Seed sampling, mixing and dividing
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The document outlines best practices for seed sampling, focusing on obtaining a uniform and representative sample from a seed lot in accordance with ISTA rules. It details various sampling methods, sample types, and instructions for sample submission to ensure accurate seed testing. Additionally, it describes mixing and dividing techniques to create a homogeneous working sample for analysis.
Seed sampling, mixing and dividing
- 1. SEED SAMPLING, MIXING AND DIVIDING Nirmal Raj R
- 2. Objectives Sampling is done to get a uniform and representative sample from a seed lot. The size of the submitted sample required for testing is small as compared to the size of the lot, therefore, care must be taken to ensure that the submitted sample represents the lot of the seed to be tested. Hence it is essential that the samples be prepared in accordance to ISTA rules to ensure that the small size sample should represent truly and in the same proportion all constituents of seed lot.
- 3. Samples The seed lots received by laboratory for analysis and testing are given an accession number of each variety for future reference. A seed lot to be sampled must not be heterogeneous i.e. the primary samples drawn from the lot should be similar in constitution. If there is any evidence of heterogeneity test of the primary samples drawn, as defined by ISTA rules, further sampling and testing from the seed lot should not be continued.
- 4. Seed lot: Seed lot is a specified quantity of the seed of one cultivar of known origin as physically identifiable Methods of sampling 1. Hand sampling This is followed for sampling the non free flowing seeds or chaffy and fuzzy seeds such as cotton, tomato, grass seeds etc. In this method, it is very difficult to take samples from the deeper layers of bag. To over come this, bags are emptied completely or partly and then seed samples are taken. While removing the samples from the containers, care should be taken to close the fingers tightly so that no seeds escape. 2. Sampling with triers/Probe By using appropriate triers, samples can be taken from bags or from bulk. The triers are used for taking free flowing seed samples. a) Bin samplers Used for drawing samples from the lots stored in the bins.
- 6. b) Nobbe Trier The name was given after the father of seed testing Fredrick Nobbe. This trier is made in different dimensions to suit various kinds of seeds. It has a pointed tube long enough to reach the centre of the bag with an oval slot near the pointed end. The length is very small. This is suitable for sampling seeds in bag not in bulk.
- 7. c) Sleeve type triers or stick triers It is the most commonly used trier for sampling: There are two types viz., 1. With compartments 2. Without compartments. It consists of a hollow brass tube inside with a closely fitting outer sleeve or jacket which has a solid pointed end. Both the inner tube as well as the outer tube have been provided with openings or slots on their walls. When the inner tube is turned, the slots in the tube and the sleeve are in line. The inner tube may or may not have partitions. This trier may be used horizontally or vertically. This is diagonally inserted at an angle of 30°C in the closed position till it reaches the centre of the bag. Then the slots are opened by giving a half turn in clockwise direction and gently agitated with inward push and jerk, so that the seeds will fill each compartment through the openings from different layers of the bag, then it is again closed and with drawn and emptied in a plastic bucket.
- 8. Types of sampling 1. Primary sample Each probe or handful of sample taken either in bag or in bulk is called primary sample. 2. Composite sample All the primary samples drawn are combined together in suitable container to form a composite sample. 3. Submitted sample When the composite sample is properly reduced to the required size that to be submitted to the seed testing laboratory, it is called submitted sample. Submitted sample of requisite weight or more is obtained by repeated halving or by abstracting and subsequently combining small random portions. 4. Working sample It is the reduced sample with required weight obtained from the submitted sample after repeated mixing and dividing with which the seed quality tests are conducted in seed testing laboratory.
- 9. Sampling intensity The intensity of sampling should be maintained in accordance to the rules described by ISTA. When seeds are stored in bags or other containers of similar capacity that are uniform in size. When the seed is in small containers such as tins, cartons or packets a 100 kg weight is taken as the basic unit and small containers are combined to form sampling units not exceeding this weight e.g. 20 containers of 5 kg each. For sampling purpose each unit is regarded as one container.
- 11. Instructions for sending samples Pre-requisite in sampling is that the seed lot received in containers / bags must be properly sealed and marked for identification with a single lot designation. At the time of sampling, all the samples drawn must bear identification corresponding to that of the lot certificate. The sampler should seal or supervise the sealing of the sample container / bags after drawing sample. After taking samples which may be more than required for seed testing purpose, a through mixing of the samples is to be done.
