Effect of flood fertigation on yield of greenhouse lettuce grown in different substrates

The hydroponic system is very often used for greenhouse vegetable production. The flood irrigation on a bench or on the flood floors is applied in the production of ornamental plants and vegetable transplants. This system is environmentally friendly, since fertigation is used in a closed system using the recirculation of nutrient solution. The aim of this study, conducted in 2010-2012, was to determine the effect of flood fertigation with different concentrations of nutrient solution (EC: 1.0; 2.0; 3.0; 4.0 mS cm-1) on the yield and quality of the butterhead lettuce cultivar Natalia grown in different substrates (coconut coir, peat and rockwool). The experiment was conducted in the spring and autumn cycle. The highest marketable yield at each concentration of the nutrient solution was achieved in the cultivation in rockwool, both within the spring and autumn. The highest nitrate content in lettuce in terms of both cultivation cycles was found in the lettuce grown in the nutrient solution concentration of EC 4 mS cm-1, and the lowest one was achieved in the nutrient solution concentration of EC 1.0 mS cm -1. Significantly less of nitrates was in lettuce grown in spring than in autumn. Higher levels of EC significantly increased the content of P and K in lettuce leaves during in both growing cycles, while the content of Ca and Mg was not significantly different. The applied substrates had a significant impact on the content of K, P, Ca and Mg in leaves of lettuce. The best concentration of the nutrient solution used for flood fertigation of greenhouse lettuce was EC 3.0 mS cm-1 for the spring cultivation and EC 4.0 mS cm-1 for the fall crop.