不同施氮水平下玉米冠层光谱反射特征分析

Spectral Characteristics of Corn under Different Nitrogen Treatments

通过田间试验研究了玉米不同生长期冠层光谱反射率的变化特征,分析了不同施氮水平下可见光区冠层光谱反射率的差异。研究结果表明：受作物群体光和能力的影响,玉米可见光区冠层反射光谱在拔节期达最高点,随后持续降低 近红外区,苗期反射率最低,在拔节期达最高点,喇叭口期有所降低而在开花吐丝期得到回升,进入灌浆期后又下降。不同施氮水平下,拔节期随施氮水平的增加,叶绿素的强吸收带（430~450和640~660 nm）玉米冠层反射曲线呈下降排列,但在550 nm附近反射率R正常〉R偏低〉R偏高 喇叭口期偏低施氮区的冠层反射率在可见光区明显高于其它施氮水平,且偏高和正常施氮区域内光谱反射强度基本相同,显示过量施肥并不会促进作物生长。分析玉米生长期间不同施氮水平下光谱反射率的差异,对监测玉米生长状况,指导田间施肥具有重要的现实意义。

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 chan- ges 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 stagc, 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, 640-660nm）. 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 RNorrnal〉RLow〉RHigh. 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.