Agriculture Reference
In-Depth Information
Many test factors must be considered when evaluating results from a conductivity test. For example,
studies have attempted to determine the minimum soak time necessary for consistent results. Wang et al.
(1994) found that conductivity results at 6 and 8 h were strongly correlated with results after 24 h for red
clover seeds. Others (Hampton et al., 1992b) have studied the effect of soak temperature and found that a
25°C soak produced greater conductivity readings than a 20°C soak even though the seed lot ranking was
unchanged. Seed moisture inluences conductivity results. Low (<10%) seed moisture increased conductiv-
ity readings for mung bean, soybean (Hampton et al., 1992a) and
Lotus
species (Hampton et al., 1994) due
to imbibitional damage. These studies recommended that seed lots be at 10-15% moisture content prior to
a conductivity test. Vertucci and Leopold (1984) showed that soybean seeds established a resistance to seed
leakage at seed moisture contents above 24%. Seed size may also inluence conductivity results because
larger seeds leak more electrolytes than smaller seeds of equivalent quality. As a result, conductivity results
are expressed on a per gram rather than a per seed basis (AOSA, 2009; Hampton and TeKrony, 1995).
Figure 8.3. Procedures of the electrical conductivity test. A: Determine the seed moisture content; B: Count
and weigh four replications of the appropriate number of seeds for the crop being tested; C: Soak for a speci-
ied period and measure the electrical conductivity of the electrolytes in the steep water (µS cm
-1
g
-1
).
Conductivity testing to determine seed vigor is not effective for all crops. In some cases, this is
because of the presence of a semipermeable nucellar membrane that permits the entry of water but not the
outward diffusion of certain electrolytes. Such conclusions have been made in lettuce (Hill and Taylor,
1989), muskmelon (Pesis and Ng, 1983; Welbaum and Bradford, 1990) and leek, onion, tomato, and pepper
(Beresniewicz et al., 1995). In other cases, the lack of success for the conductivity test is attributed to
genotype where high sugar sweet corn genotypes that possess thinner pericarps may be more susceptible to
