Developments assist with vine irrigation decisions

Not surprisingly, the soil is wet just below the surface. It has been a relatively wet winter in the San Joaquin Valley.

While that may be a bit reassuring, he knows making a judgment about how much water is available to those vines with a scuff from his boots is like judging a novel by its cover.

However, an arm’s length away from where he is standing tacked to a grape stake is an open book revealing the whole water story of that vineyard down to five feet below the surface.

All Wilson had to do was push a button on an AM400 data logger from MK Hanson and LCD screen reveals to him what the moisture content is in the soil beneath those vines 18 inches, three feet and five feet deep. Push the button again and the data logger will give him a water history five weeks back.

The data logger is connected to several Watermark electrical resistance blocks, 3-inch long cylinders that use electrodes to estimate soil moisture tension at three different levels. Attached to the bottom of half-inch PVC pipe, they operate on a principle similar to a tensiometer or gypsum block.

Needs no downloading

"What makes the Watermarks and data loggers different is that the system is inexpensive and easy to use. It costs about $400 for six probes and the data logger," said Blake Sanden, University of California Cooperative Extension irrigation and agronomy farm advisor for Kern County. "The data logger is the only one of its kind that does not require downloading to a computer for data display and analysis."

It has proven to be one of the simplest and least expensive soil moisture monitoring system yet.

This system is just one of many new technology tools growers and consultants are utilizing to measure soil and plant water levels.

Wilson has used them all from neutron probes to pressure bombs to measure leaf moisture content to muscle powered soil augers.

"I do not know of a grower who has who has personally invested as much time and energy looking at irrigation management," said Sanden, who first began working with Wilson on irrigation monitoring and management almost a decade ago.

Water is an increasingly costly agricultural input in California and Arizona, making water efficiency go directly to the bottom line.

However, the importance of water management reaches much further than that. Groundwater protection is looming as a bigger issue each day and that goes directly to fertilizer management, making sure water and nutrients stay within the useable root zone for use by plants.

While maximizing yields is directly related to good water management, crop quality is becoming a bigger factor in this era when quality may sell a crop when poor quality nets rejection of deep market discounts.

Deepest price trough

Wilson has been a grape grower in Kern County for four decades. He’s has seen the bottom of three major grape price troughs in that period of time. The one the industry is now in is deeper than any of the others, he said.

As the industry experiences what Wilson bluntly calls a "glut" Wilson expects vineyards to continue being dozed out in the coming year. What’s left in will have difficulty finding a winery home over the next few season unless the quality is what the winery wants.

Quality is determined by many factors, but deficit irrigation at the correct time in the summer growing cycle is one that is getting a lot of attention lately. One of the complaints from wineries is that SJV producers historically have gone for tonnage rather than quality and have irrigated toward that goal.

"In general, if we can give berries more light — not necessarily heat — we can improve color in red varieties. And, if color improves, flavor and quality can improve," he said.

That involves canopy management; holding down vegetative growth.

"Forty years ago Thompson seedless was a three-way grape in the San Joaquin valley; wine, table grapes and raisins and everyone farmed all grapes like they were Thompsons," he said.

That is no longer the case as growers have planted more varietal wine grapes. "People are becoming more quality conscious in producing wine grapes in the San Joaquin Valley. That involves picking the right varieties for the valley.

"A lot of the fighting varietal acreage was planted in recent years and some varietals are doing well but others are not. Syrah and Ruby Cabernet are two varieties that are making good valley wine. Chardonnay out of the valley can make decent wine," Wilson said.

Southern and Central San Joaquin Valley wine grapes may be considered bottom rung in the hierarchy of California wine, but Wilson, like so many valley grape growers, point out that 60 percent of the state’s wine grape production comes from this area.

"Everybody always talks down about the valley, but the wine from our grapes finds its way into wines sold out of other areas of the state," said Wilson.

"Quality is achievable in the valley — if we pay attention to what we are doing," he said.

Deficit irrigation

Deficit irrigating is one way to achieve that. But, timing has to be right. Wilson said that period from bloom to verasion is when he wants to manage the canopy by forcing the vine to be "thrifty" rather than go vegetative.

