[The spectral characteristics and chlorophyll content at winter wheat growth stages]

The canopy spectral reflectance and chlorophyll content of winter wheat were measured and analyzed in the whole growing season. The characteristics of canopy spectral reflectance indicated that the canopy spectral reflectance changed signifi cantly at different stages. It decreased first and increased later with growth progress in the visible region (400-750 nm) after jointing stage, then the reflectance was lowest at booting stage. In near-infrared region (750-1000 nm) the spectral reflectance climbed sharply. The canopy reflectance was declined at booting stage and rose to the highest point at flowering stage. It dropped to minimum level subsequently at milk-ripe stage. However, the spectral reflectance characteristics at jointing stage and booting stage were used to detect the chlorophyll content. High correlation was observed between the canopy spectral reflectance and chlorophyll content. The positive correlation of canopy spectral reflectance with chlorophyll content was found at jointing stage and booting stage. Because the plant spectral reflectance was effected by chlorophyll greatly in visible region, the correlation coefficient reached 0.89 at 552 nm in booting stage. On the contrary, there was a negative correlation at flowering stage. Meanwhile, the red edge inflection point as one of the most important spectral parameters was analyzed at winter wheat growth stages based on the first derivative of reflectance spectra. The relation between the red edge inflection point and chlorophyll content was observed in each plot and the analysis results illustrated that the red edge inflection points could help detect the chlorophyll content at jointing stage and booting stage. The linear model of chlorophyll content with red edge inflection points was built at jointing stage (R2 = 0.92). High correlation was found between thered edge inflection point and chlorophyll content at booting stage. It was showed that the binomial model (R2 = 0.91) was better than linear model (R2 = 0.73). It was indicated that using spectral analysis to detect the winter wheat chlorophyll content non-destructively was feasible. The obtained conclusions also provided theoretical basis for further researches on measuring methods of chlorophyll content in the field.