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The effects of different greenhouse covering materials on energy requirement, growth and yield of aubergine
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Energy 31 (2006) 1780–1788 www.elsevier.com/locate/energy
The effects of different greenhouse covering materials on energy requirement, growth and yield of aubergine Bilal Cemeka,, Yusuf Demira, Sezgin Uzunb, Vedat Ceyhanc a
Irrigation and Agricultural Structures Department, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey b Department of Horticulture, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey c Department of Agricutural Economics, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey Received 16 May 2005
Abstract Effects of UV stabilised polyethylene (UV+PE), IR absorbers polyethylene (IR+PE), double layers of polyethylene (DPoly) and single layer of polyethylene (PE), as greenhouse covers, on aubergine growth, productivity and energy requirement were investigated in a late autumn season (2001). The late and final yields of plants grown in D-Poly houses were higher than those grown in UV+PE, IR+PE and PE. Light transmission was the highest in PE, intermediate in UV+PE and IR+PE, and the lowest in D-Poly houses. Relative humidity was the highest in D-Poly, intermediate in IR+PE and UV+PE, and the lowest in PE houses. The plants in D-Poly houses grew and developed faster (more leaves and flowers) than those in IR+PE, UV+PE and PE houses. Plant growth and development in UV+PE and IR+PE houses was similar. Economic analyses showed that aubergine production was economically viable in D-Poly, UV+PE and IR+PE houses. For aubergine production in climatic conditions similar to Black Sea Region, the D-Poly greenhouse is strongly recommended, because there was a higher productivity and a lower heating requirement in comparison to UV+PE, IR+PE and PE houses. r 2005 Elsevier Ltd. All rights reserved. Keywords: Cover materials; Aubergine; Energy; Growth; Yield
1. Introduction During the last two decades, productivity and efficiency have received particular attention. Farmers have to use their resources such as land, water, etc. more effectively. So, achieving maximum yield per unit area has become a high research priority. Greenhouse makes it possible to increase crop productivity by maintaining a favourable environment for plants; and thus production by using greenhouse has become more popular than in the past. During 1980s and 1990s, greenhouse cover materials and their effects on the greenhouse environment received special attention due to high fuel costs. Noble and Holder [1] stated that the high fuel costs during the Corresponding author. Gaziosmanpasa Univ., Ziraat Fakultesi, 60240, Tokat, Turkey. Tel.: +90 356 2521616 Ext 2276; fax: +90 356 2521488. E-mail address: [email protected] (B. Cemek).
0360-5442/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2005.08.004
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Nomenclature UV+PE IR+PE D-Poly PE NAR RGR LAR SLA LWR q K0 AH AG ti ta P O M s CRF SFF i n
UV stabilised polyethylene IR absorbers polyethylene double layers of polyethylene single layer of polyethylene net assimilation rate, g cm2 d1 relative growth rate, g g1 d1 leaf area ratio, cm2 g1 specific leaf area, cm2 g1 leaf weight ratio, g g1 specific heat requirement per square meter of greenhouse floor area, Wm2 means the overall heat consumption coefficient, Wm2K1 surface area of the greenhouse, m2 floor area of the greenhouse, m2 required inside temperature, 1C average outside temperature, 1C initial investment cost of operation cost of maintenance salvage value capital recovery factor sinking fund factor interest rate useful rate
1970s and early 1980s led to a heightened interest in greenhouse cover materials which were more energy efficient than single layer of glass. Then, many researches have been conducted on the effects of cover materials on greenhouse environment and growth, development and productivity of crops [2–5]. To reduce fuel costs in recent years, Turkish growers have tended to not growing tomato, aubergine, pepper and cucumber in the cold winter months by changing crop schedules. Therefore an understanding of the effect of temperature and light on the growth of tomato and aubergine is of great importance to such growers. Crop yields were reported to depend on the responses of plants to environmental factors [6], for example, temperature has a considerable influence on crop timing and yield [4] and, of course, light is a primary determinant of crop growth. Early vegetative growth and yield of cucumber have been reported to be enhanced by either the low day or night vapour pressure deficit (VPD), and final total yield was negatively related to day time VPD [7]. High temperature stimulates plant growth and increases the early yield of various greenhouse fruits and vegetables. Little attention has been paid to the interaction of environmental factors. Greenhouse air temperature, humidity and leaf temperature are in turn affected by the light transmissivity of the cover material [3]. Therefore, it is always impossible to predict crop responses to different cover materials realistically based only on the response of the greenhouse crops to each individual environmental factor [2,4]. Experimentation under simulated commercial conditions may lead to better understanding of the responses of greenhouse crops to the commercial use of various cover materials [8]. Most of the experiments on the effects of cover materials on greenhouse crops have employed no replication for the cover materials because of the high cost of such facilities. This lack of replication has made it impossible to quantify the effects of the cover materials on the greenhouse environment, energy use and crop productivity with any statistical certainty [3]. The study reported in this article was conducted in eight minigreenhouses covered with UV stabilised polyethylene (UV+PE), IR absorbers polyethylene (IR+PE), double layers of polyethylene (D-Poly) or single layer of polyethylene (PE), with two replications. The purposes of
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this study were (i) to determine the effects of these four cover materials on aubergine growth and yield, (ii) to explore heating energy requirement for different cover materials, (iii) to compare alternative energy supply, and (iv) to determine economic feasibility of aubergine production in greenhouses with different cover materials. 2. Materials and methods
50 200
250 300
150 900 0m
1m
2m
Fig. 1. Description of the dimensions greenhouses (solid areas represent side and roof ventilation gaps).
