Influence of different ammonium and nitrate ratios on quality of rocket

Nitrogen fertilization is very important in baby leaf vegetables and affects the nitrate accumulation in edible leaves. In soilless systems, nitrogen supplied as ammonium can reduce the leaf nitrate concentration. It is well known that the increase of ammonium can affect the growth of plants. The aim of this work was to find qualitative and quantitative differences in baby leaf rocket (Eruca sativa Mill.) as a response to different N-ratios (NH4+/NO3-). The influence of the two nitrogen forms and their biochemical interactions in the plant metabolism were assessed. Plants were grown in a floating system using a nutrient solution containing 12 mM total nitrogen and treatments were differentiated for their nitrogen form concentrations: 0% NH4+ - 100% NO3-; 25% NH4+ - 75% NO3-; 50% NH4+- 50% NO3-. At harvest, yield, chlorophyll, carotenoids, nitrate concentration, and secondary metabolites were determined in leaves. Yield did not change among treatments and was in average 2.8 kg m-2. Chlorophyll index (assessed in vivo) increased by increasing ammonium concentration. Nitrate concentrations were between 1410 and 1570 mg kg-1 fresh weight and no significant differences were founded among treatments. Nitrogen balance index (NBI) increased by enhancing the ammonium percentage in the nutrient solution. Secondary metabolites, such as phenolic, flavonoids and total carotenoids were not affected by ammonium and nitrate ratio.