POTENTIAL OF USING FIELD SPECTROSCOPY DURING EARLY GROWTH FOR RANKINGBIOMASS IN CEREAL BREEDING TRIALS

The use of field spectroscopy for the non-destructive ranking of cerea l breeding plots at the early stages of crop growth was investigated u sing measurements of spectral reflectance over 222 wavebands between 4 00 and 2500 nm using the single beam GEOSCAN Portable Field Spectrorad iometer (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 reflectanc e 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 indepe ndent 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 Rat io, performed poorly in ranking plots according to biomass. However, a t 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 ag reed closely with the actual ranking. To apply these results in practi ce, the accuracy of the simpler CROPSCAN portable field radiometer (PF R) was found to be greater than the GEOSCAN PFS for comparable NIR and VIS wavebands. It was therefore concluded that it is practically feas ible to use field spectroscopy to rank cereal plots for biomass at ear ly 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.