Journal
of Horticultural
Science & Biotechnology
(2004) 79 (5) 699-703
Measurements of net radiation absorbed by isolated acid lime trees
{Citrus latifolia Tanaka)
1
1
2
3
By L . R. A N G E L O C C T , N. A . V I L L A N O V A , M . A . C O E L H O F I L H O and E R. M A R I N
departamento de Ciências Exatas, Escola Superior de Agricultura "Luiz de Queiroz", Universidade
de São Paulo, CP 9, CEP 13418-900, Piracicaba, SP, Brazil
Centro Nacional de Pesquisa de Mandioca e Fruticultura, E M B R A P A , Cruz das Almas, BA, Brazil
Centro Nacional de Pesquisa de Monitoramento de Satélite, E M B R A P A , Campinas, SP, Brazil
(e-mail: lrangelo@carpa.ciagri.usp.br)
(Accepted 5 April 2004)
2
3
SUMMARY
B y using net radiometers mounted on a circular frame rotating around the canopy, measurements of total all-wave
radiation absorbed by t w o ' T a h i t i ' acid lime trees were carried out i n an orchard in Piracicaba, S ã o Paulo State, Brazil.
The rotating system around the canopy o f a tree was formerly idealized and used i n New Zealand, allowing integration
o f all-wave radiation and photosynthetically active radiation absorbed. I n an experiment i n December 1997, a first
device using six net radiometers mounted o n a light frame was used. A bigger device, more like the one used i n New
Zealand, in terms of the number of radiometers and the frame, w i t h a different torque system, was used i n another
tree on some days from July t o September 2000. The performance of b o t h devices is discussed, including the possible
error sources when using the first model (1997) and the problems of torque transmission on the second. Despite the
lack of a test to check the performance of the device and the problems presented i n the year 2000, the results confirm
the possibility of providing reliable measurements of the net radiation absorbed by isolated trees. Relations o f the net
radiation per unit area of projected canopy on the ground were determined with integrated values over different time
scales (from 15 min t o 24 h ) . U n i q u e relations between net radiation and incoming solar radiation were obtained for
both trees over several time scales. These relations are applicable only to high leaf density conditions and canopy
geometry similar to the used i n this study.
' T ' h e net radiation absorbed by a tree canopy is a
A determinant
variable
of
transpiration
and
photosynthesis, w i t h application i n a g r i c u l t u r a l and
environmental studies. I n tree species, it is i m p o r t a n t to
determine the relations o f the radiant energy with the
plants, which depend on the tree canopy geometry, leaf
area density, trees spacing and o t h e r factors that
d e t e r m i n e the losses and gains o f energy. The
measurements as well as the estimations are complex
due to the number o f factors involved.
Some papers have been w r i t t e n on the determination
of light interception by canopies, such as those of apple
trees (Charles-Edwards and Thornley, 1973; CharlesEdwards and Thorpe, 1976; Thorpe, 1978; W ü n s c h e et al.,
1995). I n New Zealand, M c N a u g h t o n et al. (1992) used a
device named a " w h i r l i g i g " , formed o f net radiometers
and quantum sensors mounted o n a circular frame. The
frame rotated a r o u n d a Robinia pseudoacacia
tree,
allowing integrated measurements of net radiation ( R n )
and photosynthetically active radiation ( P A R ) fluxes
passing through the surface enclosing the tree. Green
(1993) used this technique to estimate net radiation and
P A R absorbed by a walnut single tree. Further, Green
et al. (1995, 2001) and Green and M c N a u g h t o n (1997)
also used the technique i n studies with an apple tree.
In the present paper, results and measurements of net
•Author for correspondence.
radiation absorbed by the canopy of t w o trees of 'Tahiti'
acid lime (Citrus latifolia Tanaka) are presented and
discussed, using the " w h i r l i g i g " technique developed in
New Zealand. The relations between the canopy net
r a d i a t i o n and i n c o m i n g solar r a d i a t i o n are also
presented and discussed.
MATERIAL A N D METHODS
Data were obtained for two periods. The first was 12
days in December, 1997 and the other with a further 6 d
from the end o f July to September of 2000, in a 'Tahiti'
acid lime orchard, with tree spacing of 8.0 m x 7.0 m ,
g r o w i n g i n the " L u i z de Q u e i r o z " Campus o f the
University of S ã o Paulo, Piracicaba, S ã o Paulo State,
Brazil (latitude 2 2 ° 4 2 ' , longitude 4 7 ° 3 8 ' W, altitude
540 m above mean sea level).The orchard, surrounded in
the west and in the north by an eucalyptus windbreak 20
m tall, was irrigated by mini-sprinklers.To the south, there
was a mango orchard and l o w vegetation to the east.
