Interactive Effects of Nitrogen Source and Salinity on Growth Indices and Ion Content of Indian Mustard

ABSTRACT

The interactions between salinity and different nitrogen (N) sources nitrate (NO₃ ⁻), ammonium (NH₄ ⁺), and NO₃ ⁻ + NH₄ ⁺ were investigated on Indian mustard (Brassica juncea cv. RH30). Treatments were added to observe the combined effect of two salinity levels (8 and 12 ds m^{− 1}) and three nitrogen sources (NO₃ ⁻, NH₄ ⁺, and NO₃ ⁻ + NH₄ ⁺) on different growth parameters and mineral composition in different plant parts, i.e., leaves, stem, and root. Salinity has been known to affect the uptake and assimilation of various essential nutrients required for normal growth and development. Different growth parameters, i.e., leaf area, dry weight of different plant parts, absolute growth rate (AGR), relative growth rate (RGR), and net assimilation rate (NAR) declined markedly by salinity at pre-flowering and flowering stages. All growth indices were less sensitive to salinity (12 d s m^{− 1}) with the nitrate form of nitrogen. It is pertinent mention that a high dose (120 kg ha^{− 1}) of nitrogen in ammonium form NH₄ ⁺, acted synergistically with salinity in inhibiting growth. Plants fed with combined nitrogen (NO₃ ⁻ + NH₄ ⁺) had an edge over individual forms in ameliorating the adverse effects of salinity on growth and yield. Under salt stress, different nutrient elements such as N, phosphorus (P), potassium (K⁺), and magnesium (Mg^{2 +}) were decreased in different plant parts (leaves, stem, and root). The maximum and minimum reduction was observed with ammoniacal and combined form of nitrogen, respectively, while the reverse was true of calcium (Ca^{2 +}), sodium (Na⁺), chloride (Cl⁻), and sulfate (SO₄ ²⁻) at harvest. Nitrogen application (120 Kg ha^{− 1}) in combined form had been found to maintain highest concentrations of N, P, Mg^{2 +}, and Ca^{2 +} along with reduced concentrations of Na⁺, Cl⁻, and SO₄ ^{2 −}. However, reverse was true with ammoniacal form of nitrogen.

Keywords::

• mineral elements
• plant growth
• total leaf area
• absolute growth rate
• relative growth rate
• net assimilation rate
• salinity
• nitrogen source

ACKNOWLEDGMENT

The authors are grateful to Professor Govind Singh (Incharge, Plant Biotech centre, Rajasthan Agricultural University, Bikaner) for critical evaluation and correction of the manuscript. Thanks are due to the Indian Council of Agricultural Research for awarding Senior Research Fellowship to the first author during Ph.D. program.