Department of Plant Sciences

Leaf analysis is a useful tool to evaluate the nutrient status of citrus trees, but diagnosis standards for ‘Clementine mandarin’ are not available. Thus, a three-year (2005-2007) field experiment was conducted in North East Tunisia with 25 years old ‘Clementine mandarin’ trees (Citrus reticulata Osbeck) on ‘Sour orange’ (Citrus aurantium Osbeck) rootstock; grown on a sandy soil (loamy mixed thermic mollic xerofluvent); to establish leaf nutrient (N and K) concentration standards for optimum fruit production and Quality. Nitrogen and potassium rates from 160 to 232 kg ha-1yr-1 and 200 to 290 kg ha-1yr-1, respectively, were applied through a drip irrigation system. Irrigation was scheduled based on tensiometer readings at the root zone. Fruit yield was significantly correlated with N (r2=0.91) and K (r2=0.84) rates; it was also correlated with leaf N concentrations (r2=0.92). These findings indicate that 192 and 200 kg ha-1yr-1 of N and K2O, respectively, are needed to support optimal fruit yield of 43 Mg ha-1yr-1 and optimum fruit quality. At 90% of maximum relative fruit yield, leaf N and K concentrations were 27 to 29 and 10 to 12 g kg-1, respectively. These leaf nutrient concentration ranges could be recommended as optimum levels of N and K for ‘Clementine mandarin’ grown under similar Mediterranean conditions to those of this work.

Keywords: Leaf nutritional status; optimum fruit yield; Clementine mandarin; Mediterranean conditions; fruit quality.