Yield and Microbial Quality of Head Lettuce as Affected by Field Moisture at Harvest

Abstract

The effect of moisture conditions on microbial quality (as total aerobic bacteria) and yield of head lettuce was investigated. Head lettuce cv. Honcho II grown at the Yuma Agricultural Center was evaluated for microbial population at harvest and postharvest quality either following different irrigation termination schedules or after a rainfall event. The last irrigation was scheduled 24, 16 and 6 days prior to harvest resulting in soil’s water content of 15.9%, 17.0% and 17.2%, respectively, at harvest. Lettuce receiving the last irrigation 6 days before harvest had 10% more weight, higher total aerobic bacteria and shorter shelf life than plants irrigated 24 days before harvest. The plants with the last irrigation scheduled 16 days before harvest showed similar weight at harvest, lower total aerobic count and longer shelf life than plants with irrigation termination scheduled 6 days prior to harvest. The effect of field’s moisture prior to harvest on quality was further evaluated with lettuce harvested 1 and 7 days after a rainfall event. A day after rain the microbial population in both outer leaves and head leaves increased. The microbial population in head leaves continued increasing during the week after rain. The results from this study suggest that managing moisture conditions at harvest is important to enhance quality of lettuce. Although the potential decrease in weight produced with an early irrigation termination is a great concern of growers, it was shown in this study that excessively late pre-harvest irrigation of lettuce is not necessary to obtain maximum weight at harvest.