PASTURES & SOILS SEED COATING
AT A GLANCE
▸▸ Seed coating on legumes usually
contains fungicide, insecticide, lime
build-up and rhizobial inoculant
▸▸ Seed coating on grass species may
contain a fungicide or an insecticide or
both
▸▸ A lime build-up in the seed coating
on grass seeds serves no agronomic
purpose and will effectively make the
seed more expensive
▸▸ For tropical grass species a seed coat
is usually added to help the seed run
through seeders more readily
▸▸ Seeding rates may need to be adjusted
to account for seed coating, especially if
the coating contains lime build-up as the
build-up may account for a significant
proportion of the weight of the seed
product
When establishing phalaris pastures there is
no agronomic benefit in using coated seed.
Photo – Jill Griffiths.
▸▸ Rhizobia in inoculants in pre-coated
legume seeds have a limited shelf life
Pasture seed coating
– a case of buyer beware
The seed industry has been coating seed for commercial sale for many decades now but
what exactly is in those coatings and how necessary are they? Jill Griffiths reports
N
ew South Wales Department of
Primary Industries agronomist
Richard Hayes tells the story of
a batch of mixed pasture seed his
father recently bought for the family’s farm
at Goulburn, NSW.
“The mix included two varieties of
phalaris and one of them was coated and one
wasn’t,” Hayes said. “I was curious about
this so my son and I sorted a subsample of
phalaris seed out and I weighed them.
“In the small sample I took there were
153 uncoated phalaris seeds which weighed
0.26 grams. There were 166 coated phalaris
seeds and they weighed 1.02g. Now if you
do the maths on that it works out the coated
phalaris seeds are 3.61 times as heavy as the
bare seed. Following that through, where we
thought we were planting 1.5kg/ha of seed
of that coated phalaris cultivar, we actually
sowed 0.42 kg/ha (i.e. 1.5/3.61). This falls
well below minimum recommended sowing
rates for phalaris. We would have to sow
5.4kg/ha of coated seed to achieve the same
plant population as 1.5kg/ha of uncoated
seed.”
This experience has confirmed Hayes’
professional observations over recent years
that there is a danger of miscalculating
actual sowing rates and paying too much for
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seed when coated pasture seed is used.
“But why would you put a coating
on phalaris seed? It’s ridiculous. In our
situation for every 1.5kg of coated seed,
we were buying 1 kg of lime. We already
purchased 5 t/ha of lime at a cost of $53/t
for that paddock before we sowed it. The
lime on the phalaris seed cost us close to
$15000/t.”
PGG Wrightson Seeds product
development manager Kelly Burke tends to
agree with Hayes on this point.
“I can see where Richard is coming from
and we wholeheartedly agree that lime
coating grass seeds in unnecessary,” he said.
“There’s no reason to put a lime build-up on
phalaris seed. It has no agronomic benefit.
The only seeds we put a lime build-up on
are the legumes.”
COATINGS VARY
PGG Wrightson uses two different forms of
coatings on seeds the company supplies.
“We use Superstrike on our legume
seeds,” Burke said. “This contains a
systemic insecticide, a fungicide, a lime
build-up and an inoculant. The build-up on
the legume seeds offers two advantages.
Firstly, it provides a localised pH buffer.
But most importantly, it physically separates
the fungicide from the inoculant, to ensure
the inoculant is still viable when the seed is
sown. Contact with the fungicide would kill
the inoculant.
“What we are trying to achieve with
coated legume seed is to provide a rounded
package. The insecticide and fungicide in
the coat help get the seed out of the ground
and may prevent the farmer having to do
a second pass over the paddock to control
some pest problems before the plants are
even out of the ground.
“The other type of coating we use is
what we call a film coat (Ultrastrike) and
this goes on the brassicas and grasses.
This simply contains an insecticide or a
fungicide. There’s no lime build-up in it.
“Sometimes seeds such as cocksfoot and
phalaris may go out bare, but in situations
where there may be a heavy black beetle
infestation in the paddock for example,
we want to put the seed out with some
protection against that, just to help get the
pasture up and going.”
ASSESSING THE RISKS AND
BENEFITS
Hayes maintains that there are several risks
associated with sowing pre-coated pasture
seed.
No. 283 August 2015 Farming Ahead
77
PASTURES & SOILS SEED COATING
The coating on legume seeds often contains an
inoculant, a lime build-up, a fungicide and an
insecticide. The rhizobia in the inoculant has a
limited shelf life and the date should be ckecked
before sowing. Photo – PGG Wrightson Seeds
“Farmers are commonly unaware of how
much seed coat they are purchasing with
their seed,” Hayes said. “This makes it very
difficult to determine actual pasture sowing
rates, or adjust sowing rates accurately to
account for the seed coating.”
