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Energy efficiency of organic pear production in greenhouses in China

Published online by Cambridge University Press:  18 March 2010

Yuexian Liu ,
Henning Høgh-Jensen ,
Henrik Egelyng  and
Vibeke Langer
Yuexian Liu*
Affiliation:
Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, Højbakkegaard Alle 9, DK-2630Taastrup, Denmark. Information Institute, Beijing Academy of Agriculture and Forestry, Beijing100094, P.R. China.
Henning Høgh-Jensen
Affiliation:
Department of Policy Analysis, National Environmental Research Institute, Aarhus University, Frederiksborgvej 399, DK-4000Roskilde, Denmark.
Henrik Egelyng
Affiliation:
Danish Institute for International Studies, Strandgade 56, DK-1401Copenhagen, Denmark.
Vibeke Langer
Affiliation:
Department of Agriculture and Ecology, Faculty of Life Sciences, University of Copenhagen, Højbakkegaard Alle 9, DK-2630Taastrup, Denmark.
*
*Corresponding author: liy@life.ku.dk
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Abstract

The development of organic protected cultivation taking place in densely populated areas has raised the question whether it is an environmentally friendly production system. The present study investigated energy consumption of organic pear production in two production systems, namely in traditional Chinese solar greenhouses and in the open field. In both production systems, energy output/input ratio and energy productivity were used as indicators to determine the energy efficiency; yield, cost of production, net economic return per land area unit and benefit/cost ratio were used to evaluate economic productivity. The analysis results indicated that energy input and energy output per land area unit in the solar greenhouse were higher than in the open field; whereas energy efficiency in terms of output/input ratio and energy productivity were lower in the solar greenhouse than those in the open field. However, if energy input sequestered in the protected structure was excluded in the solar greenhouse production system, energy efficiency was higher in the greenhouse system than in the open-field system. Our analysis further showed that the economic costs, the yield, cost of production, gross product value and net income per land area unit in the greenhouse were more than twice as high as those in the open field due to a higher tree density and a premium price. However, the production taking place in the open field used a great share of renewable energy and higher energy efficiency, which may comply more with the principles of organic farming than the greenhouse production system.

Keywords

organic pearenergy efficiencyeconomic analysisgreenhouse
Type
Research Papers
Information
Renewable Agriculture and Food Systems , Volume 25 , Issue 3 , September 2010 , pp. 196 - 203
Copyright
Copyright © Cambridge University Press 2010

Introduction

A substantial greenhouse industry has emerged near Chinese cities concentrating on high-value products like certified organic fruits for domestic consumption. In 2004, the total area of protected cultivation in China was 2.5 million ha accounting for 1.6% of the total arable land areaReference Zhang1. About 50% of the protected cultivation area is occupied by traditional Chinese solar greenhousesReference Luo2. This development of organic protected cultivation is driven by several factors: the shortage of land in the densely populated peri-urban areas and a growing market for fresh organic produce. The solar greenhouses offer an opportunity for extending the season, providing the farmers with the benefit of early harvests and good premium prices. However, little attention has been given to the energy costs in this type of organic protected cultivation and its compliance with the expectations of organic production systems of environmental soundness.

Efficient use of energy is an important parameter in the evaluation of the environmental impact of production systems. Previous studies on energy consumption in protected cultivation by Fluck and ShawReference Fluck and Shaw3, StanhillReference Stanhill4, Biondi et al.Reference Biondi, Monarca and Panaro5 and El-HelepiReference El-Helepi6 indicated an increase of energy input with an improved productivity as a result of intensive inputs of protected structures. Comparing open field and various protected tomato production systems, StanhillReference Stanhill4 reported that the indirect energy sequestered in the protective structures accounted for more than 50% of the total energy inputs in an unheated glasshouse system. However, he did find the energy intensity of the studied unheated glasshouse system to be of the same magnitude as plastic covers and tunnels, whereas the intensity in heated glasshouses was 30 times higher. This suggests that systems like the traditional Chinese solar greenhouse, exploiting natural advantages like high winter solar radiation, may have potential as an environmentally sound production system in areas with a scarcity of land.

Farmers, however, are interested in profitability rather than in energy efficiency, especially in regions with limited agricultural land. Economic benefit per area is the major driving force for the protected cultivation. Therefore, a combination of economy and energy analysis of a production system is appropriate for the application of best practice strategies for sustainable developmentReference Reganold, Glover, Andrews and Hinman7.

