Association of “Greenness” in Corn with Yield and Leaf Nitrogen Concentration

Abstract

Efficient use of N fertilizer has become crucial due to fertilizer costs and the impact of excessive N on the environment. Diagnostic tools for estimating plant N status have an important role in reducing N inputs while maintaining yield. The objective of our study was to quantify corn (Zea mays L.) leaf greenness with a digital camera and image‐analysis software and establish the relationship with yield, leaf N concentration, and chlorophyll meter (or SPAD, soil plant analysis development) values. In 2008 and 2009, field experiments were conducted at five sites with N treatments ranging from 0 to 336 kg N ha−1 At tasseling, the ear leaf was sampled for color analysis and SPAD measurements, and then analyzed for total N. Hue, saturation, and brightness (HSB) values from digital images were processed into a dark green color index (DGCI), which combines HSB values into one composite number. Including calibration disks in images and changing the background color in photographs to pink greatly improved DGCI precision in 2009 over 2008. There was a close relationship (typically r2 ≥ 0.70) of SPAD and DGCI with leaf N concentration. Within a location, yield increased linearly in most cases with both SPAD (average r2 = 0.79) and DGCI (average r2 = 0.78). Digital‐image analysis was a simple method of determining corn N status that has potential as a diagnostic tool for determining crop N needs.