physical purity test.pptx

PHYSICAL PURITY TEST

1. Exercise No. 06 PHYSICAL PURITY TEST   Objective: To determine whether the submitted seed sample conforms to be prescribed quality standards in regard to purity components, objectionable weed seeds, other inseparable crop seeds and seeds of other distinguishable varieties .

2. Principle : In accomplishing the objectives of purity analysis, each and every seed as well as particle is examined and separated into the following component parts ( i ) pure seeds (ii) other crop seeds (iii) weed seeds and (iv) inert matter. The composition of the sample is determined and the results are expressed as percentage on weight basis .

3. Pure seeds (PS): The pure seed shall refer to the species stated by sender or found to predominate in the test and shall include all botanical varieties and cultivars of the species. Generally, they are intact seeds or broken seeds that are more than one half of their original size whether immature, undersized, shrivelled , diseased or germinated provided they can be definitely identified as that of the species. Other crop seeds (OCS): Shall include seeds and seed like structures of any plant species other than that of pure seed. The classification for immature, damaged, diseased and empty seeds of other crop is the same as that provided for pure seed. Weed seeds (WS): Shall include the weed seeds, bulbets or tubers of plants which are recognized as weeds by laws, official regulation or by general usage

4. Inert matter (IM): Shall include seeds, seed like structures and other matters as follows: Pieces of broken or damaged seeds, achenes , mericarps and caryopsis which are one half the original size or less. Broken or empty glumes, lemmas, paleas , unattached sterile florets and florets with caryopsis less than the minimum size prescribed. Seeds of the Leguminosae , Cruciferaceae and Coniferaceae with the seed coat entirely removed are regarded as inert matter. Split cotyledons of peanut, cowpea, and soybean are also classed as inert matter. Other inert matter shall include soil, sand, stems, leaves, pieces of bark, cone scales, wings, flowers, nematode galls, fungal bodies (such as ergot, other sclerotia and smut balls), caryopsis of Gramineae replaced by insect larvae . Any other matter that is not seed.

5. Equipments and materials required: ‘ L’ shaped purity working table. Physical purity work board with illuminating light. Wide field hand-lens or Magnifying glass of 3 to 7 X magnification. Binocular microscope. Balances viz., i ) One with a capacity of 100—200 gm with accuracy of 0.1 mg (analytical balance) and ii) One with a capacity of 1000 gm with accuracy of 10 mg (precision balance). Sieves and sample pans. Seed blowers and dividers. Spoons, spatula, forceps, scalpel, needles, shallow trays, watch glass, etc. Small seed containers to hold separated seeds and other matters (vials with corks).

6. Procedure: The size of the submitted sample sent to the Seed Testing Laboratory is larger than the working sample to be used for purity analysis. Generally, a purity working sample is a weight estimated to contain 2,500 to 3,000 seeds subject to a minimum of 0.5 grams and a maximum of 1,000 grams or otherwise not less than the specified weight as per ISTA rules, 2004. The analysis may be made on one working sample of this weight or on two sub samples of at least half this weight, each drawn independently from the submitted sample. Prior to purity analysis, the submitted sample is thoroughly mixed three times with the help of mechanical seed dividers . Then, the correct size of the working sample is obtained from the submitted sample by repeated halving or by abstracting and subsequently combining small portions. In any case, the working sample must not be altered by adding or removing seed by hand. In case, if the submitted sample contains very large quantity of extraneous materials, then the preliminary separation of small inert matters like chaff, dirt and other light matters should be removed by using seed blower and screens .

7. The physical purity analysis should be done on the clean surface of a purity working board Examine each and every seed and inert matter of the working sample. Separate the sample by the forceps into four components such as pure seed, other crop seed, weed seed and inert matter the purity separations are also mane by taking the advantage of seed shape. The round seeds can be separated from flat seeds and chaffs by allowing the seeds to roll down on a slightly inclined surface. Then weigh each component on an appropriate balance to the desired decimal place. Check original weight against final weight as a check against loss of material or other error. The difference between original and final weights should not be more than 6 per cent.

8. Calculation of results: The percentage by weight of each of the components shall be calculated to one decimal place. Percentages must be based on the sum of the weights of the components or on the original weight of the working sample used for physical purity analysis. Component Weight (g) Percentage Pure seed (PS) A= A  E x 100 = Other crop seed (OCS) B= B  E x 100 = Weed seed (WS) C= C  E x 100 = Inert matter (IM) D= D  E x 100 = Final weight E= 100 per cent

9. Percentage of purity analysis up to “one decimal place ” Percentage of all components should be total to “100” If a component is nil “0.0” If a component is ≤ 0.05% “Traces” If a component is 0.05 to 0.1% “0.1%” Percentage of components on “sum of weight all components” Not on the weight of “original working sample” The name of each crop species “with Latin name” If, difficult “only by genus” Reporting results: Note: If gain or loss in weight during purity analysis exceeds 5% of the initial weight, a re-test is required.

10. Study questions : Write the use of seed blower in physical purity test How to test physical purity of pelleted seeds Write the relation between physical purity and planting value of seeds What do you mean by planting value of seeds?