In this study, energy efficiency, energy intensity and the amounts of renewable energy use, as well as net returns per land area unit and the benefit/cost ratio, were compared between organic pears produced in an open field and in a traditional solar greenhouse, with the aim of identifying possible strategies for reducing energy consumption in protected organic cultivation.

Materials and methods

Description of the two organic pear production systems

The study was conducted in two organic pear production systems in Beijing suburbs, China during 2007–2008. The traditional Chinese solar greenhouse used for the organic pear production is located in the east of Beijing (40°17′N, 117°16′E), Pinggu District, and the open field is located in the southeast of Beijing (39°60′N, 116°49′E), Daxing District. The traditional Chinese solar greenhouse is the so-called ‘energy-saving greenhouse’Reference Chen8, shown in Figure 1. The greenhouse consists of a concrete non-transparent wall and gables on the north, west and east sides, respectively, and a transparent plastic incline roof on the south sideReference Luo2. Energy for heating stems from solar radiation, as insulation mattress are rolled up during the daytime, and put down from late afternoon to early morning to prevent heat loss. The north wall stores solar energy by absorbing solar radiation during the daytime and the thermal radiation from the wall maintains the temperature in the greenhouse during night. The pear variety produced is Pyrus pyrifolia (Burm. f.) Nakai, called Whangkeum Bae. In the greenhouse, pears were harvested at the beginning of June, while in the open-field pears were harvested in the middle of August.

Figure 1. Structure of the traditional Chinese solar greenhouse: 1, concrete north wall; 2, the back roof; 3, the heat insulation mattress; 4, the frame of the front roof; 5, the ditch for preventing greenhouse heat loss through horizontal soil heat conduction.

The open-field system represents a common organic production system in the Daxing District, covering c. 300 ha of land in 2007. The system of organic pears produced in the greenhouse is seen more occasionally (approx. 3 ha in the district), but the solar greenhouse is widespread. Tree density in the greenhouse production system is almost twice as high as in the open-field system (990 and 405 trees ha−1, respectively).

Data collection

The open-field farm is owned by an association and the data were collected through personal interviews with the production manager. The data in the greenhouse farm were collected through personal interviews with the grower.

The boundary of the energy analysis was the field gate, and marketing, sorting and storage of the products were not included. For example, transport from the production sites to final users in both systems was assumed to be the same, therefore, the difference of transportation costs in terms of energy and economic costs were not considered in the analysis. For both production systems, energy, material and fuel consumption, as well as time needed to complete field operations, were recorded. Information on labor hours, tools (pruning scissors and hoe, etc.), machinery, energy consumption, uses of farmyard manure and organic pesticides was collected. Field operations in the greenhouse and in the open-field system during the study period (2007–2008) are shown in Table 1. In both organic pear production systems, farmyard manure and organic compost were used as organic fertilizers.

Table 1. Field operations in organic pear production systems in the Beijing area.

Energy accounting

The energy analysis conducted in this study was aimed at estimating the difference in total energy inputs between organic pears produced in the open field and in the greenhouse. Input categories were machinery, labor, fossil fuel, organic fertilizers, organic pesticides, mulch input and protective structure of the traditional Chinese solar greenhouse, as described by some other researchersReference Fluck and Shaw3, Reference Stanhill4, Reference El-Helepi6.

The following applications were identified to be the possible sources of additional energy use in the greenhouse system: (1) heat insulation mattress, including agricultural polyethylene film and straw mulch; and (2) the amortization of the solar greenhouse. The energy sequestered in the amortization of the solar greenhouse was included and calculated in 20-year depreciation, whereas the energy on machinery and labor for the construction of the solar greenhouse was excluded in this study.

In addition, input energy in this study was categorized into two groups: fossil energy and renewable energy. Fossil energy included direct energy (electricity, gasoline and diesel fuel) and indirect energy (machinery, bags, mulch input and protective structure of the solar greenhouse). Renewable energy included labor, organic fertilizers and organic pesticides.

For the energy output side in the two organic production systems, we considered only biological energy that is embodied in cash crops, i.e. organic pears.

