Accumulation of macronutrients in onion bulbs as a function of sulfur application

The amount of nutrients extracted by the bulbs represents an important component of nutrient removal from the soil, and its evaluation must be used to define the amount of nutrients to be replaced in the soil, through fertilization programs. The objective of the study was to verify the accumulation of nutrients in onion bulbs due to the application of sulfur at different phenological stages. The experiments were carried out in a conventional system, in a completely randomized design, in a 2 x 5 x 2 factorial scheme, with two cultivars (Dulciana and Vulkana), in five times of S application (control; transplanting; stage of 6 to 7 leaves; bulb differentiation stage, and full bulbing), and 2 years of cultivation, with four replications. After curing, four (4) bulbs of each treatment were chosen randomly, one per replication of each commercial plot formed by 20 bulbs from the field experiment, which were identified and taken to the laboratory for nutrient analysis. Subsequently, the amount accumulated in the bulb of each nutrient was determined. Fertilization with sulfur promotes greater accumulation of K and N. The order of extraction of nutrients in the presence of sulfur was K> N> P> S> Ca> Mg. The highest sulfur accumulations in the bulb occurred at the bulbing stage for both cultivars.