Comparison of Two Commercial Active Optical Sensors Regarding Their Relationship Between Early-Season Sensor Readings and Final Corn (Zea mays, L) Yield.

Ground-based active-optical (GBAO) crop sensors have been shown useful in predicting corn (Zea mays, L.) yield early in the growing season. Our objective was to compare the relationship between sensor reading and the ‘in-season estimate of yield’ (INSEY) from both the GreenseekerTM sensor and the Crop Circle sensor. Fifteen dryland sites were selected in 2011 on cooperator fields. The experimental design was a randomized complete block with four replications and six N rate (ammonium nitrate) treatments; control, 45 kg ha^-1, 90 ha^-1, 134 ha^-1, 179 ha^-1, and 224 ha^-1 were applied preplant within 1-5 days of planting. Each experimental unit was about 6-m long by 3-m wide. The GBAO sensors were used at 5-8 leaf stage, and about 10-14 days later. One of the interior rows of corn were hand-harvested when the corn was mature and shelled after drying. The relationships varied with location. In locations where the corn yield response to N was small, the R2 of the sensor readings from both instruments at both growth stages were small. Where response to N was large, the relationships between sensor reading and INSEY were large. The Crop Circle sensor averaged an R² of about 0.78. the Greenseeker relationship averaged about 0.52. There was a particularly improved relationship between sensor reading and INSEY by the Crop Circle sensor at the second reading, usually about the 10-14 leaf stage.