Solar radiation distribution in plant canopies and rue

1. Solar Radiation- Distribution in plant canopies
and RUE
P. Dhamodharan
2019502205
Department of Agronomy

2. • The Sun is the universal source of energy for the earth and the organisms living on it.
• At the outer limits of the Earth’s atmosphere, the intensity of the radiation is 1360 W m-2
(Solarconstant).
• More than half is lost, being cast back into space as a result of refraction and diffraction
in the atmosphere, or scattered or absorbed by particles in the air.
• The radiation reaching Earth’s surface is called global radiation, and ranges from 290 to
3000 nm.
• On average, 45% of the incoming solar radiation falls within the range of 389 to 710 nm,
which is the range utilized by photosynthesis by plants. This range is often defined as
photosynthetically active radiation, PAR, and is often denoted by the range between 400 to
700 nm.
SOLAR RADIATION
Introduction:

3. • Radiation at shorter wavelengths (UV-A 315 to 380 nm and UV-B 280 to 315 nm) is known as
ultraviolet radiation, and is absorbed in the upper atmosphere by ozone and oxygen.
• If we do not have the absorption of the ultraviolet radiation by ozone and oxygen, life on this planet as
we know it could not survive because of the excessive levels of UV.
• UV radiation (<300 nm) are absorbed by nucleic acids and proteins.
• These high-energy wavelengths cause degradation of these molecules.
• The upper end of the spectrum is known as infrared radiation (IR 750 to 4000 nm).
• Plants do receive long wave radiation known as thermoradiation (IR 4000 to 105 nm) and
themselves emit this type of radiation.
• Our eyes, for example, are sensitive to only a small range of frequencies – visible light region
of the electromagnetic spectrum.

4. Solar radiation
• Solar radiation is radiant (electromagnetic) energy from the sun. It provides light and heat for the
Earth and energy for photosynthesis.
• This radiant energy is necessary for the metabolism of the environment and its inhabitants .
• The three relevant bands, or ranges, along the solar radiation spectrum are ultraviolet, visible
(PAR), and infrared.
• Of the light that reaches Earth’s surface, infrared radiation makes up 49.4% of while visible light
provides 42.3% .
• Ultraviolet radiation makes up just over 8% of the total solar radiation.
• Solar radiation is measured in wavelengths or frequency.

6. PAR
• Photosynthetically Active Radiation (PAR) is the light wavelength range that is best fit for
photosynthesis to occur.
• Photosynthesis is a process that requires light energy and optimally occurs in the 400 to 700
nanometer (nm) range .
• This range is also known as visible light.

7. Solar irradiance
• Solar irradiance is the intensity with which radiation enters
Earth’s atmosphere.
• An relatable way to think about solar irradiance is by looking
at the difference between a 20-watt light bulb and a 100-watt
light bulb.
• Both produce visible light in the same wavelengths, but the
brightness and intensity are very different.
• The 100-watt bulb has a higher intensity, or irradiance.
• Solar irradiance is the amount of radiant flux on an area, and
is measured in watts per meter squared (W/m²) . Annual surface solar irradiance received in 2008. The
equator receives solar radiation at a higher intensity
(irradiance) than the norther and southern
hemispheres. Data compiled by P. Wang, P. Stammes,
R. van der A, G. Pinardi, M. van Roozendael (2008),
FRESCO+

8. Irradiance
• Radiant energy can be measured in joules. The basic unit of
power is the watt (joules/second).
• The sun emits 384,600,000,000,000,000,000,000,000 watts
(3.846 x 1026W) .
• Luminance and illuminance attempt to define the brightness
and the light projected from a given source.
• The greater the angle of the sun, the lower the lux will be, as
the lumens are spread out over a greater area
• On most sunny days (out of direct light), illuminance is usually
10,000-25,000 lux

9. Albedo
• Albedo is the measure of the diffuse reflection of solar radiation out of the total solar radiation
and measured on a scale from 0, corresponding to a black body that absorbs all incident
radiation, to 1, corresponding to a body that reflects all incident radiation.
• The lower the albedo, the more radiation from the Sun that gets absorbed by the planet, and
temperatures will rise.
• If the albedo is higher, and the Earth is more reflective, more of the radiation is returned to space,
and the planet cools.
• An example of this albedo effect is the snow temperature feedback.

10. Light interception
 Sun light intercepted by tree canopy, relative to total incoming sunlight is called as the light
interception.
 In the interception of light (LI) by a canopy, difference between the solar incident radiation and
reflected radiation by the soil surface (Villalobos et al., 2002)
 It is a determining factor in crop development and provides the energy needed for fundamental
physiological processes such as photosynthesis and transpiration.

