Crop Canopy Sensor Orientation for Late Season Nitrogen in Corn.

Increasing nitrogen use efficiency (NUE) in irrigated corn production is of great importance to overall agricultural sustainability.  Studies have shown that crop canopy sensors can aid in this pursuit as they allow for the determination of N requirements in split applications later in the growing season.  Fertigation can also increase NUE as many split applications can be conducted.  If crop canopy sensors could be used to direct N fertigation rates overall NUE may be increased even further. However, in some cases N differences may need to be determined later in the growing season after corn has tasseled, which can cause issues with crop canopy sensor readings.  Therefore, a study was initiated to evaluate the potential of a crop canopy sensor to differentiate between N levels at two corn (Zea mays) growth stages (R1 and R3) after the corn had tasseled.  The sensor was placed in three orientations to evaluate which best determined corn N status across two sensor calculated indices while avoiding taking measurements involving the corn tassel. These orientations were 1) nadir, between corn rows (above canopy), 2) 45° off nadir within the corn canopy (below corn tassel), and 3) 90° off nadir within the corn canopy (below corn tassel).  The results of this study show that N differences in late season corn can be determined by utilizing crop canopy sensors in an inter-row orientation.  Results also show that the ReNDVI index is superior to the NDVI index for late season N determinations in corn.  These results suggest that crop canopy sensors could be an effective tool for determining N requirements of corn late in the growing season.