Agriculture Reference
In-Depth Information
unIforM bLoWInG ProCEdurE
Uniform blowing methods for certain grass species have been developed by both AOSA and ISTA. These
provide ways to determine the percentage of pure seed and inert matter by using a blowing point to sepa-
rate inert matter from pure seed. The use of uniform blowing points has resulted in great time savings for
analysts as well as increased uniformity of results among both analysts and laboratories. Uniform blowing
methods utilize specially prepared calibration samples comprising speciic mixtures of stained pure seed
and inert matter such as empty lorets. Each laboratory calibrates its blowers using the calibration samples
to remove the precise amount of inert matter for each species.
The AOSA uniform blowing procedure, which was revised in 2010, depends on the uniformity of the
calibration samples. In 2006, Oregon State University (OSU) Seed Laboratory prepared master calibra-
tion samples for Kentucky bluegrass and orchardgrass. The OSU Seed Lab also introduced the concept of
“equivalent air velocity value” to indicate the optimum air speed to be used for separating light inert matter
from pure seed in a seed sample of a particular species.
Attributes of Master Calibration Samples
Master calibration samples are used to identify the optimum blowing point (OBP). Such samples already
exist for some species (e.g.,
Poa pratensis
and
Dactylis glomerata
). The OBP is the point at which almost
all the light inert materials, including empty lorets and those containing empty caryopses that are less
than 1/3 the length of the palea, are blown out of a test sample along with a minimal number of marginal
pure seeds. The OBP is determined by the value of the air gate opening of a blower and the corresponding
equivalent air velocity value for such a point. To achieve the separation of light inert matter, samples are
blown for three minutes. After the blowing procedure is completed, the heavier lorets that remain in the
pure seed cup contain caryopses that are 1/3 the length of the palea or larger and have a high planting value.
A master calibration sample has to be developed based on accurate identiication of the OBP to separate
similar types of lightweight inert matter from the pure seed of a crop. Such a sample can be used to cali-
brate any General Blower across labs and across countries. The name “master calibration samples” is being
introduced to the seed testing community to indicate a group of calibration samples of proven uniformity.
The AOSA calibration samples are administered by the U.S. Federal Seed Laboratory in North Carolina
on a loan basis. Master calibration samples for other grasses such as tall fescue are under consideration.
The use of Air Velocity Concept in blower Calibration
The principles of the new blowing method are based on the following: (1) the use of master calibration
sample of proven uniformity, e.g., OG or KBG, for only one time to determine the optimum blowing (sepa-
ration) point and (2) afterwards, the equivalent air velocity value (EAV) for that point is measured using
an anemometer. This EAV value can be used subsequently for calibrating that blower without the need to
reuse the standard calibration sample any more unless a major change in the blower has been made such as
changing the motor, the fan, or the glass column.
The consistency of the blowing procedure depends on the uniformity of the master calibration samples
that are used to calibrate each blower and on the accurate determination of the EAV values for the optimum
blowing point. Maintaining the integrity of the master calibration samples is important to preserve the
calibration samples as long as possible (unpublished paper by A. Garay, S. Elias, and H. Nott).
Blower calibration is described in detail in the AOSA Rules for Seed Testing, Volume 2: Uniform
Blowing Procedure.
