Effectiveness of Spectral Radiometers for the Detection of N Stress in Corn.

Improving Nitrogen Use Efficiency through variable rate application of fertilizer as guided by remotely sensed data has been a focus of research within the agronomic community. A new generation of active multi-spectral remote sensing instruments enables more frequent sampling of crops due to their ability to collect reflectance measurements under variety of sky conditions. The addition of new spectral bands to these instruments allows the investigation of the effectiveness of different vegetation indices for detecting N stress at various growth stages. A multi-year assessment of the potential for remote sensing instrumentation to discern N stress in corn has been conducted at two diverse locations in Maryland from 2004 to 2008. Plant height, LAI, leaf chlorophyll content, development stage, and the remotely sensed data were acquired weekly from growth stages V6 to R1. This enabled an examination of the relationship of growth stage with the expression of N stress in the corn and the sensors ability to detect the stress. Temporal exhibition of N stress varied from year to year due to residual soil N and meteorological variables (rainfall and temperature). Correlations between remotely sensed vegetation indices and leaf chlorophyll content typically increased as the corn developed, and N-stress intensified. Vegetation indices incorporating red edge bands showed improved detection of leaf chlorophyll variability when compared with indices that did not utilize the red edge. Significant correlation between leaf chlorophyll content and remote sensing derived vegetation indices typically occurred at, or after, a growth stage of V8.