[Spectral characteristics of corn under different nitrogen treatments]

The canopy spectral reflectance and chlorophyll content of corn were measured and analyzed under different nitrogen treatments. The trends of chlorophyll content were discussed based on different growth stages and different nitrogen levels. It was observed that the chlorophyll content increased with the increase in nitrogen, and could be affected by the environment changes including the temperature, rain, fertilizer treatment and so on. The characteristics of canopy spectral reflectance indicated that the canopy spectral reflectance changed significantly at different stages. In the visible region (400-750 nm), the reflectance increased and reached the maximum until the shooting stage, and decreased subsequently with the growth progress. In near-infrared region (750-1 000 nm), the spectral reflectance climbed sharply. It increased from tillering stage to shooting stage first, and then began to decline at trumpet stage and was raised again at anthesis-silking stage. At milking stage, the reflectance was decreased again. There were clear distinctions of visible reflectance in different nitrogen regions. At shooting stage, with the increase in nitrogen the reflectance decreased at chlorophyll absorption band (430-450 nm, 640-660 nm). Investigating the reflectance of the corn canopy under the different nitrogen treatment, it was found that the reflectance was higher in normal fertilizing region than others in 550 nm, with R(Normal) > R(Low) > R(High). At trumpet stage, the canopy reflectance in low fertilizing region was higher than others in the visible region. It was clear that the corn canopy reflectance of normal fertilizing region was the same as high fertilizing region. The results indicated over fertilizing could not help increase the corn nitrogen uptake. The study provided the basic information of chlorophyll measurement based on spectral technology and could help to guide the precision fertilizer in the field.