Energy equivalents calculation

The energy equivalents of inputs used in the two organic pear production systems are listed in Tables 2–4. The embodied energy of machinery and human labor was determined. Total energy embodied in machinery included energy for raw materials, manufacturing, repairs and maintenance, and energy for transportation (Table 3). Taking into account the total weight and the life of machinery as used in practice, the energy required for each operation was calculated.

Table 2. Energy equivalents of inputs of consumables and human labor and outputs.

Table 3. Energy equivalents of machinery and hardware used in the study.

Table 4. Energy equivalents of inputs for the traditional Chinese solar greenhouse. (The construction of the solar greenhouse was sourced from the GB/T 19561–2004. ‘Rules for constructing the energy saving sunlight greenhouse in cold zones’, issued by the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) and Standardization Administration of the People's Republic of China in 2004.).

Energy equivalents for biological pesticides were not recorded in the literature. However, these are permitted and used for pest management on certified organic production in China. Therefore, we estimated the energy equivalent of biological pesticides based on the active ingredient, as for chemical pesticides.

Depending on the context, manure may be considered either a valuable source of nutrients replacing synthetic fertilizers, a waste product from livestock production, or a potential energy source, e.g. for biogas production. In this study, we regarded manure as a source of nutrients, and the ‘substitution method’ was used to calculate the energy input of animal manure, which equates the energy equivalent of farmyard manure with that of mineral fertilizer equivalents corresponding to the fertilization effect of the applied manureReference Parr, Colacicco and Helsel16, Reference Stout22, Reference Hülsbergen, Feil, Biermann, Rathke, Kalk and Diepenbrock23, Reference Deike, Pallutt and Christen24. Since nitrogen availability of organic manure is lower than that of mineral fertilizer, 1 kg of N in organic fertilizer is assumed to substitute 0.428 kg mineral fertilizer NReference Hülsbergen, Feil, Biermann, Rathke, Kalk and Diepenbrock23. The effectiveness of organic fertilizer P and K was assumed to be similar to that of mineral P and K for the sake of simplicityReference Schilling25. The energy content of farmyard manure used as fertilizer was calculated by multiplying available N, P and K contents with the energy required to produce the corresponding amount of synthetic N, P and K fertilizers, respectively.

Calculation of energy balancing indicators and economic indicators

In this study, energy balancing indicators such as output–input ratio (energy efficiency), energy productivity and energy intensity for organic pear production were calculated using the following equations (1)–(3); economic indicators such as net income and benefit–cost ratio were calculated using the equations (4) and (5):

(1)
{\rm Output} \ndash{\rm input \ ratio} \equals {{{\rm Energy \ output}\ \lpar {\rm MJ}\sol {\rm ha}\rpar } \over {{\rm Energy \ input}\ \lpar {\rm MJ}\sol {\rm ha}\rpar }}
(2)
{\rm Energy \ productivity} \equals {{{\rm Energy \ output}\ \lpar {\rm MJ}\sol {\rm ha}\rpar } \over {{\rm Pear \ output}\ \lpar {\rm kg}\sol {\rm ha}\rpar }}
(3)
{\rm Energy \ intensity} \equals {{{\rm Energy \ input}\ \lpar {\rm MJ}\sol {\rm ha}\rpar } \over {{\rm Pear \ output}\ \lpar {\rm kg}\sol {\rm ha}\rpar }}
(4)
\eqalign{ {\rm Net}\,{\rm income} \equals \tab {\rm Gross}\,{\rm product}\,{\rm value}\ \lpar \$ \sol {\rm ha}\rpar \cr \tab \minus {\rm Cost}\,{\rm of}\,{\rm production}\ \lpar \$ \sol {\rm ha}\rpar \cr}
(5)
{\rm Benefit}\ndash {\rm cost \ ratio} \equals {{{\rm Gross \ product \ value}\ \lpar \dollar \sol {\rm ha}\rpar } \over {{\rm Cost \ of \ production}\ \lpar \dollar \sol {\rm ha}\rpar }}

Results and discussion

Distribution of energy inputs for field operations between two production systems

Energy inputs for field operations per land area unit for organic pear production in the open field and in the solar greenhouse are summarized in Table 5. Overall, organic pears produced in the greenhouse were more than ten times as energy demanding as in the open field. This was mainly due to the large energy cost of the protective structure including the amortization of the greenhouse and heat insulation mattress, which accounted for 84% of the total energy use in the solar greenhouse.

Table 5. Energy inputs (GJ ha−1) for field operations in the open field and in the greenhouse systems.

