The Effects of Calcium Chloride and Ammonium Sulfate on Onion Bulb Quality at Harvest and During Storage

Sandy soils in the onion ( Allium cepa L.) growing region of southeastern Georgia are generally low in calcium (Ca). Bulbs grown in these soils are often soft and susceptible to postharvest diseases. Preliminary greenhouse studies have indicated that supplemental calcium chloride (CaCl 2 ) can improve bulb firmness. The effects of supplemental CaCl 2 on the quality of field-grown onions were therefore investigated. Other preliminary studies indicated that CaCl 2 may inhibit sulfur (S) uptake in onion and decrease bulb pungency. Thus, ammonium sulfate (NH 4 ) 2 SO 4 and CaCl 2 levels were varied to determine if CaCl 2 could improve flavor at different levels of nitrogen (N) and S fertility. Onions, cv Georgia Boy, were grown with 0, 250, and 500 kg·ha −1 (NH 4 ) 2 SO 4 and 0, 115, and 230 kg·ha −1 CaCl 2 in a factorial combination in 2005 and 2006. Total bulb yield increased with increasing (NH 4 ) 2 SO 4 , but was unaffected by CaCl 2 . The percentage of diseased bulbs increased during storage in both years, and was affected by (NH 4 ) 2 SO 4 fertility in 2006. Bulb scale firmness increased with supplemental CaCl 2 fertility and decreased significantly during storage in both years. Fertility treatments had little effect on bulb pectin composition, although total pectin concentrations fell during storage in 2005 and 2006. In addition, bulb pungency decreased with additional CaCl 2 in 2006. However, CaCl 2 had a limited effect on flavor precursor concentrations. There were no interactions between fertility treatments, but there were CaCl 2 and (NH 4 ) 2 SO 4 by storage duration interactions affecting firmness and disease incidence, respectively. With the exception of yield, differences among years in the parameters measured were generally small.