Lesson 3.1: Classical Growth Analysis
Lesson Summary
Growth analysis involves the study on how a treatment affects plant growth and hence the final
yield, during the development of the crop from germination to final harvest. For the agronomist,
understanding of the final yield in response to a treatment is of great importance. Of similar
value is the knowledge on how a treatment affects plant growth.
Learning Outcomes
By the time you are done with this lesson, you should be able to:
1. calculate and interpret the different components of growth analysis.
Motivation Question
What valid parameters will you be using in
comparing the rate of growth or
productivity of the two varieties under
controlled and open environment?
Discussion
Since our topic is about growth, let us review
first the definition of growth.
In Agronomy 21 and Crop Science 21 even in your Biology, we commonly define growth
as the irreversible increase in size. Implying that there is change in weight, change in leaf area,
change in height and girth.
Generally, agronomists define growth as the
increase in dry matter. This includes now the
process of differentiation which contributes
greatly to dry matter accumulation.
The increase in size or increase in number of cells if plotted against time the graph shows ‘S’
shaped curve called sigmoid growth curve as shown in the Figure 12. In here, we could see the
rate of growth of an organism.
Figure 12. The sigmoid growth curve (Source: https://padeepz.net/plant-growth-and-measurement-of-plantgrowth/)
The rate of plant growth is slow in the early stages and this phase is called lag phase.
This is followed by a rapid growth phase called log phase. In the third and final phases, the
growth slows down and the organism maintains the size it has already attained. This phase is
known as stationary phase or steady state phase. As the plant senesce and dies growth curve
declines.
How can we determine changes in growth by
looking at the above graph?
We could determine changes in growth through the slope of the line. The rate of growth is the
same if it is linear but, there came a time when growth is no longer linear thus, early researcher
proposed the different components of growth analysis.
Ways to do Growth Analysis
1. Classical Growth Analysis/Traditional
2. Functional Approach
For this course we will be focusing our discussion
on classical growth analysis which is commonly
and widely used in the experiment in crop
production and plant breeding.
Blackman’s (1919) concept of compound interest states that the increase in dry weight
is similar to the amount of money deposited in the bank, earning an interest. Plant increased in
dry weight by adding dry matter everyday through photosynthesis. The concept is represented
by this equation:
W = Woert
Where: Wo = initial dry weight
W = dry weight at any given time
e = efficiency index
t = time
r = interest
Components of Growth Analysis
1. Relative Growth Rate (RGR) - change in dry weight per unit change in time relative to initial dry
weight.
Where: W1 = plant weights at time 1 (g)
W2 = plant weight at time 2 (g)
t2 – t1 = time interval (days)
ln = natural log
Take note that RGR is not absolute. It should always be relative to the initial dry weight. If
we want to compare the growth of individual plant in a community it should be relative because
seeds are at different physiological state, some are high vigor and some are low vigor and,
therefore they give rise to seedlings of different vigor. If we use absolute term, then it can be
biased, since the capacity of the plant to accumulate dry matter is dependent on their
photosynthetic rate likewise photosynthesis is dependent on leaf area.
A community of plants start at a different level or they are not strictly or absolutely in
uniform growth because they start at different vigor.
Example:
Table 2. Leaf area and changes in dry weight of a plant
Plant
Sample
Leaf area
(cm2)
Dry weight
(g) (W0)
Dry weight
∆W (g)
1
5
12
18
6
2
7
18
25
7
3
15
25
28
3
4
10
20
24
4
(W1)
Which is efficient in terms of dry weight relative to the initial weight? In terms of leaf area?
(Write your answer on the Assessment letters C and D)
2. NAR (Net Assimilation Rate) = change in dry weight per unit leaf area per unit time
NAR = W2 – W1 (lnLA2 – lnLA1) = g cm-2 d-1
t2-t1 (LA2 - LA1
Where: ln = natural log
LA1 = leaf area at time 1
LA2 = leaf area at time 2
W1 = total plant dry weight at time 1
W2 = total plant dry weight at time 2
T2 – T1 -= time interval between first and second
measurement
3. CGR (Crop Growth Rate)= change in dry weight per unit ground area per unit time
CGR = W2 – W1
= g m-2 wk-1
(t2 – t1) LA
Where: W1 = total plant dry weight at time 1
W2 = total plant dry weight at time 2
T2 – T1 = time interval between first and
second measurement
LA = land area
4. LAR (Leaf Area Ratio) - ratio of the leaf area/total plant dry weight
LAR = A/W
Where: A = total green leaf area of the plant
W = total plant dry weight
LAR has 2 components:
a) LWR (leaf weight ratio) = leaf weight/total plt. dry weight
LWR = LW/W
Where: LW = leaf weight
W = total plant dry weight
b) SLA (Specific leaf area) = leaf area/total leaf weight
SLA = A/LW
where: A = leaf area
LW = leaf weight
5. LAI (Leaf Area Index) = ratio of the total leaf area to the ground area occupied by a plant
LAI = L x W x CF
ground area occupied by the plant
where: L = length
W = width
CF = correction factor
6. HI (Harvest Index) – ratio of the economic yield to the biological yield
HI = Economic yield
Biological yield
Application and Limitation
1. RGR - is applicable only at initial or early growth stage when growth rate is exponential and
no competition
2. NAR – measurement of assimilatory capacity, rough measurement of PS
The assumption: that there is linear relationship between leaf area and dry weight
components of NAR : PS and Respiration
3. CGR – used anytime or any stage of development of the crop
CGR of a species is usually closely related to interception of solar
radiation
components of CGR: NAR and LAI
CGR could be computed as:
CGR = NAR x LAI
4. LWR – indicates partitioning –how much assimilates partitioned to the leaf relative to total
dry weight of the plant
5. SLA connotes how thin or how thick are the leaves.
6. LAI – refers to the total green leaf area only
An LAI of 3.00 means that total green leaf area is 3x greater than that of the ground area
occupied by the plants
Sampling method
RGR– random individual plant
CGR = row segment, quadrat
LAI = random individual plant, row segment, quadrat
Alterations of growth pattern:
1. influence of environmental stress
a. drought - During drought, the tendency for the plant is to invest its assimilates on root
system. Plants exposed to drought have thicker leaves.
b. waterlogging
c. low soil fertility
d. pest and diseases
2. influences of intra and interspecific competition
Intraspecific competition – plant to plant interaction of the same species
Interspecific competition – interaction between different species
Interaction could be either: competitive or complementary