Yield and Postharvest Quality of Lettuce in Response to Nitrogen, Phosphorus, and Potassium Fertilizers

Commercial lettuce production requires adequate levels of nitrogen (N), phosphorus (P), and potassium (K) to provide high-quality postharvest attributes needed for longer shelf life. Factorial experiments were conducted in Salinas, CA, to evaluate yield and postharvest quality of both romaine and iceberg lettuce using fertilizers containing various levels of N, P, and K. Lettuce was evaluated for yield and postharvest quality parameters, including color, wilt, turgidity, glossiness, decay, brittleness, fringe burn, and salt burn. Uptake of N, P, K, calcium, and silicon by plants was also determined. Regardless of fertilizer treatment, shelf life and visual quality were better in the iceberg lettuce than romaine lettuce when cold-stored at 1 °C for 14 d. Yield increased with increased N application rate, but post-harvest quality fell at high levels of N (337 kg·ha −1 ) and P (225 kg·ha −1 ). The most economical treatment providing the highest yield and best post-harvest quality was the combination of 225 kg·ha −1 N and 112 kg·ha −1 P.