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The micrometeorology of a pigeon pea stand
Agricultural Meteorology, 17(1976)205--210 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
THE MICROMETEOROLOGY OF A PIGEON PEA STAND
E. G. TAITT and J. A. SPENCE
Grain Legume Programme, University of the West Indies, St. Augustine (Trinidad) (Received February 20, 1976; accepted April 26, 1976)
ABSTRACT Taitt, E. G. and Spence, J. A., 1976. The micrometeorology of a pigeon pea stand. Agric. Meteorol., 17:205--210. Data are presented on the microclimate above the crop canopy of a large stand of pigeon pea (Cajanus cajan) growing at the Field Station of the University of the West Indies, Trinidad. There are also additional data on certain physiological parameters -- stomatal resistance and leaf water potential. Complementary data from potted plants whose soil moisture was controlled are also presented.
INTRODUCTION The search is o n t o find o u t w h e t h e r t h e r e are varieties o f pigeon pea w h i c h can t o l e r a t e or avoid t h e e f f e c t o f d r o u g h t while giving a reasonable yield at the same time. O t h e r t r o p i c a l l y g r o w n crops -- c o t t o n , s o r g h u m -- have s h o w n wide variation in the value of s t o m a t a l resistance and leaf w a t e r p o t e n t i a l (Sharpe, 1973). A s t u d y is m a d e o f the soil w a t e r status to discover its e f f e c t on these p l a n t p a r a m e t e r s . MATERIAL AND METHODS The e x p e r i m e n t was c o n d u c t e d at the University Field Station d u r i n g the " d r y s e a s o n " o f 1 9 7 4 and 1 9 7 5 . F o r the field e x p e r i m e n t , plants were a p p r o x i m a t e l y 0.15 m a p a r t in each r o w and the r o w spacing was a b o u t 0.45 m. This resulted in a p l a n t d e n s i t y o f a b o u t 1 5 , 0 0 0 plants per hectare. The area o f the field was a b o u t 0.6 h a divided into f o u r blocks each having d i m e n s i o n s 1 8 0 m × 8 m. Seeds o f the pigeon pea (Cajanus cajan) were s o w e d d u r i n g the s h o r t - d a y length p e r i o d ( F i g . l ) on 2 2 n d J a n u a r y 1 9 7 5 and the soil m o i s t u r e sampling was started. Probes a n d masts were installed f o r the c o l l e c t i o n o f d a t a as follows: p r o b e s i n c l u d e d soil flux plates to m e a s u r e soil h e a t flux, t h e r m i s t o r s to m e a s u r e soil t e m p e r a t u r e ; masts f o r the p u r p o s e o f m o u n t i n g p s y c h r o m e t e r s to m o n i t o r v a p o u r pressure and t e m p e r a t u r e at d i f f e r e n t levels above
206
crop canopy. Daytime net radiation, temperature, humidity and light intensity over the stand were recorded continuously with a 12-channel recorder* (potentiometer) on the days when runs were made. Net radiation was measured with a shielded net radiometer m o u n t e d 1.4 m above ground. Samples of leaf area and dry weights were taken on April 21 and 29, and on
13
1
8 12
d~
N
D
J Month
F M of yeqr
A
M
Fig.1. Day length at geographical site.
