Effect of various nitrogen rates on MR303 rice yield performance and NDVI spectral reflectance

Effective nitrogen management is critical for maximizing rice yield and improving nitrogen use efficiency (NUE). However, assessing in-season crop nitrogen status remains challenging due to environmental variability and the limitations of conventional monitoring methods. This study aimed to (1) evaluate the correlation between NDVI, SPAD values, and nitrogen content score (NCS) at different growth stages; (2) determine the effect of varying nitrogen fertilizer rates on yield components; and (3) compare plant responses under greenhouse and field conditions. A randomized complete block design (RCBD) with five nitrogen rates (T0: 0g, T1: 0.39g, T2: 0.78g, T3: 1.17g and T4: 1.56g) was applied to MR303 rice under both greenhouse and field settings. Physiological measurements, including NDVI, SPAD values, and chlorophyll content (NCS), as well as yield attributes such as panicle number (panicles per plant), grain number per panicle (grains per panicle), and 1000-grain weight (g), were recorded. Results showed a significant correlation between NDVI and SPAD during the late vegetative (r = 0.713, r 2 = 50.09%) and reproductive stages (r = 0.739, r 2 = 54.7%), while early-stage correlation was weak (r = 0.161, p > 0.05). NDVI was also significantly correlated with NCS (r = 0.725, r 2 = 52.57%, p < 0.001). Nitrogen application significantly improved panicle number (T4: 23.55 ± 1.62), grain per panicle (T4: highest, p < 0.05), and 1000 grain weight, with consistent trends in both environments but greater variability in field trials. The findings highlight the reliability of NDVI and SPAD as diagnostic tools at later stages and reinforce the importance of timely nitrogen input. NDVI measurements are best taken during the late vegetative to reproductive stages to ensure improved monitoring of nitrogen status and reliable yield prediction.