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Microsprinkle for Higher Yields

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Are microsprinklers raising the water line on yields? Some veteran users think so. And recent research citing turbocharged yields under microsprinkler is adding new luster to this style of low volume irrigation. Microsprinkled trees at Nickel's Estate near Arbuckle posted 1994 yields of 300-500 pounds above those of drip-irrigated trees, reports UC-Davis irrigation specialist Larry Schwankl.

While those results are turning the heads of growers still undecided about microsprinklers, not a few producers are already seasoned practitioners, including Blue Diamond® growers Tom Fry, Chowchilla, and Chico's Rich Sehorn. Both producers have tried microsprinklers for several years, and find rumors of its efficiency to be soundly based.

"I achieve an overall better balance in the orchard using microsprinklers," proclaims Fry. "Trees tend to keep their leaves longer, and remain healthier."

Sehorn is also convinced. "Efficiency using microsprinklers is a day and night difference" from his prior conventional sprinkler system, he said. "We're now putting microsprinklers on every new acre we plant."

While neither grower knows precisely how much his yields have jumped under microsprinklers, they agree production has improved markedly.

Schwankl's work, however, is putting numbers with the use of microsprinklers, data that has not been previously available. Importantly, his 1994 figures were first-year findings showing yields under microsprinklers which were 500 pounds better than those of surface drip, and 300 above underground drip results in Arbuckle. The yields in 1995 showed no significant difference between the microsprinklers, surface drip, or underground drip irrigation treatments.

"Yields in 1995 were down as compared to 1994 in all irrigation treatments due to the late spring rains," said Schwankl. He will continue to monitor the test treatments in 1996 and hopes that a heavier nut load will provide better information to evaluate the irrigation system effects.

The Nickels' Soil Laboratory study set up in 1990 is a 22-acre microirrigation almond planting that allows a comparison with drip, surface and subsurface. Separate submains apply the drip and microsprinkler systems, allowing irrigation times to be set differently, "ensuring that all trees receive the same amount of water even though the application rate of the microsprinklers is significantly higher than that of the drip systems," explains Schwankl

The microsprinkler trial is outfitted with Bowsmith Fan-Jets, one placed in the treerow midway between adjacent trees. Discharge rate was about 10 gallons per hour with a wetted diameter of 12 feet, said Schwankl. Using this configuration, he was able to show the following comparisons in 1994 and 1995:

While results will vary from farm to farm depending on soil types, variety, climate and other factors, producers like Fry declare yields are indeed better under microsprinklers. With 56 of his 70 almond acres now in microsprinkler, the Chowchilla orchardist is a dedicated convert who has recently added 30 new acres to his microsprinkler program. Still, he doesn't always depend strictly on the system for his water needs. "Sometimes we need to use flooding to make sure the tighter soils will get enough water," he explained. That's particularly important on the hottest days of mid-summer. "But we depend on the microsprinklers a good 80 percent of the time," he estimates.

On his toughest soils, where even flood water does not seem to penetrate well, he says the slow continuous wetting of microsprinklers encourages the moisture to sub down over time. "The bottom line on this is that while I've seen trees on the less desirable soil suffer for water days after flooding, since switching to microsprinklers I've found these trees are developing better root systems than ever," Fry notes.

As an aside, he senses that the soil-churning worm activity is also enhanced under microsprinkler. "It seems when the orchard dries up using other systems, the worms disappear, and that means the soil doesn't get the nitrogen help it needs," says Fry.

First turning to microsprinklers five years ago, Fry says that while it's hard to put numbers on tree production improvements, "I can see there are increases" using the system. "We're talking better tree growth, better tree health, and a tree that simply has more crop on it."

He offers this observation: "I averaged 1,700 pounds before microsprinklers were added, and today I'm seeing top yields in the 2,200 pound range. I can't say for certain microsprinklers make the difference, but I can't say what else might have."

Fry uses a variety of microsprinkler spacing configurations, including sprinklers on either side of younger trees on tight soil, and single nozzles between trees on an older planting.

In one block he placed the sprinklers two feet away from the trees using heads that do not spray water on the trunks. "This is the one I like best," he says. "I'll use it in my future plantings."

His preferences in sprinkler heads is for those easiest to take apart to clean. Peach twig borer eggs often collect in the microsprinklers and need to be cleaned out periodically, he explains.

The system "saves money and some water, but not a lot," says Fry, who adds he selected the system mainly for its better control of irrigation and improved uniformity. "I've got the concept down well, but not quite so regarding management," he smiles. "Still, I don't have to get up in the middle of the night to run water any longer. That's a real improvement in itself, I'd say!"

