Understanding a Seed Testing Certificate
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- Last Updated on Monday, 22 August 2011 13:22
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When buying seed, the purchaser should always insist on receiving a copy of the seed testing certificate (also known as a Certificate or Statement of Seed Analysis) for that seed. It will tell you what you need to know about the seed’s germination potential, as well as any other seeds, particularly weed seeds, which are present.
However, for those who are not used to them these certificates may not be easy to read. This article is designed to explain what to look for, and what the figures tell you about that seed lot.
Firstly the seed lot number. This usually will be printed near the top of the certificate, along with the name of the person or company who submitted the sample for testing. Always ensure that the seed lot number on the certificate is the same as the seed which is being offered to you. If it is not, then clearly the certificate refers to another lot of seed.
Secondly, check the date of the test. The purity analysis, which shows you what other seeds are present, won’t change over time, but the germination capacity of the seed usually does. If the certificate is more than a year old, the germination test is no longer relevant. If it is more than 6 months old, look closely at the germination and find out where and how the seed has been stored. If it has been stored in a hot and/or humid situation, then the germination test may be suspect. If the germination result on the certificate is relatively low, then it is probably wise to look for another seed lot.
Next check the result of the germination test. Keep in mind that the test will have been carried out under almost ideal germination conditions, so the result will be just about the maximum germination the seed lot is capable of. Also note that usually there will be two germination counts, representing the number of normal seedlings produced at that time. The first is conducted a relatively short time after the seed was placed under test – usually between 4 and 7 days, depending on the type of seed. The second figure is the final count, and it is carried out at a time when the maximum germination should have been achieved. This may be anything from 7 to 28 days, again depending on the species being tested. Usually, the more vigorous the seed, the higher the germination at the first count. If a seed lot has a low first count and an acceptable final count, then be aware that the seed may have lost some of its germination vigour, and may not perform well when planted in less than ideal conditions in the paddock. However, if the seed was tested quite soon after harvest, a low first count may simply be an indication that some of the seeds were still dormant.
If there are several seed lots available with different germination counts, the one with the higher first count figure is usually the best option.
The germination section of the certificate also contains other information. This usually will include the percentages of fresh ungerminated seed, abnormal seedlings, hard seed and dead seed.
Fresh ungerminated seed is generally seed which is dormant and which will not germinate until that dormancy is broken. This means it may not germinate in the paddock with the rest of the seed, but may germinate later. Depending on the individual situation, this may be an advantage or a disadvantage.
Abnormal seedlings develop from seeds which have germinated, but not produced a normal seedling. They usually are a sign of seed which has been damaged. Damage may occur before or during harvest or handling, or when seed has been stored under less than ideal conditions. A high abnormal seedling count is an indication of damaged or aged seed, and it may be wise to look for another seed lot.
Hard seeds occur mainly in legumes, most notably the pasture legumes like sub clover and the annual medics. Hard seeds have a seed coat which is impervious to water, and they cannot germinate until that coat is broken down and water can be absorbed. This happens naturally in the paddock, and usually over time during storage. Bear in mind that hard seeds won’t germinate with the rest of the seed, and in fact may not germinate for a year or more.
If the germination figures show that the seed lot is vigorous and has a high germination count, then look at the purity analysis. This test involves the careful examination of a small sub sample of the seed, during which the sample is divided into the Pure Seed (the seed you want), Other Seed, including seeds of other valuable species and weed seeds, and Inert Matter. The Inert Matter may include soil, broken seeds, seed husks, fungal bodies, insects and all other non-seed matter
The percentage of Pure Seed should be as high as possible, relative to the species. For some species this may be as high as 99% but for some, for example many tropical grass species, the figure may be much lower.
Other Seeds will be expressed as a percentage by weight and, in some cases, also as the number of seeds per kilogram of seed. The seed will have been identified to species level wherever possible, but there are instances when this is not possible. The certificate may include the common name as well as the scientific name. Clearly a seed lot with the least contamination by weed seeds will be the most desirable, provided that it does not contain even a few seeds of a species which the buyer has taken steps to eradicate from his property!
When particular weed seeds are expressed in numbers per kilogram it is possible to calculate what that means in terms of planting. If for example there are 10 seeds per kilogram of an undesirable weed, and the seed is to be planted at 5kg per hectare, then the result will be 50 seeds of that weed per hectare. If the seed is to be planted at 50kg per hectare the result would be one weed plant per 20 square metres and, at that density, the weeds would be very noticeable.
If the Other Seeds are expressed as a percentage by weight the calculation will be useful but not quite as accurate. For example, if a weed seed is present at 0.2% by weight and the seed is to be sown at 5kg per hectare, this will result in 10g of the weed seed being sown per hectare. (5000g of seed X 0.2 divided by 100).
Very few seed lots are entirely weed-free. Whether the seed is certified, uncertified or a proprietary variety, the buyer should always insist on seeing a test certificate for the seed lot they intend to buy. Then it is possible to see what contamination is present and whether it can be managed. If there is a significant contamination of a weed seed or other unwanted seeds, consider looking for another seed lot, or asking for the seed to be re-cleaned.
Good seed doesn’t cost – it pays! Always insist on seeing a test certificate so you can see what you are being offered.