Effect of shade on the growth and yield of tomato plants

Abstract

Tomato seedlings (Lycopersicon esculentum Mill.) cv. Prigade were transplanted in July, 1994 in a well N fertilized soil which was fertiled with P and K. Shade screen was suspended at 1.5 m above the plants 10 days after transplanting to provide 30% shade. North and south sides were left open to provide good ventilation while the east and west sides were completely covered with the screens. Results showed that shade has a significant effect on main stem length and leaf area but not on leaf number or intercepted Photosynthetically Active Radiation (PAR). Shade also reduced total dry matter production significantly. Air and leaf temperatures under shade conditions were lower than that of the open field during day time and average 2°C, while it was higher under shade conditions than that of the open field during the night. Data show that applying 30% shade to tomato plants didn't affect fruit yield under the experiment conditions. The results of this work and other works showed that shade didn't affect tomato fruit yield consistently and its use is not justified. Meanwhile, Shade can be used to improve fruit quality such as reducing sun burn.

Full text

EFFECT OF SHADE ON THE GROWTH AND YIELD OF TOMATO PLANTS
A.M.R. Abdel-Mawgoudl , S.O. EI-Abd
l,
S.M. Singer
l,
A.F. Abou-Hadid+ , T.e. Hsiao-
IHorticulture Res. Dept., National Res. Cent, Dokki, Cairo, Egypt
2Horticulture Dept., Fac. Agric., Ain Shams Univ., Cairo, Egypt
3LAWR Dept., Univ. of California, Davis, CA 95616, USA
Abstract
Tomato seedlings (Lycopersicon esculentum Mill.) cv. Prigade were transplanted in July,
1994 in a well N fertilized soil which was fertiled with P and K. Shade screen was
suspended at 1.5 m above the plants 10 days after transplanting to provide 30% shade.
North and south sides were left open to provide good ventilation while the east and west
sides were completely covered with the screens. Results showed that shade has a
significant effect on main stem length and leaf area but not on leaf number or intercepted
Photosynthetically Active Radiation (PAR). Shade also reduced total dry matter
production significantly. Air and leaf temperatures under shade conditions were lower
than that of the open field during day time and average 2°C, while it was higher under
shade conditions than that of the open field during the night. Data show that applying
30% shade to tomato plants didn't affect fruit yield under the experiment conditions. The
results of this work and other works showed that shade didn't affect tomato fruit yield
consistently and its use is not justified. Meanwhile, Shade can be used to improve fruit
quality such as reducing sun burn.
1. Introduction
Temperature plays an important role in plant growth and productivity. Tomato plant
productivity is limited to a large degree because of high temperatures in many regions in
the world. Studies have showed different effects of high temperature on growth and
productivity of tomato plants. High day and night temperature resulted in faster stem
growth giving thin stems and many trusses with weak flowers (Abdalla and Verkerk,
1968). Smith (1932) reported that high temperature is a significant factor contributing to
tomato blossom drop which may have been caused by reduction in viability and
effectiveness of the pollen produced at high temperature. Reduction in fruit set by
disturbing the process of gametogensis and efficiency of the fertilization is another effect
of high temperatures on tomato, (Iwahori and Takahashi.I 964; Smith and Cochran 1935;
Johnson and Hall 1953; Iwahori 1965, 1966
&
1967). Although many studies concluded
that night temperature is the major factor that affect fruit set, it was found that high day
temperature also reduced fruit set (Howlett 1962).
Shading was often suggested as a solution to overcome the effects of high
temperature. El-Gizawy et al., (1992) mentioned that increasing shade resulted in
increasing tomato fruit yield with best results when applying 35% shade. Rylski (1986)
found that applying 25% shade to pepper plants resulted in yield increase. However,
Russo (1993) reported that shade didn't increase tomato fruit yield consistently and its
use is not justified.
The aim of this study is to investigate the effect of shading on the growth of tomato
plants growing in the summer season to asses the benefits of shade in terms of improved
crop yield.
Strategies for Mark. Orient. Greenhouse Production
Eds. A.F. Abou-Hadid. R.A. Jones
Acta HOM. 434, ISHS 1996
313