May 7 and 13, 1975. The leaf area was recorded from 10 plants removed from the field at random, using a commercial type of leaf area meter-~. The soil water potential of the root zone was deduced from the soil retention curve for the site in conjunction with soil moisture percentage by weight sampled at three different levels 0.15, 0.30 and 0.45 m. Leaf diffusion resistances were measured with a commercially available porometer$. Measurements were made every 15 min during the morning and afternoon periods and the total leaf diffusion resistance calculated, using the formula: 1 rL
1
--
rad
+
1 rab
where r L leaf diffusion resistance; r~d = diffusion resistance of the adaxial surface; and r~b = diffusion resistance of the abaxial surface. The leaves chosen were four sunlit leaves since the leaf resistance of the shade leaves was n o t appreciably different from that of the sunlit leaves. Leaf water potential was determined b y the pressure chamber technique of Scholander et al. (1965). The potential was usually measured on the four sunlit leaves chosen for diffusion resistance measurement. =
* Eric Weinhart, T.E.M. Sales (England) t Hayashi Danko, automatic area meter, model A A I I 5 (Japan) $ Delta-T Systems (England)
207
Estimates o f e v a p o r a t i o n using the M o n t e i t h t y p e ( M o n t e i t h , 1 9 6 5 ) e q u a t i o n were o b t a i n e d f o r t h e s t a n d a n d t h e B o w e n ratio ~ c a l c u l a t e d theref r o m using t h e relation that/3 is t h e ratio of sensible h e a t H t o e v a p o r a t i o n ~,E ( B o w e n , 1 9 2 6 ) . Mean values f o r ~ a n d ~E are given in Table I. TABLE I Mean c o m p u t e d values for e v a p o r a t i o n }~E a n d B o w e n ratio ~ for several days in 1976
Date May May May May May
6 8 14 22 26
~kE *
fl
(R N - G )*
9.3 7.0 5.8 5.8 5.2
0.33 0.52 0.56 0.65 0.25
12.7 10.8 8.5 9.5 6.5
* In mcal. c m -2 sec -~.
The f o r m u l a used is: A(Rn - G) + pc[e~(T)
- e]/r a
~E=
A+7
1+
where ~E = e v a p o r a t i o n (cal. c m -2 sec -1 ); A = slope of the s.v.p, curve at air t e m p e r a t u r e ; Rn = n e t r a d i a t i o n (cal. c m -2 sec -1 ); G = soil h e a t flux (cal. c m -2 sec -1 ); p c = v o l u m e h e a t c a p a c i t y o f d r y air (cal. c m -3 °C -1 ); e s ( T ) = s a t u r a t i o n v a p o u r pressure at t e m p e r a t u r e T; e = v a p o u r pressure o f air at h e i g h t z; ra = a t m o s p h e r i c diffusion resistance (sec c m -1 ); rs = r r , / L A I = c a n o p y resistance (sec c m - 1 ) ; L A I = leaf area i n d e x ; 7 = p s y c h r o m e t r i c c o n s t a n t ; r L = leaf diffusion resistance (sec c m -~ ). T h e r e were also c o n t r o l l e d g r e e n h o u s e e x p e r i m e n t s w h e r e p o t s were bagged ( p o l y t h e n e bags) a n d plants irrigated at certain p r e d e t e r m i n e d intervals. T h e r e were f o u r t r e a t m e n t s and five replicates of each t r e a t m e n t . D a t a were c o l l e c t e d o n the variation o f s t o m a t a l resistance with t r e a t m e n t . Stress treatm e n t s were as follows: t r e a t m e n t 1 - - p l a n t s were w a t e r e d three t i m e s w e e k l y ; t r e a t m e n t 2 - - plants were w a t e r e d o n c e w e e k l y ; t r e a t m e n t 3 -- e v e r y n i n e t e e n d a y s ; a n d t r e a t m e n t 4 - - plants were n o t irrigated. R E S U L T S AND D I S C U S S I O N
S t o m a t a l resistance in the u p p e r epidermis was always greater t h a n t h a t in the lower. In t h e field this differential was far l o w e r t h a n t h a t f o u n d with
208
potted plants (Figs.2 and 3) possibly due to the high degree of stress obtained with the latter. It would seem t hat the stomata in the lower leaf surface would be a useful indicator of the onset of stress in view of the fact that resistance of the u p p er surface stomata remained relatively high t h r o u g h o u t the day b o t h in the field e x p e r i m e n t and in the p o t t e d plant experiment. One noticeable p h e n o m e n o n was that the upper stomata showed frequently the ability to close before those on the lower surface. * \N
~7 E
]-8 ......- / i - 1 0
\\+
20
\ ~
J'~" /
I -!4 J,_16 ®i I%.
4.
8 ®
lO
®
2 v 5 E o
J
10
11
12 13 Time of day
14
15
1
Fig. 2. Diurnal variation of stomatal resistance (upper and lower epidermis) and leaf water potential in the field on 8th May, 1975. × = leaf water potential; ~)= adaxial resistance; @ = abaxial resistance. 35
3O
25
20 c
2
E 0
9
10
11 12 13 Local time of doy
14
15
16
Fig. 3. Stomatal resistanee Oower e ~ e r m i s ) of potted plants for four treatments (two dry; ×, . ; two wet" A, @).
