 | Methods and Types of Sampling |
| Sampling Intensity |
| Quantity and Despatch |
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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.
Definition of 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.
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.
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.
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.
Sleeve type triers
This trier is used for drawing seed samples from the seed lots packed in bags or in containers. Thief trier should not be used because it is not long enough to take representative portion of the sample from the individual container.
Method of preparing composite samples
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When the primary samples appear uniform they are combined and thoroughly mixed to form the composite sample.
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From composite sample, submitted sample of requisite weight or more is obtained either by repeated halving or by abstracting and subsequently combining small random portions.
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.
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Seed Size Maximum quantity per lot
Larger than wheat and paddy20,000 kg
Smaller than wheat and paddy 10,000 kg
Maize 40,000 kg
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.
a. For seed lots in bags (or container of similar capacity that are uniform in size)
up to 5 containers Sample each container
but never < 5 Primary Sample (PS)
6-30 containers Sample atleast one in every 3 containers
but never> than 5 Primary Sample31-400 containers Sample atleast one in every 5 containers
but never < 10 Primary Sample Sample401 or more Sample atleast one in every 7 containers
but never < 80 Primary Sample
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.
b. For seeds in bulk
Up to - 500 kg Atleast 5 Primary samples
501 - 3000 Kg One primary sample for each 300 kg but not less than 5 primary samples
3001-20,000 Kg One primary sample for each 500 kg but not less than 10 primary samples
20,001 and above One primary sample for each 700 kg but not less than 40primary samples
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.
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.
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Quantity and despatch of sample for testing
Weight of submitted sample
The minimum weight for submitted samples for various tests are as follows.
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
| Crop | Lab only (g) | Field plot & Lab (g) |
| Peas, beans, maize, soybean and crop seeds of similar size | 1000 | 2000 |
| Barley, oats, wheat and crop seeds of similar size | 500 | 1000 |
| Beet root and seeds of similar size | 200 | 500 |
| All other genera | 100 | 250 |
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.
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.
For other tests like purity and count of other species
| Crop | Size of seed lot (Kg) | Size of submitted sample (g) | Size of working Sample for purity analysis(g) | Sample count of other species(g) |
| Paddy | 20,000 | 400 | 40 | 400 |
| Wheat | 20,000 | 1000 | 120 | 1000 |
| Maize | 40,000 | 1000 | 900 | 1000 |
| Sorghum | 10,000 | 900 | 90 | 900 |
| Bajra | 10,000 | 150 | 15 | 150 |
| Redgram | 20,000 | 1000 | 300 | 1000 |
| Greengram | 20,000 | 1000 | 120 | 1000 |
| Blackgram | 20,000 | 1000 | 150 | 1000 |
| Bengalgram | 20,000 | 1000 | 1000 | 1000 |
| Cowpea | 20,000 | 1000 | 400 | 1000 |
| Soybean | 20,000 | 1000 | 500 | 1000 |
| Groundnut(pods) | 20,000 | 1000 | 1000 | 1000 |
| Groundnut(Kernels) | 20,000 | 1000 | 600 | 1000 |
| Gingelly | 10,000 | 70 | 7 | 70 |
| Sunflower(variety) | 20,000 | 1000 | 250 | 1000 |
| Sunflower(Hybrid) | 20,000 | 1000 | 125 | 250 |
| Cotton linted(variety) | 20,000 | 1000 | 350 | 1000 |
| Cotton delinted(variety) | 20,000 | 350 | 35 | 350 |
| Cotton linted(hybrid) | 20,000 | 350 | 35 | 350 |
| Cotton delinted (hybrid) | 20,000 | 250 | 25 | 250 |
| Brinjal | 10,000 | 150 | 15 | 150 |
| Chillies | 10,000 | 150 | 15 | 150 |
| Bhendi | 10,000 | 150 | 15 | 150 |
| Tomato(variety) | 10,000 | 70 | 7 | 70 |
| Tomato(hybrid) | 10,000 | 7 | 7 | 7 |
| Cabbage | 10,000 | 100 | 10 | 100 |
| Cauliflower | 10,000 | 100 | 10 | 100 |
| Knolkhol | 10,000 | 100 | 10 | 100 |
Source: M. Bhaskaran et al. (2003). Text book of “Principles of seed production and quality control”.
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