2019 ASHS Annual Conference

Root structure and function is an understudied component of citrus research, especially now, in the age of Huanglongbing (HLB) disease. A better understanding of how roots react to different nutrient concentrations and root enhancers can potentially lead to better management options in the future. Fertilization guidelines utilize leaf nutrient concentrations to generate fertilizer recommendations for N, P, K, Ca, Mg, and micronutrients. Interestingly, there are currently no guidelines for optimal nutrient concentrations in healthy roots. A greenhouse study was conducted on twenty-five lemon trees and twenty-five oranges for 6 months. Lemon (var. Bearrs Lemon) and orange (var. Valencia) trees grafted on ‘Sour Orange’ rootstocks were employed. Five different treatments were designed to test different Osmocote (15-8-11) fertilizer concentrations in combination with a commercial root growth enhancer (oGRO). The overall treatments were: (a.) 150 gr/kg Osmocote (Control), (b.) 150 gr/kg Osmocote + 1% oGRO, (c.) 150 gr/kg Osmocote + 0.5% oGRO, (d.) 75 gr/kg Osmocote + 1% oGRO, (e.) 75 gr/kg Osmocote + 0.5% oGRO. Five repetitions were used for each treatment. The lemon and orange trees were grown in natural sand collected from the UF/IFAS IRREC experimental field. During the experiment, height, trunk diameter and stomatal conductance were measured every 15 days for 6 months. At the end of the experiment fresh and dry weights were determined. Similarly, nutrition concentrations (N, P, K, Mg, Mn, B, Ca, etc.) in leaves, stems and roots and leaf chlorophyll contents were analyzed. Photos of each plant were also taken to analyze root system architecture responses to different treatments. As a result, the orange trees treated with more fertilizers and more oGRO showed enhanced physiological and nutritional levels, while the lemon trees showed significant changes in chlorophyll contents and root growth and development. The results clearly indicate a role of genotype (lemon vs. orange) in response to different nutrition levels.