Ground measured spectral estimation of N in differentially managed paddy rice monitoring growth
2001
Ara, W.D. (Kagoshima Univ., 1-21-24 Korimoto, Kagoshima 890-0065 (Japan). Lab. of Agricultural System Engineering)
In a range of N fertilization, spectral reflectance of paddy rice were measured in a field experiment by handheld spectroradiometer. The widely used normalized difference vegetation index (NDVI) and relative vegetation index were examined as an indicator of N fertilization and other biophysical state like LAI, dry weight and also net assimilation rate. RVI was found useful to distinguish different N fertilizer level. Whereas NDVI was poor indicator when compared to RVI. Both NDVI and RVI had a good correlation with the biophysical parameters, especially when natural log of RVI was taken. Special regards were taken in the growth phase of panicle formation and full heading stage. Overfertilization of N by 40% of the optimal rate was separated from the optimal rate and lower level of optimal N fertilization prior to full heading stage. The result also separated lower level of the optimal N fertilization significantly, which yielded good over the optimal rate. A relation with grain yield and indices were also examined. Both the indices had significantly high correlation approaching full heading prior to panicle formation stage
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