209 The value of stomatal resistance in the field e x p e r i m e n t indicated t hat the plants were n o t u nder as severe a stress as exhibited by the results for the
'E X
.<
7
: ~
6
L 1~
1'~
1~
1'3
1:4
15
16
T i m e of doy
Fig.4. Evaporation from crop on 8th May 1975.
25
__[---1
T 20 'E
10 L_
o
D
J
F Month
M A of y e o r
M
Fig.5. Incoming solar variation for the growing period of the crop. p o t t e d plants and a m o d e r a t e l y high value for the transpiration rate would be e x p e c t e d (see Fig.4) albeit a dry atmosphere linked with high radiation (Fig.5) values. The field plants were e x p e c t e d to be under severe moisture stress u n d er these conditions, but no visible signs were revealed after measurements of the stomatal resistance were examined. One probable answer was th at there was residual water in the soil originating from a water table producing a capillary fringe placing water at the disposal of the plants' roots or th at the soil had not dried out appreciably from the previous wet season because of its p o o r conductivity (see Fig.6). Here the available water was d eter min ed using results of soil-moisture sampling, bulk density and the
210
soil-moisture retention curve assuming t h a t soil water at the permanent wiltin~ point is not "available" to the plant.
IO v
2
JAN
FEB
MAR Period of g r o w t h
APR
MAY
Fig.6. Available soil water in the t o p 45 cm layer
ACKNOWLEDGEMENT
The work described was part of a Grain Legume Programme conducted at
the University of the West Indies, Trinidad, and sponsored by the Bri~sh Overseas Development Ministry. REFERENCES Bowen, I. S., 1926. The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev., 27: 779--787. Monteith, J. L., 1965. Evaporation and environment. Syrup. Soc. Exp. Biol., 19: 205--234. Scholander, P. F., Hammel, H. T., Bradstreet, E. D. and Hemingsen, E. A., 1965. Sap pressure in vascular plants. Science, 148: 339--346. Sharpe, P. J., 1973. Adaxial and abaxial stomatal resistance of cotton in the field.Agron. J., 65: 570--574.
THE MICROMETEOROLOGY OF A PIGEON PEA STAND
E. G. TAITT and J. A. SPENCE
Grain Legume Programme, University of the West Indies, St. Augustine (Trinidad) (Received February 20, 1976; accepted April 26, 1976)
ABSTRACT Taitt, E. G. and Spence, J. A., 1976. The micrometeorology of a pigeon pea stand. Agric. Meteorol., 17:205--210. Data are presented on the microclimate above the crop canopy of a large stand of pigeon pea (Cajanus cajan) growing at the Field Station of the University of the West Indies, Trinidad. There are also additional data on certain physiological parameters -- stomatal resistance and leaf water potential. Complementary data from potted plants whose soil moisture was controlled are also presented.
INTRODUCTION The search is o n t o find o u t w h e t h e r t h e r e are varieties o f pigeon pea w h i c h can t o l e r a t e or avoid t h e e f f e c t o f d r o u g h t while giving a reasonable yield at the same time. O t h e r t r o p i c a l l y g r o w n crops -- c o t t o n , s o r g h u m -- have s h o w n wide variation in the value of s t o m a t a l resistance and leaf w a t e r p o t e n t i a l (Sharpe, 1973). A s t u d y is m a d e o f the soil w a t e r status to discover its e f f e c t on these p l a n t p a r a m e t e r s . MATERIAL AND METHODS The e x p e r i m e n t was c o n d u c t e d at the University Field Station d u r i n g the " d r y s e a s o n " o f 1 9 7 4 and 1 9 7 5 . F o r the field e x p e r i m e n t , plants were a p p r o x i m a t e l y 0.15 m a p a r t in each r o w and the r o w spacing was a b o u t 0.45 m. This resulted in a p l a n t d e n s i t y o f a b o u t 1 5 , 0 0 0 plants per hectare. The area o f the field was a b o u t 0.6 h a divided into f o u r blocks each having d i m e n s i o n s 1 8 0 m × 8 m. Seeds o f the pigeon pea (Cajanus cajan) were s o w e d d u r i n g the s h o r t - d a y length p e r i o d ( F i g . l ) on 2 2 n d J a n u a r y 1 9 7 5 and the soil m o i s t u r e sampling was started. Probes a n d masts were installed f o r the c o l l e c t i o n o f d a t a as follows: p r o b e s i n c l u d e d soil flux plates to m e a s u r e soil h e a t flux, t h e r m i s t o r s to m e a s u r e soil t e m p e r a t u r e ; masts f o r the p u r p o s e o f m o u n t i n g p s y c h r o m e t e r s to m o n i t o r v a p o u r pressure and t e m p e r a t u r e at d i f f e r e n t levels above
206
crop canopy. Daytime net radiation, temperature, humidity and light intensity over the stand were recorded continuously with a 12-channel recorder* (potentiometer) on the days when runs were made. Net radiation was measured with a shielded net radiometer m o u n t e d 1.4 m above ground. Samples of leaf area and dry weights were taken on April 21 and 29, and on
13
1
8 12
d~
N
D
J Month
F M of yeqr
A
M
Fig.1. Day length at geographical site.
