EFFECT OF ROOT ZONE HEATING ON GROWTH,
PRODUCTIVITY AND QUALITY OF GREEN BEAN
GROWN UNDER PROTECTED CULTIVATION
Shehata ,S. A. 1, R. S. Bekehet1, G. M. Abdel- Rahman2, M. M. Wadid3, M.A. Mohammed.3
1
Vegetable Crops Department, Faculty of Agriculture, Cairo University. Giza.
2
Agriculture Engineering Department, Faculty of Agriculture, Cairo University. Giza.
3
Central Laboratory for Agricultural Climate, , Dokki, Giza.
ABSTRACT
This study was carried out in Central Laboratory for Agriculture Climate
(C.L.A.C.), to investigate the effect of root zone heating on snap beans plants
behavior and yield under greenhouse conditions. The two cultivars of snap beans
Phaseolus vulgaris L. were used, i.e., Alhama (undetermined cv), Polista
(determined type). Seeds were sown directly on 11th and 15th of October for both
seasons 2004-2005 and 2005-2006, respectively. Five treatments were used, i.e., hot
water tube, straw mulch, straw with microorganism's mulch, plastic mulch and
control. Plant growth, yield and quality of pods in addition to carbohydrates and
fiber content of pods were determined in response to soil heating treatments
compared to the control. Results indicated that using hot water treatment gave
the highest fresh weight, number of leaves per plants and plant dry weight.
Where, the tallest plant height was obtained with using plastic mulch treatment.
No significant differences were found in number of shoots per plant and stem
diameter in all treatments. The highest values of early and total yield/m2 were
obtained in hot water tube treatment in both seasons. No significant differences
were found in pod fresh weight, pod diameter and pod length among treatments.
The lowest value of total fiber content of pods was found in straw with
microorganism's mulch treatment. The highest value of carbohydrates content of
pods was observed in hot water tube treatment.
INTRODUCTION
Studing the root zone meedia environment and its effect on the rate of growth
and development of the grown plants is on of the major concern factor for
greenhouse growers. (Reiss et al. 2007) developed and validated a numerical
simulation model of a greenhouse floor heating system using data collected in a
research greenhouse. located at Cook College, Rutgers University, New Brunswick,
New Jersey. The model was then modified and used to evaluate two different heat pipe
diameters and spacings that are typical in the greenhouse industry today: 13 mm
diameter pipe placed on 22.9 cm centers, and 19 mm diameter pipe placed on 30.5 cm
centers. The simulation results showed that the smaller diameter pipe placed closer
together and at a lower elevation provided the best temperature uniformity without
compromising other performance criteria. The model was then further modified to
simulate flats with growing media placed on the floor surface. Model simulations were
conducted for six different supply water temperatures ranging from 32.2 to 60°C, while
maintaining a target ambient greenhouse air temperature of 15.6°C. The simulation
outputs showed that using the smaller diameter pipe placed closer together resulted in a
higher surface heat flux, a higher growing media temperature, and greater temperature
uniformity within the growing media, for each supply water temperature simulated.
1
The common bean is an annual legume cultured for its green pod and dry seed,
both of which are eaten. In common with all other legumes it is a good source of
protein (Halterlien, 1983). Snap bean is an important crop in Egypt for local
consumption as well as for exportation. Mulching increase plant spread and dry
matter production. In addition, Early, late, and total yields were improved by
application mulch and increase the profitability of growing crop (Lamont, 1993).
