Grass Growth and Pasture Management

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Grass Growth and Pasture Management

• Part of the Ruminant Livestock Facing New
  Economic Realities Meetings

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Grass Plant Tillers
Seed head
Lead Tiller
Rhizome Tiller
Crown Tiller
Source L.L. Manske North Dakota State University
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Grass Physiology

• Cool season grasses initiate flower buds on the
  crown when exposed to low temperatures and long
  nights.
• Carbohydrates are stored late in the growing
  season (fall management is critical).
• In the spring, new growth is initiated from the
  crown using carbohydrate reserves stored in the
  roots, rhizomes, stolens, and/or stem bases.
• As day length increases throughout spring, at
  some point a flowering response is triggered.

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Grass Physiology

• Not all tillers produced by the plant are
  reproductive tillers, but
• Because reproductive tillers grow taller than the
  vegetative tillers they shade out the vegetative
  tillers and in addition
• As seed heads develop they produce plant hormones
  that retard the development of other vegetative
  tillers

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Grass Physiology

• Removing the seed head by grazing or clipping
  will promote development of vegetative tillers
• Because most cool season grasses require cool
  temperatures and long nights to once again
  develop reproductive tillers, after seed heads
  are removed, vegetative growth is produced for
  the remainder of the year

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UNDERSTANDING PLANT GROWTH

• Light
• Roots/Carbohydrate Reserves
• Temperature
• Water
• Fertility/Nutrients

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PLANT REGROWTH AFTER HARVEST

• From Carbohydrates Produced by Remaining Leaf
  Area
• From Carbohydrate Reserves

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Defoliation Stresses Forage Plants

• Reduces or eliminates photosynthesis
• Stops nutrient uptake from the soil
• In legumes, nitrogen fixation stops within hours
  of harvest

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Leaf Removal vs. Root Growth
Leaf Removed
Percentage Root Growth Stoppage
Source Crider, 1955
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Grazing Principle

• For Rapid Regrowth
• Take Half
• Leave Half
• (By weight/volume recognize forage is denser
  towards base of plant)

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What You Leave Behind

• Affects re-growth rate
• Affects root growth
• Affects soil temperature
• Affects organic matter
• Affects water infiltration rate and water-holding
  capacity
• Affects nutrient cycling

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Animal Intake and Pasture Residual

• Forage Systems Research Center work has found
  about 80 of the variation in grazing intake is
  correlated with post-grazing residual.
• When forage mass drops below a critical level,
  intake is restricted
• In other words, the reason the top end of
  graziers are getting better animal performance
  compared to lower end graziers is because they
  know when to get their livestock out of a pasture
  paddock.

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Managing Grazing Heights Pure or dominant grass
stands
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Managing Grazing Height
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Grazing Principle

• Provide plants with adequate rest period
• to re-grow to correct grazing height

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Relationship of rest period to pasture mass
during periods of rapid vs. slow growth
Lbs. DM / acre
Optimum Rest Period
0 5 10 15
20 25
Period of fast plant growth (days)
Source Craig Saxe, University of
Wisconsin Extension
0 10 20 30
40 50
Period of slow plant growth (days)
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Rest Period Management

• Paddock number determines flexibility and the
  degree to which the grass plant can be managed.
• For example in a 4 paddock system if my goal is
  not to graze the new re-growth until 8 inches,
  then my rotation flexibility is 12-16 days in the
  spring and 28 to 32 days in the summer
• In a 10 paddock system, rotation flexibility is
  10 to 30 days in the spring and 50 to 70 days in
  the summer
• More paddocks can result in higher utilization
  rates

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MANAGEMENT TO OPTIMIZE PLANT GROWTH

• Avoid production of seed heads, keep the plant
  vegetative
• Maintain leaf canopy (residual management)
• Recharge plant root reserves
• Vary rest periods by season and rainfall
• Frequent shifts of short duration
• Provide adequate soil nutrients

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Growing Season Management

• The reason behind using rest periods and residual
  management is to increase productivity and to put
  the grazier in the position to extend the grazing
  season through
• Quicker green up in the spring
• Quicker recovery from drought
• Fall/Winter grazing?

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Management Changes?