Push Early Yield With Advanced Citrus Production Systems

ACPS grove in Florida

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Living in the era of HLB, growers clearly understand that the days of managing groves like the generations that came before them are over. They’ve already begun adjusting production to include aggressive foliar nutrition and intensive psyllid control to live in the presence of the disease.

While these steps are important, more radical approaches are being considered like advanced citrus production systems (ACPS). This style of production incorporates elements of open hydroponics or intensive fertigation, high planting density, and a suitable rootstock capable of developing a compact tree and an efficient root system in the fertigated soil zone.

The driving force behind ACPS is the idea of bringing a new grove into commercially viable production quicker than traditional plantings. This will be increasingly important as HLB threatens to shorten the productive lifetimes of trees and groves. Only a handful of growers have tried the system, including Pete Spyke who was featured as Florida Grower’s cover story in October 2008.

UF/IFAS has been collaborating with other growers to build data on ACPS and its potential in Florida. According to Dr. Arnold Schumann, a soil and water scientist with UF/IFAS, the practice is showing some significant early yields in trials.

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In one trial with Gapway Groves in Auburndale, trees that turned three years old in December yielded 220 boxes per acre using this system. Typically, trees are four to five years old before they begin producing similar yields in a traditional configuration.

The economic advantage of early, high production and return on investment with drip open hydroponics and high-density planting is significant. About one to two years of production costs are saved with ACPS. Economic break-even can occur much earlier (e.g., eight years) with high-density ACPS than with conventional citrus production (13 to 18 years), assuming that trees are kept healthy.

The Auburndale site is located on typical Ridge soils at an elevation of about 160 feet above mean sea level. It was previously used for a traditional low-density citrus grove with a standard production system using old fully grown trees with resetting.

Several densities of trees were planted in the grove with a conventional spacing planted as a control. Densities included: 10×20 feet (218 trees per acre), 8×18 feet (303 trees per acre), and 8×15 feet (363 trees per acre). All rows are orientated north-south with four replications in a randomized complete blocks design, covering a 14-acre block.

“To make a credible economic comparison requires full analysis of all establishment costs, the production costs for three years, and the fruit yield and quality for two seasons,” says Schumann. “We are in the process of conducting this analysis. In the interim, it is fair to say that by growing trees faster, the time saved in years are therefore savings of production costs, too. For example, if ACPS gets the trees to a productive size in three years, equivalent to 4½-year-old trees grown conventionally, then the method has saved the grower one and a half years of production costs.”

“I think this grove trial has demonstrated that we can bring a grove into production quicker,” says John Strang, Gapway’s grove manager. “Thus far, the 8×18 (302 trees per acre) looks good to me. I think as long as you have a rootstock that will make a smaller tree, this spacing might be a good compromise between early yields and something that can be maintained and harvested with existing equipment.”

Push Early Yield With Advanced Citrus Production Systems ctd.

Arnold Schumann and John Strang

The Name Of The Game: Fertigation

An essential element of ACPS is intensive management of irrigation and fertigation. At the Gapway Groves location, automated computer controllers and soil moisture sensors are used to manage the drip fertigation to develop an efficient ball of feeder roots at each drip emitter.

“We installed a Netafim NMC Jr irrigation controller to automate the irrigation and fertilizer injection for the different experimental treatments,” says Schumann. “Remote control of the controller is possible via a data radio link and broadband Internet service. The system can be monitored and controlled from a PC or an iPhone.

“Drip fertigation is scheduled to maintain the rootball of each tree at near field capacity, while applying dilute balanced nutrient solution on a daily basis. The strategy of keeping solution nitrogen (N) at close to 100 to 150 ppm worked well in the first two years, and by recognizing the tree size and fruit load in the third year, we applied about 0.5 g N per tree per day. Quarterly leaf tissue samples were analyzed for nutrient concentrations and were used to make course corrections in the fertigation schedule.”

“As for irrigation, I think you need both drip and the microjets,” says Strang. “Without drip, I don’t think you really have an ACPS, and I wouldn’t want to go without the cold protection the microjets provide.”

Understanding that many groves are already equipped with microsprinkler irrigation, Schumann conducted trials using fertigation through these systems as well. His findings are that fertigation with microsprinklers is less frequent on two- to three-day intervals when compared to drip application. Data shows that tree growth and yield per tree for the two fertigation systems was comparable in the second year but in the third year the drip fertigation outperformed microsprinkler fertigation.

 

Fertigation with microsprinklers is difficult in the rainy summer months.Schumann used a single application of Harrell’s UF controlled release fertilizer in June to supply the trees with nutrients from June to September. There was no fertigation with liquid fertilizer during that period. Schumann adds that fertilizer and water use efficiency with microsprinkler fertigation is lower than with drip fertigation.

HLB Rages Onward

Unfortunately, the incidence of HLB has tracked along with other new citrus blocks in Gapway’s ACPS grove. HLB was discovered for the first time in August 2010, remained low (0.1%) into the beginning of the third year, and infected trees were destroyed. In October 2011, the HLB incidence exploded dramatically to an average of 8.5%, with close to 24% in the western boundary area. Closer examination revealed a number of infected neighborhood yard trees with a separation of only 95 feet from the experiment’s western boundary. “We expect that adult psyllid fly-ins from the neighboring trees would have contributed greatly to the rapid upturn in HLB incidence,” says Schumann.

Other factors contributing to the alarming HLB infection include a diminishing efficacy of systemic soil drench neonicotinoid pesticides as the trees grow beyond 5 feet tall, and the recent increase in PCR-positive adult psyllids in this region of Polk County. With current label restrictions, systemic neonicotinoid pesticides also have limited utility in high-density plantings because the annual dose limit is based on area and is not a fixed amount per tree.

Because of the onslaught of HLB, a foliar nutrition program is being utilized in the Gapway grove and the program will be intensified in the coming year.

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