Chinese Journal of Agrometeorology ›› 2020, Vol. 41 ›› Issue (03): 173-186.doi: 10.3969/j.issn.1000-6362.2020.03.006

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 Hyperspectral Features of Rice Canopy and SPAD Values Estimation under the Stress of Rice Leaf Folder

 ZHOU Xiao, BAO Yun-xuan, WANG Lin, DU Zheng-zhen, TANG Qian, CHEN Can   

  1.  1. Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China; 2. Jiangsu Key Laboratory of Agricultural Meteorology, Nanjing University of Information Science & Technology, Nanjing 210044; 3. Key Laboratory of Meteorological Disaster, Ministry of Education(KLME)/Joint International Research Laboratory of Climate and Environment Change(ILCEC), Nanjing University of Information Science & Technology, Nanjing 210044
  • Received:2019-09-21 Online:2020-03-20 Published:2020-03-20
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Abstract:  The second instar larvae of Cnaphalocrocis medinalis Guenee (Rice Leaf Folder, RLF) cultured in the Laboratory of Agrometeorology and Insect Ecology of Nanjing Agricultural University were used as the experimental objects in 2017-2018. In the rice field of the agricultural meteorological experimental station of Nanjing University of Information Science & Technology, six levels treatments, including 50, 100, 200, 300, 400 RLFs·100plants-1and Control Treatment (CK) were set, in order to test the relationship between spectral characteristics and SPAD values under such different initial pest population condition. During the experiments, the spectral reflectance of rice canopy and the SPAD values of the flag leaves were measured by ASD Field Spec3 (Analytical Spectral Devices Inc) and SPAD-502 (Soil and Plant Analyzer Development), respectively. The variation patterns of original spectrum, trilateral parameters and SPAD values in different growth stages were analyzed. Consequently, the vegetation indices and trilateral parameters based on the observed spectral data were calculated using the reflectance values in the bands with strong correlations with SPAD. And the regression estimation models of the SPAD valuesof rice were established.The results showed that: (1) the spectral reflectance values of rice canopy damaged by RLFs were significantly different from those of the control (P<0.05). In the visible bands, the reflectance values of the former were lower than those of the latter during tillering-booting stages, and was higher than the latter during the flowering-maturity stages.(2) In the near-infrared band, the reflectance values of the injured treatments were lower than those of the control. And they decreased with the increase of the pest’s population, among which the reflectance of 300 RLFs·100plants-1(Level 4) was the lowest.(3) With the increase of the pest’s population, the red-edge position values appeared the ‘blue-shift’ trend. (4) The SPAD values decreased gradually with the increase of the pest’s population, and the Level 4 treatment had the lowest values. (5) The Normalized Difference Vegetation Index (NDVI), Red-Edge Normalized Difference Vegetation Index (NDVI705) and the position of red-edge had a close correlation with SPAD values.(6)The single factor estimation model and multiple stepwise regression model of SPAD were constructed using the hyperspectral features of rice. The exponential model with NDVI had the best estimation effect, with the highest coefficient of determination (0.72) among all the estimation models. The results indicate that it is feasible to use the spectral parameters of rice canopy to establish a model for estimating the SPAD values of rice leaves under the stress of rice leaf folder in the whole growth stages. This method is fast and nondestructive, and is convenient for continuous, dynamic and long-term located observation.

Key words:  Cnaphalocrocis medinalis Guenee, Canopy spectrum, Vegetation indices, Estimation models of SPAD

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