3m
323.78
26°
73.16
40
The experiment was carried out in the late autumn 2001 in eight independent mini-greenhouses oriented Earth–West (Fig. 1) at Samsun (421N), Turkey. The eight greenhouses of the identical size (9 3 2.5 m, L W H) and shape were constructed to conform to two replications in randomised complete block experimental design. The cover materials of the greenhouses were PE-UV, PE-IR, D-PE and PE with a thickness of 150 mm. Ni quenchers were used as UV stabilisers in UV+PE and IR was used as absorbers to prevent long waveradiation heat exchange in IR+PE. According to the commercial description, light transmissions of the used covering materials were 89–92%, 86–92%, and 92–93% for PE-UV, PE-IR, and PE, respectively. On the other hand, transmissions of 5000–14 000 nm wavelength radiation of the covering materials were 56%, 33% and 54% for PE-UV, PE-IR and PE, respectively. Seeds of aubergine (cv.Valentine F1) were sown in mini-pots. Sowing and planting dates for each experiment were 7 June and 14 August, respectively. First harvest date was 15 September while that of last harvest was 16 November. Pots were filled with peat-based compost. The plants were planted in growing bags (0.4 1 m, W L), containing 35 l of peat compost. Three plants were placed in each growing bag and totally 15 growing bags were included in each mini-greenhouse. Randomly selected six representative plants were used for plant growth and fruit production evaluation. Temperature and relative humidity in each greenhouse were recorded simultaneously by using thermohygrograph (Sato Keiryoki, Mfg. Co. Ltd., R-704., Japan) and measurements were taken 1 m above the ground in the middle of the greenhouses. Photosynthetically active radiation (PAR) was measured daily with sun scan canopy analyser (Delta-T devices type SS1, England) at the centre of each greenhouse from 1:00 to 2:00pm inside and outside greenhouses. The measurements were made of 50 cm intervals from 0 to 200 cm at four levels. The daily light transmissions of greenhouses were measured with a sun scan canopy analyser. Two plants in each greenhouse were retained until the end of each experimental period in order to study the relationships between plant growth parameters. Plant fresh weight was determined and leaf area of each plant was measured with a (Placom) digital planimeter. Dry matter partitioning between different plant organs, namely leaf, stem, root and fruit was also examined. Destructive harvesting started from 15th day after planting and continued at 15 day intervals until the end of each experimental period. The plant material was placed in paper bags and arranged not to impair the airflow inside the oven to insure uniform drying. Plant dry
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weight was determined after oven drying at 80 1C (until a constant dry weight was obtained), specific leaf area was calculated as the dry weight per unit leaf area [9]. Plant growth and development and growth parameters were also quantified. The examined plant growth parameters were net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR). Non-destructive measurements included plant height and leaf number. Leaf number was counted when leaves were greater than 2–3 mm. Vernier callipers were used to measure stem diameter at 5 cm above ground level. Error bars were presented as standard error of means. Heat energy requirements of greenhouses were estimated according to [10]. The specific heat requirement per square meter of greenhouse floor area becomes: q¼
AH xK 0 ðti ta Þ ðW m2 Þ, AG
(1)
where K0 (W m2 K) is the overall heat consumption coefficient (UV+PE (8.34), IR+PE (6.27), D-Poly (4.75), PE(8.51)); AH(m2) the surface area of the greenhouse; AG(m2) the floor area of the greenhouse; ti (1C) the required inside temperature; and ta(1C) the average outside temperature. A temperature requirement for optimum yield conditions of aubergine was determined to be 22–23 1C in [9,11]. Heat energy requirement of greenhouses were determined based on the difference between present conditions with optimum conditions. After determining internal temperature in prevailing conditions, heating energy requirements were calculated assuming optimum growth temperature for aubergine is 22 1C. Different energy sources such as lignite, coal, fuel oil and liquid propane gases (LPG) were evaluated and compared based on both energy requirements and energy market price. Cost/benefit analysis was used to analyse the economical feasibility of the aubergine production in a greenhouse covered with different cover materials. The initial investments (P) including installation cost were calculated based on market price. The cost of operation and maintenance (O and M) and the salvage value (s) were assumed 15% and 10% of the P, respectively. The capital recovery factor (CRF) and sinking fund factor (SFF) were CRF ¼ ½ið1 þ iÞn =fð1 þ iÞn 1g and SFF ¼ ½i=fð1 þ iÞn 1g, respectively, where i (interest rate) ¼ 0.05 and n (useful life) ¼ 20 years. Thus, the total cost (TC) was calculated using the P CRF+(O and M) CRFS SFF formulae [12–14]. 3. Results Monthly average air temperatures in D-Poly and IR+PE houses were higher than that of UV+PE and PE houses. The average monthly air temperature was the highest in D-Poly and was followed by IR+PE, UV+PE and PE covered greenhouses (Table 1). The highest and lowest temperatures were observed in July and November, respectively. Table 1 Monthly average inside and outside temperature (1C) in greenhouses covered with different covering materialsa Month
Outside the greenhouse
Inside the greenhouse UV+PE
June July August September October November a
IR+PE
D-Poly
PE
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
22.5 28.2 26.0 18.0 20.0 19.0
14.7 21.0 21.3 16.4 11.1 9.9
19.6 23.6 24.5 17.2 15.9 13.1
31.0 33.0 29.5 24.3 25.0 22.0
16.5 24.8 23.5 17.8 13.0 14.0
25.1 28.1 26.9 21.0 19.6 16.1
30.0 33.0 31.3 23.0 26.5 23.0
17.3 26.8 24.0 18.3 15.5 14.8
25.5 28.8 27.6 21.0 20.8 18.2
32.5 34.5 32.5 25.3 26.3 24.0
19.3 26.0 24.0 19.5 16.0 15.3
26.6 29.4 28.9 21.4 21.3 19.1
28.0 30.8 28.0 22.5 22.8 18.0
15.7 23.3 23.0 17.3 12.0 14.0
23.2 26.3 25.5 18.4 18.1 16.0
UV+PE, UV stabilised polyethylene; IR+PE, IR absorbers polyethylene; D-Poly, double layer polyethylene; PE, single layer polyethylene.
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The highest relative humidity was observed in D-Poly greenhouse and was followed by IR+PE, PE and UV+PE greenhouses (Table 2). The highest monthly average relative humidity was recorded in October while the lowest was measured in August. PE greenhouse had the highest light intensity (Table 3). The highest light transmission was measured in PE covered greenhouses in July and was followed by UV+PE, IR+PE and D-Poly (Table 3). Plant height, fruit numbers in D-Poly houses were significantly higher than those in other houses (Table 4). The leaves of plants grown in UV+PE and PE had higher dry content and lower specific leaf area than the plants in D-Poly and IR+PE houses. Plant growth and development in D-Poly and IR+PE houses were similar. The highest net assimilation rate was obtained from the plants in PE covered greenhouses and was followed by UV+PE, IR+PE and D-Poly covered greenhouses, respectively. The highest leaf weight ratio was obtained from the plants grown in UV+PE covered greenhouses. There was no significant difference between D-Poly and IR+PE covered greenhouses regarding specific leaf area whereas the plants in UV+PE and PE covered greenhouses differed from the others (Table 4). The highest yield was obtained from the greenhouses covered with D-Poly and was followed by IR+PE, UV+PE and PE covered greenhouses. The highest late yield was obtained from D-Poly greenhouses (Fig. 2). Cost/benefit analyses results showed that aubergine production in greenhouses is economically viable in all greenhouses covered with D-Poly, IR+PE and UV+PE but not with PE. The cost/benefit ratios for UV+PE, IR+PE and D-Poly were 0.77, 0.74 and 0.55, respectively (Table 5). Tiwari and Sharma [15] obtained similar results for cucumber in production greenhouses. Since the ratio of PE was more than 1, greenhouse production was also economically viable in PE greenhouses.
