Citrus Production Systems to Survive Greening: Horticultural Practices

ADDITIONAL INDEX WORDS. open hydroponic, irrigation, fertigation, tree density , rootstocks, girdling Fruit yield is a critical component in the long-term profi tability of citrus growers in Florida. Increasingly, two factors outside the control of the growers are forcing Florida citrus growers to re-evaluate the sustainability of their current operations. These factors are: 1) impact of canker and greening diseases on tree health and yields and 2) continued urbanization within the state. A key to increased profi tability may be improved early and sustained production on high density groves. Improved early and sustained yields may allow growers to reach earlier return on investment and thus, better deal with potential decreased production due to tree loss from disease. The use of automated irrigation systems and intensive nutrient management may provide critical enhancement to production systems for achieving increased tree growth and yield. A widely discussed approach for maintenance of soil moisture and nutrient concentrations in the tree root zone near optimum levels is known as the Open Hydroponic System (OHS). The system must be adapted for the Florida summer rainy season and sandy soil characteristics so that current fertilizer best management practices (BMPs) are not exceeded and nutrient leaching is not increased. Current OHS management practices utilized in selected citrus producing countries around the world will be reviewed and compared to proposed Advanced Production Systems practices for high density citrus plantings in Florida. Practices considered will be nutrient ratios and application timing, irrigation scheduling and methods, root density distribution, and girdling. Adoption of these intensive citrus management practices has the potential of conserving water, improving nutrient use effi ciency, reducing leaching in addition to improving tree growth and yield. Citrus tree acreage in Florida decreased to 576,577 acres in 2008, the lowest number of citrus producing acres since 1966 (Florida Agricultural Statistics Service, 2009). Cited reasons for lower production acreage were urban development, canker (Xanthomonas axonopodis), and hbruanglongbing (Liberibacter a siaticus, citrus greening). Acreage decreases were recorded in 25 of the 30 counties included in the annual citrus tree survey. Citrus acreage loss in the Indian River production area was the greatest, with Martin County losing 34% last year alone. Improved tree growth from intensive management practices could reduce the time required from planting to economic break-even production, thus providing potentially valuable management options in light of current devastating diseases such as canker and greening. Florida growers must also adopt Best Management Practices (BMPs) that reduce nutrient leaching by limiting the amount of fertilizer that can be applied, and the time of year when fertilizer can be applied. These BMPs are based on research under low-intensity management systems that apply both water and nutrients at intervals that are less than optimal. However, production systems that combine grove design and irrigation management to increase yield and grove operational effi ciency have not been studied in Florida. High density plantings of sweet oranges on low-vigor rootstocks have known advantages, but their long-term behavior and changes in the functional relationship of tree density, growth rate, and yield over time are not well understood.