Also, enhanced weed control reduced nutrient leaching, and favorable soil
temperature and moisture (Bhella, 1988). While, uptake and translocation of
essential nutrients, root growth and development and root cell differentiation of
plants is directly influenced by root zone temperature (Daskalaki and Burrage
1998). Moreover, improving moisture uniformity in the soil and raising air and
soil temperatures, thus creating favorable microclimate for the growth of some
crops (Soltani, et. al., 1995). So, mulching vegetables crops in greenhouse has long
been a practice of growers to increase production and promote earlier yields in
many of the warm season vegetable crops. The objective of this trial conducted to
study the different soil heating methods and investigate the effect of root zone
heating on snap beans plants behavior and yield under different treatments. One
of the most recent approach to heating up the root zone media is using an electric cable
heating systems offer great possibilities for the development of growing substrates in
greenhouses, either by using a heat storage system or by direct substrate heating. The
system was established and been tested by (Rodreguez et al. 2006) had studied and
analyzed the influence of the installation depth and spacing of the heating cable, and
establishes management techniques to obtain a heating system capable of providing the
substrate located between depths of 75 and 150 mm with appropriate temperatures for
the development of the crop roots in an optimal thermal environment. The heating cable
was installed in a greenhouse bench with a sand substrate at three different depths: 150,
225, and 300 mm, and at three different spacing for each depth: 100, 150, and 200 mm,
which provided nine different configurations of the heating cable that resulted from
combining the different depths and spacings.
An experimental controlled environment system for plant propagation was developed
(Wilkerson and Gates 2003) to provide three replications of a gradient in root zone
temperature treatments to poinsettia cuttings. The system consisted of three propagation
chambers and a transpiration chamber for water status tests. It was possible to control
both Vapor Pressure Deficit VPD of air and Photosynthesitic Active Radiation.. Two
different constant temperature water baths provided water that flowed through
aluminum channels welded to opposite sides of an aluminum plate. The temperature of
the two water sources could be set to provide a temperature gradient along the width of
the plate. Cuttings were propagated in covered aluminum trays oriented along the
length of the thermo gradient table to provide multiple cuttings at different media
temperatures. The thermo gradient table maintained root zone temperatures within 0.5
o
C of all five treatment set points. Performance of the propagation chambers, some
demonstrative results of use, and some limitations in ability to maintain air temperature
and relative humidity in high radiation situations are presented
2
MATERIALS and METHODS
The experiment was performed in autumn season of 2004 and 2005 at Dokki
Proteceted Cultivation Experimental Site “Laboratory for Agricultural Climate”
(CLAC), Agriculture Research Center (A.R.C.), Ministry of Agriculture and Land
Reclamation at Giza Governorate. Two green snap bean cultivars were used, i.e.,
Alhama (undetermined cv.) and Polista (determined cv.) both cultivars classified
as fine type. Seeds were sown on October 11th and 15 th for two winter seasons of
2004-2005 and2005-2006, respectively. Seeds were sown in hills 25 cm apart on
ridges having 50 cm width. Seeds were sown.
A standard single plastic greenhouse of 540 m2 (9 m width, 60 m long and 3.25
m height). It was divided into five ridges (1 m width and 60 m long) seprsted by
pathways each of 60 cm width. All agricultural practices were performed as
recommended by Ministry of Agriculture. The experiments were carried out in
split plot design with three replicates. The cultivars were arranged in the main
plots, whereas the heating root zone treatments were arranged in the sub plots.
Each replicate was divided into two lines; one for each cultivar. Five heating root
zone treatments were used .The treatments were:
1-Water tube treatment:
Using, six P.V.C. tubes (½ inch diameter and 10 meter long) to carry the hot
water for the risospher area. Two tubes were laid in the middle of each ridge
before sowing. All tubes were conducted with pump put in 100 litter tank.
Electricity heater (2000 watte) was used to rising the water temperature to 40°C.
2-Straw mulch treatment:
Rice straw (20 kg) with 10 cm deepth was applied before seven days from
sowing seeds, by digging a dick of 40 cm width in the middle of each ridge.
3-Straw mulch with microorganism's treatment:
Was prepared by following the same steps in straw mulch treatment.
Moreover, inoculation the straw mulch by amix of Bacillus subtilis, B. megaterium,
B. circulans, Azotobacter crococum.
4-Plastic mulch treatment:
Sheets of black polyethylene film 1 m width and 30 m long with thickness of 50
micron were used as mulch. Strips of plastic mulch were placed after prepared soil
and anchored with metal to prevent plastic billowing.
5-Control treatment:
Plants were sowing in the greenhouse as the grower treatment.
