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Pasture Ecology

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  1. Pasture Ecology ANSC 110 August 31, 2010

  2. 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

  3. 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

  4. What influences pasture ecology? • Energy • Water & Temperature • Pasture site • Space available • Competition • Grazing habits • Plant anatomy • Soil characteristics • Decomposers/Pests

  5. 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

  6. Solar Energy Volume ofplants Area of leaf Duration of growth Savory, 1988

  7. 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

  8. 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

  9. 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

  10. Water • Rainfall is primary water source for pastures • Irregular rainfall  deficient or excessive soil water • Direct effect on plant productivityand persistence

  11. Drought

  12. Drought • Plant leaf area decreases • Plant root growth increases • Decreased ability to take up nutrients

  13. Drought • Ability of legumes to fix N decreases • Carbohydrate storage supplies decrease • Nutrient levels highest at surface

  14. 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

  15. Temperature • Second most important influence • Plants are adapted to certain climatic conditions • 68° F • Plants that can adapt to temperature fluctuations will do better

  16. Temperature • Mean annual air temperature for our zone (Zone D in textbook) is ~ 58° F

  17. 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

  18. 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

  19. 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

  20. Competition • Water • Nutrients • Light • Carbon Dioxide • Oxygen • Environmental stressors • Means of pollination/seed disbursal

  21. 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

  22. 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

  23. 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

  24. Grazing Horses • Animals  more complex pasture • Selective grazing • Manure and urine • Treading - Walking, running, jumping, lying down, scratching, pawing

  25. Management • Plant height – especially during leaf development and elongation • Grazing frequency • Grazing intensity • Soil fertility

  26. Management • Weedy pastures • Understocked lax grazing • Overgrazing

  27. 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

  28. Overgrazing • Not necessarily number of animals • More a function of the timethat 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

  29. 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?

  30. 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

  31. 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!

  32. Soil Characteristics • Microorganisms • Earthworms • Nematodes • Nutrients

  33. Soil Characteristics • Various soil nutrients levels favor different plant species • Knowing general fertility requirements of various pasture plants has practical application

  34. 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

  35. 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

  36. Earthworms

  37. 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

  38. 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)

  39. 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)

  40. 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

  41. 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)

  42. 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