Table 2 Monthly average inside and outside relative humidity (%) in greenhouses covered with different covering materialsa Month
Outside the greenhouse
Inside the greenhouse UV+PE
June July August September October November
IR+PE
D-Poly
PE
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
86.0 83.0 83.3 87.0 92.3 90.0
63.0 53.0 55.0 74.0 64.7 48.0
75.3 73.3 72.9 80.5 80.3 70.9
94.3 74.0 86.0 72.0 83.7 79.3
51.3 38.3 37 59.3 58.3 53.0
68.7 58.4 62.8 65.7 72.2 68.8
9.7 71.7 80.0 77.7 89.3 95.3
46.7 46.7 58.3 68.3 59.3 59.3
66.0 64.8 68.7 74.4 75.5 73.0
96.7 82.7 82.0 88.0 97.7 87.7
56.0 57.7 44.3 54.3 62.0 75.0
70.8 73.7 71.2 78.7 81.2 80.1
93.3 74.7 78.0 75.0 93.3 97.7
56.7 72.7 56.8 59.0 58.0 51.7
68.0 60.5 67.4 73.5 78.8 72.7
a UV+PE, UV stabilised polyethylene; IR+PE, IR absorbers polyethylene; D-Poly, double layer polyethylene; PE, single layer polyethylene.
Table 3 Monthly average photosynthetically active radiation (PAR) inside and outside the greenhousea Month
June July August September October November a
Photosynthetically active radiation (PAR) (mmol m2 s1) UV+PE
IR+PE
D-Poly
PE
Outside
1035 1155 942.5 710.0 415.0 270.0
1097.5 1057.5 872.5 687.5 400.0 267.5
975.0 995.0 802.5 577.5 360.0 225.0
1187.5 1282.5 1025 765.0 442.5 290.0
1522.5 1605.0 1385.0 1110.0 692.5 467.5
Photosynthetically active radiation (PAR) was measured daily with sun scan canopy analyser at the centre of each greenhouse from 1:00 to 2:00 pm inside and outside greenhouses.
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Table 4 Plant growth and development under UV+PE, IR+PE, D-Poly and PE greenhouse cover Parameters
UV+PE
IR+PE
D-Poly
PE
Height (cm plant1) Stem diameter (mm plant1) Leaf number per plant Fruit number per plant Leaf fresh weight (g leaf1) Leaf area (cm2 leaf1) Leaf dry weight (g leaf1) Leaf dry mass content (%) Relative growth rate (day1) Net assimilation rate (mg cm2 day1) Leaf area ratio (cm2 g1) Leaf weight ratio Specific leaf area (cm2 g1)
147.5 b 20.4 a 10.4 a 4.20 c 18.4 a 708.9 a 3.22 a 17.6 a 0.67 a 0.38 a 179.3 a 0.83 a 220.3 b
152.7 b 19.8 a 10.2 a 5.10 b 17.2 a 696.2 a 2.88 b 16.6 b 0.56 b 0.34 b 165.2 b 0.68 b 241.5 a
165.8 a 19.5 a 8.6 b 6.80 a 16.4 a 667.3 a 2.64 b 16.1 b 0.58 b 0.32 b 183.4 a 0.72 a 253.2 a
136.4 c 20.8 a 11.6 a 3.80 c 18.6 a 714.6 a 3.82 a 20.7 a 0.46 c 0.40 a 114.7 c 0.60 b 186.9 c
Plant height, stem diameter, leaf number per plant and fruit number per plant were measured on November 2, 2001; means presented
are averages 20 plants in each of two greenhouses with the same cover. The leaf fresh weight, leaf area, leaf dry weight, specific leaf area and leaf dry mass contents were determined from samples collected on November 8, 2001; means presented are the averages of 6 plants in each of two greenhouses with the same cover. Different letters in the same row indicate significant difference (po0:05), according to the LSD test.
Fig. 2. Marketable fruit yield of aubergine grown in UV+PE, IR+PE, D-Poly and PE houses in 2001. Accumulated yield (a) and total yield (b) presented are average from six plants in each of two greenhouses with the same cover (accumulative yield between September 15–November 16, 2001). Different letters on the error bars indicate significant differences (po0:05), according to the LSD test.
Table 5 Results of cost/benefit analyses for aubergine production in greenhouses covered with different covering materialsa Covering materials
P ($)
O and M ($)
S ($)
TC ($)
Yield (kg year1)
Price ($)
Benefit
Cost/benefit ratio
UV+PE IR+PE D-Poly PE
429 450 450 393
64.35 67.50 67.50 58.95
42.90 45.00 45.00 39.30
38.18 40.05 40.05 34.98
91.31 100.33 134.14 83.87
0.54 0.54 0.54 0.54
49.31 54.18 72.44 45.29
0.77 0.74 0.55 0.42
a
All values calculated for total floor area that is 27 m2.
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Heat energy requirement (MJ m-2 month-1)
600000 UV+PE IR+PE D-Poly PE
500000 400000 300000 200000 100000 0 September
October
November
Fig. 3. Monthly heat energy requirements in unheated greenhouses with different cover materials.
Heating of a greenhouse is an essential requirement for proper growth and development of winter growing crops [16]. Monthly heating energy requirements in greenhouses with different covers were presented in Fig. 3; considering all months, the lowest heating energy requirement was in D-Poly houses. Heating energy requirement in greenhouses were the highest in November.
4. Discussion The selection of the greenhouse cover material depends on many factors, such as initial investment, maintenance cost, its effects on greenhouse crop productivity, local climate and technological support and developments [3]. Several studies on the effect of covering materials on growth, development and yield of plants have indicated that the local climate conditions have a great influence on the effectiveness of covering materials [3,17,18]. The results of the present study were found to be in agreement with the results of Papadopoulos and Hao [3] because of the similar latitude of the locations. Many researchers indicated that temperature and relative humidity in D-Poly greenhouses were higher than standard single-layer polyethylene greenhouses resulting in higher plant yield [3,7,19–21]. Results from the present study support this conclusion. Stromme et al. [21] suggested that the air temperature in double-skinned houses might be higher than in a single-skinned house at the same temperature set point. The higher air temperature may stimulate plant growth and development in double-skinned greenhouses. This has been proven to be true in this study. The air temperature in D-Poly and IR+PE houses was up to 2–3 1C higher than in the UV+PE and PE houses, and the largest difference occurred in the coldest month. This increase in air temperature might have compensated for the loss in light since high temperature in young plants increases leaf growth and promotes the interception of light [22]. The higher air temperature was part of the positive effect of double-skinned houses in terms of insulation. In this study, heating requirement was reduced by 5% in D-Poly compared UV+PE, IR+PE and PE houses. High humidity levels resulted in an increased photosynthetic rate [19,20], fresh and dry weight, stem length and leaf area, and final total cucumber yield was positively related to daytime humidity, when the other variables are kept constant [7]. The greenhouse PAR transmission and heating energy requirements are not only affected by cover materials, but also by many other factors, such as greenhouse structures, size, orientation and thermal screens [23,24]. Therefore, the microclimate and crop responses in mini-greenhouses might be slightly different from to large multispan greenhouses and, therefore, some caution should be exercised in the interpretation of our findings.
