Temporal Changes In NDVI And Nitrogen Content: A Study On Paddy Vegetation Reflectance Under Daily Light Variation

Abstract

 Remote sensing tools such as the Normalized Difference Vegetation Index (NDVI) are widely used to assess crop nitrogen status. However, variability in light intensity across the day can affect the reliability of NDVI readings. This study aimed to (1) examine the diurnal variation of lux intensity, (2) evaluate NDVI changes at different times of day, and (3) compare NDVI values between greenhouse and field trials. The experiment was conducted using MR303 rice grown under two conditions: a greenhouse and a field in Melaka, Malaysia. A randomized complete block design (RCBD) with five nitrogen treatments (T0–T4) was applied. Measurements of lux, NDVI, SPAD, and nitrogen content score (NCS) were taken during the reproductive stage in the morning, noon, and evening. Findings showed that lux intensity was significantly higher at noon (47,304 ± 20,422 lux) than in the morning (6,615 ± 2,568) or evening (4,829 ± 1,935) (p < 0.05). NDVI values were significantly lower at noon in both environments (p < 0.05), while morning and evening values were statistically similar. No significant differences were found in NDVI values between greenhouse and field conditions. Although no statistically significant differences were found in NDVI values between greenhouse and field conditions, readings within the greenhouse were consistently slightly higher than those in the field. To ensure accurate nitrogen estimation, measurements should be taken under consistent timing and light intensity conditions for reliable comparison. 
These results support the development of standardized NDVI protocols to improve nitrogen monitoring accuracy in rice production systems.