Precision irrigation helps farms flourish in arid Southwest

This plot of farmland has all the rural charm of a freshly graded landfill. No water flows down these dry, cloddy, reddish furrows. Sheets of gray plastic two feet wide run between them under the desert sun. One would never guess something was growing here.

But cantaloupe is sprouting under the plastic, and water is flowing under these clods. This is high-precision irrigation, where moisture and nutrients can be monitored and adjusted every day, with the help of a computer.

Water is becoming a commodity that demands precision around here, as urban growth slurps at an already overdrawn supply.

The new technology that farmer Ron Rayner is adapting to these fields is no more novel than the drip-irrigation system that suburbanites use to water trees and bushes.

But on a farm like Mr. Rayner's, this is a radically different way of irrigating. In his cotton fields, drip irrigation uses from a half to a third as much water as the traditional practice of running water down the furrows. Even more important, he is expecting 30 to 50 percent more cotton on each plant.

The conventional method is to run siphon hoses from an open trench down into the furrows every couple of weeks, soaking the surface enough to keep the roots moist until the next irrigation. Now he can irrigate every day to keep the ground around the seedlings at just the right mix of water and fertilizers.

On the sun-blasted deserts of Israel, farmers have been using drip irrigation since about 1965. Since then, California growers have widely adopted it for valuable, intensively cultivated, row crops like strawberries and tomatoes.

Now drip is spreading to the farmers of the American desert, both for the higher yields it promises and for water efficiency.

The ancestry of the technique is apparent from the Hebrew banter coming over the two-way radio in Rayner's office. Like many American farmers in recent years , Rayner took a tour of Israeli farms to learn how growers there coped with a very spare water supply.

He came back, formed a joint venture with two Israelis who had developed a computer-controlled drip system, and began to rig his own acreage with plastic pipe.

About 25,000 acres of Arizona cotton was drip irrigated by the end of last year. By the end of this year, there will be 35,000 acres, according to Dale Bucks, agricultural engineer with the United States Water Conservation Laboratory in Phoenix.

Arizona already has the highest cotton yields per acre in the country, but each acre will need to show a half bale to a bale more cotton to make the drip system pay for itself, Dr. Bucks says. Those results are not in yet.

Rayner has about 300 of the 7,000 acres he and his brothers own under drip now, and he is proceeding with the rest as he can afford it. At a cost of about farm again,'' he admits.

One attraction, though, is that the ground doesn't need to be plowed every year when it's not surface irrigated. And since farm workers can stand in dry furrows, the crop can be irrigated and harvested at the same time.

A drip system also upgrades farm work. Instead of an irrigation crew carrying spades, the system demands a technician who understands nutrients (which are dissolved into the irrigation water) and can program them into the computer.

But saving water is the real reason for drip. Even with the Colorado River water that the Central Arizona Project will be piping into south-central Arizona in a few years, farmers will still be on a strict water regimen.

Farms around Arizona cities are barred outright from tilling land that was not already under cultivation in the late 1970s. Farms outside the restricted areas are still subject to water quotas, based on past use and conservation standards.

''The greatest benefit (of drip irrigation) is the greater use of land in water-limited areas,'' Rayner points out. In other words, a drip system can make the same amount of water cover more acreage.

''What has really brought water management to the fore is not the water shortage but the cost of water,'' notes Herman Bauer, director of the US Water Conservation Laboratory. Water costs about twice what it did a decade ago, mostly in higher energy bills for pumping it.

At the Water Conservation Laboratory, experimenters have achieved irrigation efficiencies of 80 to 90 percent, that is, where that much of the water pumped into the soil is actually transpired by the plant. Some desert farmers, Dale Bucks says, have come close to those efficiencies in the field.

Some, like Rayner, are trying out drip systems on high-value vegetable crops not usually grown in Arizona, and on corn and cotton that are usually surface irrigated. Others are switching to desert crops that require less water, such as jojoba, guayule, and sesame. Others are simply adopting more efficient irrigation methods.