Experiment:-1 Physical Purity Analysis
Physical purity
analysis refers to the determination of different components of the purity viz.
pure seed, other crop seeds, weed seeds and inert matter in terms of
percentages (by weight) of the kind consideration.
Thus, Physical Purity Analysis helps in:
i. Improving the plant stand (by increasing the pure seed
component).
ii. Raising a pure crop (by eliminating other crop seed
and weed seeds).
iii. Raising a disease free-crop (by eliminating inert matter).
Purity Components:- The working sample
obtained for purity analysis is separated into the following four components.
a)
Pure seed
b) Other crop seeds
c)
Weed seeds
d) Inert matter
Pure seed:- The pure seed refer to the seeds of the kind/species stated by a
sender or found predominantly in the test sample.
General criteria for pure
seed
a) The whole seed or pieces
of seed units that is larger than one half of the original size.
b) The seed structures (even
if immature, undersize, shriveled provided they can be definitely identified as
of that species), unless transformed into visible fungal sclerotia, smut balls
or nematode galls.
Other crop seeds:-The other crop seeds include the seeds and seed like structures of
any plant species, which are
Weed seeds:-This category includes
the seeds of those plants normally recognized as general weeds or specified as
weeds in the official regulations and laws (Seed Act).
Inert matter:- It includes all other materials and structures that are not included
in pure seed, other crop seeds and weed seeds fractions such as broken pieces
of seeds and seed units that are less than half of the original size. It also includes chaff, straw , leaves ,
flowers , fungal bodies , soil , sand and stone particles etc.
General principle:- The working sample is separated into 4 components namely pure
seed, other crop seed, weed seed and inert matter. The percentage of each component
is determined by weight. All species of other and weed seeds present shall be identified
as far as possible.
Equipment and Tools:- Seed divider, purity work board, seed blower, a set of sieves with
different perforations, magnifying glasses, microscope, balances, forceps,
spatula, needle, reflected light and watch glasses etc.
Working sample:- The purity analysis shall be made on a sample obtained from the
submitted sample by one of the methods of laboratory sampling. The size of the
working sample for purity analysis shall be either a weight estimated to
contain at least 2500 seed units subjected to maintain a minimum of 0.5g
(tobacco) and a maximum of 1000g (caster).
General procedure of separation:-
1) Purity analysis is
performed on working sample of prescribed weight of the crop under examination.
2) After weighing place the
working sample on the clean surface of the working sample or a purity work
board slightly to the rear and left of centre.
3) With the help of forceps
having straight smooth edges, draw a few seeds at the time from the pile,
spread them apart by pulling towards the front of board.
4) Examine each seed, seed
unit and particles carefully, judged individually and separate them into
different component parts with prescribed rules. Continue this operation until the
entire sample is separated.
5) Reexamine each component
to ensure that separation has been made accurately.
6) After separation, each
of the component part shall be weighed separately that is upto required no. of decimal places.
Calculation of component percentage:- Add together the weights of
all the component fractions separated from the working sample. Percentage must
be based on the weights of the component parts, not on the original weight of
the working sample. The percentage by weight of each of the component is
estimated as per the formula given below:-
Let;
Weight of pure seed= a
Weight of other crop seed= b
Weight
of weed seeds= c
Weight of inert matter= d
Total
weight of all components= a+b+c+d= z
Therefore,
Pure seed (%) = a/z x 100
Other crop seed (%) = b/z x 100
Weed seeds (%) = c/z x 100
Inert matter (%) = d/z x 100
Example: Prepare a final
test report of purity analysis made on a working sample of pepper variety as
per rules and separated in to four component parts viz. pure seed (14.75g),
other crop seeds (nil), weed seeds (0.10g) and inert matter (0.15g).
Solution:
Weight of working sample= 15g
Weight of pure seed=
14.85g
Weight of other crop seeds= nil
Weight of weed seeds=
0.10g
Weight of inert
matter= 0.15g
Total weight of all
components= 14.75+0+0.10+0.15= 15.00g
Calculations of percentages:
Pure seed (%) =
14.75/15 x 100= 98.33
Weed seed (%) =
0.10/15 x 100= 0.67
Inert matter (%) = 0.15/15
x100= 1.00
Total =
98.33+0.67+1.00 =100
Reporting of results
Pure seed (%) = 98.3
Other crop seeds (%) = 0.0
Weed seeds (%) = 0.7
Inert matter (%) = 1.0
Total = 100 per cent
The pure seed
fraction (98.3%) is higher than the minimum prescribed (98%). Hence the sample
is approved and by inference the seed lot is of good quality and found suitable
for distribution and marketing with regard to purity.
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