EXPLAINING THE VARIATION IN YIELD RESPONSE TO DISEASE CONTROL THROUGH ESTIMATES OF RADIATION INTERCEPTION BY CROP CANOPIES - AN OPPORTUNITY FOR REMOTE SENSING
RJ BRYSON1, WS CLARK1, AC MADEIRA2, ND PAVELEY3 and R SYLVESTER-BRADLEY1
lADAS Boxworth, Boxworth, Cambridge CB3 8NN, UK; 2Depart. Ciencias do Ambiente, Institute Superior de Agronomia, 1300, Lisbon, Portugal; 3ADAS High Mowthorpe, Duggleby, Malton, N. Yorks., Y017 8BP, UK
Background and objectives
Results and conclusions
In two experiments at ADAS Terrington, on the susceptible winter wheat variety Slepjner, epidemics of yellow rust (Puccinia striiformis) ranged from nil to severe with 60 (1994) and 52 (1995) different combinations of fungicide dose and timing. Assessments of disease severity (%) integrated over time as area under disease progress curve (AUDPC) could only account for yield differences within each season but not between seasons. In-field assessments of GLAI integrated over time, or healthy area duration, showed a curvilinear relationship with grain yield (1994, R2=0.63; 1995, R2=2 0.73). Estimates of intercepted radiation by healthy green tissue (i.e., healthy area absorption HAA) were determined from GLAI and total incident radiation measurements using the Beer's Law analogy (k=0.5). Accumulated intercepted radiation by green tissue accounted for more variation in yield response to disease control with R2=R20.80 (1 994) and R2=0.92 (1995).
Spectral reflectance measurements of both healthy and diseased (P. ;striiformis) crop canopies were made using a LICOR LI-1800 spectroradiometer over the wavelength range 350-800nm at 2-nm intervals. Contrasting spectral reflectance signatures were obtained for healthy and diseased crop canopies. Differences in spectral reflectance signatures within the visible spectrum related to the amount of incident radiation absorbed and utilized by the crop canopy. Changes in the infrared spectrum related to changes in leaf water content owing to the presence of disease. It is suggested that measurements of spectral reflectance, using remote sensing techniques, may be exploited in the future to relate the absorption of radiation by green tissue over time to yield response due to disease control.