| Summary: | Modern agriculture has posed a great impact upon natural resources in terms of exploitation and their luxurious use. Ever increasing population pressure has exhausted the sustainable agricultural production system by exploiting land and water resources. High external inputs, required for high yield targets, are nowadays heavily dependent upon artificial sources and ways, amongst which nitrogen (N) is of global concern. Nitrogen is required by crops for active growth and photosynthetic machinery throughout the crop cycle. Among cereals, maize has the highest yield potential, hence it removes huge amounts of N and water from soil. To achieve high yields, farmers mostly use high dose of N fertilizers, causing soil, water and environmental pollution in the form of soil degradation, eutrophication and volatilization, thus reducing nitrogen use efficiency (NUE). This review critically focuses on N fertilizer management and regulation in maize farming systems with high population density. Achievements have been summarized in regard of NUE improvement through certain advanced molecular breeding and transgenic approaches, as well as agronomic options to optimize N-uptake and its utilization, especially after silking in maize. Rational use of fertilizers with right doses at right time, as well as integrated agronomic management options are proposed. More research is required to modify assimilatory pathways during source-sink translocation through proteomic and transcriptomic studies, to improve NUE in high density maize. Wider scope exists for molecular breeding to exploit natural variation for efficient root architecture, lodging resistance, anthesis-to-silking interval, photosynthetic efficiency, stay green and large sink capacity for optimum NUE.
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