Effect of growing method and lettuce fertilization on changes of nitrate content in leaf

The effect of different amounts of Ca-ammonium nitrates on yield and the accumulation of nitric nitrogen-NO3 was studied in open field and under greenhouse conditions, with special attention for the outer (green) and inner (light green) leaves. The results shows that the application of nitrogen (50 - 200 kg/ha) increased the lettuce yield and the nitric nitrogen content by 21-59% and 42-250% in relation to the control variant, for which 30 t/ha of manure was applied. The average content of the nitrates was markedly higher in the lettuce grown in the greenhouse and, for both growing methods, in the outer leaves.