Light interception

Question 1

What is light interception?

Answer 1

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.

Question 2

What is light quality?

Answer 2

Determined by wavelength. The ratio between red = 660 + 30 and far red 730 _+30

Question 3

PAR

Answer 3

Photosynthetically active radiation.
0.5 of total radiation.
400 - 700 of visable light spectrum absorbed

Question 4

How much infra red is reflected

Answer 4

700-3000

Question 5

What are photochromes

Answer 5

Sense the quality of light.
How these percepted the R:Fr ratio changes plant morpholgy.

Question 6

Red light

Answer 6

absorbed by the leaves

Question 7

1.

Far red

Answer 7

Pass through canopy to be reflected or transmitted to base of crop.

Question 8

Canopy closure (LAIc)

Answer 8

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.

Question 9

Yield as a function of incidient radiation.

Answer 9

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.

Question 10

Leaf area index

Answer 10

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.

Question 11

LAI effected by

Answer 11

Temp, N status, water & PP

Question 12

LAI interception

Answer 12

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.

Question 13

Critical LAI

Answer 13

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.

Question 14

Canopy architecture

Answer 14

How the leaves are arranged in a crop, varries LAIc.

Question 15

Wide leaves

Answer 15

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.

Question 16

Narrow leaf

Answer 16

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>

Question 17

PAR penetration through canopy.

Answer 17

Depends on reflection, thickness, size, shape and arrangement of leaves. Explain by K.

Question 18

What is K?

Answer 18

The extension coefficient to describe PAR penetration through the canopy. Senesitive to leaf angle.

Question 19

K is used in Beer’s law. What is beers law?

Answer 19

Describes the decline of light through the canopy. Can be measured by
R/Ro = 1 - exp(-K x LAI).

Question 20

R/Ro = 1-exp(-K x LAI) explain.

Answer 20

Fraction of light intercepted as a fractrion of the coefficient of extension and LAI.

Question 21

How to calculate R/Ro=1-exp(-K x LAI).

Answer 21

We know R/Ro from a sunscaner, we know LAI from deconstructive measurements. Isolate -K into the equation
Ln(R/Ro)x LAI

Question 22

Explain Ln(R/Ro) x LAI

Answer 22

Log of transmitted fraction of radiation.
For every increase in LAI there is a reduction in light penetrating through the canopy.

Question 23

Transmitted fraction.

Answer 23

Calculating LI.
Transmitted/incident =R/Ro
1-transmitted fraction = PAR intercepted.

Question 24

Equation for the exponential curve

Answer 24

Y = -exp (-Ax)
X= LAI, A=K coefficient.