In 1997, a six year old tree was used with a total leaf
area of 39.9 m , located about 25 m from the windbreak
to the west. The canopy was pruned just before the
system installation to eliminate branches exceeding the
limits of the frame, allowing its free movement. I n 2000,
a nine year o l d tree was used, located 14 m from the east
border o f the orchard, 38 m from the windbreak, with a
total leaf area o f 51.2 m , after the p r u n i n g to allow the
2
2
Acitl
lime net rndiutioii
absorption
by I wo vertical circles ami two horizontal ones (Figure
la), manufactured with a l u m i n u m tubes of I ) m m
outside diameter (Figure l a ) , rotated by a 0.25HP
electric motor, with direct transmission of the movement
by a reduction system attached directly to the upper pole
of the frame. The motor was held by an horizontal bar
attached to a mast from which the frame was suspended.
The mast was positioned so as to minimize shading the
tree.
1
The measurements in 2000 were performed using a
frame whose structure was composed o f two concentric
circles of mild steel lubes o f 40 m m outside diameter
(Figure l b ) . Hie circles were interconnected by small
bars of similar material and the outer tube was flattened
where the radioniclers were mounted. Pie circular frame
was mounted on a horizontal turntable, composed o f one
mild steel stationary circle mounted in I luce levelling
jacks. A b o v e this stationary circle, there was another
circle of flat-section steel fitted with nylon wheels resting
on the stationary circle.The upper circle and the vertical
frame rotated, powered by a I I I I * motor, with a
reduction gearbox. Torque was transmitted by a belt
drive from the driven pulley of the gearbox to the upper,
rotating circle. In both devices, the rotation speed of the
frame was about three revolutions per minute, as used by
McNaughton ci <;/. (1992).
In December 1997. six net radiometers R E B S
(Radiation and l.ncrgv Balance Systems. Seattle. W A ,
USA) model 0 * 7 were used, two fewer than the number
used in the New Zealand experiments. In 2000, eight net
radiometers were used. Hie radiometers used in l'W7
were used i m m e d i a t e l y after purchase, so the
calibrations factors supplied by the manufacturer were
used. In 2000. the net radiometers were calibrated
against a C N R I net radiometer ( K i p p & Z o n e n . Delft,
The Netherlands). McNaughton <•/ .//. (1992) found that
placing the sensor plate of the net radiometers in
non-horizontal positions in which the) were calibrated
did nol affeel theit calibration factors,
FIG. 1
Top: view of ihc rut.ilinir Ir.imc (without ihc ncl radiometers) used in
December 1997. Bottom:device used in 2000.
frame 10 rotate. The drip-line leaf area index (canopy
leaf area per ground area w i t h i n the plant's d r i p line) was
4.(>ft for the first and 3.09 for the second tree. Estimation
of c r o w n porosity, by the use o f frontal canopy
photographs taken from the four cardinal points with a
white sheet suspended vertically behind the canopy and
their image processing, showed the low average porosity
on a vertical plane traversing the canopy, 2% on the first
and 5% on the second tree.
The windbreak started to project shadows on the trees
between 1700 and 1730 hours (local lime).
Measurements in December I W 7 used a modified
rotational system based o n the one proposed I n
McNaughton el al. (1992). It consisted of a frame formed
The t e r m i n o l o g y and the calculation procedures
described by M c N a u g h t o n el al. (1992) were adopted.
The sensing sphere radius was 1.65 in lor the tree used in
1997 and 1 3 1 in in 2000. In 1997. the sensors were
mounted at equi-latitudinal intervals, at latitudes +75'.
+45". +15". -15 . —45 . -75 (positive: sensor above the
equatorial circle of the sphere: negative: below I . In 2000.
the equi-latitudinal disposition was adopted exactly as
used by M c N a u g h t o n el al. (1992) at latitudes of +78.75°,
+56.25°. +33.75°. +11.25°. -11.25°. -33.75°. -56.25°.
-78.75°.