Measurements:
1-Growth parameter:
Three plants were chosen randomly from each experimental plot in order to
determine plant height (cm), number of leaves, stem diameter (mm) and shoot
number per plant. Total fresh and dry weights of whole plant were determined in
g/plant. Plants were air dried and then put into the oven at 70°C for 24 hrs after
45 and 100days from sowing date.
2- Yield and its components
a- Total yield:
3
Green pods were picked at green maturity stage. This was carried out 8 times
during harvesting season. Harvested pods were counted and weighed at each
picking time.
b- Early yield:
Weight of green pods were taken from the first three harvesting
c-Pod characters:
Pod samples (100g) were taken at every harvest for determination of Physical and
chemical properties as follow:
1-Physical properties:
a. Pod length: The average pod lengths were measured in cm by Venire caliper.
b. pod diameter: The average pod diameter was measured in cm with Venire
caliper.
c. The average weight of the pod was determined in gm.
2- Chemical properties:
a. Pod dry matter percentage: known weight of each fresh sample was separately
oven dried at 70 °C till constant weight was reached.
b. Fibers: was determined as gm/100gm dry weight according to A.O.C. (1984)
c. Total carbohydrate: was determined as gm/100gm dry weight according to
Mgnetski et al. (1959)
Statistical analysis:
Split plot designs was applied where two green bean cultivars distribuited
in main factor and heating treatments as sub-main factor in three replicate. Each
replicate consisted 20 plants. L.S.D. was statistically analyzed according to
Snedecor and Cochran (1981). Significant Difference test “ L.S.D. “ at 5 % level of
probability in two seasons of experimentation.
RESULT
Vegetative growth:
Data in Table (1) shown the effect of heating treatments on plant fresh weight,
plant height and number of leaves per plant. Resuts obtained that the hot water
treatment gave the highest value of plant fresh weight and number of leaves per
plant and followed by plastic mulch treatment. When, the lowest value of plant
fresh weight and number of leaves per plant was found in control treatment. No
differences in plant height were observed between the hot water treatment and
mulch treatment in all over the growing seasons. The same trend was true in two
seasons. Interaction between heating treatments and cultivars were affected
significantly. The best treatments were hot water treatment with Alhama cultivar
and plactic mulch with polista cultivar in both seasons.
Results of (Table 2) illustrate the effect of heating treatments on number of
shoots per plant, plant dry weight and stem diameter. Different soil heating
treatments affected significantly in the studied chatacres. During the first season
4
hot water treatment recorded the highest number of shoots and plant dry weight.
However, stem diamter was sgnificantly higher when using plastic mulch. In the
second season, hot water also coused the highst number of shoots followed by
plastic mulch without any significant different between them. In addition, no
significant diferent was found between straw + micro mulch, plastic mulch and
hot water. Regarding to the interaction between cultivars and heating treatment,
there were no significant effect was found in number of shoots in both seasons,
stem diameter in the first season. Interaction between Alhama and hot water
recorded the highest plant dry weight in the two seasons. In the second season, all
heating treatments coused increament in stem diameter and without any
significant different between them and the control tratment with both cultivars.
Yield and its components:
The early yield of green snap bean pods was significantly affected by applying
the heating treatments. The hot water treatment was the most favorable for
producing the early yield with no significant differences between hot water
treatment and the application of plastic mulch. Also, data showed clearly that
there were significant effects on total yield due to the applied hot water treatment.
No significant differences were detected between hot water treatment and plastic
mulch in both season (Table 3). In first season, plastic mulch the most effective
treatment in increasing the pod character fresh weight. There were insignificant
differences in fresh weight between two cultivars. The appliction of plastic mulch
and Alhama cultivar increased the fresh weight pods. While, in seconed season,
there is no significant differences were detected neither among heating treatments
nor between the two cultivars (Table 3).
Data in Table (4) showed that, length and diameter of pods were not influenced
by the investigated heating treatments and cultivars. Where, The application of
deffirient heating treatments were significantly affect on dry weights of green snap
bean pods. The plastic mulch treatment showed the highest values of dry weight of
pod followed by hot water treatment. Alhama green pods had higher values of dry
weight compared to those of Polista plants. The most effective interaction in
increasing dry weight of green pods was observed with plastic mulch with Alhama
cultiver (Table 4). The same results were recorded in both growing seasons.
