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Estimating total leaf nitrogen concentration in winter wheat by canopy hyperspectral data and nitrogen vertical distribution
DUAN Dan-dan, ZHAO Chun-jiang, LI Zhen-hai, YANG Gui-jun, ZHAO Yu, QIAO Xiao-jun, ZHANG Yun-he, ZHANG Lai-xi, YANG Wu-de
2019, 18 (7): 1562-1570.   DOI: 10.1016/S2095-3119(19)62686-9
Abstract223)      PDF in ScienceDirect      
The use of remote sensing to monitor nitrogen (N) in crops is important for obtaining both economic benefit and ecological value because it helps to improve the efficiency of fertilization and reduces the ecological and environmental burden.  In this study, we model the total leaf N concentration (TLNC) in winter wheat constructed from hyperspectral data by considering the vertical N distribution (VND).  The field hyperspectral data of winter wheat acquired during the 2013–2014 growing season were used to construct and validate the model.  The results show that: (1) the vertical distribution law of LNC was distinct, presenting a quadratic polynomial tendency from the top layer to the bottom layer.  (2) The effective layer for remote sensing detection varied at different growth stages.  The entire canopy, the three upper layers, the three upper layers, and the top layer are the effective layers at the jointing stage, flag leaf stage, flowering stages, and filling stage, respectively.  (3) The TLNC model considering the VND has high predicting accuracy and stability.  For models based on the greenness index (GI), mND705 (modified normalized difference 705), and normalized difference vegetation index (NDVI), the values for the determining coefficient (R2), and normalized root mean square error (nRMSE) are 0.61 and 8.84%, 0.59 and 8.89%, and 0.53 and 9.37%, respectively.  Therefore, the LNC model with VND provides an accurate and non-destructive method to monitor N levels in the field.
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Heterogeneity Analysis of Cucumber Canopy in the Solar Greenhouse
QIAN Ting-ting, LU Sheng-lian, ZHAO Chun-jiang, GUO Xin-yu, WEN Wei-liang , DU jian-jun
2014, 13 (12): 2645-2655.   DOI: 10.1016/S2095-3119(14)60776-0
Abstract1546)      PDF in ScienceDirect      
Detailed analysis of canopy structural heterogeneity is an essential step in conducting parameters for a canopy structural model. This paper aims to analyze the structural heterogeneity of a cucumber (Cucumis sativus L.) canopy by means of analyzing leaf distribution in a greenhouse environment with natural sunlight and also to assess the effect of structural canopy heterogeneity on light interception and photosynthesis. Two experiments and four measurements were carried out in autumn 2011 and spring 2012. A static virtual three-dimensional (3D) canopy structure was reconstructed using a 3D digitizing method. The diurnal variation of photosynthesis rate was measured using CIRAS-2 photosynthesis system. The results showed that, leaf azimuth as tested with the Rayleigh-test was homogeneous at vine tip over stage but turned heterogeneous at fruit harvest stage. After eliminating the influence of the environment on the azimuth using the von Mises-Fisher method, the angle between two successive leaves was 144°; at the same time, a rule for the azimuth distribution in the canopy was established, stating that the azimuth distribution in cucumber followed a law which was positive spin and anti-spin. Leaf elevation angle of south-oriented leaves was on average 13.8° higher than that of north-oriented leaves. The horizontal distribution of light interception and photosynthesis differed significantly between differently oriented leaves. East- and west-oriented leaves exhibited the highest photosynthetic rate. In conclusion, detailed analysis of canopy structural heterogeneity in this study indicated that leaf azimuth and elevation angle were heterogeneous in cucumber canopy and they should be explicitly described as they have a great impact both on light distribution and photosynthesis.
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