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This article in AJ

  1. Vol. 96 No. 1, p. 135-142
     
    Received: Feb 2, 2003
    Published: Jan, 2004


    * Corresponding author(s): caow@njau.edu.cn
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doi:10.2134/agronj2004.1350

Monitoring Leaf Nitrogen Status in Rice with Canopy Spectral Reflectance

  1. Lihong Xue,
  2. Weixing Cao *,
  3. Weihong Luo,
  4. Tingbo Dai and
  5. Yan Zhu
  1. Key Lab of Crop Growth Regulation, Ministry of Agric., Nanjing Agric. Univ., Nanjing, Jiangsu 210095, P.R. China

Abstract

Nondestructive monitoring and diagnosis of plant N status is necessary for precision N management. The present study was conducted to determine if canopy reflectance could be used to evaluate leaf N status in rice (Oryza sativa L.). Ground-based canopy spectral reflectance and N concentration and accumulation in leaves were measured over the entire rice growing season under various treatments of N fertilization, irrigation, and plant population. Analyses were made on the relationships of seasonal canopy spectral reflectance, ratio indices, and normalized difference indices to leaf N concentration and N accumulation in rice under different N treatments. The results showed that at each sampling date, leaf N concentration was negatively related to the reflectance at the green band (560 nm) while positively related to ratio index, with the best correlation at jointing. However, the relationships between leaf N accumulation and reflectance at green band and ratio index were consistent across the whole growth period. The ratio of near infrared (NIR) to green (R810/R560) was especially linearly related to total leaf N accumulation, independent of N level and growth stage. Tests of the linear regression model with different field experiment data sets involving different plant densities, N fertilization, and irrigation treatments exhibited good agreement between the predicted and observed values, with an estimation accuracy of 96.69%, root mean square error of 0.7072, and relative error of −0.0052. These results indicate that the ratio index of NIR to green (R810/R560) should be useful for nondestructive monitoring of N status in rice plants.

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