Relationship of vegetation indices and SPAD meter readings with sugarcane leaf nitrogen under Pampanga Mill District, Philippines condition

Nitrogen (N) is an essential macronutrient in sugarcane that promotes vegetative growth and yield development. A study was conducted to evaluate the relationship of vegetation indices (NDVI and GNDVI) and SPAD meter readings with sugarcane leaf N and to introduce the best sampling date for the evaluation of plant N. SPAD meter readings (SMR), soil moisture, NDVI and GNDVI were gathered from 15 sampling sites in Pampanga Mill District, Philippines under different N fertilization practices and these were correlated with actual plant N. Six to thirteen, 21-28, 36-43, 100-107 and 147-154 days after fertilization (DAF) were sampling dates maintained each location. Results showed that SMR has a high positive correlation with plant N (0.86, 6-13 DAF), GNDVI (0.80, 147-154 DAF), soil moisture (0.79, 147-154 DAF) and NDVI (0.73, 147-154 DAF). Among sampling dates, it was recommended that 21 to 28 DAF using GNDVI and SPAD meter is best sampling date for evaluation of plant N status; since it coincides with stalk elongation stage and grand growth phase when rapid leaf production and vigorous vegetative development occur. Measurement of vegetation index and SPAD meter readings have potential in evaluating plant N through rapid assessment and ground validation, respectively.