Varietal Reponses of rice (Oryza sativa L.) to different Nitrogen levels under Conventional Production Systems

Rice (Oryza sativa L.) is a vital staple crop globally, with its cultivation expanding to meet increasing demand. In Sub-Saharan Africa, particularly Ghana, rice productivity is often limited by poor soil fertility. Farmers frequently apply high nitrogen (N) fertilizer rates to boost yields; however, excessive nitrogen use contributes to environmental problems such as nutrient leaching and pollution. While optimal nitrogen application rates have been extensively studied, limited research has focused on varietal responses among rice genotypes. This study evaluated the response of five rice varieties (CRI-Agra Rice, Togo Marshall, CRI-Amankwatia, CRI-Enapa, and Jasmine 85) to different nitrogen rates (0, 30, 60, and 90 kg N/ha), focusing on morphophysiological, biomass and yield-related traits. The findings showed significant (p < 0.001) variations in these traits with increasing nitrogen levels. Application of 90 kg N/ha led to substantial improvements: 40% increase in chlorophyll content, 34.3% in culm length, 71.4% in panicle number, 28.3% in straw dry weight and 42.9% in grain yield over the control (0 kg N/ha). Nitrogen significantly promoted vegetative growth, delayed flowering and enhanced biomass and grain production. Genotypic differences in nitrogen use efficiency were also observed. Togo Marshall, CRI-Agra Rice and Jasmine 85 showed over 30% increases in chlorophyll content, while CRI-Enapa exhibited higher plant height and panicle number at 90 kg N/ha. Togo Marshall and CRI-Enapa recorded the highest biomass and yield responses, indicating superior nitrogen utilization. Overall, CRI-Enapa and Togo Marshall performed best at 60-90 kg N/ha. These findings highlight the importance of genotype-specific nitrogen management strategies for improving rice productivity and sustainability in Ghana and similar regions.