Comparison of Trimble GreenSeeker and CropCircle (Model ACS-210) Reflectance Meters for Assessment of Severity of Late Leaf Spot
2019
Jordan, B. S. | Branch, W. D. | Coffin, Alisa W. | Smith, Coby M. | Culbreath, A. K.
Four field experiments conducted in 2015 were used to examine the relationships among normalized difference vegetation index (NDVI) measurements from two canopy crop sensors and visual estimates of defoliation by late leaf spot (Nothopassalora personata) of peanut (Arachis hypogaea). For each evaluation, reflectance was measured with the two meters, and leaf spot severity was measured visually within as short a time as possible. Linear and nonlinear regression was used to characterize the relationships between percent defoliation from late leaf spot and NDVI measured with the GreenSeeker (NDVIGS) and Crop Circle (NDVICC) instruments and the relationships between NDVIGS and NDVICC. NDVIGS decreased with increasing percent defoliation according to linear functions in two of the four trials, and according to a two linear segment piecewise function in one trial. NDVICC decreased with increasing percent defoliation according to a linear function in one trial and according to a to a two- linear segment piecewise function in two trials. NDVICC increased with increasing NDVIGS according quadratic functions in two trials, but there was no significant regression for those variables in two trials. In three of the four trials, NDVICC linear regression had a better fit for predicting percent defoliation. There was no indication for either instrument that the same NDVI reading corresponded with the same level of defoliation across trials. Results indicated that NDVI measurements from the two instruments are not interchangeable.
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