Combination of spectral reflectance and ultrasonic sensing to monitor the growth of winter wheat

A preliminary study is reported in which a two channel (660 and 730 nm wavelength) radiometer system and ultrasonic sensor were attached to a tractor mounted boom and used in parallel to measure the normalised difference vegetation index (NDVI) and height respectively of three varieties of winter wheat (Claire, Consort and Riband). Each variety was planted at three seed rates (50, 150 and 250kg ha(-1)) in a replicated trial involving a total of 27 plots. The NDVI was shown to represent a typical canopy expansion and senescence curve for winter wheat and proved useful for monitoring the crop up to growth stage (GS) 31 (first node detectable). The ultrasonic sensor measurements were most suited for monitoring crop growth once it has reached GS 30 (early stem elongation). In addition, the ultrasonic data provided a measure of crop density particularly pre GS 45 (mid-booting). This study has indicated the potential for using radiometers and ultrasonic sensors in combination, enabling the crop to be assessed throughout the growing season. Results from the study have illustrated the potential to combine ultrasonic density and NDVI measurements pre GS 31 (first node detectable) to provide information about crop cover and physical characteristics of the crop canopy. (C) 2003 Silsoe Research Institute. All rights reserved Published by Elsevier Ltd.