Pedosphere 30(6): 769--777, 2020
ISSN 1002-0160/CN 32-1315/P
©2020 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Nondestructive estimation of bok choy nitrogen status with an active canopy sensor in comparison to a chlorophyll meter
Rongting JI1,2, Weiming SHI1,2, Yuan WANG1, Hailin ZHANG3, Ju MIN1,2
1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008(China)
2University of Chinese Academy of Sciences, Beijing 100049(China)
3Department of Plant and Soil Sciences, Oklahoma State University, Stillwater OK 74078-6028(USA)
      Precise estimation of vegetable nitrogen (N) status is critical in optimizing N fertilization management. However, nondestructive and accurate N diagnostic methods for vegetables are relatively scarce. In our two-year field experiment, we evaluated whether an active canopy sensor (GreenSeeker) could be used to nondestructively predict N status of bok choy (Brassica rapa subsp. chinensis) compared with a chlorophyll meter. Results showed that the normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) generated by the active canopy sensor were well correlated with the aboveground biomass (AGB) (r=0.698-0.967), plant N uptake (PNU) (r=0.642-0.951), and root to shoot ratio (RTS) (r=-0.426 to -0.845). Compared with the chlorophyll meter, the active canopy sensor displayed much higher accuracy (5.0%-177.4% higher) in predicting AGB and PNU and equal or slightly worse (0.54-1.82 times that of the chlorophyll meter) for RTS. The sensor-based NDVI model performed equally well in estimating AGB (R2=0.63) and PNU (R2=0.61), but the meter-based model predicted RTS better (R2=0.50). Inclusion of the days after transplanting (DAT) significantly improved the accuracy of sensor-based AGB (19.0%-56.7% higher) and PNU (24.6%-84.6% higher) estimation models. These findings suggest that the active canopy sensor has a great potential for nondestructively estimating N status of bok choy accurately and thus for better N recommendations, especially with inclusion of DAT, and could be applied to more vegetables with some verification.
Key Words:  aboveground biomass,GreenSeeker,model prediction,N diagnosis,normalized difference vegetation index,plant N uptake,root to shoot ratio,ratio vegetation index,soil and plant analyer development (SPAD)
Citation: Ji R T, Shi W M, Wang Y, Zhang H L, Min J. 2020. Nondestructive estimation of bok choy nitrogen status with an active canopy sensor in comparison to a chlorophyll meter. Pedosphere. 30(6):769-777.
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