Results in Table (5) revealed that all investigated heating treatments decreased
the pod contont of fibers compared to control treatment. The lowest result
recorded with straw + micro mulch. Polista cultivar gave higher value compared
with Alhama cultivar. Applying straw + micro mulch with Alhama cultivar
recorded the best result of fibers percentage. These ruslts were decated in both
seasons. Except cultivars, in seconed season were not significant. Data in (Table 5)
indicated that hot water treatment increased carbohydrates content compared to
other treatments. Whereas, there is no differences between two cultivars in pod
content of carhydrates. Also, carbohydrates content in green pods were increased
by the application of hot water treatment with Alhama cultivar. Same trained was
true in both seasons.
DISCUSSION
From the overall results it is clear that using hot water to heat soil increasing
vegetative growth as mentioned by Maher (1980). The increase of vegetative
5
growth lead to more yields as suggested by Maher (1980), Moorby and Graves
(1980), Moss (1983), Tanko (1988), Economakis (1992) and Economakis and Krulj
(2001).This also, confirm the suggestion made by Ikeda and Osawa (1984) that the
root temperature is one of the major factors, which directly affects on plant
growth and correspondingly increase the yield of some vegetable crops. That is
due to the amount of heat added by heating up the root media were not only
stimulated the root system in water and uptake of the elements.
On the other hand, the faster growth rate of plants in plastic mulch treatment
may be due in part to soil temperature increases caused by black plastic mulching
(Soltani et al.1995; Jenni et al. 1996), because black mulch absorbs 96% of short
wave radiation while it transmits and it reflects very little (Teasdale and AbdulBaki 1995). This absorbed radiation is held by the upper layer of the soil, causing
it to heat.
Finally, although using hot water treatment to heat soil gave the highest yield
but using straw mulch was more economically (Medany et al. 1990).
6
Table (1): Effect of heating treatments on plant fresh weight, plant height and number of leaves per plant after 100
days from sowing during the two growing seasons of 2004/2005 and 2005/2006.
2004/2005
Cultivar (A)
plant height (cm)
plant fresh weight (gm)
Treatments(B)
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
Alhama
735.26
1739.46
1079.93
1131.81
864.59
1110.21
49.07
16.0
16.0
699.67
1659
1029.67
1077
823.68
1057.8
22.78
14.04
14.04
Polista
152.83
374.27
189.11
462.83
327.55
301.32
138
356
184
428
311
283.4
mean
444.05
1056.87
634.52
797.32
596.07
418.83
1007.5
606.85
752.5
567.31
Alhama
284.8
403.9
319.2
372.3
329.2
341.9
60.91
16.59
16.59
Polista
45.4
66.9
70.5
73.1
62.7
63.7
2005/2006
273.33
43.33
386.67
65.00
307.00
62.33
375.67
68.00
320.00
59.67
332.53
59.67
65.96
18.96
18.96
7
number of leaves per plant
mean
Alhama
Polista
mean
165.15
235.40
194.89
222.73
195.97
109.68
291.84
199.17
213.63
154.69
193.80
4.19
5.41
5.41
40.42
90.32
50.40
79.23
62.47
64.57
75.05
191.08
124.78
146.43
108.58
158.33
225.83
184.67
221.83
189.83
106.00
281.67
191.67
205.67
147.67
186.53
17.58
5.39
5.39
35.67
86.33
47.00
73.67
59.00
60.33
70.83
184.00
119.33
139.67
103.33
Table (2): Effect of heating treatments on number of shoots per plant, plant dry weight and stem
diameter of snap beans plant during the two growing seasons of 2004/2005 and
2005/2006.
