不同氮素水平油菜冠层反射光谱特征研究

2002～2003年油菜生长季节,在浙江大学实验农场设置了4个品种、3个供氮水平处理、3个重复的油菜田间小区试验,测定了不同发育时期的冠层光谱反射率及对应叶片、茎以及角果的鲜重和干重。结果表明：不同供氮水平的油菜冠层和叶片光谱差异明显,冠层光谱反射率随发育期推移,开花前在可见光范围逐渐降低、在近红外区域逐渐增大,开花后在可见光范围逐渐增大,在近红外区域逐渐降低。不同供氮水平的油菜冠层光谱差异明显,4个品种的油菜具有相似的变化规律,在近红外表现尤其明显,随着供氮水平的增加,光谱反射率明显升高;而在可见光波段处,随供氮水平提高,反射率反而降低。前期随发育期推移,NDVI和RVI都逐渐增大,在4月22日达到最大,其中N2和N3在4月14日受开花影响,NDVI和RVI有所降低。4月22日以后,由于后期叶片衰老变黄,NDVI和RVI都逐渐减小。

Spectra Characteristics of Rape Canopy at Different Nitrogen Levels

The spectral reflectance of the canopy of four rape varieties were measured by a ASD FieldSpec Pro FRTM? in field under three nitrogen levels at different development stages. The measurements were carried out at experiment field in the Zhejiang university during growth season of 2002 to 2003. At the same time, leaf wet biomass and leaf dry biomass, stem wet biomass and stem dry biomass and so on corresponding the spectrum were obtained in laboratory. The results showed that the spectral differences were significant for the canopy of rape under different nitrogen levels and the spectral reflectance changed with different development stage. The spectral reflectance of the canopy was gradually getting smaller in the visible region and bigger in the near infrared region before flowering, but with reverse change after flowering. There were significant differences for the spectral reflectance of canopy of the rape under different nitrogen levels. The four rape varieties have the same trend, especially in the near infrared region. The spectral reflectance of the canopy was gradually getting bigger with increasing of nitrogen level. However, it becomes smaller with increasing of nitrogen level in visible region. In the early stages, NDVI and RVI are gradually getting bigger, and then they reach the peaks on 22nd April. During the period, because of effect of flowering NDVI and RVI become smaller on 14th April. After 22nd April, NDVI and RVI all decline due to yellow leaves.