Chlorophyll is important for crops. The chlorophyll concentration is commonly used as the principal symptom of
senescence. The objective of this paper was to study the relationship between the chlorophyll concentration and the time
after the leaves being separated from the canola to confirm the detached leaves' senescence rate. The chlorophyll meter
(SPAD meter) has been used in chlorophyll concentration measurement of fruit trees, sugar maple leaves in forest, corn
with varying color and so on. In the experiment, a Minolta SPAD-502 chlorophyll Meter was used for measuring the
chlorophyll concentration after picking off the canola leaves for 0 hour, 5 hours, 15 hours, 25 hours and 40 hours, and 25
samples were measured. As a result, the leaf senescence rules were found by observing the changing curves of the leaves'
SPAD values. The original detached canola leaves were divided into three kinds of samples, and a certain senescence rule
was found for each kind of samples. The results could provide good methods support to delay leaf senescence.
This paper presents the development of a multi-spectral nitrogen deficiency sensor, which uses three channels (green, red, near-infrared) of crop images to determine nitrogen level of the rape. The core of this investigation is the calibration methods between the multi-spectral references and the nitrogen levels in crops measured using a SPAD 502 chlorophyll meter which may be used to measure N (g)/leaf area (m<sup>2</sup>). Some noticeable relationships between the multi-spectral reflectance and SPAD readings were found from this study.