Dr. Lee Manske with
soil sample; Toby
at Dickinson State
ND rancher Wayne
Gerbig (L), who has
used the twice-over
system for more
than 12 years.
native grasses need to be grazed to
Cool-season grass vegetative secondary
tillers begin growth during
fall, then go dormant over winter
and resume growth in spring. Proper
grazing management can increase
the number of secondary tillers grass
plants develop, but the length of the
growing season doesn’t allow for
development of a third set of tillers.
“The number of sets of tillers determines
the number of times each pasture
in a rotation system can be grazed,” Dr.
Mansk e says. “Two sets of tillers permit
two-rotation grazing periods (twiceover
grazing system developed by
Dr. Manske). Grazing more than twice
doesn’t coordinate with grass plant
growth, which means grass plant biological
requirements aren’t met and
satisfactory results cannot be met.”
3. NUTRIENT RESOURCES UPTAKE
Plants and the rhizosphere microbes
have a very symbiotic relationship –
each heavily depends on how robust
and active the other is.
In the rhizosphere, bacteria, protozoa,
nematodes, mites, small insects
and fungi interact in a way that is
critical for energy and nutrient fl ow
in grassland ecosystems. When the
rhizosphere is not functioning properly,
microbes won’t have access
to the energy from root exudates,
which affect rhizosphere microorganism
activity. Yes, it’s a vicious cycle!
(EDITOR: to imply this is “complicated”
may well be the understatement of the
year, but I’m still with you, carry on).
“As the amount of root exudate
increases, so do the biomass and activity
of benefi cial rhizosphere organisms,”
he continues. “Partial defoliation
that removes 25%-33% of grass
lead tillers between the 3.5 new leaf
stage and the fl ower stage result in
increased carbon exudation from grass
However, a grazing strategy has to
support and stimulate this cycle.
“Root exudate amounts are higher
on twice-over rotation systems,” Dr.
Manske says. “This greater infl ux of
carbon infl uences rhizosphere fungi
quantity. With increased rhizosphere
fungi activity, grass plant rhizospheres
are more robust and soil aggregates
adhere more securely to root surfaces
4. WATER USE EFFICIENCY
In studying water defi ciency conditions
in western North Dakota, Dr.
Manske found that during 32.7% of
the months in an average 6-month
growing season the grass plants
were stressed by water defi ciency
“Growing seasons without water
defi ciency conditions were actually
the abnormal phenomenon during
this study, occurring only about
5.9% of the time,” he says. “Water
defi ciency conditions during growing
season months caused water
stress in perennial rangeland plants
that limited herbage biomass growth
in quantity and quality, which, subsequently,
reduced livestock weight
The water use effi ciency mechanisms
require 100 lbs/ac of available
mineral nitrogen. Herbage production
decreases 49.6% per inch of
rain received when available mineral
nitrogen is less than 100 lbs/ac.
“The twice-over system activates
vegetative reproduction of secondary
tillers from axillary buds,” Dr. Manske
explains. “That stimulates soil organism
activity in the rhizosphere and
reduces the negative impacts of plant
water stress by increasing plant density,
reducing soil temperature, reducing
evaporation of soil water, improving
soil structure and water infi ltration,
improving soil water holding
capacity, and increasing available
soil mineral nitrogen to levels greater
than 100 pounds-per-acre.”
GRAZE IT: BUT DO IT PROPERLY!
When grass is overgrazed or not
grazed at all, biogeochemical process
begins degrading because adequate
resources for their proper function are
generated through partial defoliation.
Over a period of two to three years,
biomass production greatly decreases.
Over time, when grass plants have
greatly reducing nutrient resource
uptake competitiveness, their occupied
space will continue to shrink
allowing weeds and/or shrubs and
trees to back fi ll into the empty spaces.
“In my studies, I’ve found twiceover
grazing the most effective way
to properly stimulate the cycle of the
grass ecosystem,” Dr. Manske comments.
“That’s because it provides the
biological requirements to all above
and below ground components by
activating the biogeochemical processes
in both the ecosystem and
defoliation resistance mechanisms.”
Revitalized conditions resulting from
twice-over grazing cause improvement
of soil structure and functional quality,
mineralization of greater quantities of
essential elements, enhancement of
grass growth and tiller development,
increases in forage quantity and nutritional
quality, and improvement of livestock
growth and weight performance.
“That all allows range managers to
capture greater wealth from renewable
land resources,” he concludes.
“A 12-month pasture and forage management
strategy based on twice-over
grazing is biologically effective and
economically effi cient.”
For more information on the twiceover
rotation grazing system go to
grazinghandbook.com and hdl.handle.
32 I WORKING RANCH I JANUARY / FEBRUARY 2019