Pre-season and early in-season loss of N continues to be a problem in corn. One method to improve nitrogen use efficiency is to fertilize based on in-season crop foliage sensors. The objective of this study was to evaluate two different ground-based, active-optical sensors and explore the use of corn height with sensor readings for improved relationship with corn yield. Two different ground-based active-optical sensors (GreenseekerTM and Holland Crop Circle SensorTM) were used within established corn (Zea Mays, L.) N-rate trials in North Dakota at two different growth stages. A corn height measurement was also recorded the same date as sensor data was collected. At the 6-leaf growth stage of corn, the Greenseeker (GS) relationship to yield and the INSEY (in-season estimate of yield) value was improved when the sensor reading was multiplied times corn height. At the 10-12 leaf stage, about 10-14 days later using the GS, the INSEY relationship with yield was also generally increased. The Holland Crop Circle sensor (CC) INSEY relationship with yield was increased only at the first sensor date, but not with the second. The second CC sensor INSEY relationship with yield was maximized using sensor reading only.

Splitting the thirteen site data set into the five sites with a high clay texture (clay or silty clay loam) and the eight sites with a medium texture (loam to sandy loam) improved all INSEY relationships compared to pooling all thirteen sites.