Sources and levels of nitrogen and onion yield in the submedio São Francisco region

Abstract

Two experiments were carried out with onion crop (Allium cepa L.) under irrigation in 1987 and 1988, in Petrolina, PE, Brazil, in a Red-Yellow Latosol, with 10% of clay, 85% of sand, 0,6% of organic matter, and pH 6.5, with the objectives of evaluating new sources of N and obtaining an optimum level of this element in fertilizations. A randomized complete block design with a factorial arrangement was used, having three levels (40, 80 and 120 kg/ha of N) and three sources of N (urea, urea compacted with gypsum and "nitrossulfocalcium"), with two additional treatments (control and urea + gypsum), replicated four times. The onion crop showed a positive and significant response to N application. In 1987, urea compacted with gypsum contributed to a yield significantly superior in 35% to that obtained with only urea, whereas in 1988, there was no significant difference among N sources. In 1987, the N level which gave the maximum expected yield (29.58 t/ha) was 114 kg/ha, and in 1988 the maximum expected yield (54.31 t/ha) was achieved with 119 kg/ha of N. The average economic level of N was 115 ± 2.7 kg/ha.