Don Curlee: Peaches can thrive with less water

Researchers are finding that the 25,000 acres of peach trees in the San Joaquin Valley can produce just as well with about 25 percent less water than has been used traditionally.

Experiments performed by crop scientists from the US Department of Agriculture have shown that applying lower amounts of irrigation water to the trees after harvest permits them to perform all their normal and natural functions and still come back strong for the following season.

The hottest summer weather occurs after the earlier varieties of peaches have been harvested in May and June. Some of these varieties formed the bulk of the research showing that the trees do just as well through the extreme heat of July and August, the time when two-thirds of the year's volume of water is applied, when applications are reduced well below traditional levels.

Conserving water means that costs to pump it from wells are reduced, a result growers surely welcome. Pumping less water also means that their wells last longer.

Deepening wells and installing larger pumps have been recurring expenses for years for growers of peaches and other tree fruits.

USDA researchers Dong Wang and James Ayars performed their deficit irrigation research on a four-acre plot of Crimson Lady peaches at the University of California's Kearney Agricultural Center in Parlier. Three types of irrigation were used: microspray, subsurface drip irrigation and traditional furrow application. Standard commercial practices for fertilization, pruning and fruit thinning were followed.

Their results showed that applying only 25 percent of the water normally used resulted in a negative impact on the following year's fruit yield and quality, and an increase in deformities. But cutting normal water applications by 50 percent resulted in a 60 to 69 percent savings of water use with minimum effect on the following year's fruit quality and yield.

They found that trees needed less pruning and maintenance because the deficit irrigation slowed plant growth. "Most of the water savings we saw occurred during the hottest part of the year," Ayars said, "when demand for water is highest, so there's real potential for savings."

Subsurface drip irrigation tended to result in the lowest yields within a given year, but the differences from the other two means of application were judged generally not to be statistically significant.

A caution of sorts was issued by the researchers' finding that the margin of error is much smaller in regard to avoiding yield losses when trees are managed under deficit irrigation. Both the amount of water and the time it is applied must be carefully managed.

Researcher Wang and agricultural engineer Jim Gartung at the USDA Agricultural Research Service facility, also in Parlier, are evaluating to find whether thermal technology can help save water by determining precisely when peach growers need to irrigate their orchards. Infrared temperature sensors, instruments used consistently in the 1970s, have been their basic measuring stick.

They have found that the differences in temperature between the tree canopies and the surrounding hot summer air can be between 10 and 15 degrees for the water-stressed trees. The canopy-to-surrounding air differential in trees not water-stressed is normally three to four degrees.

"We have proved that this is a viable approach to managing deficit irrigation in peaches," Wang said in an article in the November-December issue of the USDA publication Agricultural Research. "Now we want to give growers the tools they need to use it."

Talking tools to any grower is sure to hold his attention. Talking water savings to almost anybody in the thirsty San Joaquin Valley guarantees a captive audience.

CONTACT Don Curlee at agwriter1@sbcglobal.net