Representative grain sampling
Representative grain samples
Representative samples are grain samples that accurately represent a specific quantity of grain, such as the contents of an entire grain bin. Representative samples are made by combining many smaller individual grain scoop samples into one larger composite sample. By methodically taking individual scoop samples from throughout the grain bulk to build the composite sample, you can ensure the composite sample accurately represents the entire lot of grain. The composite sample can then be used for grading before you make marketing decisions or deliver your grain.
The quality of grain harvested from different areas of the same field can vary. This means the grade, dockage and protein can vary from truckload to truckload during harvest. As a result, grain quality can vary both within a bin, and from bin to bin. Building composite samples that are representative will help you get accurate information about the quality of your crop.
To make a representative sample, you’ll need:
- four identical pails that hold at least 20 litres, with two labelled A and two labelled B
- a grain scoop
- sealable containers for the final samples
The best time to make a representative sample of a grain bin is while the bin is being filled. Before you start filling the grain bin, decide how often you’ll take individual scoop samples. Scoop samples must be taken directly from the grain stream using a grain scoop.
The intervals between individual scoop samples must be the same to ensure the samples are representative of the entire lot of grain. The length of interval should take into account:
- the amount of grain being sampled
- the size of grain scoop you are using
- how much sample you’ll need when marketing your grain
The larger the auger being used or the smaller the load of grain, the shorter the interval should be. Using short, consistent intervals and taking many individual scoop samples will make the final composite sample more accurate.
When taking scoop samples:
- use the same grain scoop to take every sample
- take the same number of samples from each truck, if multiple trucks of roughly the same size are filling the same bin
- make sure you take enough samples to fill one 20 L pail to at least three-quarters full
How to make a representative sample of a grain bin
To make a sample representing the entire contents of a grain bin, you will need a composite sample of each truck filling the bin.
Grain from one truck
To build a composite grain sample representing one truckload of grain:
- start unloading the grain truck and insert the grain scoop into the grain stream with the cup of the scoop facing down
- turn the grain scoop up to catch grain when the scoop is in the correct position
- alternate between taking samples from the left, middle and right of the grain stream
- continue taking samples at consistent intervals until the truck is finished unloading
- place all the scoop samples for the truck in one of the pails labeled A to create a composite sample that represents the entire truckload of grain
Grain from multiple trucks
Large grain bins may be filled by multiple trucks. To prepare a composite sample that represents more than one truckload of grain:
- determine how much sample you will need from each truck to fill pail A to three-quarters full
- follow the procedure to make a composite sample for each truck
- reduce the composite sample from each truck to the desired quantity using the procedure to reduce a composite sample
- combine all the reduced samples in one pail labelled A
- mix the combined samples in pail A thoroughly by hand
Pail A now contains a composite sample that represents the contents of your entire grain bin.
Alternate diagram format
Reduce your composite grain sample
Use this procedure to reduce your composite sample into a smaller sample that’s still representative of the grain in the bin. This will make the sample easier to handle and store. Keep in mind that you may need multiple samples for different purposes.
To reduce a composite sample:
1. mix the contents of pail A thoroughly by hand
2. place the two empty pails labelled B, side by side and touching on a level surface
3. pour the contents of pail A at the point where the pails touch, ensuring that half the stream flows into each pail labelled B
4. pour one pail of sample labelled B back into pail A
5. pour the contents of the other pail labelled B back into the bin
6. repeat this process with the remaining sample until you have the amount you need for your marketing purposes.
7. place the final sample into the remaining pail labelled A
8. place the final composite sample or samples in sealed containers and label each container to show the bin it represents
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