The excessive use of fertilizers and liming as well as monoculture is rather common in the onion-producing region of Santa Catarina State, Brazil. Such practices have resulted in visual symptoms of micronutrient deficiency, mainly of micronutrients. This study aimed to measure the effect of B, Zn and Mn fertilizers on yield and quality of onion bulbs. Three individual trials, one for each nutrient, were carried out in the field, in Ituporanga, southern Brazil, from 2006 until 2009. In each experiment, treatments consisted of increasing rates of each micronutrient applied to the soil before planting and also of a single rate sprayed onto the leaves six times per season. Rates applied to the soil varied from 0 to 4 kg ha-1 for Zn, from 0 to 4.4 kg ha-1 for B, and from 0 to 15.6 kg ha-1 for Mn. The spray solutions contained zinc sulfate, boric acid and manganese sulfate, at concentrations of 0.5, 0.25 and 1.0 %, respectively. The application of Mn or B, regardless of the form, and Zn sprays, had no effect on onion yield in any growing season. The application of Zn to the soil increased onion yield in all three years, by 10-14.5 %. Maximum yield was obtained with Zn rates of 2.7 kg ha-1 in 2006/2007 (22.3 t ha-1), up to an estimated quantity of 4.5 kg ha-1 in 2008/2009 (35.6 t ha-1). The bulb quality was not affected by micronutrient application (Mn, B, or Zn), regardless of the form. It is therefore important to apply Zn to the soil for onion production in the State of Santa Catarina, even where Zn concentration exceeds the critical level established for the region, which is probably due to the requirement of this crop.
zinc; boron; manganese; foliar nutrition; Allium cepa
