Potential of using field spectroscopy during early growth for ranking biomass in cereal breeding trials

Abstract

The use of field spectroscopy for the non-destructive ranking of cereal breeding plots at the early stages of crop growth was investigated using measurements of spectral reflectance over 222 wavebands between 400 and 2500 nm using the single beam GEOSCAN Portable Field Spectroradiometer (PFS). Measurements were made on 54 barley plots at the 5- and 7-leaf stages of growth with biomass varying between 10 and 96 g/m2. The optimal multiple linear regression relationship between reflectance and biomass included wavebands from the near-infrared (NIR) and mid-infrared (MIR) with a standard deviation of 4.8 g/m2. The ranking of plots according to biomass by this optimal relationship or the Simple Ratio of NIR to visible (VIS) reflectance, which is a common index of greeness, agreed closely with actual ranking. Tested against an independent set of wheat plots at the 4-leaf stage with biomass ranging from 3 to 32 g/m2, the barley-derived relationship, but not the Simple Ratio, performed poorly in ranking plots according to biomass. However, at the 7-leaf growth stage, when the biomass range had increased to 48-117 g/m2, both the Simple Ratio and the barley-derived relationship agreed closely with the actual ranking. To apply these results in practice, the accuracy of the simpler CROPSCAN portable field radiometer (PFR) was found to be greater than the GEOSCAN PFS for comparable NIR and VIS wavebands. It was therefore concluded that it is practically feasible to use field spectroscopy to rank cereal plots for biomass at early growth stages where the difference between plots is of the order of 5-7 gm/m2. Such biomass differences were more apparent at the 7-leaf than 4-leaf stage of growth.