Estimation of percent infection of leaf blast in rice plants from canopy spectral characteristics
Journal
Proceedings of the 6th International Conference on Precision Agriculture and Other Precision Resources Management
Pages
1644-1658
Date Issued
2002
Author(s)
Chwen-Ming Yang
Chang, Y.C.
Abstract
Reflectance spectra (350-2500 nm) of hyperspectral resolution from rice (Oryza sativa cv. Tainung 67) canopy infected with various percentages of leaf blast (Pyricularia oryzae) during the maximum tillering stage were collected and analysed using a field portable spectroradiometer. Percent infection (Y) started from 0% (healthy plants) up to 25%, based on blast disease affected leaf area. By the correlation intensity analysis between reflectance and Y, it showed that reflectance at ultraviolet (350-400 nm) and infrared (740-2500 nm) regions had greater correlation coefficients than those in the visible light (400-740 nm). The maximum value of coefficient (r=0.982) was located at 1436 nm. Among the 10 classified wavebands of the measured spectral range, short-wave infrared had the highest coefficient of determination (R2=0.968, P<0.001) between Y and mean reflectance, and followed by violet (R2=0.964, P<0.001) and near-infrared (R2=0.955, P<0.001) and others. The spectral indices, RED/GREEN ratio (reflectance ratio of red light minimum to green light peak), NIR (reflectance at near-infrared maximum), RED, red edge slope, and red edge mid point were all positively correlated with Y. By the multiple linear regression analysis with GREEN, RED and NIR as variables, the model was Y=-9.391 + 6.265RED + 0.340NIR-3.381GREEN, with R2=0.929 (P<0.01). When 8 optimum narrow bands selected from reflectance spectrum were analysed, the best 3-variable model was Y=-21.401 + 1.162R620 nm + 4.855R1436 nm-3.914R2198 nm (R2=0.980, P<0.001).
Event(s)
Proceedings of the 6th International Conference on Precision Agriculture and Other Precision Resources Management
Publisher
University of Minnesota, Precision Agriculture Center
Description
Includes papers and proceedings from the conference held July 14-17, 2002 at the Radisson Hotel South and Plaza Tower, Minneapolis
Type
conference paper