Grass Growth and Pasture Management

Part of the Ruminant Livestock: Facing New Economic Realities Meetings

Grass Plant Tillers

RhizomeTiller

CrownTiller

LeadTiller

Seed head

Source: L.L. ManskeNorth Dakota State University

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.

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

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

UNDERSTANDING PLANT GROWTH

• Light

• Roots/Carbohydrate Reserves

• Temperature

• Water

• Fertility/Nutrients

PLANT REGROWTH AFTER HARVEST

• From Carbohydrates Produced by Remaining Leaf Area

• From Carbohydrate Reserves

Defoliation Stresses Forage Plants

• Reduces or eliminates photosynthesis

• Stops nutrient uptake from the soil

• In legumes, nitrogen fixation stops within hours of harvest

Leaf Removal vs. Root Growth

0 20 40 60 80 100

80%

70%

60%

50%

40%

30%

20%

10%

% LeafRemoved

Percentage Root Growth StoppageSource: Crider, 1955

Grazing Principle

For Rapid Regrowth:

Take Half

Leave Half

(By weight/volume: recognize forage is denser towards base of plant)

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

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.

Managing Grazing Heights: Pure or dominant grass stands

Species Pre-graze inches Post-graze inches

Perennial Ryegrass 6-7 3

Orchardgrass 8-10 3 - 4

T. Fescue (E+) 5-6 1-2

T. Fescue (E-) 8-10 3 - 4

Brome grass Pre or late jointing

2-3

Timothy Pre or late jointing

4

Managing Grazing Height

Grass Legume Mixtures

Species Pre-graze inches

Post-graze inches

Bluegrass/w clover 4-5 1 - 2

OG/L clover 6-8 2 - 3

T fescue/L clover 5-8 1.5 - 2

Alfalfa with grass bud 2 - 3

Red clover with grass

bud 2 - 3

Grazing Principle

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

Relationship of rest period to pasture mass during periods of rapid vs. slow growth

Period of fast plant growth (days)

Period of slow plant growth (days)

0 5 10 15 20 25

0 10 20 30 40 50

Lbs.

DM / acre

Optimum

Rest

Period

Source: CraigSaxe, Universityof WisconsinExtension

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

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

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?

Management Changes?