2. Materials and methods
Tomato seedlings (Lycopersicon esculentum Mill) cv. Prigade were transplanted in
July, 1994 in a spacing 35 ern between plants and 75 cm between rows. Two trails with
two weeks interval was carried out. The soil was yolo clay loam, fertile with P and K,
fertilized before transplanting with 150 N /h. The area was divided into two treatments
with three replicates. The treatments were normal light and 30 % shade provided by
using black polyethylene nets. The nets were suspended at 1.5 m height using metal bars
and wires. The nets also covered both east and west sides while north and south sides
were left open to provide good ventilation. Irrigation was carried out on a regular basis
(approximately 14 days) so the plants would not be exposed to any degree of water
stress. Leaf water potential was measured using a pressure chamber. Light interception
was measured at mid day using a l-m long photosynthetically active radiation (PAR)
sensor ( Li-191, LICOR Inc., Lincoln, NE, U.S.A.). Leaf temperature was measured
using fine (0.03 mm diameter) constant and copper thermocouples (three thermocouples
for each replicate) glued to the lower side of the leaf. Air temperature in the open field
and under shade was measured using the same kind of thermocouples. All
thermocouples were calibrated in a constant temperature water bath for 9 sets of
temperature ranging from 5-45
D
C and a regression was made for each before attachment
to the leaves. The Millivolt data from all thermocouples were read and recorded by a
portable data logger (polycorder, OMNIDATA, Logan, Utah, USA) which scanned 10
channels every 10 seconds and averaged every 10 minutes. Other measurements such as
plant height, leaf number, leaf area and dry matter were taken in 10-day intervals. Dry
matter samples consisted of plants in 1.5 m length of raw. One plant was left between
each two consecutive sample area and all sampled rows were boarded by unsampled
rows. Two samples were taken for each replicate (6 samples for each treatment) each
time. Total fresh yield and dry matter content were recorded.
3. Results
20 30
40
50 60
Figure I shows that length of the main stem increased under shade conditions
compared to normal light treatment. This difference was significant starting from the
second sample (20 days after applying shade). Difference in leaf number between shaded
and unshaded plants showed in Figure 2 was not significant. In contrast, EI-Gizawy et
al.,
(1992) reported that shade significantly reduced leaf number. Late in the season, the
older leaf began to seriescence. Yellow leaf number was higher in unshaded plants
compared to that in shaded plants as given in Figure 2.
I
Fig. (1): Effect of shade on length of the main stem of tomato plants.
E
100
~ 80
60
40
20
o
10
..
-
-
-
•
-
-
-
..
-
-
04
-
-
".
..
".
~I""-Normal light
- •• Shade
•..
.:::
Cl
'a;
s:
•..
c
CIS
ii:
Days after applying shade
L...-___________ _---,
---1
314

Difference in leaf size illustrated by Figure 3 was not significant at the beginning of
the season, but starting from the fourth sample (40 days after applying shade) the
average area / leaf was significantly higher under shade compared to unshade treatment.
Similar results were reported by El-Gizawy et aI., (1992); Cockshull et al., (1992) and
Ryliski (1986).
PAR interception showed in Figure 4 was slightly higher under shade for some
sampling dates than in open. However this difference in PAR intercepted wasn't
statistically significant.
Fig. (2) : Effect of shade on the number of green (G.L.) and yellow (Y.L.) leaves of
tomato plants.
'C
C
ns
c
t/)
Q) ~
~ :ll
Ol_
e ~
•..0
Q)=
.Q
Q)
E
>-
:::J
Z
80
60
40~~-r--~~~~~
~Normal(
20
G.L.)
- ~ Shade (G.L.)
o
+-----~--~--~----~--~_T~----~----~
10 20 30 40 50 60
70
Days after applying shade
I
Fig. (3) : Effect of shade on the average area/leaf ( sq. cm ) for tomato plants.
_N
300
••
•
••
Q)
E
...-...-.
••
••
.!!!
0
200
,,-
•••
Q);:-
----
••
••
Ol
ns
~Normal
•••
ns
Q) 100
-.J
~
•..
-
Q) -
-
~
Shade
>
ns
« ~
0
ns
10 20 30 40 50 60
Days after applying shade
Fig. (4): Effect of shade on midday light interception pecentage (or ground cover %) of
tomato plants
100
80
~60
0
0
40
C)
20
05
-
-
-
15 20 30 43
Days after applying shade
315

Leaf and air temperature in day time given in Figure 5 rose faster in the morning in the
open field. The difference between air temperature in the open field and under shade
continued to increase throughout the day. This difference averaged about 1"C. Leaf
temperature showed the same trend as that of air temperature. Leaf temperature was
higher in the open field than that under shade for the morning early afternoon. The
difference became more clear starting from 10 A.M. In the evening approached, leaf
temperature of unshaded plants started to decline faster than that of shaded plants. Leaf
and air temperatures under shade became higher than that in the open field.
I
Fig. (5) : Air and leaf temperatures of tomato plants as affected by using shade.
- •• Tc (sun)
Tc (shade)
-0
Air (sun)
-- Air (shade)
0
<:>
..•
••
w
,..
'"
en
...•
co
II>
..•
..• ..•
..•
..•
..• ..•
..•
..• ..•
••
~
N N N
<:> <:> <:> <:> <:> <:> <:> <:> <:> <:>
..•
N
W
,..
'"
en
...•
co
II> <:>
N
w
,..
<:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:>
<:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:> <:>
Time (hours) (PST)
Total dry matter production (gm/sq.m), showed in Figure 6 was higher in the
unshaded plants compared to shaded plants except for the fourth and last samples where
the difference was not significant.
Total fresh fruit yield, as shown in Figure 7 was not significantly different between the
two treatments. Similarly, difference in dry matter content (gmlkg fresh yield) was not
significant between the two treatments as presented in Figure 8.
I
Fig. (6) : Effect of shade on the total dry matter production of tomato plants.
E
800
C'
~7 00
§
600
c:
5 00
0
"E
4 0 0
"
'0
300 ~Norm a I
e
0..
2 0 0
i; I 00
•
S had e
t:
ee
0
E
z-
O
20 4 0 60 8 0
0
D A P
316

