The experiment was led in a protected greenhouse in the FCAV/Unesp, Jaboticabal Campus -SP, during the period of November of 2005 to January of 2007. The study objective was to evaluate the development of components and the nutritional state of seedlings of 'Valencia' orange grafted on lemon tree citrumelo 'Swingle' rootstock, in function of nitrogen, phosphorus and potassium levels. The experimental design was entirely randomized, in factorial scheme 3³ + 1, being 3 factors (nitrogen, phosphorus and potassium - NPK), 3 levels and a witness (without fertilization), with 3 replications. The experimental unit was constituted of a 'Valencia' sweet orange seedling grafted on lemon tree citrumelo 'Swingle' rootstock in a bag with 2,5 kg of substratum. The treatments were constituted of application of the following doses of nutrients in mg for dm³ of substratum: N1/2:459, N1:918 and N2:1836; P1/2:92, P1:184 and P2: 368; K1/2:438, K1:876 and K2:1752. In the 424 days after the planting, the plants were divided in root and aerial part for the determination of the mass of the dry matter, height, leaf area, diameter of the stem and content of nutritious. The fertilization with N, P and K provided larger growth and larger accumulation of N, P and K in the aerial part and in the roots of the orange tree seedlings, in substratum of Pinus bark and vermiculite. In the orange tree ' Valencia' grafted on lemon tree citrumelo 'Swingle' the half of the recommended dose of N (459 mg dm-3) and, the recommended dose of P and K (184 and 876 mg dm-3), respectively, provided better growth of the aerial part of the seedlings; however, in the recommended dose of N of 918 mg dm-3, it happened larger growth of the root system.
N P K; mineral nutrition; orange seedlings; Citrus ssp
