A critical review of nitrogen metabolism and its role in improving cotton productivity

Abstract

Nitrogen is a vital macronutrient required for plant growth and development due to its essential role in amino acids, nucleic acids, chlorophyll, and various metabolic cofactors. Although nitrogen is the most abundant atmospheric element (78%), plants can utilize it only in ammonium (NH₄⁺) and nitrate (NO₃⁻) forms. While some nitrogen-fixing microbes help convert atmospheric nitrogen into plant-available forms, modern crop production mainly relies on inorganic fertilizers to meet nitrogen needs. In plants, nitrogen assimilation is tightly regulated by a coordinated enzyme network, including nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase. In cotton, nitrogen availability directly influences vegetative–reproductive balance, chlorophyll content, boll formation, lint yield, and fiber quality. Therefore, improving nitrogen use efficiency (NUE) is critical for reducing production costs and increasing profitability. NUE can be enhanced through agronomic adjustments, physiological improvements, biological interventions, and genetic approaches aimed at strengthening innate nitrogen utilization pathways. Developing cotton cultivars with superior NUE will also contribute to environmental sustainability by reducing nitrogen losses through leaching and volatilization