By Tom Burfield

Fertilizer prices have dropped from last year’s record levels, but the product still accounts for a major portion of your growing costs, and there’s no guarantee that prices won’t start to inch upward again.

University experts and industry professionals say there’s a lot you can do to rein in fertilizer costs. Researchers have logged savings of up to 40 percent by improving application efficiencies and adjusting fertilization practices.

One method that seems to be gaining favor among Florida citrus growers is variable-rate application.

Growers who use this method take into account the varied maturity levels of trees in a grove, the size of the trees’ canopies and other factors that can affect the trees’ nutrient needs, rather than just spreading an equal amount of fertilizer across an entire grove—including areas where nothing is growing.

“There are a number of different ages of trees in the grove at any given time,” says Arnold Schumann, associate professor in the soil and water science department at the University of Florida’s Citrus Research and Education Center in Lake Alfred.

That’s especially true in Florida, where hurricanes, freezes and diseases have wiped out thousands of citrus trees, resulting in large numbers of resets in some groves.

Young trees need less

Nutrient requirements for younger trees are less than those for more mature trees, so it makes sense to limit costs by adjusting the amount of fertilizer you apply.

Schumann helped tweak equipment that basically measures a tree’s canopy and then applies the appropriate amount of fertilizer for that particular tree. The practice has been used for grove spraying for about 20 years. By making some refinements, researchers were able to adapt that technology to fertilizer spreaders about six years ago.

Most existing granular fertilizer spreading equipment with a spinner disk can be retrofitted with hydraulic controls, which turn applicators on and off, and “tree-see” sensors that determine when and where to apply fertilizer.

“The machines are adapted to apply fertilizer independently to the left and right sides,” Schumann says.

The amount of fertilizer you can save is proportional to the variability of the trees in the grove. The higher the variability, the more you’ll save.

Although Schumann saved 40 percent in one old grove with many reset trees, he says the average cost saving is 25 percent to 30 percent.

He estimates the cost to retrofit is $10,000 to $15,000, depending on the devices and the type of equipment they’re installed on.

Hundreds of the spreaders have been sold, he says, but still, about half the industry has not yet picked up on them.

“Technology takes awhile to be adopted,” he says.

Hurricane damage

As a result of hurricanes four years ago, Gapway Grove Corp. in Lake Alfred ended up with several non-uniform blocks, says owner John Strang.

For awhile, he did his best to manually control the amount of fertilizer he applied to the new trees. When it came time to replace his fertilizer spreader, he bought one with a split chain applicator and had the necessary hydraulic valves and electronics installed to convert the unit into a variable-rate spreader.

Photo by Andrew Schumann, University of Florida

Tree-sensing technology has been added to existing fertilizer equipment to apply nutrients based on tree canopy size.

After only eight months, Strang says he saved enough fertilizing his 2,300 acres of citrus for the unit to pay for itself.

Using the system requires some training, available from the university or from the manufacturer. Strang suggests having one person drive the tractor and another to monitor the application process to make sure the fertilizer hits the right spot, and that the right amount is coming out.

Once you get the hang of it, the process is quicker than traditional spreading and reduces the need to keep refilling the spreader, he says.

Money-saving steps

A number of other cost-saving practices are relatively easy to implement.

For example, you can use slow-release fertilizers, says Tom Hackle, salesman for Growers Fertilizer Corp. in Lake Alfred. They cost more initially, but they eliminate labor costs for repeated applications.

Another suggestion: Make more frequent fertilizer applications—perhaps four or five rather than three—but use less product. You’ll also give your trees a more constant feeding of nutrients throughout the crop year.

Hackle says, for example, a grower might apply 170 pounds of nitrogen per acre to every other row, every other month rather than applying up to 240 pounds per year. At $600 per ton, the savings can be significant over a 1,000-acre grove.

If you’re not sure about the ratio of nitrogen, phosphorous and potash to use, simply consult with your salesman, he says.

Efficient fertigation

Fertigation—injecting liquid fertilizer into your irrigation system—is a highly efficient application method and another way to save money. But Schumann says it can’t be used with a variable-application setup.

“It’s a good supplementary system,” he says, especially in Florida during the summer when rain can wash away granular fertilizer.

The two methods can be used in conjunction by applying the same amount of nutrients to all the trees through fertigation, then making up the difference for older trees through variable-rate application.

Barben Groves, a 1,000-acre ranch in Avon Park, saves 15 percent to 25 percent by using variable-rate fertilization and fertigation, says vice president Bobby Barben.

“When I fertigate, I put (fertilizer) just where the root zone is,” he says.

He also makes more applications—perhaps six dry and four liquid—with smaller amounts of fertilizer.

Barben says he doesn’t necessarily use less fertilizer, but he tries to get more out of the fertilizer he does use.

“I don’t apply it to where a tree is not,” he says.