number of shoots per plant
Treatments(B)
Alhama
Polista
2004/2005
Cultivar (A)
plant dry weight (gm)
mean
Alhama
100.22
369.89
145.03
116.93
331.13
212.64
15.81
5.41
5.41
2005/2006
96.00
356.00
135.87
113.40
317.10
203.67
12.79
5.82
5.82
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
4.64
10.94
7.41
8.17
5.71
7.37
1.41
1.97
N.S
10.41
17.18
16.66
16.14
16.61
15.40
7.53
14.06
12.03
12.15
11.16
7.53
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
3.33
10.33
4.67
7.00
5.67
6.20
N.S
2.25
N.S
10.67
16.33
14.00
15.33
14.00
14.07
7.00
13.33
9.33
11.17
9.83
8
Polista
mean
stem diameter(mm)
Alhama
Polista
mean
22.17
76.33
35.05
25.60
66.13
45.06
61.20
223.11
90.04
71.26
198.63
0.84
1.26
1.21
1.26
1.26
1.17
N.S
0.060
N.S
0.84
1.21
1.26
1.31
1.26
1.18
0.84
1.23
1.23
1.29
1.26
22.33
72.03
34.00
24.90
64.80
43.61
59.17
214.02
84.93
69.15
190.95
0.77
1.13
1.17
1.17
1.20
1.09
N.S
0.093
0.093
0.83
1.20
1.20
1.17
1.20
1.12
0.80
1.17
1.18
1.17
1.20
Table (3): Effect of heating treatments on Pod dry weight, Pod length and Pod diameter of snap
bean during the two growing seasons of 2004/2005 and 2005/2006.
2004/2005
Cultivar (A)
Pod length(cm)
Pod fresh weight (gm)
Treatments(B)
Alhama
Polista
mean
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
5.74
6.81
5.24
7.56
5.61
6.19
N.S
0.12
0.12
5.56
5.32
5.28
5.31
5.10
5.31
5.65
6.06
5.26
6.43
5.35
5.65
control
Hot water
Straw+ micro mulch
Plastic mulch
Straw mulch
mean
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
5.88
5.99
5.11
6.24
5.38
5.72
N.S
N.S
N.S
5.24
4.79
4.69
4.61
4.74
4.81
5.56
5.39
4.90
5.42
5.06
Alhama
13.37
13.63
13.52
13.87
13.38
13.55
N.S
N.S
N.S
2005/2006
12.84
13.11
12.77
12.95
12.19
12.77
N.S
N.S
N.S
9
Polista
Pod diameter(mm)
mean
Alhama
Polista
mean
13.97
10.73
13.78
13.76
13.42
13.13
13.67
12.18
13.65
13.82
13.40
0.76
0.79
0.72
0.78
0.76
0.76
N.S
N.S
N.S
0.76
0.75
0.75
0.74
0.76
0.75
0.76
0.77
0.74
0.76
0.76
13.13
8.96
13.06
13.02
12.73
12.18
12.98
11.03
12.92
12.98
12.46
0.72
0.74
0.68
0.73
0.73
0.72
N.S
N.S
N.S
0.73
0.73
0.73
0.69
0.73
0.72
0.72
0.73
0.70
0.71
0.73
2
Total yie ld/m
25
Kg
20
15
Alhama
10
Polista
5
0
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
2004/2005
2005/2006
Tre atme nt
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
1.30 2.14
1.49 1.88
1.49 1.88
Fig(1): Effect of heating treatments on Total yield/m2 of snap bean during
the two growing seasons of 2004/2005 and 2005/2006.
Ea rly yie ld/ m 2
5
Kg
Alhama
Polista
0
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
2004/2005
2005/2006
Tre atme nt
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
0.16 0.15
0.53 0.54
0.53 0.54
Fig(2): Effect of heating treatments on Early yield/ m2 of snap bean during
the two growing seasons of 2004/2005 and 2005/2006.
10
Pod dry weight
5
gm
Alhama
Polista
0
Straw
mulch
Plastic
mulch
Straw+
micro
mulch
Hot
water
control
Straw
mulch
Plastic
mulch
Straw+
micro
mulch
Hot
water
control
2004/2005
2005/2006
Treatment
L.S.D(A) 0.03 0.03
L.S.D(B)
0.11 0.11
L.S.D(A*B) 0.11 0.11
Fig(3): Effect of heating treatments on Pod fresh weight of snap bean
during the two growing seasons of 2004/2005 and 2005/2006.
