Project Overview
Commodities
- Fruits: citrus
Practices
- Crop Production: fertilizers, nutrient management
Abstract:
Over the past decade, Florida’s iconic citrus industry has been devastated by a disease known as citrus greening (Huanglongbing; HLB). Although no cure is currently available, growers have found some success in managing the disease, and research has shown that increased nutrient applications have extended the productive life of affected trees. Using leaf nutrient analysis to determine the nutritional requirements of the plant has become a standard practice for citrus growers in the United States. However, it is difficult to detect nutritional deficiencies in the early stages because traditional leaf nutrient analysis shows nutrient accumulation for the entire season, reducing the overall precision of fertilizer management.
One management tool gaining attention is sap analysis. This approach can increase the sustainability of citrus operations by improving the precision in determining tree nutrient status and fertilizer application. For this reason, sap analysis is considered by many as a real-time analysis method, indicating the concentration of nutrients available to the plants during the season. This method analyzes the nutrient concentration of the fluids from the xylem and phloem in the leaf (sap).
In this study, the treatments tested were one citrus variety (‘Ray Ruby’ grapefruit), two planting densities (standard single row and high-density staggered row), and two analysis methods (standard plant leaf tissue analysis and plant sap analysis) arranged in a completely randomized design with four replications. Leaf samples were taken during the most important phenological stages (i.e., flowering, fruit set, fruit fill, and pre/early harvest) from 8:00 am to 11:00 am, including both new and old growth. Similarly, standard soil and plant leaf tissue analysis was conducted. The results for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn were compared to the standard leaf nutrient concentration ranges currently used for citrus production in the area.
Project objectives:
The main objectives of this study were to (i) compare the efficacy of leaf sap analysis of micro- and macro-nutrient concentrations to traditional plant leaf tissue analysis and (ii) assess the differences in these analyses between standard and higher planting densities. This was done by collecting leaf samples from grapefruit trees in a commercial grove and analyzing foliar macro- and micro-nutrient concentrations using plant leaf tissue analysis (Waters Agricultural Laboratories Inc., Camilla, GA) and plant sap analysis from two different laboratories (New Age Laboratories, South Haven, MI, USA, and NovaCropControl, Netherlands) in the HLB-endemic region of the Indian River Citrus District.