I
Fig. (7): Effect of shade on the fruit yield (kg!sq.m) of tomato plants.
Treatments
5
4
3
2
Yield
(kg/m')
o!..---
I
Fig. (8): Effect of shade on the dry matter content in the tomato fruit (gm! kg fruit).
There was a slight difference in light use efficiency CLUE ) between the two
treatments as represented by the slope of the curve of cumulative intercepted PAR
against cumulative biomass given in Figure 9.
1000
I
Fig. (9): Light use efficiency of tomato plants as affected by applying shade.
Linear
(Shade)
--Linear
CI (Sun)
0~--~----~--~~--~----4~--~~1
o
1/1
1/1
CII
E
o
in ~
600
CII
E
~S
400
..!!!
::J
E
::J
o
800
200
0.2 0.4 0.6 0.8
Cumulative
PAR
intercepted (mole/rn")
• Shade
o
Sun
317

4. Discussion
The results of vegetative parameters (plant height, leaf area and leaf number) explain
the difference in intercepted PAR where shaded plants tried to increase intercepted light
by increasing interception area. Jones (1992) indicated that shade resulted in increasing
water content in shaded plants which increased the ability of leaves in absorbing
radiation and decreasing reflection. Using screens for shading probably redistribute light
on the canopy in a qualitatively way depending on the properties of the screen material
(color, thickness and material). The reduction in total dry matter production during the
season resulted from the reduction in light intercepted by the plants, this also was
reported by Cockshull et al., (1992) where they mentioned that a 1% light loss led to a
1% yield loss at least in the first period of harvesting of greenhouse tomatoes. Although
chlorophyll content was not measured, other studies on the effect of shade on plants
reported that shade decreased chlorophyll content (El-Gizawy, 1992). This factor could
also be considered as a factor in reducing dry matter production.
The difference in air and leaf temperatures can be explained as a result of difference in
ventilation between the two treatments and because of the radiation exchange process
between plants of the two treatments and the surrounded objects.
In
the day time, leaf
and air temperatures under shade were lower as a result of reducing intercepted
radiation. At night, For unshaded plants, plants started to exchange radiation with the
facing surface (sky its temperature below zero) while shaded plants exchanged radiation
with the facing surface (screen) which had a temperature much higher than the sky
(radiation is proportionally related to the fourth power of the body's absolute
temperature). Because harvesting was done on two dates, there was some ripe fruit
remain for a while on the plants which continued in consuming dry matter in respiration
process and this was higher in un shaded plants. This probably is the reason that reduced
the dry matter in the last biomass sample in the unshaded plants and according to this
possibility the slope of cumulative PAR against cumulative biomass would higher and
probably identical to that of shaded plants.
5. Conclusion
Results obtained show that under the experiment conditions, applying 30% shade does
not have a significant effect on the final yield of tomato crop. Although many studies
have reported that shade reduced the effect of high temperature on tomato plants, our
data show that for 30% shading this reduction in temperature averaged about 20C at
noon. This reduction in temperature does not seem enough to affect the productivity of
the plants in terms of fruit yield. However, using shade may have effect on reducing the
extremes of temperature and this may have effect on plant productivity under certain
climates. The reduction in the total dry matter production was mainly due to the
reduction in light intensity. This also support the idea that shade as a solution for
improving tomato crop yield is questionable in the same conditions of this experiment
and looking in other directions for improving crop yield is required. One of these
directions is improving the harvest index of the crop. Meanwhile, shade can be used to
improve fruit quality. However, Another factor should be considered before recommend
shading, the cost of shading relate to improved quality or yield.
Abdalla A.A., Verkerk K. (1968) Growth, flowering and fruit-set of tomato at high
temperature. Neth J Agric Sci 16: 71-76
Cockshull K.E., Graves c.J., Cave C.R.J. (1992) The influence of shading on yield of
glasshous tomatoes. J Hort Sci 67(1): 11-24
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