Potassium Management for Optimizing Citrus Production and Quality

Abstract

Potassium (K) is highly mobile in plants at all levels, that is, from individual cell to xylem and phloem transport. This cation plays a major role in (1) enzyme activation; (2) protein synthesis; (3) stomatal function; (4) stabilization of internal pH; (5) photosynthesis; (6) turgorrelated processes; and (7) transport of metabolites. Citrus trees generally do not show visible deficiency symptoms across a wide range of K status in the leaves, except when the leaf concentrations drop below 3-4 mg kg21. However, fruit quality is quite sensitive to varying levels of K availability. High levels of K cause large fruit size with thick and coarse peel. In contrast, K deficiency produces smaller fruits with thin peel. With regard to juice properties, K nutrition has a significant role in juice acidity; that is, high juice acidity with high K availability, while low K availability causes decrease in juice acidity. High K availability in the soil can reduce the uptake of other cations, primarily magnesium, calcium, and ammonium N. In this paper, the available information on the effects of varying availability of K on the fruit yield, postharvest quality of fruit, as well as juice quality is summarized. The current recommendations on the application of soil and leaf analysis for evaluation of the K nutritional status and guidelines for K fertilization are also discussed.

Key Words:

• Oranges
• grapefruits
• mandarins
• soil test calibration
• critical nutrient concentrations
• postharvest fruit quality
• fruit peel disorders
• postharvest fruit pitting
• foliar potash fertilization