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The plants in D-Poly houses achieved optimal usage of their resources through reduced specific leaf weight, and a greater leaf and fruit growth. Plants in D-Poly houses showed different biomass distribution and thus higher yields than UV+PE, IR+PE and PE, houses. Uzun [25] found that there was a positive relationship between light intensity and plant stem diameter in both tomato and aubergine. It was also found that stem diameter in tomato and aubergine increased curvilinearly with increasing temperatures as well as an interactive effect of temperature and light intensity on stem diameter. It was also found that an increase in temperature from 10 to 32 1C would result in increasing plant height in tomato and aubergine [2,9,11,26–28]. Cemek [27] indicated that the greenhouses covered with D-Poly had higher temperatures and increased plant height in cucumber. In the present study, the highest plant height was obtained from the aubergine plants grown in D-Poly covered greenhouses, which also had higher temperature. Increase in daily mean light integral caused a decline in both SLA and LAR, as the effect of decreasing temperature. It was also observed that the changes in RGR with the lowest daily mean light integral was related to changes in LAR of aubergine rather than by NAR, whereas changes in RGR of the aubergine grown with higher daily mean light integral (PE) was determined mainly by NAR but also by LAR. This is in good agreement with [9,29,30], which showed that changes in RGR due to temperature regime are mainly caused by the changes in LAR. When considering changes in RGR due to daily mean light integral, Bruggink [31] reported that there was a negative correlation of LAR with NAR at different light levels. In the present study, it was also observed that the relationships between NAR and either LAR or LWR were negatively related for aubergine. It could be suggested that the decline in LAR, SLA and LWR with increasing light levels and the increase in NAR with the same light integrals caused the negative relationship between NAR and either LAR or LWR in each greenhouses. Many studies have shown that SLA increases linearly with increasing temperatures and declines with increasing light intensities [9,28,29]. When considering the results obtained from the present study, the highest SLA value was obtained from the plants grown in D-Poly greenhouses. D-Poly greenhouses had higher temperatures and lower light intensities than the other greenhouses. As a result of this, higher SLA values were obtained from the plants grown in DPoly greenhouses. Higher SLA values from the plants in IR+PE covered greenhouses than those of greenhouses covered with PE and UV+PE can be explained by higher leaf area values in IR+PE greenhouses. To meet the heating requirement in greenhouses, the most economic way was to use fuel oil for heating in aubergine production in greenhouses while the reverse was the case for lignite. When comparing covering material in terms of energy cost, D-Poly has the minimum energy costs compared to others due to energy saving. IR+PE and UV+PE followed it (Table 6). Gupta and Chandra [23] suggested that double wall glazing enabled reduction in the heating requirement of the gothic greenhouse by 23%. Farmers engaged in aubergine production have to produce 19 kg per m2 more aubergine to compensate for the heating cost. Farmers had to produce 19 kg aubergine to meet heating cost if they use fuel oil to heat greenhouses covered with D-Poly. While that number for lignite is 26 kg aubergine.
Table 6 Seasonal energy requirements for greenhouses covered with different cover materials according to different energy sources and their costs for per small greenhouse (9 3 m2)a UV+PE
Lignite (kg) Coal (kg) Fuel oil (kg) LPG (kg) a
IR+PE
D-Poly
PE
Requirement
Cost ($)
Requirement
Cost ($)
Requirement
Cost ($)
Requirement
Cost ($)
197.8 101.2 65.32 54.28
41.54 40.58 30.05 36.37
108.56 59.38 33.12 29.44
22.80 21.34 15.24 19.72
67.16 32.48 22.26 18.31
14.10 12.99 10.24 12.27
268.84 132.48 82.80 92.00
56.41 52.99 38.09 61.64
When calculating energy requirements for greenhouses, thermal value for lignite, coal, fuel oil and LPG were assumed 12 500, 25 000, 40 000 and 46 000 kJ kg1, respectively.
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5. Conclusions In the light of our empirical findings, the most convincing results were obtained from D-Poly greenhouses when compared to IR+PE, UV+ PE and PE covered-greenhouses. D-Poly houses were not only more profitable but also had a lower heating energy requirement compared to others. Hence, It could be suggested that D-Poly greenhouses be used for late production of aubergine in autumn season in Samsun, in the Black Sea Region or region having similar climate conditions. References [1] Noble R, Holder R. Pot plant production under various greenhouse cladding materials. J Hortic Sci 1989;64:485–93. [2] Cockshull KE, Graves CJ, Carol RJ. The influence of shading on yield of glasshouse tomatoes. J Hortic Sci 1992;67(1):11–24. [3] Papadopoulos AP, Hao X. Effects of greenhouse covers on seedless cucumber growth, productivity, and enery use. Sci Hortic 1997;68:113–23. [4] Blom TJ, Ingratta FJ. The use of polyethylene film as greenhouse glazing in North America. 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A comparison of the effects of single glass and acrylic sheeting on plant plant growth and development. Acta Hortic 1981;115:401–8. [18] Winden CMM, van Uffelen JAM, Welles GWH. Comparison of the effect of single and double-glass greenhouses on environmental factors and production of vegetables. Acta Hortic 1984;148:567–73. [19] Acock B, Charles-Edwards DA, Hand DW. An analysis of some effects of humudity on photosynthesis by a tomato canopy under winter light conditions and a range of carbon dioxide concentrations. J Exp Bot 1976;27:933–41. [20] Bunce JA. Effects of humidity on photosynthesis. J Exp Bot 1984;35:1245–51. [21] Stromme E, Sebesta Z, Reiersen D. Experience with double acrylic cladding for tomatoes in Norway. Tag-Ber, Akad LandwirtschWiss DDR, Berlin 1986;238:167–72. [22] Challa H, Heuvelink E, Meeteren U Van. Crop growth and development. In: Bakker JC, Bot GPA, Challa NJ, van de Breaak, editors. Greenhouse Climate Control—an integrated approach. Wageningen: Wageningen Press; 1995. pp. 62–84. [23] Gupta MJ, Chandra P. Effect of greenhouse design parameters on conservation of energy for greenhouse environmental control. Energy 2002;27:777–94. [24] Weimann G. Development of energy saving greenhouse conceptions. Acta Hortic 1984;148:683–90. [25] Uzun S. The relationship between some growth, yield parameters and temperature and light intensity in tomato and aubergine grown in greenhouse. 6. Ulusal Seracılık Sempozyumu, 5–7 Eylu¨l 2001, Fethiye-Mugla, Turkey, p. 85–91. [26] Atherton JG, Harrıs GP. Flowering. In: Atherton JG, Rudich J, editors. The tomato crop. London: Chapman and Hall; 1986. p. 167–200. [27] Cemek B. Effects of different covering materials on growth, development and yield of crop and environmental conditions inside greenhouses. Unpublished Ph.D. thesis, Ondokuz Mayis University, Samsun Turkey, 2002. [28] Pearson S. Modelling the effect of temperature on the growth and development of horticultural crops. Unpublished Ph.D. thesis, Reading University, 1992. [29] Nilwik HJM. Growth analyses of sweet pepper (Capsicum annum L.) 2. Interacting effects of irradiance, temperature and plant age in controlled conditions. Ann Bot 1981;48:137–45. [30] Heuvelink E. Influence of day and night temperature on the growth of young tomato plants. Sci Hortic 1989;38:11–22. [31] Bruggink GT. A comparative analysis of the influence of light on growth of young tomato and carnation plants. Sci Hortic 1992;51:71–81.
