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Seeding rates examined

..confusion and seeding rate...


November 19, 2007
By Kevin Elmy

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One of the biggest points of confusion that most producers have is seeding
rate. Most use a historical rate, never varying from year to year. Many press
drills have seized at a certain opening, creating a 'fixed' seeding rate. Researchers
over the last few years have been looking at different seeding rates and have
shown that more seed per acre, to a point, improves quality and yield.

The problem with historical seeding rates is that even using the same variety
of grain, seed size changes from year to year with climate and production practices.
As the seed size changes, the amount of seed required per acre will change.
The standard measure of seed size is the thousand kernel weight. Simply put,
take 1000 kernels and weigh them, usually in grams to the first decimal point.
Seeding calculators are available, based on germination, seedling mortality,
row spacing, targetted plant populations and thousand kernel weight.

There is a list of seeding rate calculators found at the Alberta Agriculture
site at: www.agric.gov.ab.ca/app19/calc/index.jsp?type=Crop

Another good system that producers in North Dakota use is the number of plants
per acre. For this, the number of kernels in each pound is required. From there,
the target is 1.0 to 1.25 million living seeds per acre. Once again, taken into
account are the germination and seed size. The challenge would be counting the
number of seeds in a pound. Wheat can range from 10,000 to 15,000 seeds per
pound. But by aiming for a seed target, the plant stand will not vary from year
to year, or from variety to variety.

Seeding rates can change with the moisture levels in the soil, type of soil,
seeding date, seed quality and the expected rainfall. With greater soil moisture,
heavier soils, later seeding rate and higher rainfall, higher seeding rates
are needed. With higher seeding rates, cereal crops will be shorter, more uniform,
less tillers and earlier maturing crop. Lower seeding rates will allow the crop
to withstand moisture stress better, but will have more tillers. Tillers will
always be taller, later and have weaker straw than the main plant. Under stress,
the plant will cut nutrients to the tillers and try to allow the main stem to
survive.

Row spacing will also affect the seeding rate. Wider row spacing, such as 12
inches, will require less seed per acre than eight inch spacing. The wider row
spacing will have more seeds per linear metre of row with the same number of
pounds per acre of seed than eight inches, so the seeding rates need to compensate
for this.

Special attention to seedling mortalities is something that should be monitored
every year and field to field. With good seeding conditions, mortality rates
are normally low with good seed and proper seeding techniques. Seed placing
too much fertilizer, cold wet soils, poorly treated seed, low vigour or germination
seed, insects, incorrect seeding depth, poor seed to soil contact all increase
mortality of seed.

When seeding early, seed treatments, phosphate, potassium, zinc levels, tillage
type, residue spread and seed quality will all affect emergence. Any decrease
in the potential emergence, the seeding rate has to be increased.

A good example of this is canola. An average canola seed sample would require
two pounds per acre (900 grams per acre) of seed. The problem is seedling mortality.
Germination is usually 90 percent plus for canola seed. Seedling mortality can
be as high as 70 percent. This is why most canola has a recommended seeding
rate of five pounds per acre to ensure proper plant stands. Under ideal conditions,
the two pound seeding rate will work fine. The problem is that under less than
ideal conditions in which different problems may occur in different parts of
the field, mortality rates will change. Less than an ideal plant population
is going to create some problems with weed competition, plant branching height
and maturity.

One of the easiest ways of producing more consistent malting barley for most
people is to increase seeding rates, especially with two row barley. Most malt
growers find that when they increase the seeding rate on a plump two row barley,
they get less tillers. Less tillers means more even maturity and less green
kernels, which delivers an acceptable product to the maltsters.

When a producer complains about a new variety being weak strawed or late maturing,
they should ask a few more questions, like seeding rate and seed size. Most
producers when growing a new variety will buy just a few bushels and then stretch
the seed out to get seed stock. A decision based on this is not fair to the
variety. Some of today's high yielding wheat varieties like Superb get extra
yield from the larger seed size. Growing Canadian Prairie Spring wheat or durum
also requires higher seeding rates due to seed size. Oats are probably the most
dramatic for variations in seed size and seeding rate. Seeding rates can vary
from 80 pounds per acre to 160 pounds per acre.

Then there are forages
Forages are the crop that can drive most people crazy. A quick rule of thumb
is to aim for 40 seeds per square foot. For large seeded forages like sainfoin
or meadow brome, it relates back to a much higher seeding rate than does a Russian
wild rye and alfalfa blend. For each blend, calculating the seeding rate is
necessary to ensure the proper amount of seeds per acre.

Corn seeding can be a real eye opener also. Corn is sold in an 80,000 kernel
bag, so the bag will seed a set number of acres because when seeding corn, a
target population is calculated. The seeding rate is based on this target population.
Therefore, corn growers are not necessarily interested in how many pounds per
acre they are seeding, they want to know how many plants per acre. As plant
densities change, the characteristics of the corn variety will change. If the
seeding rate changed in the middle of the field, it may look like two different
varieties.

The take home message is to know your seed size and what plant population is
best for your crops. Watch the spring seeding conditions and your seed quality
so you have an idea of what kind of mortality rate there could be! Manage for
that. Seed treatments, fertilizer blend, seed-placed fertilizer, seeding speed
and pre-seeding tillage are going to be the things that are going to affect
the emergence of your crop. There is no perfect way to seed the crop from year
to year and from field to field. Having an open mind and willing to switch from
zero-till to minimum-till and conventional tillage, or narrow openers to shovels,
as conditions warrant is going to be best.

Do an accredited germination test. At that time, you could request the laboratory
to do a 1000 kernel test. Once the seed is in the ground, there is no good way
to change it. A good crop starts with good seed used at the correct rates.

Kevin and Christina Elmy operate Friendly Acres
Seed Farm near Saltcoats, Saskatchewan. Kevin is also a crop advisor for
Western Ag Labs. www.friendlyacres.sk.ca