Evaluation of Canopy Reflectance Technology Using a Delta Yield Approach

Abstract

Canopy reflectance measurements have been proposed as a method to variably apply N to corn (Zea mays L.). This study was conducted to determine if normalized difference vegetation index (NDVI) is correlated with corn N response spatially across a field. Whereas most studies use fertilizer N strips to impose N response variation, the current study assesses ability of NDVI to predict N response against naturally occurring soil N levels. The experiment was conducted on commercial corn fields in southern Ontario, Canada in 2006 and 2007. A GreenSeeker System (NTech Industries, Inc., Ukiah, CA) was used to measure NDVI at the 6 to 7, 8, 10, and 11 to 12 leaf stages on 9 by 4.5 m subplots of two treatments receiving 0 and 30 kg N ha−1 starter, respectively. Delta yield estimates that spatially corresponded with NDVI subplot measurements were determined by bordering each subplot plot with a nonlimiting N rate subplot and a zero N rate subplot and measuring differences in yield. Corn response to N fertilizer, as measured by delta yield, was highly variable spatially across each field in both years. Delta yield values ranged between 100 and 7200 kg grain ha−1 in 2006, and −2300 and 5000 kg grain ha−1 in 2007. Similarly NDVI varied spatially with coefficient of variations ranging from 6 to 16% depending on leaf stage and year. Correlations between NDVI measurements and delta yield were not significant at any leaf stage. The relationship between N response and NDVI may be determined by factors other than N or by N mineralization occurring beyond the 11 to 12 leaf stage.