Relationship Between Coefficient of Variation Measured by Spectral Reflectance and Plant Density at Early Growth Stages in Winter Wheat

ABSTRACT

The use of by-plot coefficient of variation (CV) has not been evaluated in precision agricultural work. This study evaluated the relationship between CVs determined from normalized-difference vegetative index (NDVI) sensor readings, plant population, and sensing direction on NDVI values. Randomly selected plots, measuring 1 m² (2003) and 3 m² (2004), were established for this study. Plots in 2004 were divided into three 1 m² subplots with, 0 and 120 kg ha⁻¹ fall-applied N, and 80 kg ha⁻¹ topdress nitrogen (N). Sensor reading of subplots were taken at Feekes 5 and 7 using the Green Seeker hand-held sensor. Results showed that the relationship between vegetative RI (RI_NDVI) and harvest RI (RI_Harvest) improved with increasing CV values. The prediction of RI_Harvest was improved when CV was integrated into the RI_NDVI calculation. RI_Harvest can be better predicted with RI_NDVI when the CV of spectral radiance measurements is used in the RI_NDVI equation.

Keywords:

• coefficient of variation
• response index
• plant stand
• normalized vegetative index
• winter wheat

Contribution of the Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, OK, USA.