Estimating Tiller Density and Leaf Area Index of Winter Wheat using Spectral Reflectance and Ultrasonic Sensing Techniques

A 2-year study is reported in which tractor-mounted radiometer and ultrasonic sensing systems were evaluated to determine if the combined arrangement could be used to estimate tiller numbers (tillers m−2) and the leaf area index (LAI) of winter wheat. The system was tested over two growing seasons, on a range of winter wheat varieties planted at different seed rates on different soil types. By using a combination of the coefficient of variation (CV) of the normalised difference vegetation index (NDVI) and a new form of compound vegetation index derived from the radiometer and ultrasonic sensor height output measurements, the tiller numbers and leaf area index were estimated to an accuracy of ±125 tillers m−2 and ±0·47 LAI, respectively, without using any other direct field measurements. This study has shown that a tractor-mounted sensing system can be used to assess tiller numbers and leaf area index. These values offer the potential to be used directly with canopy management principles to aid the agronomic decision-making process. They can be used to help determine the optimum level of inputs such as fertilisers, fungicides and growth regulators at a given stage of crop development and to account for variations within a field.