Estimating the Mean Leaf Inclination Angle of Wheat Canopies Using Reflected Polarized Light

Abstract

In this study, we extended previous work linking the polarization of reflected light from crop canopies with characteristics of the canopy structure, such as the leaf inclination angle. We obtained reflectance and polarized reflectance in 8 spectral bands from the canopies of two varieties of wheat, planted in plots fertilized with a basal dressing and topdressed at the jointing and booting stages. The optical measurements were carried out on 3 clear-sky days when the plants were at the stem-elongation, heading and ripening stages, respectively. On each measurement date, we assessed the leaf orientation geometry of the plants using a Plant Canopy Analyzer (LAI-2000), measured the leaf greenness (an indicator of leaf chlorophyll content) using a handheld SPAD-502 (SPAD) optical sensor, and also measured plant height. Both polarization and leaf greenness observations at the heading stage were able to distinguish the canopies that had received topdressing from those without topdressing. However, no significant correlation was observed between the polarization in the blue, green and red bands and the SPAD (r = 0.425?0.456, n = 12 observations, p < 0.05). On the other hand, the mean leaf inclination angle (= mean tip angle: MTA) measured by the LAI-2000 was inversely correlated with the polarization in the 3 visible bands (r = ?0.85??0.88, n = 12, p < 0.001). Adjusting the view zenith angle according to the solar position at the time of measurement improved the accuracy. We tested a linear regression model to predict the MTA of the two wheat varieties based on polarized reflectance in the red band centered at 660 nm (r ² = 0.73, n = 12, p < 0.001). Validation of this model obtained in the subsequent cropping season confirmed that polarization measurements were potentially useful for estimating the MTA of wheat stands in which the panicles were located below the topmost leaf layer of the canopy.     

小麦冠层叶片性状配合力与环境互作分析

为了研究小麦冠层叶片性状的配合力与环境互作．随机选用7个亲本．连续3年组配成21个双列杂交组合进行试验。结果表明．旗叶的开张角、长、宽、叶鞘长和倒二叶的宽、叶鞘长的一般配合力与环境互作显著,冠层各叶片性状的特殊配合力与环境互作均显著;各叶角性状和旗叶鞘长以加性效应为主;叶长和倒二叶鞘长环境效应作用最大．加性效应次之;叶宽环境效应作用最大。各性状的一般配合力都具有较高的稳定程度．而特殊配合力的稳定程度相对较低。最后讨论了配合力的测度和冠层叶片性状遗传改良的亲本选配与后代选择的原则。