With the objective of evaluating the levels and application forms of nitrogen (soil and leaves) in the sweet potato Rainha Branca cv. an experiment was carried out from July to November/2003, in the Centro of Ciências Agrárias from Universidade Federal of Paraíba, Areia, Brazil, in Quartz Psamment soil. The experimental design was randomized blocks, in a factorial scheme 5x2, with five levels of N (0, 50, 100, 150 and 200 kg ha-1), tow applications forms (soil and by foliating), in four replications. The plots with 28 plants, spaced at 0.80x0.30cm. The total and uncommercial yield of roots increased linearly in function of the levels of N applied in the soil, corresponding approximately to 45.52 and 12.64 kg ha-1, respectively to each kilogram of N. The commercial yield in function of the N levels applied in the soil, reached the maximum value of 19255 kg ha-1 with 154 kg ha-1 of N. The total, commercial and uncommercial roots yields obtained in function of the N levels applied to the leaves did not suffer significant changes with rates of 13800, 12600 and 1200 kg ha-1, respectively. The most economical N level applied in the soil related to commercial roots yield was 144 kg ha-1, with roots estimated yield of 19123 kg ha-1. The nitrogen supplied in the soil was more efficient for the sweet potato to express its maximum commercial roots yield, with increment of 6555 kg ha-1, when compared to the leaves application.
Ipomoea batatas; nitrogenous fertilization; foliating fertilization; root production
