The presentation is on crop physiology and ecology, basically how the environment affects crop performance and yield. Here different parameters used to describe plant growth are discussed.

1. Crop Ecology
and
Physiology
CUCS201
Lecturer: Dr. A. Maodzeka

2. Module outline & assessment areas
Module Duration >>> 3.75 weeks
Assessment work >>> Assignments + Practicals + Quiz + Presentations + Exam
Assessment work >>> Lectures (Face-Face + Virtual)

3. Measurement of plant growth
What is growth?
Growth is an irreversible increase in plant size
accompanied by a quantitative change in biomass
(weight).

4. Measurement of plant growth
How do you measure plant growth?
Growth can be measured by a variety of parameters as follows:
• Fresh weight: Determination of fresh weight is an easy and
convenient method of measuring growth. NB: highly
variable due to tissue water content.
• Dry weight: The dry weights of plant organs are usually
obtained by drying the materials for 21–48 h at 70–80℃
and then by weighing it.
• Length: Measurement of length is a suitable indication of
growth for those organs that grow in one direction with
almost uniform diameter such as roots and shoots.
• Area: It is used for measuring plant organs such as leaf. The
area can be measured by a graph paper or by a
photoelectric device (digital leaf area meter).

5. Measurement of plant growth
Relative Growth rate (RGR)
• Rate of mass increase per unit mass present
(efficiency of growth with respect to biomass)
• the rate of accumulation of new dry mass per unit
of existing dry mass, is a major determinant of
plant competitiveness.
• It is the change or increase in plant biomass in a
given period of time divided by the initial weight.

6. Measurement of plant growth
Relative Growth rate (RGR)
• RGR is an indirect measurement of the rate of
resource acquisition.
• High RGR increases weed suppression abilities.
• The faster an individual accumulates biomass, the
more carbon is available to increase growth of
roots and shoots for greater access to light and soil
nutrients, which in turn enables greater biomass
accumulation.

7. Measurement of plant growth
Relative Growth rate (RGR)
Where logeW1 and logeW2 are the natural logs of
dry weights at two sampling times t1 and t2,
respectively

8. Measurement of plant growth
Crop Growth Rate (CGR)
• It is defined as the increase of dry matter in grams
per unit area per unit time. The mean CGR over an
interval of time t1 and t2.
Where W1 and W2 are the dry weights at two
sampling times t1 and t2 respectively and P is the
land area.

9. Relationship between grain number of wheat and crop
growth rate. [Sandaña and Pinochet (2011), Sandaña et al.
(2012)]
Measurement of plant growth
Crop Growth Rate (CGR)

10. Measurement of plant growth
Net Assimilation Rate (NAR)
• The NAR is a measure of the amount of
photosynthetic product going into plant material,
that is, it is the estimate of net photosynthetic
carbon assimilated by photosynthesis minus the
carbon lost by respiration.
• The NAR can be determined by measuring plant dry
weight and leaf area periodically during growth and
is commonly reported as grams of dry weight
increase per square centimeter of leaf surface per
week.

11. Where W2 and W1 are plant dry weights at
times t1 and t2, logeA2 and logeA1 are the
natural logs of leaf areas A1 and A2 at times t1
and t2
Measurement of plant growth
Net Assimilation Rate (NAR)

12. Measurement of plant growth
Leaf Area Ratio (LAR)
• The LAR is a measure of the proportion of the plant
which is engaged in photosynthetic process. It gives
the relative size of the assimilatory apparatus.

13. Measurement of plant growth
Leaf Weight Ratio (LWR)
• It is one of the components of LAR and is defined as
the ratio between grams of dry matter in leaves
and total dry matter in plants. Since the numerator
and denominator are on dry weight basis. LWR is
dimensionless. It is the index of the plant on weight
basis..

14. Measurement of plant growth
Specific Leaf Area (SLA)
• Ratio of leaf area to leaf mass (a measure of
thickness of leaves relative to area)
SLA = A/WL (m2 g–1)

15. Measurement of plant growth
Specific Leaf Weight (SLW)
• The reversal of SLA is called SLW. It is defined as the
ratio between total leaf dry weight in grams and
leaf area in cm2. It indicates the relative thickness
of the leaf of different genotypes.

16. Measurement of plant growth
Leaf Area Index (LAI)
• It is defined as the functional leaf area over unit
land area. It represents the leafiness in relation to
land area. At an instant time (T) the LAI can be
calculated as
• For maximum production of dry matter of most
crops, LAI of 4–6 is usually necessary. The leaf area
index at which the maximum CGR is recorded is
called optimum leaf area index.

17. Measurement of plant growth
Leaf Area Density (LAD)
• LAD is defined as half the total leaf area per unit
volume (m2m-3)
LAD = LA/V