Effect of fertilization on the nutritive quality of lettuce

Lettuce production is mostly based on conventional growing system which can lead to an unbalanced relationship and disturbances of the processes in soil. Therefore, we investigated different systems of lettuce fertilization to ensure nutritional value and environmental protection. The aim of this study was to determine the impact of fertilization on the nutritive quality of lettuce produced in different conditions. The experiment was set on two sites (Križevci and Velika Kladuša) in randomized block design and with four repetitions to monitor the effect on the lettuce yield (A. mineral: 750 kg ha^-1 NPK 7-14-21 and 300 kg ha^-1 of calcium ammonium nitrate in two applications, B. integrated: 500 kg ha^-1 7-14-21 and 150 kg ha^-1 of calcium ammonium nitrate and C. organic: 5 t ha^-1 of composted chicken manure). Nutritive value of lettuce was analyzed during the harvest. Analysis of variance showed statistically significant differences (P<0.05) of the effect of site and fertilization on the concentration of N, crude protein and nitrate, which were the highest in the treatment A. Fertilization also had a significant effect on the concentration of vitamin C, which was at its maximum with reduced mineral fertilization (treatment B). However, there was no statistically significant effect of either site or fertilization on the concentration of P and K. For economic and environmental reasons, in future practice we recommend a reduced system of fertilization, since it gives a better quality lettuce (less nitrate, more vitamin C), while less endangering the environment.