originally bought his reporting station to alert him when overnight temperatures drop near frost levels. The computer is rigged to call his home phone number and report temperature levels in a synthesized voice.

“We’ll eventually save 50% on our water costs, but that’s not my only incentive,” said Pommer, who believes that the state should issue low-interest loans for farmers to buy their own systems. “My goal is to grow a tree to its genetic potential. This gives me a lot of information that I used to just guess at.”