Influence of nitrogen doses on the chemical composition and proportions of nutrients in selected vegetable species

The experiments on celery, curly kale and lettuce reported in this paper were carried out in a greenhouse, with plants grown in 2 dm3 pots filled with peat substrate. The trials were established in a completely randomized design. The aim was to determine the effect of increasing nitrogen doses (0.3, 0.6, 0.9, 1.2 g N dm-3 of substrate) on N-tot., NO3-N, concentrations of P, K, Ca, Mg, Fe, Zn, Mn and Cu as well as ratios between these elements in three vegetable species such as curly kale, lettuce, and celery, distinguished by different degrees of sensitivity to salinity. An increase in the content of total nitrogen and NO3-N in lettuce, curly kale and celery appeared to be parallel to the increasing doses of nitrogen, while the average total nitrogen content was similar in all the tested species, and the content of N-NO3 in kale was about five-fold lower than in lettuce and celery. The level of nitrogen fertilization influenced the content of potassium and magnesium in lettuce as well as the content of phosphorus, potassium, calcium and magnesium in celery. The nitrogen doses significantly differentiated proportions between the nutrients in plants, mostly the K:Mg and Zn:Cu ratios. The increasing doses of nitrogen modified the content of microelements and proportions between various components in the tested plant species.