The integration method proposed bv McNaughton
el al. (1992) to calculate the value of Rn over the sensing
sphere, was adopted, with weighting factors considering
ihc m o u n t i n g positions (fable 11.
C R - 1 0 X Dataloggers (Campbell Scientific. Logan. U T .
I I S A ) were used in 1997, and model 21-X in 2000.
IAIU I I
Prtunul UWC7I//MC ftiiiors tor etich mounting position itwil in the intetrillion itiUiilu\. \l. \2
YN* M-ipiential inountinv position for the ncl
radiometers, \ l being the upper
h.
I
\
n.134
O.IK.7
\
0.365
(1.221
\
0.501
D.326
\ :
\-
0.501
0.386
0.365
0.38ft
V
0.134
0.32ft
\~
\-
0.221 n.oh7
1.. R. A M ii I I I I c I , N . A . V I L I
\ N O V A . M . A . C O B L H O F l L l l o and
mounted on platforms fixed w> the rotating pari of the
turntable recorded signals from the sensors at a sample
rale of I 11/ and calculated averages every 15 m i n .
R l SI I I S A M ) D I S C U S S I O N
Figure 2 shows examples of the daytime course of
net radiation for each measurement position of the two
trees, w i t h averages every 15 m i n . A l t h o u g h the
measurements were also carried out at night, they are
not show n, because the net r a d i a t i o n differences
among the different measurement positions around the
canopy in the day were much more pronounced than at
night, due to the fact that daytime net radiation is
dominated I n short-wave r a d i a t i o n , which depends on
atmospheric t u r b i d i t y and the incidence angle o f the
sunbeam on the sensor plates, which explain the high
positive values of Rn a r o u n d midday at more positive
latitudes and slightly positive or negative at more
negative latitudes.
On the first tree with six net radiometers, values
during the course of the day varied around zero at - 4 5 ° .
becoming more negative at - 7 5 ° . O n the second tree,
with more sensors, values close to zero or slightlv
negative occurred at position 7 (latitude: -56.25 ) and
negative at position S (latitude: -7S.75 ). In a general
way. the variation patterns observed in each position can
he compared to those found by M c N a u g h t o n end. (1992)
for a single Robinia pseudoacacia tree on a sunny day.
with differences between the two cases related to the
number of sensors used, to geographical location, to
season, to leal density and to the canopy geometry.
A s affirmed by McNaughton el til. (1992), it is difficult
to evaluate the accuracy of the measurements by the
" W h i r l i g i g " system. In the present study, tests were not
done when the sensing sphere was totally empty to check
if the radiometers had matched
characteristics.
Theoretically, if they are matched, record zero should
occur when the sensing sphere is empty, but it depends
on the structure used and on the net r a d i o m e t e r
placemen! and performance.
McNaughton <•/ ul. (1992) concluded that
in their
F. R. M \ K I N
701
system, the zero deviation was smaller than 5".. of the
radiation absorbed d u r i n g midday, lite type o l structure
used m 2000 had little change in relation to the one used
in New Zealand, which is w i n we can also admit thai in
our case the zero deviation could have the same value.
The structure used in 1997 was mounted with steel tubes
of a smaller diameter w h i c h could p r o b a b l y have
interfered less for net radiation than the one used in New
Zealand and in our 2000 experiment. In 1997. the
presence of an additional circular tube in the horizontal
plane and another in the vertical could have increased
the structural effect on the record zero. Rut. based on the
results of McNaughton ct til. (1992). we assume thai the
total absorption o l all-wave radiation of our devices was
not a serious problem.
In relation to the net r a d i a t i o n measurements.
McNaughton ft til. (1992) did not obtain reliable results
when Ihey used sensors of several ages ami different
manufacturers, but in 1997 we used brand-new
equipment of a single manufacturer. In 2000. all the
sensors useil were re-calibrated.
