Post on 20-Dec-2015
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Photosynthically Active Radiation Use Efficiency of Dactylis glomerata in a Hardwood
Silvopasture
Charlie Feldhake
Dave Belesky
Photosynthically Active Radiation Use Efficiency of Dactylis glomerata in a Hardwood
Silvograss-sward
Charlie Feldhake
Dave Belesky
USDA-ARSAppalachian Farming Systems
Research CenterBeaver, West Virginia
Appalachia is 23% larger than the state of California
Question 1: How efficientlydoes orchardgrass utilize PARat different PAR levelsunder deciduous trees?
Question 2: Do juvenile plantsfunction differently thanvernalized (mature) plants?
(0) Open Site(Eo) 2 m within forest edge(Ew) 7 m within forest edge(W) 30 m within forest
Grasses were grown in 15 cm dia. pots which wereplaced in the ground after bottoms were removedOne set placed in May 2001Another in August 2001 for harvesting in 20023 Harvested at 20 cm height, others clipped to 5 cm
Day of Year
120 140 160 180 200 220 240 260 280 300 320
Re
lati
ve
PA
R
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
PAR at EoPAR at EwPAR at W
2D Graph 2
Y D
ata
PA
R (
Mo
l m-2
d-1
)
0
10
20
30
40
50
60
70
PAR MaxPAR at OPAR at EoPAR at EwPAR at W
139 239 339 74 174
Day of Year
2001 2002
(b)
Table 1. Summer solstice (7-week average) actual and relative PAR.Measurement Site
O Eo Ew W MaxPAR (Mol m-2 d-1)
2001 39.7 18.7 9.7 4.9 59.32002 26.8 10.7 6.9 3.7 59.3
% of Open (100-Shade)2001 100 47 24 12 2002 100 40 26 14
% of Max2001 67 32 16 8 2002 45 18 12 6
Day of Year
Lea
f M
ass
(g)
0
1
2
3
4
OEoEwW
100 150 200 250 150 200 250 300
2001 2002
Day of Year
Pla
nt
Mas
s (g
)
0
10
20
30
40
50OEoEwW
100 150 200 250 150 200 250 300
2001 2002
Day of Year
leaf
/pla
nt
0.04
0.06
0.08
0.10
0.12
0.14
0.16OEoEwW
100 150 200 250 150 200 250 300
2001
2002
PAR Use Efficiency is equal to total PAR summed from the
previous harvest divided by dry leaf mass.
Day of Year
Lea
f M
ass/
PA
R (
g M
ol-1
)
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018OEoEwW
100 150 200 250 150 200 250 300
2001
2002
PAR Use Efficiency Eo/O Ew/W W/O
2001 1.4 3.4 3.0
2002 1.2 1.7 2.6
Given one of the most important objectives of agriculture is to
harvest solar radiation for human use, then C3 grass open pasture in a temperate, humid climate is not a very efficient way to do it.
But: These Grass Roots Were Not Competing With Tree Roots.
What Happens In The Real World?
Hour of Day
6 8 10 12 14 16 18 20
Re
lati
ve S
ola
r In
ten
sity
Above Pine
Below Pine
1
0
Leaf Growth Decreased With Daily PAR But Less Rapidly.
There Was Less Than A 2-Fold Increase In PAR Use Efficiency.
Hour
4 6 8 10 12 14 16 18 20 22
Rel
ativ
e P
AR
0
1 Between Black Locust
Under Black Locust
Leaf Growth Did Not Decrease With Daily PAR. There Was A 5-
Fold Increase In PAR Use Efficiency.
The Duration Of Daily PAR Is Important In Addition To The
Amount Of Daily PAR.
Forages Under Deciduous Trees Also Receive A Spring And
Autumn “Spike” In PAR That Does Not Happen Under Conifers
If you can utilize much of the solar radiation by trees midday
through early afternoon and during peak summer intensities you can substantially increase overall system solar radiation
harvesting efficiency.
Star PAR
Extra-Solar PAR contributes about 5 mg ha-1 yr-1 to corn grain yield.