 |
     |
© 1997, 1998 Streamline Publications
Successful seed germination depends
on moisture, temperature and oxygen. Warm, moist, aerated soil will help your
lawn or turfgrass emerge sooner and grow healthier. Essential to the process is constant
moisture. A seed that dries out for as little as fifteen minutes will stop
germinating and may die if it happens to be close to the time of emergence.
Molecular Phenomena and Gravity
Water moves through soil by either the
force of gravity or by capillary action, depending on the volume of water
involved. Large volumes of water, which can be roughly defined as anything
between a raindrop and the world's oceans, are influenced by the force of
gravity. Water moves down because its weight responds to the pull of the
gravitational forcCapillary action, on the other hand,
causes water to rise. Capillary action occurs in very narrow tubes or channels.
A liquid moves up a tube because of an adhesive attraction between the water
molecules and the container. Capillary action occurs because of this molecular
adhesion. Molecular adhesion is the phenomena that causes coffee to be drawn
upward at the sides of a cup, overcoming gravity's pull. A candle wick moves
molten wax (fuel) up to the flame by capillary action. The woven wick creates
the many fine channels necessary for the wax to move through by molecular
adhesion.e. In soil made up of fine particles,
sufficiently compacted, this capillary action works to move water from a lower
point to the surface. 
During rain or watering, topsoil becomes saturated. Gravity causes water to collect at its lowest point.
Water rises by capillary action as soil dries.
Seeds that are sown at bare soil surface are dried out by sun and wind. Water evaporates as it reaches the surface.
Seeds are rolled into soil. Top dressing protects seed from sun and wind and allows air circulation. Rising water stops at a boundary between soil and top dressing.
When water from rain or irrigation
falls on the soil, gravity causes it to continue downward, percolating through
the soil to a lower level where it collects (top figure). In the next figure, the rain or
irrigation has stopped. The soil has begun to dry out. Capillary action begins
as the tiny channels formed by the fine soil particles regain their porosity.
Water rises toward the surface of the soil. If seeds are sown and lie on a bare
soil surface, in the absence of precipitation, sun and air movement dry the
seeds even if they were previously watered. Moisture, that a germinating seed
needs constantly, cannot reach the seed. Water that migrates to the surface
evaporates. Under these conditions germination can fail completely. To properly germinate, seeds should be
surrounded by moist soil. So why not furrow the soil, bury the seeds and wet it
down? To take full advantage of water's tendency to rise to provide moisture
between waterings, the soil should not be disturbed. If the soil compaction is
broken, the particles are separated and the water has no way to move upward.
If the soil layer containing the seeds
becomes too coarse from tilling, the seeds are isolated from moisture rising to
the surface. Water reaching the seeds then depends on water passing downward
from irrigation or rain. There are several problems with
germinating seeds this way. The high water use is not only wasteful, it's
impractical. Overwatering will also leach nutrients out of the soil, nutrients
that are necessary to starting a good growth. In some areas where soil and water
are high in salts, excess water will build up the salts in the soil. Salty soil
hinders the seed's ability to take up water through osmosis.
Using the Elements
The fact that capillary action and
molecular adhesion are stopped by coarse material can be put to use in helping
seeds germinate. The bottom figure shows an ideal
condition. The seeds are sown and pressed into the bare soil using a roller. A
coarser top dressing is laid over the seeds.
Water Works Wonders Water passes down through the top
dressing and seeks its lowest level, wetting the seeds as it passes. The top
dressing protects the wet seeds from being dried out by sun and wind. Water
rises through the undisturbed soil and reaches the level of the seeds where it
stops. The top dressing, being coarser, won't support further rise so water
collects at the boundary between the soil and top dressing where the seeds are.
Germination is enhanced and the plants get a healthy start.
Balance
Moisture balance is necessary for
proper germination. Lots of water may not be enough if it doesn't reach the
seeds. Regular watering that replaces water runoff and evaporation will assure a
good start for lawns, turfgrass or any other planting.
Seeding | LEAF-let Newsletter | Bioregions | Catalog & Orders | Albright Info