But add in a legume cover crop and another short-season oilseed crop, and an intensive rotation may make financial sense, according to trials led by Dan Chellemi, a research plant pathologist with the Agricultural Research Service in Ft. Pierce.
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He stressed that the data are very preliminary and are only from one year of trials.
But Chellemi says the results are promising enough to warrant continuing the trials this season.
“It’s not a system that I’m going to recommend yet,” he says. “It’s something that looks good enough that I’m going to try it again.” David Neill, a tomato grower near Ft. Pierce and a trial cooperator, says the rotation is worth looking at.
“You basically have to have $4 a gallon or better fuel for the economics to work out,” he says. “It’s viable if fuel is north of $4 a gallon and is going to stay north of $4. If we get into and stay at $5 or $6 a gallon, I’d devote part of my farm to growing my own fuel.”
Rotations as pest control
With tighter soil-fumigation rules looming, Chellemi in 2007 began looking at how crop rotations might help break pest cycles caused by growing the same crop season after season.
“What we’re trying to do is incorporate management of soilborne pests into the overall crop management system,” Chellemi says.
But the question remained, how do you entice growers to take land typically planted to a high-value crop out of production?
“The light bulb went off about five years ago,” Chellemi says. “Maybe if they made money on their rotational crops, they would be more inclined to [rotate].”
Several trials had been conducted with sunflowers in North Florida during the 1970s and 1980s as part of an active oilseed research program.
More recently, researchers in Mississippi looked at yield potential of mid-oleic sunflower hybrids in several locations in 2008. After a literature search, Chellemi says he determined that dwarf hybrid sunflowers would be a good candidate, because the crop had relatively good oil yields per acre and required low inputs outside of fertilizer.
After the seeds are pressed, the cake can be sold as high-protein livestock feed.
In addition, Central Florida has three biodiesel processing plants—Lakeland, Dade City and Orlando.
Results not all sunny
During the 2007 fall, Chellemi conducted field trials with three sunflower cultivars on ground near St. Lucie that had been in tomatoes and peppers since 2000.
Because of lodging problems with two of the hybrids, he selected the hybrid dwarf S672 from Triumph Seed Co. of Ralls, Texas, to plant in a spring 2008 trial.
What he found was sunflowers do well during unusually dry periods. But they don’t like wet periods, such as after tropical storms that dump inches of rain on fields.
In addition, they are susceptible to rootknot nematodes, sunflower head rot, Bidens mottle virus and phytotoxicity from herbicide residue carryover.
Sunflower head rot, caused by Sclerotinia sclerotiorum, also causes wilt and stalk rot in sunflowers. It’s one of the most prevalent sunflower diseases in the world.
Growing sunflowers in the same field year after year could increase disease incidence, Chellemi says.
Bidens mottle virus is widespread in the weed Bidens pilosa, which is common in Florida. The virus, which is spread most commonly by aphids, also infects lettuce, escarole, endive, and several other ornamental and agronomic crops.
Should sunflower production ever take off, he says the virus could be a limiting factor unless management techniques are developed.
The 5-acre sunflower test plots produced about 1,700 pounds of seed per acre. These were similar to yields reported in earlier trials conducted in North Florida.
After drying and crushing, Chellemi’s plots yielded about 90 gallons of high-grade oil per acre.
What Chellemi says he also discovered was the oil, if exposed to heat during harvesting or storage, quickly oxidizes, decreasing its quality.
Regardless of the cultural challenges, the economics of growing sunflowers for oil don’t pencil out as long as biodiesel remains less than about $5 per gallon, Chellemi says.
Under Florida conditions, growing sunflowers requires about $500 to $600 per acre in production costs. The largest portion—about 60 percent—is from the 140 pounds of nitrogen required by the crop.
“So we started looking at how we could reduce the production costs and spread the costs out,” he says.
Double cropping helps the economics
During 2010, he added a legume cover crop, which would supply part of the nitrogen, into the rotation. After 60 days, the legume crop is turned under and may provide up to 200 pounds of nitrogen. But not all of the nitrogen is available at once, since it is slowly released during decomposition.
Next, Chellemi planted sunflowers, but only applied 70 pounds of nitrogen.
Once the sunflowers were harvested, he returned with Camelina sativa, a deeprooted 70-day mustard crop known for producing seeds with high oil and high protein content. Because camelina also is a good nutrient forager, Chellemi applied no nitrogen to the plots.
“Now we can make two oil-seed crops with half the fertilizer,” he says of the oneyear cropping system.
Among the questions Chellemi says still need to be answered are ways to reduce fungicide use on the sunflowers and possible pest spectrums for two relatively new crops to the area.
Even if Chellemi addresses potential pests, Neill says the state will need infrastructure to handle the oil seed crops.
“It’s not just going out and planting it and making money,” he says. “You have to extract the oil, market the byproducts and decant the oil.”