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.