Nitrogen is important for oilseed rape production and even moderate deficiencies will substantially reduce yield and
profit, but excessive N can pollute both surface and ground water. Thus, farmers are walking a thin line. In order to find
the relationship between the SPAD value and the nitrogen content of oilseed rapes, a Minolta SPAD-502 Meter can be
used for on-farm measurement of the N content, and then the Kjeldahl method has been used for measuring the nitrogen
content of these oilseed rapes. Every leaf had 10 points SPAD value in average for measuring by SPAD, according to the
area of the leaves, the points were increased or decreased. The Kjeldahl method has been used for organic nitrogen determination
for over a century. Before using the Kjeldahl method to measuring the nitrogen content, all the leaves has
been washed and dried. The results of these two methods has been fitted, as a result, the correlation coefficient is 0.863.
Another sample was used to check if the result was perfect, the error of the forecasting value is about 7.4%. A new
method for measuring the nitrogen content quickly of oilseed rapes has been found, the nitrogen content of the oilseed
rape can be measured nondestructively and quickly.
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.