Agriculture Reference
In-Depth Information
High quality
Low quality
Figure 5.8. High and low quality corn seedlings germinated for 7 days in warm soil.
for germination testing. If the soil is too heavy and contains excess clay, some sand can be added to make it
easier to handle and provide a more optimum germination environment. Regardless of the sand or soil used,
it is best to sterilize the substratum before using. This will kill any microorganisms that can cause damping-
off of seedlings and will also kill any contaminating weed seeds. However, sterilization does break down
organic materials and can result in the formation of volatile toxic compounds. Thus, it is recommended that
sterilized sand or soil not be used for approximately a week following sterilization.
GErMInATIon CHAMbErS
Germination chambers are used to provide optimum conditions of moisture, humidity, temperature and light
throughout the germination period. Historically, germinators have been used that are individually equipped
with temperature controls. For light-requiring seeds, they are equipped with artii cial light, usually from
cool, white l uorescent tubes. However, maintaining appropriate relative humidity levels is more difi cult.
One approach is to use germinators with a continuous source of water directly in the germinator. One of
the more common types used has been that with a continuous water curtain to maintain high humidity and
prevent drying. However, such “wet” germinators (Fig. 5.9) possess the disadvantages of leaks, rapid dete-
rioration of electrical components and eventual failure of gaskets and water pumps. Consequently, laborato-
ries have increasingly used “dry” germinators that provide temperature and light controls without a source
of water. To prevent evaporation and maintain adequate relative humidity around the seeds, plastic boxes
or other suitable mini-chambers are used (Fig. 5.10). Although evaporation from the substrata in the mini-
chambers is initially high, it becomes minimal after moisture equilibrium is attained. Similar humidity con-
trol can be achieved in enclosed, mobile germination carts that can be rolled into walk-in germinators and
back again to work areas for seedling evaluation. Regardless of the method used, germination tests should
be continually monitored for their moisture status. When moisture levels are low, spray bottles, rubber l o-
rist's bulbs and medicine droppers are excellent tools for adding water without the danger of overwetting.