Almond producer Rich Sehorn of Cummings-Violich Management Company began his experience with the concept "not too aggressively" in the mid-'80s on kiwifruit, but now says he has "everything on microsprinklers."

"We're working 350 acres on microsprinklers today," says the Chico grower. "We're sure of our choice."

All new almond plantings under his company's management will be put in with microsprinkler irrigation, he states. "It enables us to raise trees better on poorer soils. And, since no water hits the leaves, we cut down on our diseases" such as brown rot, shot hole and scab.

"On the other hand, a bit more rust and bacterial blast can develop under the foggier climate created by the micros, he adds. "The higher humidity that persists in the orchards can lead to a bit more rust, but in fact we haven't had a real problem."

Sehorn likes the "improved water distribution" microsprinklers offer, but while he senses actual water savings may be nominal, some efficiencies are achieved in terms of the ability to use smaller pumps, requiring less energy costs, he notes.

Estimating his system installation costs of from $600 to $1,300 an acre, Sehorn said state-of-art designs can easily pass the $1,000-an-acre mark. "But it comes with pluses," he adds, "including a great deal of ability to build more into the system. It is this flexibility that makes microsprinklers worth the money."

One such option made easier in the low volume system, he says, is the ability to be more creative in use of valving. "You can go 10 acres or 60 acres," he set one example, "and accommodate all your soil variations as you go along. The microsprinklers allow us to put on just the amount of water each section of the orchard block requires." Without the microsprinklers, he says, "we couldn't even keep trees alive on some of this ground."

What's more, Sehorn said he's been able to get into production earlier at third leaf, harvesting up to 500 pounds an acre on denser plantings under microsprinklers. "There're really no two ways about it," he declares: "You can definitely grow better trees from age one under microsprinklers." The earlier and better production comes from the additional fruiting wood created by the improved irrigation regime, he believes.

Spoon-feeding nutrients is another plus the low-volume system offers, he points out. "When we put on dry material it pushed right through the root systems under conventional irrigation," he recalls. "Now, we're giving the trees just what they need, when they need it, in small doses that gets it to the right spot. Nutrient efficiency is definitely superior under microsprinkler."

Simply put: "My trees no longer stress," he shrugs. "We're saving water and nutrients and we're growing a better tree with more fruiting spurs. What more could we want?"

On his newest planting, Sehorn believes he has found the best way to configure his microsprinklers using one per tree in 16 by 20 plantings, although he feels two per tree are better on the 28 "diamond" planting spacings.

One tip to low-volume newcomers: "If you miss a week in this kind of irrigation, you'll never catch up," warns Sehorn. "You better be on the job with this one."

Weeds add up to his biggest headache under microsprinkler irrigation, says Sehorn. "The frequency of irrigation means major weed problems," he cautions. "In a system where one little blade of grass can upset your distribution pattern badly (by blocking the water flow from the microsprinklers), weeds become worse problems than ever."

Wind also can upset distribution of the microsprinkler stream easily, and watering at times when breezes aren't present isn't always possible, he adds.

Rodents attracted by the constant moisture must also be controlled, he says, and orchard work schedules may be more difficult to complete in view of the fact the orchard floor is wet more often.

But the advantages far outweigh the drawbacks, he feels. "We're getting yields on marginal soils under microsprinklers that outperform our class one soils under conventional watering systems," he says. "That's progress!"

Schwankl's study at Nickel's will continue to yield new information for almond growers. "We added two lines per treerow in the surface drip system this year to look at the effect of wetting greater portions of the soil," he said. "And, we're using different soil moisture monitoring devices like tensiometers and gypsum blocks more extensively."

At the same time, the study will probe new placements of microsprinklers, including one on either side of the trunk that wets the soil but not the tree. "We've been using a microsprinkler placement halfway between trees, and that's not always the location of the most active roots."

Growers can find additional information in "Micro-irrigation of Trees and Vines," published in 1995 by Schwankl and UC irrigation-drainage specialist Blaine Hanson and water management specialist Terry Prichard, under a California Energy Commission (CEC) and USDA Water Quality Initiative grant.

"Drip and Microirrigation for Trees, Vines and Row Crops," published in 1994 under CEC funding as a project of the Irrigation Training and Research Center at Cal Poly, provides additional updates.

1994 Results 1995 Results
Nonpareils:    
surface drip 1,055 pounds/acre 920 pounds/acre
microsprinklers 1,535 pounds/acre 983 pounds/acre
subsurface drip 1,237 pounds/acre 1,028 pounds/acre
Buttes:  
surface drip 1,039 pounds/acre 746 pounds/acre
microsprinkers 1,551 pounds/acre 727 pounds/acre
subsurface drip 1,233 pounds/acre 877 pounds/acre