Do More With Less

Freeze protection is not the only area where Santos is trying to squeeze out water savings in strawberry production. He's also researching ways to reduce irrigation needs for plant establishment and crop maintenance.
Growers commonly use sprinklers for 10 to 12 days for plant establishment, running the sprinklers for 10 to 12 hours per day. To maintain the crop, most growers have one drip tape in the bed and irrigate anywhere from two times per week up to five times per day. On average, growers apply 14 to 18 acre inches of water per acre for crop maintenance (1 acre inch = 27,154.2857 gallons). When freezes occur, growers generally apply about 3 acre inches of water.

According to Santos, crop protectants, intermittent sprinklers, use of plant plugs, and polymers all are being studied for applications in reducing water demands for crop establishment.
"We are looking at crop protectants that are based on carbon carbonate, kaolin clay, or wax," he says. "These products can reduce transpiration and are biodegradable and — most importantly — are dirt cheap."
Santos tried to reduce the number of days plants are watered when kaolin clay was applied from the standard of 10 days. He says data indicates growers can achieve the same plant establishment with seven to eight days of sprinkler irrigation when kaolin clay was applied after the sprinklers were turned off.
"In plain English, this means you can establish the plants with 30% to 40% less water than you have been using and maintain the same yields," he says.

 

Santos and fellow scientists also are studying if cheap plant plugs could reduce costs and water needs. "Why a cheap plant plug?" he asks. "Because we are now using more expensive bare-root transplants that run anywhere from 8¢ to 13¢ per plant. If we can get a plant plug to work and get it established with minimal water, it would be a tremendous advantage to us.
"Along with this, we are working with polymers, which would allow water to stay longer around the crown of the plant. This could have a cooling effect on the root system while it is getting established and probably reduce the water needed."

In crop maintenance, drip irrigation is being studied to see what is the optimum volume and duration for best results. This is the area where programs vary the greatest from one grower to the next. Santos looked at 30-minute cycles versus one hour and two hours for drip applications and the impact on early and total yield. He found the crop yielded pretty much the same across the different timings.
"What we've settled on for a recommendation is one hour per day for irrigation," he says. "We found the highest yield with one hour of watering in two 30-minute cycles per day, although if you have low-volume irrigation, it is better to stick with one cycle. Anything over an hour, you are probably wasting time and money."

In the world of freeze protection, there is a lot to choose from. After the last several winters, Florida growers are keenly interested in sorting out practical alternatives to overhead sprinklers for freeze protection.
"We are looking at low-volume sprinklers, crop covers, foam, and high tunnels for freeze protection," says Santos. "All have pros and cons."
Field covers can provide about 5°F to 7°F of protection to plants, but are expensive and labor intensive. The covers cost about $1,000 per acre. Santos also will be testing the covers for food safety concerns, considering the covers will be put on and taken off the crops multiple times.
Foam can provide 5°F to 10°F of protection, but tends to disappear quickly. "Imagine if we have three freezes one after the other," says Santos. "The first day the foam might work, but what about the next day, because it only last 18 to 24 hours. You'll probably have to reapply."

In 2010, there wasn't much in the way of strawberry production under high tunnels in Florida. But, this year, more growers are giving the practice a try. Santos has several years of data that show the benefits of high tunnels for freeze protection and overall yields.

 

He provided an example of the benefits of high tunnels for freeze protection from a frosty night on Jan. 3, 2008. That particular event dropped temperatures to 27°F outside, requiring 3 acre inches water to protect the plots at GCREC. However, under the tunnel, it was 43°F and no water was required.
"We've not used a single drop of water to freeze protect the strawberries under our tunnels during any of the freezes since we've had them in place," says Santos.

 

Besides freeze protection benefits, higher yields with better quality have been recorded under the tunnels. "Under the tunnels, we are not killing flowers, quality is high, and we don't have rain damage," says Santos. "In addition, tunnels can allow you to produce varieties that can't be grown outside in Florida."

 

While high tunnels offer advantages, Santos cautions they are a considerable investment, which requires intensive management. "If you have that much money invested in a high tunnel, you'd better consider a second high-value crop like melons to follow your strawberries," he says.

Data collected at the GCREC shows a consistent yield advantage for strawberries grown under high tunnels.
Strawberry Yields 2007-2008 and 2008-2009

 

 

Special thanks to DuPont Crop Protection for being exclusive sponsors of the Florida Ag Expo's Extended Coverage.