Abdelkader Hammami Salah Rezgui Rachid Hellali
Leaf analysis is a useful tool to evaluate the nutrient status of citrus trees, but diagnosis standards for ‘Clementine mandarin’ are not available. Nutrition recommendations of the current fertilization practices are mainly based on the same recommended nutrient rates for orange trees. A three-year (2005 - 2007) field experiment was conducted in North Eastern Tunisia (El Gobba). This experiment was carried out using 25 years old ‘Clementine mandarin’ trees (CITRUS RETICULATA OSBECK) on ‘Sour orange’ (CITRUS aURANTIUM OSBECK) rootstock; grown on a sandy soil; to establish leaf nutrient (N and K) concentration standards for optimum biomass tree growth, fruit production and quality. Nitrogen and potassium rates ranging from 160 to 232 and 200 to 290 kg/ha/yr, respectively, were applied in a drip irrigation system (12 fertigations events/yr). Irrigation was scheduled based on tensiometer readings at the root zone. Fruit yield was positively associated with N (r 2 = 0.91) and K (r 2 = 0.84) rates; as well as with leaf N concentration (r 2 = 0.92) and tree fruit load (r 2 = 0.91). Leaf N concentration was significantly correlated with N rates (r 2 = 0.72) and biomass tree growth (r 2 = 0.52). These findings indicate that 192 and 200 kg/ha/yr of N and K2O (N:K = 0.9), respectively, are required to support optimal fruit yield of 43 T/ha/yr with tree fruit load of 2.4 kg/m 3 (fruit yield/tree canopy size ratio) 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, respectively. Leaf nutrient concentration ranging from 27 to 29 g/kg for N; and from 10 to 12 g/kg for K corresponding to a fertilizer management program of 192 kg/ha/yr and 200 kg/ha/yr, could be recommended as optimum levels of N and K for ‘Clementine mandarin’ grown under Mediterranean conditions.
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