The influence of phosphate fertilization and planting systems were evaluated on the yield and quality of sweet potato roots, Rainha Branca cv. The experiment was carried out from February to July/2003 in a Quartz Psamment soil in Paraiba State, Brazil. The experimental design was of randomized blocks with four replications. Treatments were distributed in a 5 x 2 factorial design, with five levels of P2O5 (0; 100; 200; 300 and 400 kg ha-1 ) and two planting systems (one and two stems/hole). Total and commercial sweet potato roots production, in response to P2O5 levels with one stem/hole, were 21.6 and 18.7 t ha-1 obtained with 237 and 210 kg ha-1 of P2O5, respectively. Using two stems/hole, 23.5 and 18.9 t ha-1 were obtained when 259 and 231 kg of P2O5, were employed, respectively. Levels of 173 and 194 kg of P2O5 applied for one and two stems/hole, respectively, were economically viable for the commercial roots production. The economical level in the planting system using one stem/hole, was 82% of the technical maximum efficiency (TME) and for two stems/hole was 84% TME being an indicative of economical viability of phosphorus application in sweet potato. P2O5 levels that resulted in maximum production and economical returns for commercial roots for planting systems with one and two stems/hole were 21 and 19 mg dm-3 of phosphorus available, using Melich-1 extractor. In similar soil types for commercial roots production, the phosphate fertilization will be dispensed, when available phosphorus levels were higher than 19 and 20 mg dm-3 of soil in planting systems with one and two stems/hole.
Ipomoea batatas; phosphate fertilization; branches/hole; roots production