May 7 and 13, 1975. The leaf area was recorded from 10 plants removed from the field at random, using a commercial type of leaf area meter-~. The soil water potential of the root zone was deduced from the soil retention curve for the site in conjunction with soil moisture percentage by weight sampled at three different levels 0.15, 0.30 and 0.45 m. Leaf diffusion resistances were measured with a commercially available porometer$. Measurements were made every 15 min during the morning and afternoon periods and the total leaf diffusion resistance calculated, using the formula: 1 rL
1
--
rad
+
1 rab
where r L leaf diffusion resistance; r~d = diffusion resistance of the adaxial surface; and r~b = diffusion resistance of the abaxial surface. The leaves chosen were four sunlit leaves since the leaf resistance of the shade leaves was n o t appreciably different from that of the sunlit leaves. Leaf water potential was determined b y the pressure chamber technique of Scholander et al. (1965). The potential was usually measured on the four sunlit leaves chosen for diffusion resistance measurement. =
* Eric Weinhart, T.E.M. Sales (England) t Hayashi Danko, automatic area meter, model A A I I 5 (Japan) $ Delta-T Systems (England)
207
Estimates o f e v a p o r a t i o n using the M o n t e i t h t y p e ( M o n t e i t h , 1 9 6 5 ) e q u a t i o n were o b t a i n e d f o r t h e s t a n d a n d t h e B o w e n ratio ~ c a l c u l a t e d theref r o m using t h e relation that/3 is t h e ratio of sensible h e a t H t o e v a p o r a t i o n ~,E ( B o w e n , 1 9 2 6 ) . Mean values f o r ~ a n d ~E are given in Table I. TABLE I Mean c o m p u t e d values for e v a p o r a t i o n }~E a n d B o w e n ratio ~ for several days in 1976
Date May May May May May
6 8 14 22 26
~kE *
fl
(R N - G )*
9.3 7.0 5.8 5.8 5.2
0.33 0.52 0.56 0.65 0.25
12.7 10.8 8.5 9.5 6.5
* In mcal. c m -2 sec -~.