Energy 31 (2006) 1780–1788 www.elsevier.com/locate/energy
The effects of different greenhouse covering materials on energy requirement, growth and yield of aubergine Bilal Cemeka,, Yusuf Demira, Sezgin Uzunb, Vedat Ceyhanc a
Irrigation and Agricultural Structures Department, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey b Department of Horticulture, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey c Department of Agricutural Economics, Faculty of Agriculture, Ondokuz Mayis University, 55139 Samsun, Turkey Received 16 May 2005
Abstract Effects of UV stabilised polyethylene (UV+PE), IR absorbers polyethylene (IR+PE), double layers of polyethylene (DPoly) and single layer of polyethylene (PE), as greenhouse covers, on aubergine growth, productivity and energy requirement were investigated in a late autumn season (2001). The late and final yields of plants grown in D-Poly houses were higher than those grown in UV+PE, IR+PE and PE. Light transmission was the highest in PE, intermediate in UV+PE and IR+PE, and the lowest in D-Poly houses. Relative humidity was the highest in D-Poly, intermediate in IR+PE and UV+PE, and the lowest in PE houses. The plants in D-Poly houses grew and developed faster (more leaves and flowers) than those in IR+PE, UV+PE and PE houses. Plant growth and development in UV+PE and IR+PE houses was similar. Economic analyses showed that aubergine production was economically viable in D-Poly, UV+PE and IR+PE houses. For aubergine production in climatic conditions similar to Black Sea Region, the D-Poly greenhouse is strongly recommended, because there was a higher productivity and a lower heating requirement in comparison to UV+PE, IR+PE and PE houses. r 2005 Elsevier Ltd. All rights reserved. Keywords: Cover materials; Aubergine; Energy; Growth; Yield
1. Introduction During the last two decades, productivity and efficiency have received particular attention. Farmers have to use their resources such as land, water, etc. more effectively. So, achieving maximum yield per unit area has become a high research priority. Greenhouse makes it possible to increase crop productivity by maintaining a favourable environment for plants; and thus production by using greenhouse has become more popular than in the past. During 1980s and 1990s, greenhouse cover materials and their effects on the greenhouse environment received special attention due to high fuel costs. Noble and Holder [1] stated that the high fuel costs during the Corresponding author. Gaziosmanpasa Univ., Ziraat Fakultesi, 60240, Tokat, Turkey. Tel.: +90 356 2521616 Ext 2276; fax: +90 356 2521488. E-mail address: [email protected] (B. Cemek).
0360-5442/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2005.08.004
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Nomenclature UV+PE IR+PE D-Poly PE NAR RGR LAR SLA LWR q K0 AH AG ti ta P O M s CRF SFF i n
UV stabilised polyethylene IR absorbers polyethylene double layers of polyethylene single layer of polyethylene net assimilation rate, g cm2 d1 relative growth rate, g g1 d1 leaf area ratio, cm2 g1 specific leaf area, cm2 g1 leaf weight ratio, g g1 specific heat requirement per square meter of greenhouse floor area, Wm2 means the overall heat consumption coefficient, Wm2K1 surface area of the greenhouse, m2 floor area of the greenhouse, m2 required inside temperature, 1C average outside temperature, 1C initial investment cost of operation cost of maintenance salvage value capital recovery factor sinking fund factor interest rate useful rate
1970s and early 1980s led to a heightened interest in greenhouse cover materials which were more energy efficient than single layer of glass. Then, many researches have been conducted on the effects of cover materials on greenhouse environment and growth, development and productivity of crops [2–5]. To reduce fuel costs in recent years, Turkish growers have tended to not growing tomato, aubergine, pepper and cucumber in the cold winter months by changing crop schedules. Therefore an understanding of the effect of temperature and light on the growth of tomato and aubergine is of great importance to such growers. Crop yields were reported to depend on the responses of plants to environmental factors [6], for example, temperature has a considerable influence on crop timing and yield [4] and, of course, light is a primary determinant of crop growth. Early vegetative growth and yield of cucumber have been reported to be enhanced by either the low day or night vapour pressure deficit (VPD), and final total yield was negatively related to day time VPD [7]. High temperature stimulates plant growth and increases the early yield of various greenhouse fruits and vegetables. Little attention has been paid to the interaction of environmental factors. Greenhouse air temperature, humidity and leaf temperature are in turn affected by the light transmissivity of the cover material [3]. Therefore, it is always impossible to predict crop responses to different cover materials realistically based only on the response of the greenhouse crops to each individual environmental factor [2,4]. Experimentation under simulated commercial conditions may lead to better understanding of the responses of greenhouse crops to the commercial use of various cover materials [8]. Most of the experiments on the effects of cover materials on greenhouse crops have employed no replication for the cover materials because of the high cost of such facilities. This lack of replication has made it impossible to quantify the effects of the cover materials on the greenhouse environment, energy use and crop productivity with any statistical certainty [3]. The study reported in this article was conducted in eight minigreenhouses covered with UV stabilised polyethylene (UV+PE), IR absorbers polyethylene (IR+PE), double layers of polyethylene (D-Poly) or single layer of polyethylene (PE), with two replications. The purposes of
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this study were (i) to determine the effects of these four cover materials on aubergine growth and yield, (ii) to explore heating energy requirement for different cover materials, (iii) to compare alternative energy supply, and (iv) to determine economic feasibility of aubergine production in greenhouses with different cover materials. 2. Materials and methods
50 200
250 300
150 900 0m
1m
2m
Fig. 1. Description of the dimensions greenhouses (solid areas represent side and roof ventilation gaps).
