Seed Testing

SAMPLING IN SEED TESTING LABORATORY

The seed samples received in the laboratory (submitted samples) are required to be reduced to obtain working samples for carrying out various tests. A number of methods are available for obtaining Working samples.

1. Mechanical divider method:

This method is suitable for all kinds of seeds, except the extremely chaffy types. In this method, the sample is mechanically divided by the seed dividers (the available types are Boerner and Gamet Seed dividers). The apparatus divides a sample passed through it into two approximately equal parts. The submitted sample can be mixed by passing it through the divider, recombining the two parts and passing the whole sample through a second time, and similarly, a third time if necessary. The sample is reduced by passing the seed through repeatedly and removing one half on each occasion. This process of successive halving is continued, until a working sample of approximately, but not less than, the required size is obtained.

2. Random cups method:

This method is particularly suitable for seeds requiring a working sample upto 10 gm provided that they are not of extremely chaffy structure, and provided that they do not bounce or roll (like Brassica spp.)

In principle, six to eight small cups, or thimbles, are placed at random on a tray. After a preliminary mixing the seed is poured uniformly over the tray. The seed that falls into the cups is taken as the working sample.

3. Modified halving method:

The apparatus comprises of a tray into which is fitted a grid of equal sized cubical cells, open at the top and every alternate one having no bottom. After preliminary mixing, the seed is poured evenly over the grid in the same way as it is poured in the random cups method. When the grid is lifted, approximately half the sample remains on the tray. The submitted sample is successively halved in this way until a working sample approximately, but not less than, the required size is obtained.

4. Spoon method:

It is permissible to use this method only for samples of a single small-seeded species. A tray, spatula and a spoon with a straight edge are required. After preliminary mixing, the seed is poured evenly over the tray in the same way as it is poured in the random cups method. The tray should not be shaken thereafter. With the spoon in one hand, the spatula in the other, and using both, small portions of seed from not less than five random places on the tray should be removed. Sufficient portions of seed are taken to constitute a working sample of approximately, but not less than, the required size.

5. The hand halving method:

This method is restricted to the following genera of chaffy seeds: Andropogon, Arrhenatherum, Astreble, Cenchrus, Chloris, Dichanthium, Stylosanthes (not guianenisis), Trisetum and Urochloa.

The seed is poured evenly onto a smooth clean surface and thoroughly mixed into a mound with a flat-edged spatula. The mound is then divided into half and each half is halved again, giving four portions. Each of the four portions is halved again giving eighth portions which should be arranged in the rows of four. Subsequently alternate portions are combined and retained, the process is repeated until the sample of required weight is obtained.