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 ofplants

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 productivityand 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