The f o r m u l a used is: A(Rn - G) + pc[e~(T)
- e]/r a
~E=
A+7
1+
where ~E = e v a p o r a t i o n (cal. c m -2 sec -1 ); A = slope of the s.v.p, curve at air t e m p e r a t u r e ; Rn = n e t r a d i a t i o n (cal. c m -2 sec -1 ); G = soil h e a t flux (cal. c m -2 sec -1 ); p c = v o l u m e h e a t c a p a c i t y o f d r y air (cal. c m -3 °C -1 ); e s ( T ) = s a t u r a t i o n v a p o u r pressure at t e m p e r a t u r e T; e = v a p o u r pressure o f air at h e i g h t z; ra = a t m o s p h e r i c diffusion resistance (sec c m -1 ); rs = r r , / L A I = c a n o p y resistance (sec c m - 1 ) ; L A I = leaf area i n d e x ; 7 = p s y c h r o m e t r i c c o n s t a n t ; r L = leaf diffusion resistance (sec c m -~ ). T h e r e were also c o n t r o l l e d g r e e n h o u s e e x p e r i m e n t s w h e r e p o t s were bagged ( p o l y t h e n e bags) a n d plants irrigated at certain p r e d e t e r m i n e d intervals. T h e r e were f o u r t r e a t m e n t s and five replicates of each t r e a t m e n t . D a t a were c o l l e c t e d o n the variation o f s t o m a t a l resistance with t r e a t m e n t . Stress treatm e n t s were as follows: t r e a t m e n t 1 - - p l a n t s were w a t e r e d three t i m e s w e e k l y ; t r e a t m e n t 2 - - plants were w a t e r e d o n c e w e e k l y ; t r e a t m e n t 3 -- e v e r y n i n e t e e n d a y s ; a n d t r e a t m e n t 4 - - plants were n o t irrigated. R E S U L T S AND D I S C U S S I O N
S t o m a t a l resistance in the u p p e r epidermis was always greater t h a n t h a t in the lower. In t h e field this differential was far l o w e r t h a n t h a t f o u n d with
208
potted plants (Figs.2 and 3) possibly due to the high degree of stress obtained with the latter. It would seem t hat the stomata in the lower leaf surface would be a useful indicator of the onset of stress in view of the fact that resistance of the u p p er surface stomata remained relatively high t h r o u g h o u t the day b o t h in the field e x p e r i m e n t and in the p o t t e d plant experiment. One noticeable p h e n o m e n o n was that the upper stomata showed frequently the ability to close before those on the lower surface. * \N
~7 E
]-8 ......- / i - 1 0
\\+
20
\ ~
J'~" /
I -!4 J,_16 ®i I%.
4.
8 ®
lO
®
2 v 5 E o
J
10
11
12 13 Time of day
14
15
1
Fig. 2. Diurnal variation of stomatal resistance (upper and lower epidermis) and leaf water potential in the field on 8th May, 1975. × = leaf water potential; ~)= adaxial resistance; @ = abaxial resistance. 35
3O
25
20 c
2
E 0
9
10
11 12 13 Local time of doy
14
15
16
Fig. 3. Stomatal resistanee Oower e ~ e r m i s ) of potted plants for four treatments (two dry; ×, . ; two wet" A, @).
209 The value of stomatal resistance in the field e x p e r i m e n t indicated t hat the plants were n o t u nder as severe a stress as exhibited by the results for the
'E X
.<
7
: ~
6
L 1~
1'~
1~
1'3
1:4
15
16
T i m e of doy
Fig.4. Evaporation from crop on 8th May 1975.
25
__[---1
T 20 'E
10 L_
o
D
J
F Month
M A of y e o r
M
Fig.5. Incoming solar variation for the growing period of the crop. p o t t e d plants and a m o d e r a t e l y high value for the transpiration rate would be e x p e c t e d (see Fig.4) albeit a dry atmosphere linked with high radiation (Fig.5) values. The field plants were e x p e c t e d to be under severe moisture stress u n d er these conditions, but no visible signs were revealed after measurements of the stomatal resistance were examined. One probable answer was th at there was residual water in the soil originating from a water table producing a capillary fringe placing water at the disposal of the plants' roots or th at the soil had not dried out appreciably from the previous wet season because of its p o o r conductivity (see Fig.6). Here the available water was d eter min ed using results of soil-moisture sampling, bulk density and the
210
soil-moisture retention curve assuming t h a t soil water at the permanent wiltin~ point is not "available" to the plant.
IO v
2
JAN
FEB
MAR Period of g r o w t h
APR
MAY
Fig.6. Available soil water in the t o p 45 cm layer
ACKNOWLEDGEMENT
The work described was part of a Grain Legume Programme conducted at
the University of the West Indies, Trinidad, and sponsored by the Bri~sh Overseas Development Ministry. REFERENCES Bowen, I. S., 1926. The ratio of heat losses by conduction and by evaporation from any water surface. Phys. Rev., 27: 779--787. Monteith, J. L., 1965. Evaporation and environment. Syrup. Soc. Exp. Biol., 19: 205--234. Scholander, P. F., Hammel, H. T., Bradstreet, E. D. and Hemingsen, E. A., 1965. Sap pressure in vascular plants. Science, 148: 339--346. Sharpe, P. J., 1973. Adaxial and abaxial stomatal resistance of cotton in the field.Agron. J., 65: 570--574.