Journal of Taiwan Agricultural Research

Author:Fan-Ming Chang, Chwen-Ming Yang* and Ay-Hwa Chang

Abstract:

    This study was to measure near-ground remotely sensed canopy hyper-spectral reflectance data during the growing periods under varied treatments of nitrogen (N) fertilizer and to identify spectral characteristics in related to N concentration so as to establish spectral models for estimating N status in rice plants. Results indicated that reflectance spectra of rice canopy were similar to other green plants. Applications of different amounts of N fertilizer changed the spectral patterns, but did not change the decreasing trend of N concentrations in leaves and shoot following plant development in both cropping seasons. Correlation intensity curve between spectral reflectance in range of 340-2400 nm and N concentration was similar in leaves and shoot, suggesting that responses of reflectance along the spectral domain to N concentrations in leaves and shoot were quite alike. However, the correlation intensity curve of the first crops was not conformed to that of the second crops, and varied correlation coefficients existed in different narrow bands. In general, correlation coefficients from near-infrared (740-1300 nm) to short-wave infrared region (1300-1800 nm) had larger values than the other bands. Change of correlation coefficient was in between -0.5 and 0.5 in the first crops, with the maximum absolute value of correlation coefficient located at 1240 nm (R²<0. 18). The values of correlation coefficient in the second crops had greater variability, with the maximum absolute value found at 1208 nm (R²>0.70). Results also indicated that estimation of N concentrations in leaves and shoot of rice plant may be improved by using multiple linear regression (MLR) models. The spectral wavebands suitable for the best three variables MLR models were 403 nm, 558 nm and 1607 nm for both cropping seasons. The slopes for the relationship between the estimated and the measured values of N concentrations were greater than 0.940, with the root mean square error (RMSE) less than 0.548.

Key words:Canopy reflectance spectrum, Spectral characteristics, Nitrogen content in rice, Correlation coefficient, Multiple linear regression model

Download: PDF Links