3m
323.78
26°
73.16
40
The experiment was carried out in the late autumn 2001 in eight independent mini-greenhouses oriented Earth–West (Fig. 1) at Samsun (421N), Turkey. The eight greenhouses of the identical size (9 3 2.5 m, L W H) and shape were constructed to conform to two replications in randomised complete block experimental design. The cover materials of the greenhouses were PE-UV, PE-IR, D-PE and PE with a thickness of 150 mm. Ni quenchers were used as UV stabilisers in UV+PE and IR was used as absorbers to prevent long waveradiation heat exchange in IR+PE. According to the commercial description, light transmissions of the used covering materials were 89–92%, 86–92%, and 92–93% for PE-UV, PE-IR, and PE, respectively. On the other hand, transmissions of 5000–14 000 nm wavelength radiation of the covering materials were 56%, 33% and 54% for PE-UV, PE-IR and PE, respectively. Seeds of aubergine (cv.Valentine F1) were sown in mini-pots. Sowing and planting dates for each experiment were 7 June and 14 August, respectively. First harvest date was 15 September while that of last harvest was 16 November. Pots were filled with peat-based compost. The plants were planted in growing bags (0.4 1 m, W L), containing 35 l of peat compost. Three plants were placed in each growing bag and totally 15 growing bags were included in each mini-greenhouse. Randomly selected six representative plants were used for plant growth and fruit production evaluation. Temperature and relative humidity in each greenhouse were recorded simultaneously by using thermohygrograph (Sato Keiryoki, Mfg. Co. Ltd., R-704., Japan) and measurements were taken 1 m above the ground in the middle of the greenhouses. Photosynthetically active radiation (PAR) was measured daily with sun scan canopy analyser (Delta-T devices type SS1, England) at the centre of each greenhouse from 1:00 to 2:00pm inside and outside greenhouses. The measurements were made of 50 cm intervals from 0 to 200 cm at four levels. The daily light transmissions of greenhouses were measured with a sun scan canopy analyser. Two plants in each greenhouse were retained until the end of each experimental period in order to study the relationships between plant growth parameters. Plant fresh weight was determined and leaf area of each plant was measured with a (Placom) digital planimeter. Dry matter partitioning between different plant organs, namely leaf, stem, root and fruit was also examined. Destructive harvesting started from 15th day after planting and continued at 15 day intervals until the end of each experimental period. The plant material was placed in paper bags and arranged not to impair the airflow inside the oven to insure uniform drying. Plant dry
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weight was determined after oven drying at 80 1C (until a constant dry weight was obtained), specific leaf area was calculated as the dry weight per unit leaf area [9]. Plant growth and development and growth parameters were also quantified. The examined plant growth parameters were net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR), specific leaf area (SLA) and leaf weight ratio (LWR). Non-destructive measurements included plant height and leaf number. Leaf number was counted when leaves were greater than 2–3 mm. Vernier callipers were used to measure stem diameter at 5 cm above ground level. Error bars were presented as standard error of means. Heat energy requirements of greenhouses were estimated according to [10]. The specific heat requirement per square meter of greenhouse floor area becomes: q¼
AH xK 0 ðti ta Þ ðW m2 Þ, AG
(1)
where K0 (W m2 K) is the overall heat consumption coefficient (UV+PE (8.34), IR+PE (6.27), D-Poly (4.75), PE(8.51)); AH(m2) the surface area of the greenhouse; AG(m2) the floor area of the greenhouse; ti (1C) the required inside temperature; and ta(1C) the average outside temperature. A temperature requirement for optimum yield conditions of aubergine was determined to be 22–23 1C in [9,11]. Heat energy requirement of greenhouses were determined based on the difference between present conditions with optimum conditions. After determining internal temperature in prevailing conditions, heating energy requirements were calculated assuming optimum growth temperature for aubergine is 22 1C. Different energy sources such as lignite, coal, fuel oil and liquid propane gases (LPG) were evaluated and compared based on both energy requirements and energy market price. Cost/benefit analysis was used to analyse the economical feasibility of the aubergine production in a greenhouse covered with different cover materials. The initial investments (P) including installation cost were calculated based on market price. The cost of operation and maintenance (O and M) and the salvage value (s) were assumed 15% and 10% of the P, respectively. The capital recovery factor (CRF) and sinking fund factor (SFF) were CRF ¼ ½ið1 þ iÞn =fð1 þ iÞn 1g and SFF ¼ ½i=fð1 þ iÞn 1g, respectively, where i (interest rate) ¼ 0.05 and n (useful life) ¼ 20 years. Thus, the total cost (TC) was calculated using the P CRF+(O and M) CRFS SFF formulae [12–14]. 3. Results Monthly average air temperatures in D-Poly and IR+PE houses were higher than that of UV+PE and PE houses. The average monthly air temperature was the highest in D-Poly and was followed by IR+PE, UV+PE and PE covered greenhouses (Table 1). The highest and lowest temperatures were observed in July and November, respectively. Table 1 Monthly average inside and outside temperature (1C) in greenhouses covered with different covering materialsa Month
Outside the greenhouse
Inside the greenhouse UV+PE
June July August September October November a
IR+PE
D-Poly
PE
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
22.5 28.2 26.0 18.0 20.0 19.0
14.7 21.0 21.3 16.4 11.1 9.9
19.6 23.6 24.5 17.2 15.9 13.1
31.0 33.0 29.5 24.3 25.0 22.0
16.5 24.8 23.5 17.8 13.0 14.0
25.1 28.1 26.9 21.0 19.6 16.1
30.0 33.0 31.3 23.0 26.5 23.0
17.3 26.8 24.0 18.3 15.5 14.8
25.5 28.8 27.6 21.0 20.8 18.2
32.5 34.5 32.5 25.3 26.3 24.0
19.3 26.0 24.0 19.5 16.0 15.3
26.6 29.4 28.9 21.4 21.3 19.1
28.0 30.8 28.0 22.5 22.8 18.0
15.7 23.3 23.0 17.3 12.0 14.0
23.2 26.3 25.5 18.4 18.1 16.0
UV+PE, UV stabilised polyethylene; IR+PE, IR absorbers polyethylene; D-Poly, double layer polyethylene; PE, single layer polyethylene.
