Genotypic variability of nitrate-accumulating leafy vegetables as affected by nitrogen doses: morpho-physiological and biochemical approach

Nitrogen (N) promotes plant functions at all levels ranging from plants growth, development, and metabolism to resource allocation. The present study was undertaken to study the role of N-fertilization on growth and N-metabolizing enzymes in high- and low-nitrate-accumulating leafy vegetables of Amaranthus cruentus and Brassica juncea and to find the optimum nitrogen level required by plants as per their physiological condition and age. Different doses (0, 40, 80, 120 kg/ha) of N fertilizers were given to the test plants at different growth stages along with the uniform basal dose of phosphorus (30 kg ha-1), potassium (80 kg ha-1), sulphur (40 kg ha-1) and zinc (25 kg ha-1). N-fertilization showed a significant positive influence on various growth attributes and N-metabolizing enzyme activities. Growth parameters got improved with N-fertilization up to the uppermost level of N fertilization (120 kg/ha). However, maximum and significant improvement in morphological traits and in the potential for exploitation of N-assimilatory enzymes was observed at N@80 kg/ha. The growth parameters were distinct in both A. cruentus and B. juncea and the activities of all the N-metabolizing enzymes were higher in the low-nitrate-accumulating leafy greens as compared to the high-nitrate-accumulating ones in both A. cruentus and B. juncea, suggesting a better N-assimilation in the former category of plants.