pasture management BY LORETTA SORENSEN
Twice-over grazing might be the
key to your grassland success
razing cattle appears so simple: put cattle on grass,
let them eat till it’s gone, move to the next pasture.
But range scientists like North Dakota State University’s
Llewellyn (Lee) Manske, Ph.D., say graziers
need to understand there’s another entire microscopic
world operating at ground level and beneath the soil.
Vegetative tillers develop from axillary buds.
North Dakota State University range scientist
Dr. Lee Manske (kneeling) examines grassland
with other North Dakota Agriculture teachers.
Green Will Grow
If Healthy Below
“Grass plants, soil microorganisms
and large herbaceous animals have
developed complex symbiotic relationships,”
Dr. Manske says. “Grazing
plants at the right growth stage stimulates
natural defoliation resistance
mechanisms that increase overall
herbage each growing season.”
Across the board, rangeland requires
some 100 pounds of nitrogen per acre
to produce biomass up to potential.
Nitrogen occurs naturally in soil,
but in organic form, which plants
can’t uptake. Both overgrazing and
under-grazing grasses prevents natural
conversion of that nitrogen to mineral
form. The result is nitrogen defi ciency.
“Done properly, grazing stimulates
a cycle that takes soil nitrogen from
organic form to mineral form through
biogeochemical processes,” explains
Range managers don’t need to
understand the entire scientifi c process
involved in grazing and recovery,
however Dr. Manske points to four
critical principles that can assist range
managers in knowing how to support
grassland plant growth and soil health.
1. How plants respond to grazing.
2. Regrowth by tillering.
3. Nutrient resource uptake.
4. Water use effi ciency.
1. HOW PLANTS
RESPOND TO GRAZING
Grasses typically produce
twice as much leaf area as plants
need to live, in anticipation of being
grazed. That means the oldest cells are
at the leaf tip and grazing animals can
remove portions of a grass leaf without
stopping plant growth.
“The growing point (apical meristem)
remains close to the ground and
below the reach of the grazing animal
when the shoot is in the vegetative
(non-fl owering) stage,” Dr. Manske
says. “This growth structure makes
grasses well adapted to grazing.”
Grass plants are made up of tillers,
with shoots and roots. Each shoot
contains units with four parts: a leaf, a
node, an internode and an axillary bud.
The grass plant’s crown is the lower
portion of a shoot, with at least two
nodes that can produce roots. The
growing point at the top can develop
into either leaf buds or fl ower buds.
“When the second year shoot of a
lead tiller reaches the third-leaf stage,
the growing point begins producing
fl ower buds rather than leaf buds,
although formed leaf buds continue
to grow and develop,” Dr. Manske
shares. “If the plant is defoliated
(grazed) before the shoot reaches 3.5
new leaf stage, formation of leaf buds
and leaves for the shoot are disrupted.
This weakens the plant and diminishes
its ability to produce herbage.”
Most native cool-season grasses
reach 3.5 new leaf stage around early
June with native warm-season grasses
reaching that stage about two weeks
later. If grazing begins mid-May, some
45% to 60% of the plants’ potential
biomass will be lost.
“In contrast, defoliation of a shoot
that has reached 3.5 new leaf stage
typically stimulates the natural biogeochemical
process plants have
developed in response to grazing,” Dr.
Manske adds. “Properly timed grazing,
which removes just a small portion
of the leaf, activates grass growth
mechanisms that can result in a 30%
to 45% forage production increase.”
Over many years, Dr. Manske’s
research has confi rmed that grazing
management strategies implemented
after the 3.5 new leaf stage which
coordinate rotational grazing periods
with grass growth stages, are most
likely to stimulate naturally occurring,
benefi cial plant processes to
maximize forage production.
30 I WORKING RANCH I JANUARY / FEBRUARY 2019