Use of organic fertilizers for lettuce plug plant production.

Vegetable crop production in conventional intensive agricultural systems commonly implies high fertilization rates. Recent data show that the worldwide demand for organically grown products is expanding rapidly. Increasing interest in organic vegetable production has lead to a need to produce seedlings organically. The aim of this study was to evaluate the effects of different levels of organic fertilizers applied to lettuce seedlings on plant growth and yield. Romaine lettuce seeds of cultivar Gretta R were sown on March 2007 in polystyrene plug trays in a unheated greenhouse in the Northern coast of Sicily. At the second leaf stage, seedlings were saturated with solutions containing various concentrations (3, 6, or 9 g l-1) of an organic water soluble fertilizer (Kappabios, Serbios®) containing N 3% and K20 6%. At the end of March 2007, four leaf stage plug plants were field transplanted in black polyethylene film mulched plots at a density of 6.6 plants m-2. One week after transplanting, plantlets were respectively foliar sprayed with solutions containing various concentrations (1.5, 2.5, or 3.5 g l-1) of an organic water soluble fertilizer (Azobios,, Serbios®) containing 14%N. Higher fertilization rates positively influenced seedling growth in the greenhouse and resulted in higher yields and larger head weight.