Ground Based Active Remote Sensors to Determine Nitrogen Variability in Irrigated Corn.

Enhancing the efficiency of farm inputs without negatively impacting profitability or the environment has been a primary focus of precision agriculture research for quite some time.  Quantifying the nitrogen (N) content of corn plants is an important component of this research and studies have found the normalized difference vegetation indices (NDVI) adequately quantify the variability of corn leaf N content.  There are several commercially available sensors that determine NDVI.  The objectives of this study were (i) to compare the NDVI readings of three commercially available active remote sensors when assessing N variability within irrigated corn fields (ii) to determine the ability of a ground based active remote sensors to detect previously delineated production level management zones based on corn N variability and (iii) to determine the effects of environmental factors such as wind and corn row spacing on the accuracy of ground based active sensors.  The study was conducted under greenhouse and field conditions with NDVI readings being collected at specific corn growth stages within different N fertility rates and productivity based management zones.  Results suggest that, depending on corn growth stage, two of the three active sensor units accurately quantify corn variability as affected by N fertility level.  The NDVI readings collected in corn at the V12 growth stage relate well to previously delineated high and low production level management zones and that two of the three sensors tested, accurately determine N variability across a wide range of environmental factors as long as these factors are constant.  Active remote sensors appear to have the potential for large scale use in the field to differentiate N status of corn plants over a wide range of environmental conditions.