Production onion part in the Santa Catarina state, Brazil is stored in rustic warehouses without environmental control, which favors losses weight and quality. The purpose of this study is to understand the causes of onion losses in storage, their relationship, and influence using inputs and techniques applied in cultivation and preharvest, as well as part of the production infrastructure for the two cultivars. Through the data collection with the producers and samples of bulbs of their harvest that were stored for 140 days and is evaluated the losses, was presented that in the Alto Vale do Itajaí the cv. Crioula receives more rain during the cure, is harvested with a lower fallen leaves rate, being more susceptible to budding than cv. Bola Precoce. Bulbs originating from crops with higher productivity, a greater number of plants per area, and a higher volume of nitrogen fertilization in coverage, reduce sprouting in storage. Dehydration was lower in relation to productivity, production, curing period, furthermore, experience time of farmer in onion cultivation. To rotting is lower with increased productivity, production, and potassium fertilization during cultivation. There is a waste in nitrogenous and potassic fertilizers that increase the cost of production in crops with the greater planted area.