Controlled-release fertilizers enhance yields and efficiency, but at a cost
By Renee Stern
Controlled-release fertilizers can improve efficiency, boost yield and quality, and reduce nitrate leaching, but whether the gains pay for the materials' higher costs depends on the crop and growing conditions, researchers say.
Polymer coatings on the fertilizer pellets break down gradually and release urea and other nutrients into soil, allowing growers to reduce applications to a single early-season pass through their fields or orchards.
That advantage disappears with short-season crops that already rely on one-time fertilizer applications, says Russ Wallace, vegetable and weed specialist at Texas A&M University's Agricultural Extension Center in Lubbock.
Tests of Georgia-Pacific's Nitamin 30L and Nitamin 43G in cantaloupes, watermelons, chili peppers and processing snap beans show the longer-season cantaloupe and chili peppers gain more potential benefit, Wallace says.
Robert Revels, owner of Robert Revels Farm in Hastings, Fla., has included 20 of his 500 acres of chipping potatoes in University of Florida field tests of various controlled-release fertilizers for the past two years. Current costs make their use throughout his operation prohibitive, he says.
"But one advantage is it's a one-shot deal," Revels says. "It costs money, too, to put out fertilizer in two or three applications for fuel, labor and machinery wear."
With supplies expanding while costs of fuel, labor and conventional fertilizers increase, the price differential is narrowing and making such controlled-release fertilizers as Scotts Company's CitriBlen more attractive, says Tom Obreza, professor of soil and water science at the University of Florida in Gainesville.
Obreza has focused on citrus crops, where cutting fertilizer applications can simplify grove management when younger replants that require additional nutrients are mixed among more mature trees.
Tests also show less nitrate leaching with the use of controlled-release fertilizers compared with both fertigation or conventional dry fertilizer, he says. For growers in areas where leaching is a significant concern, that benefit may tip the balance.
Benefits for growers on sandy soils
Controlled-release fertilizers are a good pick for growers working with sandy soils, says Don Genrich, county agricultural Extension agent in Adams, Wis. Models indicate that without some change, nitrate concentrations in local groundwater eventually will reach an unacceptable level of 30 to 40 parts per million.