水稻冠层光谱特征及其与LAI的关系研究

Study on Relationship between Rice Canopy Spectra and LAI

氮素营养是影响作物生长与产量的最主要限制因子之一。准确及时地监测或诊断出作物氮素营养状况,对提高氮素利用效率和作物管理水平、减少过度施氮造成的环境污染具有重要意义。本研究在不同施氮水平处理的水稻试验小区,对水稻整个生长期内冠层反射光谱进行了较系统、密集的测定,同时测定了几个重要生育期水稻的叶面积指数。研究结果表明:随着施氮量的增加,水稻冠层光谱在各生育期间呈现出一定的规律性,在近红外部分(710～1220nm),冠层光谱反射率随着施氮水平的提高而升高,而在可见光部分(460～680nm),水稻冠层的光谱反射率反而逐渐降低。经冠层光谱差异显著性检验发现:水稻灌浆期以前,对施氮水平最为敏感的波段是绿光(560～610nm)和近红外(710～760nm)部分;转换为归一化植被指数(NDVI)以后,差异最显著的是(R760-R560)/(R760+R560)。不同氮肥处理的水稻LAI随时间变化曲线大致都呈抛物线型,中低水平施氮肥水稻LAI随时间的变化曲线比较平缓,而高水平施氮肥LAI曲线则变化比较剧烈。冠层光谱反射与叶面积的相关分析结果表明:在水稻抽穗前,叶面积与冠层光谱反射率相关性较差;而抽穗后,叶面积与冠层光谱有较高的相关性。

N nutrition is one of the uppermost limitation factors for crop growth and yield. Precise and timely monitoring or detection of crop N nutrient conditions is necessary for improving the efficiency of N nutrition use and crop management, reducing environmental pollution caused by over nitrogen fertilizer application. In this paper the canopy reflectance spectra during the whole growing period on rice field plots treated with different nitrogen levels were periodically and continually measured. LAI of rice of several important growing periods was meanwhile measured. The results showed that rice canopy spectral reflectance of different growing periods changed regularly with the increase of nitrogen fertilizer application. The canopy spectral reflectance increased in 710~1 220 nm, while decreased in 460~680 nm. The varieties of canopy spectral reflectance under different nitrogen levels were analyzed and compared. The results showed that the canopy spectral reflectance was sensitive to nitrogen levels in 560~610 nm and 710~760 nm before milkfilling. After transforming canopy spectral reflectance to normalized difference vegetation index (NDVI), (R760-R560)/(R760+R560) was significantly different under different nitrogen levels. Curves of LAI of rice treated with different nitrogen levels with time were a parabola shape, and the curves of LAI of rice treated with middle and low nitrogen levels changed gently while treated with high nitrogen levels changed acutely. In addition, the correlation coefficient between LAI and canopy spectral reflectance was low before the heading period,however, was high after the heading period.