Feliciano Pabón, Paola M.

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    Fertilization practices to overcome the damage of citrus greening in ‘Improved Meyer’ Lemon (Citrus Meyeri) and ‘Rhode Red Valencia’ orange (Citrus Sinensis Valencia) in an Oxisol
    (2022-06-28) Feliciano Pabón, Paola M.; Muñoz Muñoz, Miguel A.; College of Agricultural Sciences; O’Hallorans Castillo, Julia M.; Tirado Corbalá, Rebecca; Department of Crops and Agro-Environmental Sciences; Parés Parés, Carmen P.
    Citrus greening (CG) is a deadly disease for citrus for which there is no cure but the damage can be mitigated with an integrated management approach. A study was conducted at the Isabela Agricultural Experiment Substation, UPRM to evaluate the effect of two fertilizer treatments on growth and performance of ‘Improved Meyer’ Lemon (IML) and ‘Rhode Red Valencia’ (RRV) orange scions, grafted on the ‘HRS-802’ and ‘HRS-812’. The soil at the site is Coto clay (Very fine, kaolinitic, isohyperthermic Typic Hapludox). The main objective was to assess the effect of fertilization and rootstocks, as an integrated approach to overcome the incidence of citrus greening disease. Both fertilizer treatments consisted of applications of urea (45-0-0) and a high potassium source (13-2-44) by fertigation. For fertilizer #1, a foliar application of a fertilizer mixture of magnesium sulfate, Borax (20.5% B), Fe chelate, and Zn chelate was applied every four months, and two foliar applications of Sol-U-Gro® (12-48-8) every six months. Fertilizer #2 included foliar applications of a commercial mixture of micronutrient fertilizer (Codamix®) every four months. Codamix® contains Boron (B), Zinc (Zn), Copper (Cu), Iron (Fe), Manganese (Mn), and Molybdate (Mo). Fertilizer #2 also included an application twice a year of 726 g/tree of granular fertilizer formula 15-3-19. The trees were tested for CG before field planting and after the completion of a fertilization cycle. Growth parameters were collected every three months for a period of 19 months. Incidence of CG was higher on trees under the ‘HRS-802’ rootstock than the ‘HRS-812’ rootstock for both scions. The production of suckers by rootstock ‘HRS-802’ was higher than for ‘HRS-812’, independent of the fertilizer treatment. Leaf nutrient content in symptomatic, chlorotic trees and healthy trees was similar for both scions. ‘Improved Meyer’ Lemon trees grafted on ‘HRS-812’ produced less fruits than their ‘HRS-802’ counterparts. However, the fruits were larger and higher yields were obtained. Fertilizer treatment 2 showed a total fruit yield of 5.30 kg/tree for ‘HRS-802’ and 8.36 kg/tree for ‘HRS-812’. There was no significant difference in yield among rootstocks under fertilizer treatment 1. Two soil samplings were performed, one before planting and another 19 months after field planting. The chemical analyses showed an increase in soil pH from 6.2 to 6.7 and 6.3 to 6.6 for IML plots and RRV plots, respectively. Available Bray-1 P in Fertilizer 1 treatment decreased from 22.5 to 15.7 mg kg-1 for IML plots and from 26.3 mg kg-1 to 17.5 mg kg-1 for RRV plots. Additionally, an increase in soil organic matter was observed for IML plots from an average of 3.53 to 5.27%, and for RRV plots from an average of 3.46 to 5.96%. No significant differences in exchangeable cations and micronutrient content were observed between fertilizer treatments. Soil applications of macronutrients in the early stages of growth seem to be better suited due to better absorption through the root system for a healthy tree. A combination of granular fertilizer applied to the soil, and soluble fertilizers applied folliarly are recommended to overcome the damage of citrus greening disease and for better yields. Additionally, higher applications of fertilizer are recommended during the fruiting stage due to higher demand from the crop.