Successful establishment of sown tropical perennial grass pastures is highly dependent on the quality of the seed sown. Quality can vary markedly, so you need to know what you are buying – often it is a case of ‘buyer beware’.
Always ask for a copy of a current certificate of seed analysis for the seed you are intending to purchase. Check to make sure it has high seed purity and a high germination percentage with low amounts of inert matter and other seeds.
Species that have primary dormancy may have low germination but high fresh seed, so alternative seed will need to be sourced or the seed stored until dormancy has broken.
If seed quality, purity and germination are well below the average expected for a cultivar, then it can adversely affect establishment, or it will cost extra to increase the sowing rate to compensate. Ask yourself if it is really worth buying poor quality seed.
The old saying ‘you reap what you sow’ is very true when it comes to buying seed of tropical perennial grasses as quality (germination rate, purity, dormancy, and the presence of weed seeds) can vary widely.
If you take the time to buy high quality seed, with high purity and germination, then you have taken the first step necessary for good establishment.
Sowing low quality seed is a recipe for poor or failed establishment – even if you do everything else right. The only way you can be confident that you are buying high quality seed is to ask the seller for a copy of the certificate of seed analysis.
Make sure the certificate is from an accredited laboratory and that it is no more than 12 months old. There are two main areas of the certificate to check. The first is the purity test which indicates the percentage of pure seed and conversely the percentage of inert matter (including empty florets) and other seeds.
The second is the germination test which shows the percentage of normal seedlings that germinated (usually after at least 14 days) and the percentages of hard, fresh and dead seeds and abnormal seedlings.
In grasses, fresh seeds are viable (alive), but do not germinate and include immature, damaged and dormant seeds If a current certificate of seed analysis is not available, consider having a seed analysis done.
It takes a few weeks and may cost $150–200 per sample, but compared with the cost of buying seed it is ‘cheap insurance’. Proportion of Live Seed (PLS) is a measure of the seed quality of a sample and is expressed as a number between zero and one.
The higher the seed quality the closer that PLS is to one; the lower the seed quality the closer the PLS is to zero. PLS is the purity percentage multiplied by the germination percentage (shown as a value for normal seedlings) and divided by 10,000.
Typical values for some of the more commonly sown cultivars in northern NSW were obtained from analysing the results from 168 seed certificates (Table 1).
For these cultivars, the average PLS values for Bambatsi panic, Premier digit grass and Katambora Rhodes grass were between 0.40 and 0.57, while Floren bluegrass, Bissett creeping bluegrass and Inverell purple pigeon had low average PLS between 0.20 and 0.24.
If the seed that you are considering buying has a PLS below the values shown in the table then its quality is below average and for good establishment you will have to buy more seed to increase the sowing rate, which increases the overall cost of seed.
If it has a PLS above the value shown in the table then it is probably best to maintain the sowing rate with a high potential to establish a high density stand.
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