RESPONSE OF DIVERSE LETTUCE TYPES TO FERTILIZER PHOSPHORUS

Four field experiments were conducted from 1990 to 1992 on Histosols i n southern Florida to compare the relative response of various types o f lettuce (Lactuca sativa L.) (i.e., leaf, Boston, Bibb, romaine, and crisphead lettuce) to P fertilization, All lettuce types showed large yield and quality responses to P fertilization. Because environmental conditions affected yield potential, P rates required for optimal yiel d varied for lettuce types across experiments. However, with the excep tion of Boston, the P rates required for optimal yield were similar wh en averaged over all experiments, Furthermore, the relationship betwee n relative yield and soil-test P across all seasons showed that a simi lar soil-test P index level was required for maximum yield of ad lettu ce types. Overall, the results of this study suggest that existing soi l-test-based fertilizer recommendations for crisphead lettuce are adeq uate for other lettuce types currently grown.