Light interception Flashcards
What is light interception?
The amount of light intercepted by a crop. Light is the main control of yield when other factors are not limiting. Light fuels the photosynthesis in the chloroplast.
What is light quality?
Determined by wavelength. The ratio between red = 660 + 30 and far red 730 _+30
PAR
Photosynthetically active radiation.
0.5 of total radiation.
400 - 700 of visable light spectrum absorbed
How much infra red is reflected
700-3000
What are photochromes
Sense the quality of light.
How these percepted the R:Fr ratio changes plant morpholgy.
Red light
absorbed by the leaves
1.
Far red
Pass through canopy to be reflected or transmitted to base of crop.
Canopy closure (LAIc)
When all red light is absorbed, far red is left. This high fr:R ratio at the base allows the plant to realise and deactivates bud formation for tillering.
Yield as a function of incidient radiation.
Y= (R x LI x RUE) x HI
R = incidient radiation which is PAR and total radiation.
Li = R/Ro - the amount of light that is intercepted. Relationship between what is absorbed and reflected. Incident light and light below canopy.
Leaf area index
m2/m2
Area of leaf lamina per unit of ground area.
Expresses the capacity of the crop to intercept light.
Refers to the whole canopy.
LAI effected by
Temp, N status, water & PP
LAI interception
Crops need 3-5 to intercept 90% of R.
As LAI increases, proportion of light interception decreases.
As S.D. progresses, LAI production decreases with yield.
Critical LAI
LAIc. When the crop reaches 95% of light interception. Above LAIc, max growth rate happens. Prolonged time above LAIc, the higher yield there will be.
Canopy architecture
How the leaves are arranged in a crop, varries LAIc.
Wide leaves
Close canopy faster but are more inefficient as they shade lower leaves so that they aren’t working at full capacity. The top leaves are intercepting the most light and so saturate. Above saturation photosynthetic efficiency drops.
Narrow leaf
Top leaves recieve less light, not working saturated means higher synthetic efficiency. More light going through the canopy.
Less direct light but more leaves participating in DM accumulation.
Means you can increase PP>
PAR penetration through canopy.
Depends on reflection, thickness, size, shape and arrangement of leaves. Explain by K.
What is K?
The extension coefficient to describe PAR penetration through the canopy. Senesitive to leaf angle.
K is used in Beer’s law. What is beers law?
Describes the decline of light through the canopy. Can be measured by
R/Ro = 1 - exp(-K x LAI).
R/Ro = 1-exp(-K x LAI) explain.
Fraction of light intercepted as a fractrion of the coefficient of extension and LAI.
How to calculate R/Ro=1-exp(-K x LAI).
We know R/Ro from a sunscaner, we know LAI from deconstructive measurements. Isolate -K into the equation
Ln(R/Ro)x LAI
Explain Ln(R/Ro) x LAI
Log of transmitted fraction of radiation.
For every increase in LAI there is a reduction in light penetrating through the canopy.
Transmitted fraction.
Calculating LI.
Transmitted/incident =R/Ro
1-transmitted fraction = PAR intercepted.
Equation for the exponential curve
Y = -exp (-Ax)
X= LAI, A=K coefficient.
