A critical nitrogen dilution curve for japonica rice based on canopy images

A crop's nitrogen (N) status can be determined by the ratio of the actual shoot N concentration (N%) to the critical N%, which is defined as the minimum N% required for maximum growth. However, the determination of critical N% is expensive and time-consuming. This study developed a convenient alternative rice (Oryza sativa L.) critical N dilution curve determination method using a digital camera and image processing technology. Four years of experiments involving six japonica rice cultivars were used to obtain stable results, and the rice canopy coverage level extracted from images was used instead of shoot dry matter in the determination of the critical N% and the critical N dilution curve. The newly developed critical N dilution curve was as accurate as the curve derived from shoot dry matter, but the canopy coverage can be measured much more inexpensively and quickly through the use of digital images. The critical N dilution curve, as a function of canopy coverage, effectively identified the rice N status and can be adopted as an effective tool in determining crop N levels.