Assessment of Nutrient Status of Lowland Irrigated Rice (Oryza sativa L.) using Low Altitude Remote Sensing

Abstract

Low altitude remote sensing provides near real-time information on crop nutrient status with higher spatial resolution compared to airborne and spaceborne systems. In this study, an Unmanned Aerial Vehicle System (UAVS) with on-board multispectral camera was deployed to determine the normalized difference vegetation index (NDVI) of lowland irrigated rice under different fertilizer treatments. Relationship between UAV-based NDVI and ground measurements from Soil Plant Analysis Development (SPAD) chlorophyll meter at different rice growth stages were also established. The results showed that experimental plots with high nitrogen fertilization had significantly higher SPAD and NDVI values compared with plots without nitrogen fertilization. Strong correlation between SPAD readings and NDVI values (p<0.001) was also observed as early as panicle initiation stage (r=0.7372). Hence, low altitude remote sensing can be a rapid and non-destructive tool for site-specific rice nutrient management. The use of low altitude remote sensing technique as evaluated in this study offers a practical approach in spot- or field-level application of nitrogen fertilizer during panicle initiation to enhance uniform spikelet development, and during flowering (few days before or after) to promote grain filling using foliar fertilizers.