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Arabic Version:
English Version:
HOW
TO
In
this section we provide technical/practical information that seed sector staff
may find useful. It is simple to follow instructions for technical staff in
seed production and quality control.
How to No 28: Calibration of Seed Dividers
A representative sample is a prerequisite for laboratory seed testing and
the accuracy of the test results. Seed dividers are used to prepare representative
submitted and working samples from composite and submitted samples respectively.
For a sample to be truly representative, all the components existing in the
original lot from which the sample is drawn are to be represented at the same
rate in the sample.
The Chief Officer at the Seed Testing Station for Scotland devised a simple
method for calibration of seed dividers to fulfill quality assurance requirement
in seed testing laboratories. The method can be summarized in the following
steps:
1. Prepare a calibration seed sample in line with the information provided
in the table below. The method can be adapted to your laboratory
and it is not necessary to use the same species. The essence
is that seed and admixture will be easily separated using a proper
sieve.
2. Mix the seed species and the admixture well and divide into two portions
(a & b) using the divider to be calibrated.
3. Record the weight of a, b and a+b. The difference between a and b should
be within predetermined standard (i.e. 5%).
4. Separate the admixture from the seed using sieves with the right perforations.
5. Determine the percentage of admixtures in each of the two half samples
(a and b) and in the total weight (a+b) of the original
calibration sample.
6. Check how close the figures reflect the original seed-admixture composition
in the calibration sample (a+b) and in each of the two halves
(a and b).
7. Check whether the deviations are within tolerance, using tolerated differences
for the separation of an admixture in a sample' (Miles,
1963).
|
Dividers
|
Seed species
|
Admixture
|
Calibration sample (g)
|
% Admixture
|
|
Centrifugal
|
Wheat
|
Brassica
|
800
|
15
|
|
Riffle divider (small seeds)
|
Ryegrass
|
Wheat
|
220
|
35
|
|
Riffle divider (large seeds)
|
Bean
|
Spinach
|
1200
|
10
|
The calibration should be carried out according to a specific timetable and
calibration samples should be kept in a moisture proof container after use.
The sample should be renewed whenever its size is considerably reduced or
the composition significantly changed. The level of these changes is left
to each laboratory to decide. Abdoul Aziz Niane, Seed Unit, ICARDA, P.O.
Box 5466, Aleppo, Syria; E-mail: a.niane@cgiar.org
