As shown
in the correlation between SPAD values at different measurement
points and leaf N concentration or chlorophyll indicators, the SPAD
value at different sampling region of the leaf blade was significantly
and positively correlated with LNC, Chl a, Chl b, TChl, Chl a/Chl b.
However, the average SPAD value at the midpoint of each leaf blade
(b) and approximately 1/3 of the way down from the leaf tip (c)
gave the best indication of leaf N concentration or chlorophyll content
in rice among the sampling points, especially in 3LFT. Standard
deviation of SPAD readings at different measurement positions also
showed that variation of the average SPAD value at the midpoint of
each leaf blade and approximately 1/3 of the way down from the
leaf tip (Sbc) was smaller than that of other measurement points,
which indicated that Sbc was more stable than SPAD readings at
other measurement points