The nutritional status of orange trees depends of reference values that are appropriate to reflect their nutritional condition. The objective this work was to assess the nutrient reference values and evaluated the nutritional status of sweet orange trees in several orchard fields of Central Amazonia (municipalities of Iranduba, Manacapuru, Manaus, Presidente Figueiredo and Rio Preto da Eva). We used the Diagnosis and Recommendation Integrated System for multivariate relation (DRIS) method to establish the nutrient reference values. The nutritional status of 120 commercial orchards of orange grafted on rangpur lime was evaluated by the sufficiency ranges defined from the set of nutritionally balanced plants. For macronutrients, the nutritional sufficiency ranges were (g kg-1): 28-30 (for nitogen, N); 1.6-1.7 (phosphorus, P); 7-9 (potassium, K); 26-29 (calcium, Ca); 3.6-4.0 (magnesium, Mg); 1.7-2.0 (sulfur - S) and for micronutrients (mg kg-1): 47-56 (boron, B); 8-10 (copper, Cu); 84-93 (iron, Fe); 12-13 (manganese, Mn); 14-16 (zinc, Zn). For macronutrients, the critical levels were (g kg-1): 28 (for N); 1.6 (P); 7 (K); 26 (Ca); 3.6 (Mg); 1.7 (S) and for micronutrients (mg kg-1): 47 (B); 8 (Cu); 84 (Fe); 12 (Mn) and 14 for Zn. Nutritional standards obtained by the DRIS methods are in disagreement with the normal ranges proposed in the literature for most nutrients. In about 50% of orchards, the elements P, K, Ca, S, B, Cu e Fe were found below the critical levels. This suggests that orange producers in Central Amazonia should pay more attention to these elements when planning fertilization practices.
Citrus sinensis; nutritional status; foliar analysis; nutritional monitoring