11.  Plants intercept direct and diffuse sunlight.
 The upper leaves receive both types of radiation, while the lower leaves intercept a small
portion of direct radiation.
 Diffuse radiation therefore, becomes more significant in the lower leaves due to radiation
transmitted and reflected from the leaves and the soil surface.
 From a practical point of view, the solar radiation spectrum is divided into regions, each with
its own characteristic properties

12.  Visible radiation, between the wavelengths of 400 and 700 nm, is the most important type from an
eco-physiological viewpoint, as it relates to photosynthetically active radiation (PAR).
 Only 50% of the incident radiation is employed by the plant to perform photosynthesis (Varlet-
Gancher et al, 1993).
 The quantity of radiation intercepted is influenced by leaf angle, the leaf surface affecting light
reflection, the thickness and chlorophyll concentration, which affect the light transmission, the size
and shape of the leaf phyllotaxis and the elevation of the sun and distribution of direct and diffuse
solar radiation.

13. LIGHT INTERCEPTION
 Of the 100% total energy received by the leaf only 5% is converted into carbohydrates for
biomass production later.
 Losses of energy are:
By non-absorbed wavelengths: 60%.
Reflection and transmission: 8%.
Heat dissipation: 8%.
Metabolism: 19%.
 Of the global radiation incident on the plant canopy only a proportion is used to carry out
photosynthesis: PAR (photosynthetic active radiation). 21

15. PhotosyntheticallyActive Radiation :400-700nm
15

16. EFFECT OF INTERCEPTED RADIATION ON GROWTH AND CROP PRODUCTION
Depends on
 The ability of plant cover to intercept the incident radiation.
 The architecture of vegetation cover.
 Conversion efficiency of the energy captured by the plant into biomass
 The efficiency of interception of PAR depends on the leaf area of the plant population (Varlet-
Grancher et al., 1989) as well as on the leaf shape and inclination to the canopy.
 The incident solar radiation , which is the main factor influencing the efficiency of interception of
the canopy corresponds to the capacity of the plant population in photosynthesis and the
transpiration processes (Thorpe, 1978).
 The efficient crops tend to spend their early growth to expand their leaf area; they make a better
use of solar radiation.
 Solar radiation also has an important role in the processes of evaporation and transpiration.

17.  Light (solar radiation) provides the energyto drive
photosynthesis.
 Of the light spectrum, the range that can be used by
plants for photosynthesis are wavelengths between 400
nm (blue) and 700 nm (red), and is termed
‘photosynthetically active radiation’(PAR).
 The amount of light within the crop canopy can be
measured with a ceptometer (a long thin probe with up
to 80 PAR sensors along its length), from which the
amount of PAR intercepted by the crop can be estimated.
STANDARDIZED METHODS FOR MEASURING INTERCEPTION IN CANOPIES

18. LEAF AREAINDEX
 LAI is broadly defined as the amount
of leaf area (m2) in a canopy per unit
ground area (m2)Watson (1947)
 LAI is related to photosynthesis and
primary production (biomass)
 LAI influences how light moves
through a Canopy
 LAI influences microclimate
 LAI can beused as an indicator
of canopy health or development

19. Quantum sensor forabove-
canopy
measurement of PAR
Quantum sensor forbelow
canopy
measurement of PAR

20. METHODS FOR PAR MEASUREMENT
TRIANGULAR METHOD CIRCULAR METHOD

21. The triangular method
 A triangle was formed using plastic rope
connecting three palms.
 Every arm of the triangle was divided into six equal
parts.
 Each marking point of the triangle was joined by a
plastic rope.
 Every intersection point was treated as a measuring
point, where the quantum sensor was placed for the
below canopy radiation data recording.
The circular method
 In the circular method, a circular area under the
palm tree was considered.
 The outermost circle corresponds to the frond tip
while the frond base considered as the centre point
of the circle.
 This circle was divided into sectors according to
zenith and azimuth angles for proper PAR
estimation of spatial variation.
 Each circle and line were drawn by white marking
powder.
 A total of twenty-four measuring points were used
for every palm tree in order to measure the below
canopy radiation.

22.  In both the triangular method and the circular method, the quantum
sensor was placed 0.5 meter above the ground for the below canopy
data recording.
 The line quantum sensor was used for the below canopy recording.
LI = (PAR above canopy - PAR below canopy) / (PAR above
canopy)
Or
LI = [1-(PAR below canopy) / (PAR above canopy)]

23. CALCULATION OF RADIATION
INTERCEPTION IN OILPALM CANOPY
PQ sensor
reading
Conversion
factor
Above canopy
reading
Below canopy
reading
Radiation
interception
1000.10 0.95 950.10 287.20 0.6977
967.81 0.95 919.42 256.34 0.7211
1007.40 0.95 957.03 220.30 0.7698
1013.20 0.95 962.54 216.37 0.7752
938.68 0.95 891.75 215.10 0.7587
989.41 0.95 939.94 346.80 0.6314
1025.90 0.95 974.61 296.60 0.6956
1065.10 0.95 1011.81 301.26 0.7022
1064.10 0.95 1010.89 299.35 0.7038
1036.00 0.95 984.20 289.35 0.7060 36
1013.70 0.95 963.02 276.31 0.7130
1052.80 0.95 1000.16 274.21 0.7258

