Evaluation of P Application Methods for Lettuce Production on Organic Soils.
Alan Wright, Victor Guzman, and Xing Wang. Everglades Research & Education Center, University of Florida, 3200 E. Palm Beach Rd., Belle Glade, FL 33430
Lettuce production in P-deficient organic soils of the Everglades Agricultural Area is dependent on high levels of P fertilizers (> 200 kg P ha-1). However, environmental concerns regarding P runoff from farm fields into adjacent wetlands are strengthening efforts to develop strategies to reduce field P applications. The objectives of this study were to investigate the influence of excess P application to lettuce seedlings before transplanting to fields, and of the reduction of field-applied P. Different P rates, sources, application methods, and timing were investigated to determine if P applied to seedlings and growth media in excess of plant requirements could be available to seedlings after transplanting to fields. Foliar P applied to seedlings in excess of nutrient requirements was evident in higher tissue N, P, and K levels, although optimization of rates are still needed to prevent tissue burn. However, accumulation of P in growth media was more evident than in tissue, suggesting that soil rather than foliar application would allow for greater P utilization after transplanting. Lettuce growth and yields were greater with higher P applications to seedlings, suggesting that seedling-applied P may be utilized to reduce field P application rates.