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

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

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 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