Many of Florida’s natural conditions are perfect for growing citrus. One that’s imperfect is the state’s patchwork variety of soil types, and University of Florida researchers say the situation comes with a price tag for growers and consumers.

If the soil’s nutrient content or water-holding capacity differs from place to place, it can mean lower fruit yields, lower producer profits and higher consumer prices for fresh citrus and citrus juice, said Arnold Schumann, an associate professor with UF’s Institute of Food and Agricultural Sciences.

The findings appear in the current issue of the journal Soil Science.

Citrus groves are typically managed as if the soil were uniform. Consequently, areas with poorer-than-average soil may end up deprived of nutrients or irrigation, reducing the grove’s potential yield by 10 percent to 50 percent, he said.

“Almost every grove has some problems with soil variability,” said Schumann, at UF’s Citrus Research and Education Center in Lake Alfred.

Areas with poor soil produce stunted trees with sparser leaves and less fruit than healthy counterparts, said Kirandeep Mann, a postdoctoral associate at the center.

The UF study explored soil quality indicators such as particle size, soil color and water retention and found better soil yielded more fruit. Researchers also estimated the proper depths for soil sampling in citrus groves to be 18 inches instead of the commonly used 6 inches, and said the proper distance between samples depends on known soil variability.

The research team included Willie Harris and Thomas Obreza, professors with UF’s soil and water science department, and Sanjay Shukla, an associate professor at UF’s Southwest Florida Research and Education Center in Immokalee.

Next, Schumann, Mann and colleagues will develop soil sampling and management recommendations for growers and publish them on UF’s Electronic Data Information Source, http://www.edis.ifas.ufl.edu.

Trying to remedy inconsistencies

Some growers are already mapping soil types and trying to remedy inconsistencies, said Joby Sherrod, a research and development manager with DUDA, one of the state’s largest agricultural producers.

“The striving for uniformity is one of the biggest issues the industry deals with,” said Sherrod, in LaBelle. “When you examine the best blocks of trees, you find those are some of the most uniform blocks in terms of soil condition.”

DUDA grows about 8,000 acres of citrus in Florida, all in Hendry County. The general topography of the land is called flatwoods, and it has greater soil variability than the central ridge areas farther north in the peninsula.

“Even a bad soil, if it’s uniform, is better than highly variable soil, because you can manage it,” he said.

Mann said a practice called site-specific management can address scattered soil nutrient deficiencies, using variable-rate micronutrient spraying and granular fertilization guided by GPS coordinates.

Sherrod described how his company employs site-specific management:

First, personnel test the soil’s electrical conductivity and use the data to map the grove, then divide it into management zones. Next, they choose target locations for soil sampling, take samples and analyze them for various properties.

“Then we start to drive our management practices where we can,” he said.

One property Sherrod tracks closely is soil pH. The company can raise pH in some areas by applying lime, or reduce pH in others by applying sulfur, he said.

Schumann believes soil variability might play a role in the spread of citrus greening, a disease threatening the industry nationwide.

“Soil variability can stress trees, and stress might make them more vulnerable to infection,” he said.