Agriculture Reference
In-Depth Information
Deciding which kinds of grasses and legumes to plant if you're establishing
pasture depends on the factors mentioned above. But it's usually better — and
cheaper — to see what kinds of grasses your pasture will grow when the sheep
are put on it. So many seeds are in the ground that when your grazing is man-
aged, they have a chance to germinate and grow. Your county Extension agent,
or staff from your area offi ce of the USDA Natural Resources Conservation
Service, is an excellent resource for information on which forage plants grow
best locally. Online sources that are particularly valuable for learning about
forage crops are the Forage Information System at Oregon State University
and the Samuel Roberts Noble Foundation's “Plant Image Gallery” (see pages
406-07 for Web addresses).
Feeding Your Pasture
Just like animals, plants need to eat and drink. Most of their “food” is absorbed
through the roots, though a small amount can be absorbed through leaves.
They require nutrients like nitrogen, phosphorus, potassium, calcium, and
magnesium. The true grasses have to get all their nutrients from the soil, but
the legumes can acquire part of their nitrogen from air molecules that are
trapped in the soil through a process known as
nitrogen fi xation
.
Nitrogen fi xation by
Rhizobium
depends on several factors. First, the soil
has to have some of this benefi cial bacterium living in it or, in the case of a
new pasture seeding, the seeds have to be inoculated with bacteria. Second,
the soil has to be healthy enough to support the bacteria. Soil that is low in
NITROGEN FIXATION
The ability of legumes to trap nitrogen from the soil is an amazing
process. Soil bacteria, known as rhizobiums, live in nodules on the
roots of the legumes in a symbiotic, or mutually benefi cial, relation-
ship.
Rhizobium
actually converts the nitrogen that's trapped in
soil air molecules into a form that the legumes can absorb through
their roots. Nitrogen fi xation not only provides nitrogen to the
legume; it also provides extra soil nitrogen for the grass plants that
are growing nearby (reducing the need for nitrogen fertilizers) and
increases the protein content of the legumes. Protein is important
for sheep. (See chapter 6 for more about feeding your sheep.)