The use of six net radiometers in December 1997 is
another factor that may have increased the measurement
errors lor the canopy, when compared with the use of
eight sensors. The tact of the sensing sphere railius of the
" W h i r l i g i g " of 1997 was a little smaller than Ihe one used
in New Zealand could have slightlv minimized the
problems caused by Ihe use o f only six net radiometers,
but the difference between the radii o f the sensing
sphere (0.20 m ) of the two devices was too small. The
sensing sphere radius of the " W h i r l i g i g " used in 2000 was
almost (1.5 m bigger than Ihe one used in New Zealand,
so the calculation procedure used for integrating net
radiation values can result in more errors than those
obtained in thai country. M o r e net radiometers would
improve the performance of the devices, mainly in 199"
TTie frame used in 1997 was lighter and different from
Ihe one used in 2000. which helped its installation, but
the suspended system can oscillate a little when the wind
is strong. However, most of the time winds were more
gentle, excepting on December 14. 15. Hi and 19. when
strong winils happened at short time intervals, reaching
speed between 30 k m h and 45 km h . Illis first
" W h i r l i g i g " functioned continuously for several days
without problems. Nevertheless, to avoid the problem of
oscillation, a turntable would be preferable.
:
DEC 14,1987
C~
1
400
IK
600
500
400
130«
LOCAL
On the other hand, the device used in 2000 showed
problems of torque transmission, caused by chain slip.
Sometimes, tension applied to stop slippage resulted in
stressing and failure o f the gearbox. In consequence,
there were many incomplete days of measurement and
time loss to r e p a i r the system, w i t h a worse
performance than that obtained using Ihe New Zealand
transmission system. A c c o r d i n g to M c N a u g h t o n ct al.
(1992). t h e i r system showed adequate mechanical
performance allowing continuous measurements for
periods up to two weeks.
12CC 1433 1t00 1M«
TMEim
JUL36.200C
- W
I
\
L
3 V
,00
a o
103
200
300
Daily
BOC
10UJ 1200 S400 1600 1S00|
LOCAL TIME (ht>
course
800 10O0 1J00 I4C0 1600 1600
LOCAL TIME irif,
Flo. 2
measured net r a d i a t i o n h\ ( l i e s e n s o r s
l o r s e v e r a l days i n l<W7 (top) a n d 2(100
of the
inounlinc. posiiion.
in
each
(below).
N u m b e r s following Ihe lines represent (he m o u n l i u c posiiion. from (he
up|>cr l o t h e l o w e s t r a d i o m e t e r .
Although the problems mentioned and the lack of a
better test, in our o p i n i o n the results confirm the
conclusion ol McNaughton et al. (1992) thai the devices
can give reliable and accurate measurements of net
radiation, with the possibility of testing models for
all-wave radiation and I ' A R absorbed by trees and their
application
in
studies
of
transpiration
and
< 10
el's
a 5
Kt.yvr »w
-.
J
r = 0.930
10
2
30
25
15
20
Rs (MJ m" d" )
1
-0.2
2
Rs(MJ m" 15min"')
-0.3
2
30 m i n , 1 h and for the whole daytime penou.
A number o f f i t t i n g curves were tested using the
p r o g r a m " T a b l e c u r v e " . A s t h e t w o t r e e canopy
dimensions were different, w h i c h affects the integrated
values o f net r a d i a t i o n for each tree, we used the value
of R n divided by the projected canopy area ( P A ) on the
g r o u n d ( R n / P A ) as t h e y-variable. G o o d relations
between R n / P A and Rs, were f o u n d i n the 24 h and i n
the d a y t i m e periods, w i t h significant linear f i t t i n g
(Figure 3 ) . I t is k n o w n that Rs is the m a i n variable
which determines the a m o u n t o f net radiation falling on
plant canopies i n the d a y t i m e , explaining the best
correlations f o u n d i n this p e r i o d . A l t h o u g h the linear
f i t t i n g was good i n all integration scales for the pooled
values o f the t w o trees, the linear f i t t i n g was
advantageously replaced by a sigmoid curve in the
hourly, 30 m i n and 15 m i n scales (Figure 3 ) , w h i c h
allowed a better f i t t i n g for lower values o f i n c o m i n g
solar r a d i a t i o n i n the beginning as well as at the end of
the daytime, when R n shows l o w values, negative or
positive ones. F u r t h e r m o r e , the sigmoid curve fits better
for h i g h values at midday.
Such results indicate the possibility of estimating net
radiation intercepted by trees o n these time scales from
two simple measurements, that is, i n c o m i n g solar
radiation and the projected canopy area o n the ground.
For the smaller tree here used, Angelocci et al. (1999)
found good linear relations for the daily and daytime
values between the integrated net radiation and the net
radiation measured over grass. B u t , contrary to what was
observed here, these relations were
seasonally
dependent; so, the unique relations for both trees and
different seasons here reported represent an advantage.