Hayes is also cautious about the efficacy
of inoculants in pre-coated legume seeds
and lists a few specific issues.
“Independent research shows the survival
of N-fixing bacteria on pre-coated seed is
variable and often poor, which reduces the
N-fixation potential of legumes,” he said.
“The inoculant in pre-coated legume
seeds has a very short shelf life, which
limits farmers’ capacity to sow unused
pasture seed at a later date, potentially
adding to wastage costs.
“Independent surveys show a significant
percentage of coated legume seed that is
within the advised shelf-life still fails to
meet quality standards for inoculant.”
These concerns have led Hayes to
recommend farmers consider buying
uncoated seed and go back to the old
method of inoculating legume seed prior to
sowing.
“It is very likely that in many situations,
coating on pasture seed serves to reduce
the effective sowing rate of pastures,”
Hayes said.
“In one of our research trials, the farmer
used a sowing rate of 2kg/ha of coated
seed, which has been a common sowing
rate in that region for several decades, but
pasture establishment from that rate was
disappointing. To get the equivalent of 2kg/
ha of seed into the ground using pre-coated
seed, a farmer may need to double or triple
sowing rates.
“We found considerable benefits in
lucerne performance of doubling the
sowing rate of coated lucerne seed. This
increases the unit cost of pasture seed
compared to uncoated seed which is yet to
be demonstrated to represent a sound valueproposition in most broadacre situations.
“There may be instances where a
coating on seed is justified, for example,
78
Farming Ahead August 2015 No. 283
On the left, coated phalaris seed as described in
the article. On the right, a traditional grass pasture
mix including bare phalaris and cocksfoot seed, and
inoculated/lime pelleted white and sub clover seed.
Photo – Richard Hayes
to improve the flow of tropical grass seed
through a seeder, or where local data exists
quantifying the production gains due to seed
coats. Otherwise, in general we recommend
that farmers use bare seed.
“There is a lack of available information
about the other components of seed coats,
such as insecticides and fungicides, and
that makes it difficult for a grower to assess
whether the seed coat offers additional
advantages in a particular situation and
whether other approaches, such as ground
application of insecticides, would be a
more cost-effective approach to improving
pasture establishment.
“When farmers buy coated seed they
are taking a risk,” Hayes said. “They can’t
make informed decisions to adjust seeding
rates, seed wastage costs will inevitably
increase and in the case of legumes, there is
a long history of variable and poor rhizobia
survival on pre-coated seed. Yet, there
is very little evidence that the additional
costs and risks are justified for the average
farmer.”
The NSW DPI’s Australian Inoculants
Research Group (AIRG) at Ourimbah can,
for a fee, test the viability of rhizobia on
coated legume seed. Depending upon the
strain of rhizobia and the nature of the
coating it takes one to two weeks for a
result.
“Where possible, the traditional approach
of sourcing bare legume seed and freshly
inoculating prior to sowing should be used.
If coated seed is used, farmers should
ensure that every seed lot they purchase
complies with the industry code of practice
and is labelled to specify the content of seed
coat on the seed and the date of treatment
for inoculated legume seed.”
SUPPLY CHAIN
CONSIDERATIONS
One of the underlying problems in this is the
supply chain of seed. A seed company may
produce clearly labelled pre-coated seed,
but in the process of being repackaged by a
wholesaler or retailer, that label information
may not be transferred through to the farmer
at the time of purchase.
Burke concurs that there are difficulties
inherent in this and said that ideally the
information would be transferred but that it
doesn’t always happen.
“In many ways it comes down to buyerbeware,” Burke said. “Farmers need to ask
the right questions of their retailers when
they purchase seed: Where has the seed
come from; how long has it been sitting on
the shelf; what’s in it; how many seeds are
there in a kilo; what’s the proportion of the
seed coating? Retailers need to be able to
supply that information.
“We are implementing a testing program
to ensure regular quality of all our products.
Each bag of seed we send out has a stamp
on the tag to say what day the seed was
treated. We tell our reps to check the date
stamps and to work with retailers when
they find out-of-date seed. We don’t want
retailers selling our legume seed with
out-of-date inoculant. That’s not good for
farmers and it’s not good for our brand.”
Contacts:
Richard Hayes, Wagga Wagga
Agricultural Institute
0448 231704
[email protected]
Kelly Burke, PGG Wrightson Seeds
0418 568 401
[email protected]
www.pggwrightsonseeds.com.au
Australian Inoculants Research Group
NSW Department of Primary Industries
P: 02 4348 1948 | F: 02 4348 1910
[email protected]
[email protected]
Further information and industry codes of
practice are available on the Australian Seed
Federation website: www.asf.asn.au. See
also GRDC’s 2012 publication Inoculating
Seeds: A practical guide by Elizabeth Drew
and others
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