"When you start irrigating less than the full evapotranspiration rate, you are running some risks," said Wilson. "We have learned a lot about this from the Australians, but there is a story out of Australia about the risks involved in deficit irrigating."

The seasons are opposite Down Under. It’s hot there during December. One year a producer took a four-day Yuletide holiday and when he came back his pump had broken down and he lost half his grape crop in his vineyard where he had been deficit irrigating to improve quality.

"If you want to improve quality with deficit irrigating, you have to be hands on in irrigating," said Wilson.

Watermark sensors wired to in-field data loggers make it easier.

Wilson typically puts one sensor per 40 acres block. There could be more where soil variability is greater. They measure moisture through the soil profile.

"The idea is to have adequate moisture in the soil profile without flushing water through the bottom of the profile," said Sanden.

Other measures

Wilson does not rely on the soil moisture sensors alone. He still contracts for neutron probe readings and will use a pressure bomb to gauge water uptake of vines.

"You can have adequate soil moisture, but for some reason the vine will not take it up. Measuring leaf water content will help you identify those issues," said Wilson.

"We try to use as many tools as we can," he said.

Wilson irrigates with flood and surge irrigation as well as drip. He estimates that with new irrigation monitoring technology, there is an "opportunity" to reduce water use by 25 percent from what it was just a decade ago.

"Drip has made a tremendous difference in how we manage water," Wilson said. "Most of our newer vineyards are on drip."

"Water is certainly a cost, but from an ecological standpoint you never want to waste water. What we strive for is to do the same job with less water," he said.

Reduced or better managed water use also affects other parts of the vineyard operation. "For example, if we find through oil soil monitoring that we have adequate soil moisture in the spring, we can do a few more operations like mildew control or weed management before the ground becomes wet from irrigation."

Sanden has been working with about a dozen Kern County producers over the past two season using these sensors and the Hanson data loggers.

"Farmers know that knowledge is the key to more efficient irrigation practices," said Sanden. "Knowing for sure what is in the crop root zone at any given time tells you whether you are putting on too much or too little water to meet crop needs."

Quality effects

However, just as important today is crop quality related to water management.

"Proper irrigation management at the right time is the key to increasing fruit set and quality in many crops. Wine grapes are one and canning tomatoes is another," he said.

"There is evidence that you can improve Brix in tomatoes by a little bit of deficit irrigating at the right time," he said.

"Irrigation management has always been important to fruit set in cotton. Deficit irrigating cotton to force fruit set may not be as critical as it once was with the newer varieties and Pix, but you still do not want cotton become over-lush," he said.

The plant growth regulator Pix is widely used to control cotton vigor and force fruit set, but Sanden said some of the newer varieties do not readily respond to it. "Irrigation management is the key to keeping the growth manageable. And once cotton is loaded it hits those July temperatures, you want to make sure you have sufficient water to avoid stress."

There is also some data to indicate deficit irrigating pistachios will result in weaker shells and perhaps more desirable shell spits.

"Blackeyes can tolerate a little bit of deficit irrigation until first flower," said Sanden.

Conversely, crops like alfalfa and melons do not tolerate deficit irrigation.

"With alfalfa you absolutely want to make sure it has all the water it can use, but at the same time you don’t want to waste water. Water-logging alfalfa is just as detrimental as deficit irrigating the crop," said Sanden.

Irrigation is often called more art than science. There is a mystery about it because short of backhoeing fields weekly to visibly look at soil moisture content, there is no way producers can tell for sure what is beneath the surface.

The days of irrigating when your neighbor irrigates is gone the way of high commodity prices. Growers must relay on some sort of monitoring technology.

Sanden and Wilson believe Watermark sensors and Hanson data logger are about the most reliable, inexpensive and easiest to use.

"They are not foolproof. They require maintenance. They are less reliable in certain soil conditions, like real sandy soil. They don’t work on some crops. Melons are an example of that," said Sanden.

However, Sanden said the ease of use and low cost represent a price breakthrough in taking some of the mystery out of irrigation management.

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