Produtividade e conservação de cebola afetadas pela adubação nitrogenada no sistema de plantio direto

Abstract

Yield and conservation of onions are influenced by the nitrogen (N) availability in the soil. We evaluated the effect of rates and number of side dressing applications of nitrogen in the development, nutritional status of plants, yield and post-harvest storage of onion bulbs grown in no-tillage system. Three experiments were carried out in the field, over an Haplumbrept soil, in Ituporanga, Santa Catarina state, Brazil. Treatments consisted of a factorial combination (4x3) involving four rates of N (0, 50, 100 and 200 kg ha-1) and three side dressing dates (45; 45 and 75; 30, 60 and 90 days after transplantation). For all N rates, 25% were applied at planting and the remaining amount was side dressed once or equally divided in two or three applications. The transplanting was carried out in the second half of July, and the harvest approximately 120 days later. Bulb yield was not influenced by N addition in the 2007/08 growing season, but it increased quadratically with increases on N applied in the other two seasons (2008/09 and 2010/11), and estimated N rates that provided the maximum economic efficiency was respectively 131 and 102 kg ha-1. For the 2007/08 season, the most economic dose was 0 kg N ha-1, since there was no response to fertilization with the nutrient. In the sequence of the seasons, maximum yields obtained were respectively 26, 42 and 43 t ha-1, with increments of 0, 32 and 9% relatively to the treatment without N. The addition of nitrogen to the soil influenced negatively the conservation of the bulbs in the rainiest years. Two or three side dressing applications of N had no effect on yield and post harvest conservation of bulbs in 2007/08 and 2010/11, but losses were reduced with greater fragmentation of intermediate doses (50 and 100 kg ha-1) of N in 2008/09.