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The highest relative humidity was observed in D-Poly greenhouse and was followed by IR+PE, PE and UV+PE greenhouses (Table 2). The highest monthly average relative humidity was recorded in October while the lowest was measured in August. PE greenhouse had the highest light intensity (Table 3). The highest light transmission was measured in PE covered greenhouses in July and was followed by UV+PE, IR+PE and D-Poly (Table 3). Plant height, fruit numbers in D-Poly houses were significantly higher than those in other houses (Table 4). The leaves of plants grown in UV+PE and PE had higher dry content and lower specific leaf area than the plants in D-Poly and IR+PE houses. Plant growth and development in D-Poly and IR+PE houses were similar. The highest net assimilation rate was obtained from the plants in PE covered greenhouses and was followed by UV+PE, IR+PE and D-Poly covered greenhouses, respectively. The highest leaf weight ratio was obtained from the plants grown in UV+PE covered greenhouses. There was no significant difference between D-Poly and IR+PE covered greenhouses regarding specific leaf area whereas the plants in UV+PE and PE covered greenhouses differed from the others (Table 4). The highest yield was obtained from the greenhouses covered with D-Poly and was followed by IR+PE, UV+PE and PE covered greenhouses. The highest late yield was obtained from D-Poly greenhouses (Fig. 2). Cost/benefit analyses results showed that aubergine production in greenhouses is economically viable in all greenhouses covered with D-Poly, IR+PE and UV+PE but not with PE. The cost/benefit ratios for UV+PE, IR+PE and D-Poly were 0.77, 0.74 and 0.55, respectively (Table 5). Tiwari and Sharma [15] obtained similar results for cucumber in production greenhouses. Since the ratio of PE was more than 1, greenhouse production was also economically viable in PE greenhouses.
Table 2 Monthly average inside and outside relative humidity (%) in greenhouses covered with different covering materialsa Month
Outside the greenhouse
Inside the greenhouse UV+PE
June July August September October November
IR+PE
D-Poly
PE
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
Max.
Min.
Mean
86.0 83.0 83.3 87.0 92.3 90.0
63.0 53.0 55.0 74.0 64.7 48.0
75.3 73.3 72.9 80.5 80.3 70.9
94.3 74.0 86.0 72.0 83.7 79.3
51.3 38.3 37 59.3 58.3 53.0
68.7 58.4 62.8 65.7 72.2 68.8
9.7 71.7 80.0 77.7 89.3 95.3
46.7 46.7 58.3 68.3 59.3 59.3
66.0 64.8 68.7 74.4 75.5 73.0
96.7 82.7 82.0 88.0 97.7 87.7
56.0 57.7 44.3 54.3 62.0 75.0
70.8 73.7 71.2 78.7 81.2 80.1
93.3 74.7 78.0 75.0 93.3 97.7
56.7 72.7 56.8 59.0 58.0 51.7
68.0 60.5 67.4 73.5 78.8 72.7
a UV+PE, UV stabilised polyethylene; IR+PE, IR absorbers polyethylene; D-Poly, double layer polyethylene; PE, single layer polyethylene.
Table 3 Monthly average photosynthetically active radiation (PAR) inside and outside the greenhousea Month
June July August September October November a
Photosynthetically active radiation (PAR) (mmol m2 s1) UV+PE
IR+PE
D-Poly
PE
Outside
1035 1155 942.5 710.0 415.0 270.0
1097.5 1057.5 872.5 687.5 400.0 267.5
975.0 995.0 802.5 577.5 360.0 225.0
1187.5 1282.5 1025 765.0 442.5 290.0
1522.5 1605.0 1385.0 1110.0 692.5 467.5
Photosynthetically active radiation (PAR) was measured daily with sun scan canopy analyser at the centre of each greenhouse from 1:00 to 2:00 pm inside and outside greenhouses.
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Table 4 Plant growth and development under UV+PE, IR+PE, D-Poly and PE greenhouse cover Parameters
UV+PE
IR+PE
D-Poly
PE
Height (cm plant1) Stem diameter (mm plant1) Leaf number per plant Fruit number per plant Leaf fresh weight (g leaf1) Leaf area (cm2 leaf1) Leaf dry weight (g leaf1) Leaf dry mass content (%) Relative growth rate (day1) Net assimilation rate (mg cm2 day1) Leaf area ratio (cm2 g1) Leaf weight ratio Specific leaf area (cm2 g1)
147.5 b 20.4 a 10.4 a 4.20 c 18.4 a 708.9 a 3.22 a 17.6 a 0.67 a 0.38 a 179.3 a 0.83 a 220.3 b
152.7 b 19.8 a 10.2 a 5.10 b 17.2 a 696.2 a 2.88 b 16.6 b 0.56 b 0.34 b 165.2 b 0.68 b 241.5 a
165.8 a 19.5 a 8.6 b 6.80 a 16.4 a 667.3 a 2.64 b 16.1 b 0.58 b 0.32 b 183.4 a 0.72 a 253.2 a
136.4 c 20.8 a 11.6 a 3.80 c 18.6 a 714.6 a 3.82 a 20.7 a 0.46 c 0.40 a 114.7 c 0.60 b 186.9 c
Plant height, stem diameter, leaf number per plant and fruit number per plant were measured on November 2, 2001; means presented
are averages 20 plants in each of two greenhouses with the same cover. The leaf fresh weight, leaf area, leaf dry weight, specific leaf area and leaf dry mass contents were determined from samples collected on November 8, 2001; means presented are the averages of 6 plants in each of two greenhouses with the same cover. Different letters in the same row indicate significant difference (po0:05), according to the LSD test.
Fig. 2. Marketable fruit yield of aubergine grown in UV+PE, IR+PE, D-Poly and PE houses in 2001. Accumulated yield (a) and total yield (b) presented are average from six plants in each of two greenhouses with the same cover (accumulative yield between September 15–November 16, 2001). Different letters on the error bars indicate significant differences (po0:05), according to the LSD test.
Table 5 Results of cost/benefit analyses for aubergine production in greenhouses covered with different covering materialsa Covering materials
P ($)
O and M ($)
S ($)
TC ($)
Yield (kg year1)
Price ($)
Benefit
Cost/benefit ratio
UV+PE IR+PE D-Poly PE
429 450 450 393
64.35 67.50 67.50 58.95
42.90 45.00 45.00 39.30
38.18 40.05 40.05 34.98
91.31 100.33 134.14 83.87
0.54 0.54 0.54 0.54
49.31 54.18 72.44 45.29
0.77 0.74 0.55 0.42
a
All values calculated for total floor area that is 27 m2.
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Heat energy requirement (MJ m-2 month-1)
600000 UV+PE IR+PE D-Poly PE
500000 400000 300000 200000 100000 0 September
October
November
Fig. 3. Monthly heat energy requirements in unheated greenhouses with different cover materials.
Heating of a greenhouse is an essential requirement for proper growth and development of winter growing crops [16]. Monthly heating energy requirements in greenhouses with different covers were presented in Fig. 3; considering all months, the lowest heating energy requirement was in D-Poly houses. Heating energy requirement in greenhouses were the highest in November.
