ASHS 2025 Conference

Florida ranks third in the United States for lettuce production with approximately 90% of commercial lettuce cultivated on organic soils in southern Florida. These organic soils require phosphorus (P) inputs to sustain economic production and ensure lettuce shelf-life. Lettuce shelf-life depends on quality factors such as firmness, appearance, color, texture, decay, discoloration, and wilting. Optimal P fertilizer management is necessary to improve yield, market quality, and ensure postharvest quality (shelf-life). Over-fertilization can reduce quality, while deficiencies can limit yield and shelf life. Therefore, the objective of this research was to understand how different rates of P affect the lettuce shelf-life across four cultivated morphological types. Two field trials were conducted at the Everglades Research and Education Center in Belle Glade, FL, during the lettuce growing seasons (spring, fall, and winter). Experiments were set as a split-plot designed in which P fertilizer rates (0, 48, 97, 150, 195, and 210 lbs P2O5 acre-1) were considered as the main plot and four lettuce types (romaine, iceberg, butterhead, and leaf) as the subplot. Ammonium polyphosphate (11-37-0) was used as the source of P fertilizer. Shelf-life was evaluated over 10 days at 15 °C and 90% RH using visual ratings of 9 (excellent) to 1 (poor) following the protocol for an accelerated shelf-life testing. The estimated shelf-life was considered as the number of days when lettuce reached an acceptable appearance on the rating scale of ≥5 and multiplied by a factor of 2 (2-fold factor proportional to the deterioration rate). The results indicate varying responses to P fertilizer application in shelf-life that were significantly morphological-type dependent. Overall, leaf lettuce had the shortest shelf-life and iceberg lettuce had the longest shelf-life. Butterhead had an acceptable estimated shelf-life rating of 5 at 24 days at 210 lbs. P2O5 acre-1 while romaine and leaf had a shelf-life rating of 5 at 22 and 21 days at 210 lbs. P2O5 acre-1, respectively. In addition, crisphead had an acceptable estimated shelf-life rating of 5 above 35 days at 150 lbs. P2O5 acre-1. However, an acceptable shelf-life was maintained at 48, 150, or 195 lbs. P2O5 acre-1 in iceberg lettuce over 30 days. Together these results demonstrate that there is no effect of increasing the rate of P2O5 acre-1 to maintain economic yields on the lettuce shelf-life. Rather, shelf-life quality increases with P inputs.