Optimum nitrogen fertilization of winter wheat based on color digital camera images

Site- specific nitrogen ( N) fertilizer management based on soil Nmin ( soil mineral N) and the plant N status ( sap nitrate analysis and chlorophyll meter ( SPAD) reading test) has been shown to be effective in decreasing excessive N inputs for winter wheat in the North China Plain, but the multiple sampling of soil and plants in individual fields is too time- consuming and costly for producers and farmers. In this study, a color digital camera was used to capture wheat canopy images at a specific growth stage to assess N needs. Treatments included a farmer's N treatment ( typical farmer practice), an optimum N treatment ( N application based on soil - plant testing), and four treatments without N ( one to four cropping seasons without any N fertilizer input). Digital images were analyzed to get red, green, and blue color- band intensities for each treatment. Normalized intensities of the red, green, and blue color bands were well correlated with soil Nmin, SPAD readings, sap nitrate concentration, and total N concentration of winter wheat. This research indicated the potential of using a digital camera as a tool combined with an improved Nmin method to make N fertilizer recommendations for larger fields.