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8/2/2019 Radiation and Light Use Effeiciency
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Radiation/Light Use Efficiency inRadiation/Light Use Efficiency in
Cropping SystemsCropping Systems
A.S. JADHAVDean, Faculty of AgricultureMPKV, Rahuri-413 722, Dist. Ahmednagar
Email: [email protected]
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Topics CoveredAbsorbed radiation
Intercepted radiation
Transmitted radiationRadiation distribution in a crop canopy
Factors affecting radiation distribution withinplant community
Light use efficiency (LUE)
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IntroductionIntroduction
Solar radiation is the source of energy forphotosynthesis.
Radiation in the 400 - 700 nm wavelength
interval supports photosynthesis in greenplants.
This region of the spectrum is referred as
photosynthetically active radiation (PAR).
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Absorbed PAR is algebraic sum of the incomingand outgoing flux densities measured above andbelow a plant canopy (Aarar et al., 1989).
The measurements required above the canopy are
incident PAR flux density I0
excitant PAR flux density Rc
from the canopy (including
reflected by the but not absorbed prior to arriving at thetop of the canopy).
PAR flux density transmitted, Tc
through the canopy to
the soil surface and
PAR flux density reflected by the soil, Rs.
absorbed Par (APAR) of the canopy may becomputed as:
APAR = (I0 + Rs) - (Tc + Rc).
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Intercepted PAR (IPAR) is the
difference in the PAR flux densityabove and below the plant canopy.
The two measurements required are
the incoming PAR flux densitytransmitted (T
c) through the canopy
to the soil surface:
IPAR = I0
- Tc.
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When water, nutrients and temperature are
not limiting, the quantity of dry matter produced by a crop stand W (gm-2) can beexpressed as:
W = Sfet
Where, S is the daily mean solar radiation (MJm-
2day-1)
f is the seasonal mean fractional interception of
radiation by the canopye is the seasonal mean conversion coefficient
(gMJ-1)
t is the canopy duration in days
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During the season, fractional interception(f) is related to leaf area index (LAI) by
the equation:f = I - exp (-kLAI)
Where, k is an extinction coefficient
dependent on leaf angle and distribution.
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Reflection, Transmission andReflection, Transmission and
AbsorptionAbsorptionOn an average about 75 % of the
incident radiation is absorbed byplant canopyabout 15 % is reflected
and 10 % is transmitted.
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Radiation Distribution in a Crop CanopyRadiation Distribution in a Crop Canopy
Three aspects of solar radiation are biologicallysignificant. Intensity of radiation i.e. amount of radiant energy falling
on a unit surface area in a unit time.
Spectral distribution of radiation which governs thephotochemical process of photosynthesis.
Radiation distribution in time is important forphotoperiodic phenomenon.
The rate of photosynthesis depends on the availability
of photosynthetically active radiation intercepted bythe leaves.
The rate of transpiration from the plant canopy isalso controlled to a greater extent by the radiation
energy.
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Factors Affecting Radiation DistributionFactors Affecting Radiation Distribution
Within Plant CommunityWithin Plant Community
Transmissibilityof Leaves
Leaf Arrangement and Inclination
Plant DensityPlant Height
Angle of the Sun
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Light use efficiency (LUE)Light use efficiency (LUE)
Amount of dry matter produced (gm-2)
LUE = ----------------------------------------------------------
Amount of cumulative light absorbed (MJ m-2)
Pearl millet + pigeonpea and sunflower + pigeonpeaintercroppings are gaining popularity under rainfedconditions.
Intercropping advantages are maximized by complementaryinteraction between component crops due to minimal
intercrop competition (Willey, 1979). Intercrops intercepts PAR more efficiently compared to sole
crops under rainfed conditions.
It thus, improves light use efficiency ( Sivkumar and Virmani,1984 and Willey et al., 1986).
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Extinction coefficients (k)Extinction coefficients (k)
The k value is generally influenced byrow spacing,
plant population
plant arrangements.The k values were more under narrow row
geometry than wider row geometry
because of more interception of PARunder narrow rows.
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