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