Quantification of rice canopy nitrogen balance index with digital imagery from unmanned aerial vehicle

With the rise of large-scale crop plantation in China, inexpensive but efficient remote-sensing measures for predicting the nitrogen status of crops are needed for optimal fertilizer management. In this research, a conventional digital camera with a charge coupled device was integrated into an unmanned aerial vehicle (UAV) to capture digital aerial images of paddy rice (Oryza sativa L.) at an altitude of 50 m. The fluorescence emissions of the rice leaves under light excitation were used by Multiplex® to non-destructively assess the chlorophyll and polyphenol content. The nitrogen balance index (NBI) of the rice leaves, known as the ratio of chlorophyll to polyphenols, was used to accurately determine canopy nitrogen concentrations. The dark green colour index (DGCI) available from the aerial images was used to assess the nitrogen concentrations in the field. It was found that DGCI values predicted the nitrogen concentrations and NBI with R2 (coefficient of determination) = 0.672 (p < 0.001) and R2 = 0.711 (p < 0.001), respectively. The results indicated that aerial photography from UAV had the ability to assess plant nitrogen status in the field in large-scale crop plantations.