Grass Growth and Pasture
Management
Part of the Ruminant
Livestock: Facing
New Economic
Realities Meetings
Grass Plant Tillers
Seed head
Lead
Tiller
Crown
Tiller
Source: L.L. Manske
North Dakota State
University
Rhizome
Tiller
Grass Physiology
• Cool season grasses initiate flower buds on the
crown when exposed to low temperatures and
long nights.
• Carbohydrates are stored late in the growing
season (fall management is critical).
• In the spring, new growth is initiated from the
crown using carbohydrate reserves stored in the
roots, rhizomes, stolens, and/or stem bases.
• As day length increases throughout spring, at
some point a flowering response is triggered.
Grass Physiology
• Not all tillers produced by the plant are
reproductive tillers, but…
• Because reproductive tillers grow taller than
the vegetative tillers they shade out the
vegetative tillers and in addition…
• As seed heads develop they produce plant
hormones that retard the development of
other vegetative tillers
Grass Physiology
• Removing the seed head by grazing or
clipping will promote development of
vegetative tillers
• Because most cool season grasses require
cool temperatures and long nights to once
again develop reproductive tillers, after seed
heads are removed, vegetative growth is
produced for the remainder of the year
UNDERSTANDING PLANT
GROWTH
•
•
•
•
•
Light
Roots/Carbohydrate Reserves
Temperature
Water
Fertility/Nutrients
PLANT REGROWTH AFTER
HARVEST
• From Carbohydrates Produced by
Remaining Leaf Area
• From Carbohydrate Reserves
Defoliation Stresses Forage
Plants
• Reduces or eliminates photosynthesis
• Stops nutrient uptake from the soil
• In legumes, nitrogen fixation stops within
hours of harvest
Leaf Removal vs. Root Growth
10%
20%
30%
40%
% Leaf 50%
Removed
60%
70%
80%
0
20
40
60
Percentage Root Growth Stoppage
Source: Crider, 1955
80
100
Grazing Principle
For Rapid Regrowth:
Take Half
Leave Half
(By weight/volume: recognize forage is
denser towards base of plant)
What You Leave Behind…
•
•
•
•
•
Affects re-growth rate
Affects root growth
Affects soil temperature
Affects organic matter
Affects water infiltration rate and waterholding capacity
• Affects nutrient cycling
Animal Intake and Pasture
Residual
• Forage Systems Research Center work has found
about 80% of the variation in grazing intake is
correlated with post-grazing residual.
• When forage mass drops below a critical level,
intake is restricted
• In other words, the reason the top end of graziers
are getting better animal performance compared to
lower end graziers is because they know when to
get their livestock out of a pasture paddock.
Managing Grazing Heights:
Pure or dominant grass stands
Species
Pre-graze inches
Perennial Ryegrass
6-7
Post-graze
inches
3
Orchardgrass
8-10
3-4
T. Fescue (E+)
5-6
1-2
T. Fescue (E-)
8-10
3-4
Brome grass
Pre or late
jointing
2-3
Timothy
Pre or late
jointing
4
Managing Grazing Height
Grass
Legume
Mixtures
Species
Pre-graze
inches
Post-graze
inches
Bluegrass/w clover 4-5
1-2
OG/L clover
6-8
2-3
T fescue/L clover
5-8
1.5 - 2
Alfalfa with grass
bud
2-3
Red clover with
grass
bud
2-3
Grazing Principle
•Provide plants with adequate rest period
to re-grow to correct grazing height
Relationship of rest period to pasture
mass during periods of rapid vs. slow
growth
Optimum
Lbs.
Rest
DM / acre
Period
0
0
5
10
15
20
Period of fast plant growth (days)
10
20
30
40
Period of slow plant growth (days)
25
50
Source: Craig
Saxe, University
of Wisconsin
Extension
Rest Period Management
• Paddock number determines flexibility and the
degree to which the grass plant can be managed.
• For example in a 4 paddock system if my goal is
not to graze the new re-growth until 8 inches, then
my rotation flexibility is 12-16 days in the spring
and 28 to 32 days in the summer
• In a 10 paddock system, rotation flexibility is 10 to
30 days in the spring and 50 to 70+ days in the
summer
• More paddocks can result in higher utilization rates
MANAGEMENT TO OPTIMIZE
PLANT GROWTH
• Avoid production of seed heads, keep the
plant vegetative
• Maintain leaf canopy (residual
management)
• Recharge plant root reserves
• Vary rest periods by season and rainfall
• Frequent shifts of short duration
• Provide adequate soil nutrients
Growing Season Management
• The reason behind using rest periods and
residual management is to increase
productivity and to put the grazier in the
position to extend the grazing season
through:
• Quicker green up in the spring
• Quicker recovery from drought
• Fall/Winter grazing?
Management Changes?