Nitrogen is the most important nutrient in determining overall citrus growth and yield. Due to the low water and nutrient holding capacity of Florida's sandy soils, approximately 81,000 ha of citrus are prone to excessive N leaching. Fertilizer use efficiencies for citrus range from 40 and 80%, depending on N-fertilizer rates and residence times prior to displacement below the root zone. Increased concerns pertaining to nitrate contamination of groundwater resources have prompted the Florida citrus industry to reassess current N fertilization practices. Many citrus growers have shown interest in improved use of current technology and computer-based decision support systems that can be readily integrated into their production system. In order to allow growers to benefit from these technological innovations a decision support system was developed for growers. This system integrates several production applications including site-specific irrigation scheduling for citrus. Detailed information on physiological N-requirements and tree N-budgets, along with seasonal citrus water and N-uptake parameters under specific field conditions have been determined and used to develop tree N budgets. This information provides a scientific basis for computer-based applications that will allow growers to better manage both irrigation and nitrogen applications and thus increase fertilizer use efficiencies. Use of this decision support system can facilitate development of annual grove-specific N-recommendations based on N-requirements for tree growth, target yields, and model N-losses associated with actual rainfall/irrigation events. Potentially, this software will facilitate more efficient water and N-fertilizer use and thereby provide Florida growers with a competitive edge by reducing production costs and negative environmental impacts associated with citrus production systems.