Total fiber content
15
gm
10
5
0
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
2004/2005
2005/2006
Tre atme nt
Alhama
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
Polista
0.15 N.S
0.54 0.38
0.54 0.38
Fig(4): Effect of heating treatments on Total fiber content in Pods of snap
bean during the two growing seasons of 2004/2005 and 2005/2006.
11
Carbohydrates content
20
gm
15
10
5
0
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
Straw
mulch
Plastic
mulch
Straw+
micro
Hot
water
control
2004/2005
2005/2006
Tre atme nt
Alhama
L.S.D(A)
L.S.D(B)
L.S.D(A*B)
Polista
N.S N.S
0.82 0.30
0.82 0.30
Fig(5): Effect of heating treatments on total carbohydrates content in Pods
of snap bean during the two growing seasons of 2004/2005 and 2005/2006.
12
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14
‫تأثير تدفئة منطقة الجذور على نمو و إنتاجية و جودة الفاصوليا النامية تحت ظروف‬
‫الزراعة المحمية‬
‫أجريت الدراست بموقتتا التتدقز لعةرالتتم الم م تتم – المعمتتا المريتتةم لعماتترا الةرالتتز ‪ -‬بهتتدت س نت‬
‫إنترج م وجودة م صول الفرصول ر الماتج خالل موسم الشتتر لعترمز ‪ 2006/2005 – 2005/2004‬لت‬
‫طريق سدفئم ماطقم الجذور‪ .‬ح ث ستم ررالتم صتاف مت الفرصتول ر ال هترا لمترا الهرمتر ود تر م تدود‬
‫الامتتتوبو بول نتتتتر وم تتتدود الامتتتوب‪ .‬وسمتتت ررالتتتم ال تتتذور فتتتز ‪ 11،15‬أيتتتتوبر لعتتتا التتتتوالز لموستتتمز‬
‫‪.2006/2005-2005/2004‬‬
‫وقتتد استتت دس خمتتال معتترمال لتدفئتتم ماطقتتم الجتتذور ويرن ت المعتترمال يرلتتترلزا استتت داس أنرب ت المتتر‬
‫النرخ و التغط م برستت داس قتا ازررو التغط تم برستت داس قتا ازرر المهترت إل ت بعتا أنتواا ال تريتر‬
‫الم عع ل و التغط م برست داس ال الست ك ازسود بنمك ‪ 50‬م رون برإلضرفم إلا معرمعم لدس سغط م ستط‬
‫التربم وال اترولب‪ .‬وأوض الاتر ئج وجود فروق معاويم ب معرمال التدفئم الم تعفم مقررن برلمعرمعم‬
‫ال اتتترول برلان ت م لعصتتفر ال هتتريم‪ ،‬ويرن ت العتتز الق ت م لاتتد استتت داس معرمعتتم التدفئتتم بمواس ت ر المتتر‬
‫النرخ فز يال م الورن الطررج و الجرت لعا رسر لدد لألوراق لعا ر ‪ .‬ب امر سجا العز طول لعا رستر‬
‫لصرل معرمعم التغط م برست داس ال الست ك ازسود‪ .‬فز ح لم ي لاتر فتروق معاويتم واضت م فتز يتال‬
‫م سمك النرق ولدد الفروا لعا ر فز يا معرمال التدفئم‪ .‬وأيهر أدى استت داس التدفئتم بمواست ر المتر‬
‫النرخ إلا ال صول لعا العز م صول يعا وم ر‪ ،‬ب امر لم سؤثر معرمال سدفئت ماطقتم الجتذور لعتا‬
‫صتتفر القتترون المتمفعتتم فتتز طتتول وستتمك وورن القتترون‪ .‬أمتتر برلان ت م لم تتتوى القتترون م ت ازل تترت و‬
‫ال ربول تدرا ف رنت اقتا قت م لم تتوى القترن مت ازل ترت لصترل معرمعت التغط تم بترلقا المهترت إل ت‬
‫ال ترير لعا الردم م أن ألعا م توى لع ربول درا وجد لاتد استت داس معرمعتم أنرب ت المتر النترخ‬
‫فز التدفئم‪.‬‬
‫‪15‬‬