24. Light and Carbohydrates and Dry Matter Production
• Of the 100% total energy
received by the leaf, only 5%
is converted into
carbohydrates and later for
biomass production.
• Losses of energy by non-
absorbed wavelengths: 60%
• Reflection and transmission:
8%
• Heat dissipation: 8%
• Metabolism: 19%

25. Radiation and Photosynthesis Leaf-level

26. Radiation and Photosynthesis Canopy-level
200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
Light or PPFD, µmol m-2
s-1
0
Canopyphotosynthesis,mgCO2m-2
s-1
-2
0
2
4
6
8

27. Light and Dry Matter Production

28. Radiation and Plant Life

29. Solar Radiation and Day-length

30. Solar Radiation and Day-length
In the northern hemisphere,
Summer solstice: 22 June
Winter solstice: 22 December

31. The incident light at the top of
the canopy is absorbed by
successive layers of
leaves in the canopy.
This light enters the
bottom of the canopy by:
1. Direct radiation as sun
fluxes through the gaps in
the canopy
2. Scattered light from the
leaves and soil.
3. Transmittance through
the leaves.
Radiation and
Canopy Interception

32. The interception of the light by the canopy is expressed by Beer’s law as
follows:
I = I0 e-kLAI
Where I is the intensity of the light at the point in the canopy,
I0= light intensity at the top of the canopy,
LAI is the leaf area index above that point and k represents the extinction
coefficient determined empirically.
Leaf area index is the most commonly used canopy structure
parameter, and is defined as:
Leaf Area Index (LAI) =Total leaf area / ground area
Radiation Interception

33. The decrease in light intensity or the attenuation of radiation (attenuation
coefficient) in a stand depends on:
1. Density of the foliage.
2. The arrangement of the leaves within the canopy.
3. The inclination (angle) of the leaves.
Therefore, for grain crops and grasses, the attenuation coefficient is between 0.3
to 0.5, in the dicots, for example, it is about 0.7 and in a dense forest, it is
mostly absorbed by the top canopy and very little is pass through the lower
layers.

34. Radiation Interception and Leaf Type

35. Radiation Distribution in the Soil and Water
• Radiation or light scarcely penetrates soil at all; 1% in sandy and clay soils
reaches a depth of 2-5 mm below the soil surface.
• In water, radiation is more strongly attenuated than in the atmosphere.
- Long-wave radiation is absorbed in the upper few mm, infra-red in the upper
few cm and UV penetrates up to a 1 m.
-For an example, in open ocean – 1% of the light penetrates down to 150 m
and it is about 20 – 50 m near the shorelines.
-In clear lakes, light penetrates in sufficient quantities to support vascular
plants up to 5 m.

36. Reflectance - Leaf Level
• Leaf surface properties (wax and cuticle)
• Internal structure (anatomy)
• Biochemistry (concentration and distribution)
• Leaf physiology

37. Reflectance - Canopy Level
• Soil characteristics
• Vegetation characteristics

38. Heliotropism
Plants change the orientation of their leaves in reponse to atleast three types of stimuli, and these
movements classified in three categories [Ehleringer and Forseth, 1980, p. 1094]:
• Nyctinastic (sleep movements),
• Seismonastic (movements in response to shaking), and
• Heliotropic (movement in response to changes in illumination).
Two forms of heliotropism are known:
1. diaheliotropic leaves tend to maximize exposure to the Sun by orienting their normal in its
direction,
2. paraheliotropic leaves tend to position themselves in a plane parallel to the Sun's rays, thereby
minimizing exposure.

39. • The orientation of a leaf is entirely described by two angles‘ the leaf zenith angle, which is the angle
between the normal to the leaf and the local vertical' and the leaf azimuth, which is the angle between
the projection of the normal to the leaf on the horizontal plane and an arbitrary direction taken as origin,
conventionally due south. The azimuth of a horizontal leaf is undefined.

40. Radiation Use Efficiency
• Radiation-use efficiency (RUE), defined as crop biomass
produced per unit of total solar radiation or
photosynthetically active radiation (PAR) intercepted by the
canopy, is a fundamental component of a framework to
analyse crop growth based on resource capture and use
efficiency.
• Values of RUE for tree species are generally smaller than
those for C3 herbaceous species (Kiniry et al. 1989), because
of the high energy cost of woody biomass and the respiration
of supporting organs.

41. • RUE is influenced by plant development and many environmental factors.
For example, RUE increases with increasing rate of leaf photosynthesis.
• RUE should decrease with increasing leaf age, respiration, and with the
higher energy costs of some plant constituents.
Corn 3.5 g/MJ
Rice 2.2 g/MJ
Sorghum 2.8 g/MJ
Sunflower 2.2 g/MJ
Wheat 2.8 g/MJ
RUE for field crops

42. THANK YOU