Usefulness of remote sensing for the assessment of growth traits in individual cereal plants grown in the field

Biomass determination usually involves destructive and tedious measurements. This study was conducted to evaluate the usefulness of the Normalized Difference Vegetation Index (NDVI) and the Simple Ratio (SR), calculated from the spectra of individual plants, for the assessment of leaf area per plant (LAP), green area per plant (GAP) and plant dry weight (W) at different growth stages. Two varieties of four cereal species (barley, bread wheat, durum wheat and triticale) were sown in a field experiment at a density of 25 plants m(-2). The spectra were captured on three plants per plot on eight occasions from the beginning of jointing to heading using a narrow-bandwidth visible-near-infrared portable field spectroradiometer adapted for measurements at plant level. Strong associations were found between NDVI and SR and growth traits, both indices being better estimators of GAP and W than of LAP. Exponential models fitted to NDVI data were more useful for a wide number of situations than the linear models fitted to SR data. However, SR was able to discriminate between genotypes within a species. The accuracy of the reflectance measurements was comparable to that obtained by destructive measurements of growth traits, in which differences between varieties of over 24% were needed to be statistically significant. However, differences in SR of only 18% were statistically significant (P < 0.05). The reliability of the spectral reflectance measurements and the nondestructive nature convert this methodology into a promising tool for the assessment of growth traits in spaced individual plants.