Fontes e parcelamento de nitrogênio na produção de batata-doce

Abstract

This study aimed at the evaluation of the yield of the sweet potato, variety "Rainha Branca", subjected to sources and parceling of the nitrogen. So, an experiment was carried out in the soil classified as typical “Inceptisol Regolítico Psamítico” at the Universidade Federal da Paraíba, Areia county, during the period from April to August 2007. The randomized block experimental design was used in factorial scheme 2 x 8 with, by using two sources of nitrogen fertilizer (urea and ammonium sulfate) and eight application times (100% at planting; 100% at 30 days after planting (DAP); 100% at 60 DAP; 50% at planting and 50% at 30 DAP; 50% at planting and 50% at 60 DAP; 50% at 30 and 50% at 60 DAP; 33% at planting, 33% at 30 and 33% at 60 DAP; and the treatment without N, with four replicates. The following variables were evaluated: average weight of the commercial and noncommercial roots plant-1, the total, commercial, and noncommercial productivities of the sweet potato roots and leaf nitrogen content. The highest average weight of the commercial roots was obtained with urea in the parceling 50% at planting and 50% at 30 DAP, (293.75g). The lowest average weight of the noncommercial roots was obtained in this source, as well as with 50% parceling 50 at 30 and 50% at 60 DAP (36.92g). The parceling 33% at planting, 33% at 30 and 33% at 60 DAP were responsible for the highest yield of commercial roots per plant, when the source was the ammonium sulfate (337g). The lowest yield of commercial roots per plant was obtained in the same source with parceling 50% at 30 and 50% at 60 DAP (26.48g). For the number of commercial roots, total and commercial productivities, the ammonium sulfate parceled 33% at planting, 33% at 30 and 33% at 60 DAP provided the highest values (1.50 roots, 30.5 t ha-1 and 28.4 t ha-1 respectively. The ammonium sulfate parceled 100% at 60 DAP propitiated the lowest number of noncommercial roots (0.51). The lowest productivity of noncommercial roots was obtained with parceling of the ammonium sulfate 50% at planting and 50% at 60 DAP (2.2 t ha-1). The leaf nitrogen was not significantly altered by the treatments.