Effect of nitrogen sources on the nitrogenous forms and accumulation of amino acid in head cabbage

The effect of two different nitrogen sources: ammonium nitrate and calcium nitrate, applied at increased rates, on the content of the total nitrogen, protein and non-protein nitrogen, and the content and composition of amino acids in head cabbage leaves was studied. The higher nitrogen accumulation was established at the ammonium nitrate fertilization compared to the calcium nitrate, but the application of Ca(NO3)2 resulted in a higher content of nitrate nitrogen. More protein nitrogen was also observed in plants with Ca(NO3)2 fertilization. The highest applied fertilizer rate of ammonium nitrate resulted in a significant reduction of the protein nitrogen compared to increased free amino acids. The total content of amino acids increased gradually with the increase of nitrogen rates in plants fertilized with NH4NO3. When Ca(NO3)2 was applied, nitrogen rates higher than 500 mg/kg soil suppressed the synthesis of amino acids. A greater increase was observed as regards the levels of arginine, proline and some essential amino acids as lysine, phenylalanine and histidine. The increase of proline and alanine could serve as an indicator for unbalanced nitrogen nutrition.