Agriculture Reference
In-Depth Information
Figure 11.3. Determination of seed moisture content using electronic moisture meters is one of the fast,
convenient methods used by seed testing laboratories and the seed industry.
Capacitance Meters
Capacitance meters (also known as dielectric meters) are relatively accurate at seed moisture contents
below 40 percent moisture, but have best accuracy between 6 and 25 percent moisture. Fortunately, this is
the range of moisture content that is of most interest to the seed industry. Capacitance meters operate by
exposing samples of known weight to a high-frequency voltage of 1 to 20 MHz in the meter test cell. Some
of the waves are absorbed by the H atoms of the water molecules. The strength of this absorption is known
as the dielectric constant which is translated into a percent moisture by the use of charts, direct readings
or microprocessors. Although these have been calibrated for relatively few species, eventually calibrations
could be available for all species for which moisture determinations are needed. Calibrations must be based
on many samples from different years, areas and varieties.
oTHEr METHodS
Other methods of moisture testing are available that work on different principles and are appropriate for
certain purposes.
Hygrometric methods
. These methods utilize the hygroscopic nature of seeds to measure their
moisture content. However, this relationship is dependent on temperature, as well as other factors such
as variety, seed maturity, level of deterioration, oil and protein content, and various wetting and drying
cycles. Although this method may lack certain accuracy and precision, it may be appropriate under certain
situations.
Near-Infrared Spectroscopy.
Near-infrared relectance spectroscopy (NIRS) was introduced in the
1970s and is used by the USDA Federal Grain Inspection Service (FGIS) for measuring moisture content
of ground grain as well as the protein and oil content. It requires no chemical reagents and is accurate when
conducted properly. This method uses a photodetector to measure the amount of iltered light relected
by molecules of each of these components in the grain (seed) sample at speciic wavelengths. Like other
methods, it must be carefully calibrated against a standard reference method for each kind of seed. Particle
size must be carefully controlled, but such factors as frost, immaturity, diseases and similar seed quality
