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Title: Comparison of trimble greenseeker and cropcircle (model acs-210) reflectance meters for assessment of severity of late leaf spot

item JORDAN, B.S. - University Of Georgia
item BRANCH, W.D. - University Of Georgia
item Coffin, Alisa
item Smith, Coby
item CULBREATH, A.K. - University Of Georgia

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2019
Publication Date: 12/2/2019
Citation: Jordan, B., Branch, W., Coffin, A.W., Smith, C.M., Culbreath, A. 2019. Comparison of trimble greenseeker and cropcircle (model acs-210) reflectance meters for assessment of severity of late leaf spot. Peanut Science. 46(2):110-117.

Interpretive Summary: The normalized difference of vegetation index (NDVI), calculated from the reflectance of red and near infrared light, is a measurement that is commonly used to assess the health of plants. Agricultural monitoring includes taking measurements of NDVI to precisely target crop plants affected by pathogens and insects. A number of commercial devices have been developed to quickly measure NDVI in the field for use by growers and extension agents. This research compares two such devices, Holland Scientific's Crop Circle, and Trimble's Greenseeker, in detection of defoliation by late leaf spot of peanuts. In 2015, in Tifton, Georgia, USA, we established four separate trials assessing new breeding lines and cultivars of peanuts. At each of these trials, we gathered NDVI data from both devices at the same time. We used common statistical methods of regression analysis to compare the data gathered at each trial from each device. Although both sensors gave NDVI ratings that were correlated with visual defoliation rankings, the Crop Circle typically had less variation, and that, generally, NDVI readings from the two devices were not interchangeable.

Technical Abstract: 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.