4. Discussion The selection of the greenhouse cover material depends on many factors, such as initial investment, maintenance cost, its effects on greenhouse crop productivity, local climate and technological support and developments [3]. Several studies on the effect of covering materials on growth, development and yield of plants have indicated that the local climate conditions have a great influence on the effectiveness of covering materials [3,17,18]. The results of the present study were found to be in agreement with the results of Papadopoulos and Hao [3] because of the similar latitude of the locations. Many researchers indicated that temperature and relative humidity in D-Poly greenhouses were higher than standard single-layer polyethylene greenhouses resulting in higher plant yield [3,7,19–21]. Results from the present study support this conclusion. Stromme et al. [21] suggested that the air temperature in double-skinned houses might be higher than in a single-skinned house at the same temperature set point. The higher air temperature may stimulate plant growth and development in double-skinned greenhouses. This has been proven to be true in this study. The air temperature in D-Poly and IR+PE houses was up to 2–3 1C higher than in the UV+PE and PE houses, and the largest difference occurred in the coldest month. This increase in air temperature might have compensated for the loss in light since high temperature in young plants increases leaf growth and promotes the interception of light [22]. The higher air temperature was part of the positive effect of double-skinned houses in terms of insulation. In this study, heating requirement was reduced by 5% in D-Poly compared UV+PE, IR+PE and PE houses. High humidity levels resulted in an increased photosynthetic rate [19,20], fresh and dry weight, stem length and leaf area, and final total cucumber yield was positively related to daytime humidity, when the other variables are kept constant [7]. The greenhouse PAR transmission and heating energy requirements are not only affected by cover materials, but also by many other factors, such as greenhouse structures, size, orientation and thermal screens [23,24]. Therefore, the microclimate and crop responses in mini-greenhouses might be slightly different from to large multispan greenhouses and, therefore, some caution should be exercised in the interpretation of our findings.
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The plants in D-Poly houses achieved optimal usage of their resources through reduced specific leaf weight, and a greater leaf and fruit growth. Plants in D-Poly houses showed different biomass distribution and thus higher yields than UV+PE, IR+PE and PE, houses. Uzun [25] found that there was a positive relationship between light intensity and plant stem diameter in both tomato and aubergine. It was also found that stem diameter in tomato and aubergine increased curvilinearly with increasing temperatures as well as an interactive effect of temperature and light intensity on stem diameter. It was also found that an increase in temperature from 10 to 32 1C would result in increasing plant height in tomato and aubergine [2,9,11,26–28]. Cemek [27] indicated that the greenhouses covered with D-Poly had higher temperatures and increased plant height in cucumber. In the present study, the highest plant height was obtained from the aubergine plants grown in D-Poly covered greenhouses, which also had higher temperature. Increase in daily mean light integral caused a decline in both SLA and LAR, as the effect of decreasing temperature. It was also observed that the changes in RGR with the lowest daily mean light integral was related to changes in LAR of aubergine rather than by NAR, whereas changes in RGR of the aubergine grown with higher daily mean light integral (PE) was determined mainly by NAR but also by LAR. This is in good agreement with [9,29,30], which showed that changes in RGR due to temperature regime are mainly caused by the changes in LAR. When considering changes in RGR due to daily mean light integral, Bruggink [31] reported that there was a negative correlation of LAR with NAR at different light levels. In the present study, it was also observed that the relationships between NAR and either LAR or LWR were negatively related for aubergine. It could be suggested that the decline in LAR, SLA and LWR with increasing light levels and the increase in NAR with the same light integrals caused the negative relationship between NAR and either LAR or LWR in each greenhouses. Many studies have shown that SLA increases linearly with increasing temperatures and declines with increasing light intensities [9,28,29]. When considering the results obtained from the present study, the highest SLA value was obtained from the plants grown in D-Poly greenhouses. D-Poly greenhouses had higher temperatures and lower light intensities than the other greenhouses. As a result of this, higher SLA values were obtained from the plants grown in DPoly greenhouses. Higher SLA values from the plants in IR+PE covered greenhouses than those of greenhouses covered with PE and UV+PE can be explained by higher leaf area values in IR+PE greenhouses. To meet the heating requirement in greenhouses, the most economic way was to use fuel oil for heating in aubergine production in greenhouses while the reverse was the case for lignite. When comparing covering material in terms of energy cost, D-Poly has the minimum energy costs compared to others due to energy saving. IR+PE and UV+PE followed it (Table 6). Gupta and Chandra [23] suggested that double wall glazing enabled reduction in the heating requirement of the gothic greenhouse by 23%. Farmers engaged in aubergine production have to produce 19 kg per m2 more aubergine to compensate for the heating cost. Farmers had to produce 19 kg aubergine to meet heating cost if they use fuel oil to heat greenhouses covered with D-Poly. While that number for lignite is 26 kg aubergine.
Table 6 Seasonal energy requirements for greenhouses covered with different cover materials according to different energy sources and their costs for per small greenhouse (9 3 m2)a UV+PE
Lignite (kg) Coal (kg) Fuel oil (kg) LPG (kg) a
IR+PE
D-Poly
PE
Requirement
Cost ($)
Requirement
Cost ($)
Requirement
Cost ($)
Requirement
Cost ($)
197.8 101.2 65.32 54.28
41.54 40.58 30.05 36.37
108.56 59.38 33.12 29.44
22.80 21.34 15.24 19.72
67.16 32.48 22.26 18.31
14.10 12.99 10.24 12.27
268.84 132.48 82.80 92.00
56.41 52.99 38.09 61.64
When calculating energy requirements for greenhouses, thermal value for lignite, coal, fuel oil and LPG were assumed 12 500, 25 000, 40 000 and 46 000 kJ kg1, respectively.
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5. Conclusions In the light of our empirical findings, the most convincing results were obtained from D-Poly greenhouses when compared to IR+PE, UV+ PE and PE covered-greenhouses. D-Poly houses were not only more profitable but also had a lower heating energy requirement compared to others. Hence, It could be suggested that D-Poly greenhouses be used for late production of aubergine in autumn season in Samsun, in the Black Sea Region or region having similar climate conditions. References [1] Noble R, Holder R. Pot plant production under various greenhouse cladding materials. J Hortic Sci 1989;64:485–93. [2] Cockshull KE, Graves CJ, Carol RJ. The influence of shading on yield of glasshouse tomatoes. J Hortic Sci 1992;67(1):11–24. [3] Papadopoulos AP, Hao X. Effects of greenhouse covers on seedless cucumber growth, productivity, and enery use. Sci Hortic 1997;68:113–23. [4] Blom TJ, Ingratta FJ. The use of polyethylene film as greenhouse glazing in North America. 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