1
Rs (MJ m" 30 min" )
However, we should emphasize that the relation found
in the present study can be applied only to trees w i t h
(jfld growth conditions observed i n this
jfyrjjj mih very dense"
ll
expl-(x-0.816)/0.753]
tree studied in M were twice astyi!M ( f a i
tree used in 1997, and almost identical to (lie tehtk
h
•0.5
^ o T o ! ,
2.0
3.0
40
2
Rs (MJ m" hr"')
e
T°
P y
a r e a p r o j e c t e d o n , h e
ground (or
also, the lateral area o f the crown) o f both trees T h i
an -nd.cat.on that the foliage density led to a verZ h h
and equivalent a t t e n u a t i o n ( p r o b a b l y almost
he
m a x i m u m ) o f solar radiation by the two c L 2 2 such
e
FIG 3
the geometric relations mentioned above
Iea?a rl r?nH
r
a v o i d t h e p r o b , e m s o b s e r v e d in
°-
torL V
^ r . m e n t s we intend to modify the
torque transm.ss.on system of the bigger ••Whirhgig"
r
Witl
!
g
e
°
m
C
,
r
i
e
s
a
n
d
W
drip-line
L . R . A N G E L O C C I , N . A . V I L L A N O V A , M . A . C O E L H O F I L H O and F. R . M A R I N
density different from those observed in this study. But it
seems that the observed relations may be applied t o lhe
other similar trees of the studied orchard.
703
The first two authors thank lhe Consilho Nacional di
Desenvolvimento C i e n t í f i c o e T e c n o l ó g i c o f o r their
fellowship.
REFERENCES
ANGELOCCI, L. R., V I L L A NOVA, N . A.and SENTELHAS, P. C. (1999).
GREEN, S. R. and MCNAUGHTON, K . G . (1997). Modelling effective
Medida do saldo de energia radiante na copa de lima ácida
"Tahiti' e sua relação com a medida sobre gramado. Anais do XI
Congresso Brasileiro de Agromeleorologia, Florianópolis, 1999.
stomatal resistance for calculating transpiration from an apple
tree. Agricultural and Forest Meteorology, 8 3 , 1 - 2 6 .
C D - R O M , 1292-98.
CHARLES-EDWARDS, D . A . and THORNLEY, J. H . M . (1973). Light
interception by an isolated plant: a simple model. Annals of
Botany, 37,919-28.
CHARLES-EDWARDS, D . A . and THORPE, M. R. (1976). Interception
of diffuse and direct-beam radiation by a hedgerow apple
orchard. Annals of Botany, 4 0 , 6 0 3 - 1 3 .
GREEN, S. R. (1993). Radiation balance, transpiration and photosynthesis of an isolated tree. Agricultural and Forest
Meteorology, 64,201-21.
GREEN, S. R., MCNAUGHTON, K. G., GREER, D . H. and MCLEOD, D . J.
(1995). Measurement of the increased P A R and net all wave
radiation absorption by an apple tree caused by applying a
reflective ground covering. Agricultural and Forest
Meteorology, 76,163-83.
GREEN, S. R., GREER, D. H . , WÜNSCHE, J. N . and CASPARI, H . (2001).
Measurements of light interception and utilization in an apple
orchard. Acta llorticulturae, 557, 369-76.
MCNAUGHTON, K . G , GREEN, S. R., BLACK, T . A . , T Y N A N , B . R .
and EDWARDS, W . R . N. ( 1 9 9 2 ) . Direct measurement of net
radiation and photosynthetically active radiation absorbed
by a single tree. Agriculture and Forest Meteorology, 62,
87-107.
THORPE, M. R. (1978). Net radiation and transpiration of apple
trees in rows. Agricultural Meteorology, 19,41-57.
WUNCHE.J. N„ LAKSO, A . N. and ROBINSON.T L . (1995). A compar-
ison of four methods for estimating total light interception by
apple trees of various forms. HortScience, 30, 272-6.
Pesquisa Periódicos
ragina i ae i
PESQUISA DE PERIÓDICO POR TÍTULO
Titulo:
Relação de Periódicos - Classificação relativa a dados de 2003
ISSN
0022-1589
Critérios de Classificação do Qualls por Área \
Area de Avaliação
Classificação Circulação
Título
Journal of Horticultural Science & Biotechnology
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