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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
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 productivityand persistence
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
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 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 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 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