Utilization of canopy reflectance to predict properties of oilseed rape (Brassica napus L.) and barley (Hordeum vulgare L.) during ontogenesis

Measurements of canopy reflectance may provide a fast and non-destructive tool for monitoring canopy properties in precision agriculture. A substantial gain for practical use may be achieved by further developing multi-spectral and -temporal techniques of canopy reflectance analyses in order to combine several applications like site-specific fertilizer application, disease control, and prediction of harvesting date or yield forecast, in future. For this purpose, seasonal courses of canopy properties and vegetation indices of winter oilseed rape (Brassica napus L. cv. ‘Lirajet’) and spring barley (Hordeum vulgare L. cv. ‘Barke’) were investigated simultaneously in 3-year field experiments from 2002 to 2005. Canopy properties like shoot fresh matter, shoot dry matter, shoot-N content and shoot water content of both crops were related to traditional vegetation indices of the visual (VIS) and the near infra-red (NIR) spectral bands. Typically, closer relationships between canopy characteristics and vegetation indices were found at higher wavelength bands. The index R850 introduced here for the first time allows predicting quantitative growth properties directly at the field level. The results of the current study show that the use of vegetation indices of the NIR and its determination over the entire growth period will substantially improve the application of canopy reflectance measurements in agriculture.