Forage Plant Growth Analysis

1
Forage Plant Growth Analysis
Chapter 6
2
Plant Growth Analysis

• Forage physiology tool
• Tool of the 1950s and 1960s
• Clipped forages on schedule
• Monitor growth and TNCs
• Labor intensive
• simulation models not developed
• Limited use
• 1970s-early 1990s
• simulation models developing
• revival simulation model validations
• Early Forage Physiologists
• Dale Smith
• C.J. Nelson
• P. de van Booyson

3
Plant Growth Analysis

• Rationale and Background
• Growth energy (carbohydrates) comes from
  photosynthesis (Ps) and/or stored carbohydrates
  (TNCs)
• Forage plants are unique in that it is the
  photosynthetically active part (leaves) of the
  plant (factory) that is harvested in large
  quantities (compared to fruit grain crops) and
  yet growth must be sustained.
• Because leaves are the primary source of energy,
  and are repeatedly removed, this is where the
  focus must be in forage growth analysis.
• Leaves produce photosynthates
• Excess photosynthates are converted to storage
  starch

4
Individual Plant

• Productivity
• the measurement comparing the amount produced per
  individual.
• Overall productivity is a measurement of total
  system size by individual productivity
• Economic Models
• Total
• total amount produced/ of employees
• Worker
• Total amount produced/of producers

• Economic model (cont.)
• Efficiency
• total amount produced/total money spent
• Relationships
• Income is increased by increasing amount produced
• Profit is maximized by increasing productivity
• Plant models
• Growth (productivity)
• system size system efficiency of a plant system
• utilizable plant part/expended plant energy

5
Growth Analysis

• Growth Analysis
• quantifies growth of a plant and/or plant
  community in terms of plant productivity and
  energy efficiency
• basic assumption Total plant weight increase
  linearly with time
• It does while plant remains vegetative
• It may not in reproduction
• leaf senescence
• age defoliation

6
Growth Analysis

• Methodology
• Serial harvest all treatments have an initial
  starting point (T0) with initial weight (Wo)
• can be a harvest
• can be initial growth
• Individual Plant measured
• Plants are harvested at various times
• weights at different times are used in subsequent
  calculations

7
Data Interpretation

• Absolute Growth Rate
• System Production
• Relative Growth Rate
• System Productivity
• Leaf Area Ratio
• System size
• Net Assimilation Rate
• System Efficiency

8
Absolute Growth Rate (AGR)

• AGR DW/DT
• AGR (w2-w1)/(t2-t1)
• can use height or length
• AGR formula Slope
• Assumption
• growth is linear
• AGR may be unchanging over time
• AGR is size dependent
• Increased plant size, increased amount of leaf
  and Ps
• Comparisons outside of size (experiment,
  treatment, etc.) is irrelevant

9
Relative Growth Rate (RGR)

• RGR
• RGR

• Productivity Descriptor
• Changes over time
• No longer plant size dependent
• Nonlinear relationship

AGR Mean Plant Wt.
(
)
w2 - w1 t2 - t1
1 w
x
1 w1 w2 2
(
)
(
)
w2 - w1 t2 - t1
x

(
)
(
)
w2 - w1 t2 - t1
2 w1 w2
x

10
Leaf Area Ratio (LAR)

• LAR L/W
• L Leaf area
• W Plant weight
• LAR (l1/w1 l2/w2)/2

• Similar to Leaf Area Index
• aka LAI
• Determines Ps ability within that system
• Species, moisture, etc. also affect Ps
• Optimum LAI
• Row crops 3-7
• Forages 6-9
• 12 common.

(
)
l1 l2 2

(
)
w1 w2 2
(
)
l1 l2 w1 w2

11
Net Assimilation Rate (NAR)

• NAR Dwt./unit leaf area/unit time

• Measures production over time in a uniform matter
• enables comparative production analysis between
  plants of different size.

12
Plant Productivity

• PP fnSS SE)
• plant productivity is a function of system size
  by system efficiency
• RGR LAR NAR
• Develop the formula

L/W