The objective of this work was to study the influence of the row direction of corn (Zea mays) on its spectral properties measured in the field, including the green normalized difference vegetation index (Green NDVI). Spectral properties of corn are known to be related to the nitrogen (N) status of the corn and may form the basis for real-time site-specific rates of N application. Row direction effects on spectral properties may be substantial before canopy closure. If so, it will be necessary to account for these effects in order to accurately predict the N need of corn from spectral measurements. Corn was planted directly, with no tillage, in North-South (NS) and East-West (EW) oriented rows. Nitrogen was applied as ammonium nitrate at a rate of 160 kg N ha-1. Reflectance was measured with spectral radiometers placed 30 cm above individual plants. Reflectance and green NDVI were bly dependent on time of day for corn in NS rows, and much less so for corn in EW rows. Reflectance and green NDVI were lower for corn in EW rows than corn in NS rows, but lack of replication makes it difficult to be certain that this was due to row direction. Green NDVI was less sensitive than reflectance to row direction and therefore may be more appropriate for use in a real-time variable-rate nitrogen application system.
Zea mays L.; NDVI; remote sensing
