Pasture Ecology
ANSC 110
August 31, 2010
Pasture Ecology
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Ecology- Interrelationships of grasses,
legumes, weeds, and grazing animals
with their environment
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Categories:
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Non-living components
Plants that capture solar energy
Herbivore/Carnivore consumers
Decomposers
Why do we care?
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Some plants are better able to adapt
to the environment than their
neighbors
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Has a HUGE impact on pasture
quality
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By understanding ecology, we can
better implement management
techniques
What influences pasture ecology?
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Energy
Water & Temperature
Pasture site
Space available
Competition
Grazing habits
Plant anatomy
Soil characteristics
Decomposers/Pests
Energy
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Energy runs the show
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“Free” energy in the form of sunlight
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Manage pasture to maximize
sunlight
Increase leaves/surface area
 Increase size of leaves
 Increase length of growing season
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Solar Energy
Volume of
plants
Area of leaf
Duration of growth
Savory, 1988
Energy Through Sunlight
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Sunlight is single most important
influence on pasture yield
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Light collection is influenced by:
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Forage species
Leaf angle
Canopy density
Leaf aging
Availability of water and nutrients in soil
Competition for sunlight
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When another plant shades its
neighbor, the photosynthesis rate of
that neighbor declines
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Competition for sunlight decreases
at:
Early growth in spring
 Re-growth after grazing/cutting
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Competitive advantage
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Sunlight is not like a soil nutrient
Must be used instantaneously
 Once gone, gone forever
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Position of leaves gives plants the
competitive advantage
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Leaves that are above the canopy will
get more sunlight than those below
Water
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Rainfall is primary water source for
pastures
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Irregular rainfall  deficient or
excessive soil water
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Direct effect on plant productivity
and persistence
Drought
Drought
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Plant leaf area decreases
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Plant root growth increases
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Decreased ability to take up
nutrients
Drought
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Ability of legumes
to fix N decreases
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Carbohydrate
storage supplies
decrease
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Nutrient levels
highest at surface
Wet conditions
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Too wet  plant growth slows
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Water fills soil pockets, excluding oxygen
needed by plant roots
Fungal root disease organisms will thrive and
damage roots
Longer recovery periods after wet
conditions are needed before grazing
Temperature
Second most important influence
 Plants are adapted to certain
climatic conditions
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68° F
 Plants that can adapt to temperature
fluctuations will do better
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Temperature
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Mean annual air temperature for our
zone (Zone D in textbook) is ~ 58° F
Pasture Site
Forage crops cannot escape the
locations in which they are growing
 Location influences affect pasture
composition and growth
 Important factors to consider –
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Elevation
 Soil type
 Drainage
 Slope and exposure
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Space Available
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Space within pasture is limited
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Bare spaces allow growth of unwanted
weeds
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As space becomes more limited so does:
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Moisture
Light
Nutrients needed for growth
Competition
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When all necessary growth factors
are in abundance, competition
doesn’t play a part in pasture
ecology
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Low supply of one vital nutrient will
cause competition among forage
species
Competition
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Water
Nutrients
Light
Carbon Dioxide
Oxygen
Environmental
stressors
Means of
pollination/seed
disbursal
Competition
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Success of a single plant depends on how
well its characteristics:
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Match the demands of the environment
Allow it to cope with stresses as compared to
neighboring plants
Increase the competitiveness of the
desired species and/or decrease the
competitiveness of the undesirable
species
What makes a plant a
successful competitor?
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The plant that can:
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Draw on the limited factor
Do so quickly
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Usually able to grow more roots and
leaves
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Adaptable to several environmental
conditions
Grazing Habits
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Intensity and frequency can have a
tremendous affect on competitive
ability of many pasture plants
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Pasture species vary greatly in their
tolerance to grazing
Grazing Horses
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Animals  more complex pasture
Selective grazing
Manure and urine
Treading - Walking, running, jumping,
lying down, scratching, pawing
Management
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Plant height – especially during leaf
development and elongation
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Grazing frequency
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Grazing intensity
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Soil fertility
Management
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Weedy pastures
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Understocked lax
grazing
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Overgrazing
Management
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Clover and grass
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High N from urine
and fertilizer 
grass growth,
shading of clover
More frequent
grazing  no
shading of clover,
increased
competitive ability
Overgrazing
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Not necessarily number of animals
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More a function of the time that animals
are exposed to plants
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An overgrazed pasture is one that grows
from root energy rather than solar energy
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Continuous grazing or inflexible rotational
grazing without enough paddocks
Plant Anatomy
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Plant roots have a huge effect on pasture
productivity
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Water absorption
Nutrient absorption
Nutrient storage
Root temperature = soil temperature
Rhizomes or stolons?
Taproot?
Plant Anatomy
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If overgrazing occurs, regrowth depletes
food reserves and weakens the plants
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Methods plants use to cope with being
grazed:
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Spines, thick hairs, waxes, tough leaves
Chemicals to deter grazing
Grazing’s effect on roots
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If pasture is grazed during adverse
conditions, animals will
preferentially avoid weeds
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About ½ of pasture plant growth is
in the roots!
Soil Characteristics
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Microorganisms
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Earthworms
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Nematodes
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Nutrients
Soil Characteristics
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Various soil nutrients levels favor
different plant species
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Knowing general fertility
requirements of various pasture
plants has practical application
Microorganisms
Found near the roots
 Presence of soil organisms helps
reduce nitrogen loss through
leaching
 Root area of soil is different
because:
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Release of organic materials from roots
 Uptake of nutrients by roots improved
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Rhizobium Bacteria
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“Nodulate” the legume root
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To form a small knoblike outgrowth on the
roots of many leguminous plants
Symbiotic relationship with plant
 Requires certain soil nutrients and pH
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Earthworms
Earthworms
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Pasture production can be as much as
25% higher on earthworm-containing
fields
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Aerate and loosen soil
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Incorporate dead pasture plants
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Break down manure quickly
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Eat nematodes that could harm clover
roots
Earthworms
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Move 20-30 tons of soil per acre per year!
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Application of urea (fertilizer) can cut
earthworm numbers in half
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Use ammonium nitrate instead
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Soil pH below 5.6 is unfavorable
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Herbicides, insecticides can kill them
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Need plant cover (no bare soil)
Nematodes
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Beneficial and important
Lead to rapid decay and incorporation
of organic matter in the soil
 Nutrient cycling
 Feed on bacteria, fungi and soil
protozoa
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Pathogenic forms are kept in check
by predatory nematodes (in soils
that are in good condition)
Pests
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Weeds
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Forbs (example: pigweed)
Noxious weeds (causes injury, has a bad taste
or is poisonous)
Insects
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Grasshoppers, locusts, crickets, aphids, etc.
Control by not overgrazing, provide
birdhouses, add poultry to pasture
Pests
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Diseases
About 45 disease affect pasture plants
 Mixed populations is best control
 Avoid overgrazing
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Rabbits, hares and rodents
Favored by overgrazing
 Encourage abundant diversified wildlife
(i.e. foxes, owls, eagles, even snakes)
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Things to Remember…
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Only a slight change in a particular
environmental factor may determine
death or survival of an individual plant
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Good management decisions have major
impacts on pasture productivity,
persistence, and livestock performance
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Many factors that influence pastures can
in some way be affected by management