- 12. Divide it using a seed divider and then the required amount should be submitted to the seed testing laboratory after putting proper identification mark. If mechanical divider is not available at the spot, a representative sample should be obtained by putting the entire quantity of seed on a clean floor, mixing properly and halving the sample until the desired quantity is obtained. For moisture determination, 100g of seeds for species which need grinding and 50g for all other species. Sample should be submitted in an air-tight container, like polythene bags of 700 guage or glass bottle with tight cap to the laboratory.
- 13. Quantity and despatch of sample for testing 1. Moisture test 100 g for those species that have to be ground and 50 g for all other species. 2. For verification of species and cultivar
- 14. Despatch of submitted sample Each submitted sample should be sealed and marked The label should contain all the necessary details such as variety, class of seed, quantity in the lot, to whom it belongs, name of the producer, seed treatment, date of harvesting and threshing if known, sampled by, date of sampling and the kind of tests required. After marking the sample, it should be packed so as to prevent damage during transit. For germination test sample should be packed preferably in cloth bag, for moisture content determination, sample should be packed separately in moisture proof containers. Samples should be despatched by the sampler to the seed testing laboratory without delay.
- 15. Types of sample used in Seed Testing Laboratory (STL) Service sample: Sample received from other than seed certification agencies and seed inspectors Certified sample: Sample received from certification agencies or officers Official sample: Sample received from the seed inspectors.
- 16. Mixing and dividing of seeds The main objective of mixing and dividing of seeds is to obtain the representative homogenous seed sample for analysis by reducing the submitted sample to the desired size of working sample.
- 17. Method of mixing and dividing Mechanical dividing Random cups method Modified halving method Spoon method Hand halving method
- 18. 1. Mechanical method The reduction of sample size is carried out by the mechanical dividers suitable for all seeds except for chaffy and fuzzy seeds. Objective of mechanical dividing To mix the seed sample and make homogenous as far as possible To reduce the seed sample to the required size without any bias The submitted sample can be thoroughly mixed by passing it through the divider to get 2 parts and passing the whole sample second time and 3rd time if necessary to make the seeds mixed and blended so as to get homogenous seed sample when the same seeds passed through it into approximately equal parts. The sample is reduced to desired size by passing the seeds through the dividers repeatedly with one half remain at each occasion.
- 19. Types of mechanical dividers a. Boerner divider It consists of a hopper, a cone and series of baffles directing the seeds into 2 spouts. The baffles are of equal size and equally spaced and every alternate one leading to one spout. They are arranged in circle and are directed inward. A valve at the base of the hopper retains the seeds in the hopper. When the valve is opened the seeds fall by gravity over the cone where it is equally distributed and approximately equal quantity of seeds will be collected in each spout. A disadvantage of this divider is that it is difficult to check for cleanliness.
- 20. b. Soil divider It is a sample divider built on the same principles as the Boerner divider. Here the channels are arranged in a straight row. It consists of a hopper with attached channels, a frame work to hold the hopper, two receiving pans and a pouring pan. It is suitable for large seeds and chaffy seeds. c. Centrifugal or Gamet Divider The principle involved is the centrifugal force which is used for mixing and dividing the seeds. The seeds fall on a shallow rubber spinner which on rotation by an electric motor, throw out the seeds by centrifugal force. The circle or the area where the seeds fall is equally divided into two parts by a stationary baffle so that approximately equal quantities of seed will fall in each spout.
- 22. 2. Random cup method This is the method suitable for seeds requiring working sample upto 10 grams provided that they are not extremely chaffy and do not bounce or roll (e.g.) Brassica spp. Six to eight small cups are placed at random on a tray. After a preliminary mixing the seed is poured uniformly over the tray. The seeds that fall into the cup is taken as the working sample. 3. Modified halving method The apparatus consists of a tray into which is fitted a grid of equal sized cubical cups open at the top and every alternate are having no bottom. After preliminary mixing the seed is pouted evenly over the grid. When the grid is lifted approximately half the sample remains on the tray. The submitted sample is successively halved in this method until a working sample size is obtained.
- 23. 4. Spoon method This is suitable for samples of 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. The tray should not be shacked there after. With the spoon in one hand, the spatula in the other and using both small portions of seed from not less than 5 random places on the tray should be removed. Sufficient portions of seed are taken to estimate a working sample of approximately but not less than the required size. 5. Hand halving method This method is restricted to the chaffy seeds. The seed is poured evenly on to a smooth clean surface and thoroughly mixed into a mound. The mound is then divided into 1/2 and each half is mound again and halved to 4 portions. Each of the 4 portions is halved again giving 8 portions. The halved portions are arranged in rows and alternate portions are combined and retained. The process is repeated until the sample of required weight is obtained.