Energy inputs for field operations were twice as high in the greenhouse (143 GJ ha−1) as in the open field (76 GJ ha−1), if the energy cost of the protective structure was excluded. In the open-field system, energy input for fertilizer application was the largest contributor to the energy consumption (74%). Producing organic pears in the solar greenhouse required additional energy for field operations such as pest management, weed control and irrigation compared with organic pears produced in the open field, whereas energy input on soil cultivation was lower in the greenhouseReference Fluck and Shaw3, Reference El-Helepi6.

Energy input for irrigation in the greenhouse, where trees largely depended on irrigation and the water requirement per land area unit was greater due to the higher tree density, was more than five times that of the open field. Fluck and ShawReference Fluck and Shaw3 and StanhillReference Stanhill4 also reported more energy to be required for irrigation in protected cultivation, including both direct energy for irrigation and indirect energy for irrigation systems. Also, the energy inputs for pest management in the open-field system were 50% less than those in the greenhouse system. Among these, energy input for organic pesticides was 2.6 GJ ha−1 in the open field, which was 71% less than that in the greenhouse since humidity and temperature were more favorable in the greenhouse for pest infestation. StanhillReference Stanhill4 also reported that 33–44% more energy on pesticides was consumed in an unheated glasshouse than in the open field. However, El-HelepiReference El-Helepi6 found that the protected cultivation system consumed less energy in terms of pesticides compared to the open-field system, due to a reduction in the number of treatments. The energy input for weed control in the greenhouse was much more than in the open field. In the greenhouse, the black polyethylene mulch used for weed control resulted in a large energy cost (33 GJ ha−1), which accounted for 98% of the energy inputs for weed control; whereas the energy input of the mower, and correspondingly direct energy accounted for weed control in the open field, only amounted to 0.6 GJ ha−1.

Energy inputs on soil cultivation in the open-field system were 1.5 GJ ha−1, while there were no energy inputs for soil cultivation in the greenhouse system. This is in accordance with the results by Fluck and ShawReference Fluck and Shaw3 and El-HelepiReference El-Helepi6 reported that energy consumption could be decreased with plastic mulch for fewer cultivations and fewer applications of herbicides.

The energy inputs on machinery in the open field (29 GJ ha−1) were slightly higher than that in the greenhouse (27 GJ ha−1). This can be explained by the fact that the greenhouse system involves less use of large machinery such as agricultural tractors and rotary tiller. Consequently, the energy expenditure for fuel in the open-field system (4.5 GJ ha−1) was 49% more than that for the greenhouse system (3 GJ ha−1). The machinery in the open-field system was mainly used for field operations, such as soil cultivation, weed control and pest management.

Fossil and renewable energy

The total energy input classified as fossil energy and renewable energy is illustrated in Table 6. The share of fossil energy input including direct and indirect energy was significantly higher in the greenhouse system (833 GJ ha−1) than in the open-field system (40 GJ ha−1) as a result of larger energy consumption on protective structures in the greenhouse, which accounts for 84%. Renewable energy input in the open-field system accounted for 47% of the total energy input, but 7.7% in the greenhouse system. Organic fertilizer as renewable energy resource had the highest share in the open-field systems (38%).

Table 6. Total energy input (GJ ha−1) in the form of fossil and renewable energy in organic pear production in the open field and greenhouse systems.

Assessment of energy efficiency by using different energy balance indicators in the two production systems

Energy balance indicators for organic pear production in the open field and in the solar greenhouse are summarized in Table 7. Energy input per land area unit was much higher in the greenhouse production system compared with the open-field system, while energy output in the greenhouse production system (78 GJ ha−1) was twice as high as that of the open field (35 GJ ha−1). When comparing the two production systems with regard to energy efficiency, lower output/input ratio was found in the greenhouse (Table 7), whereas energy intensity in the greenhouse system was higher compared with the open-field system. Similar results have been reported by some earlier studiesReference Fluck and Shaw3–Reference El-Helepi6—that protected cultivation systems had lower energy efficiency and higher energy intensity when compared with the open-field system. This is because, in the protected cultivation systems, the energy sequestered in the protective structure and fossil fuel represented a significant fraction of the total energy requirement as the degree of environmental control increased. In the present study, the fossil energy and energy sequestered in the protective structure accounted for 83% of the total energy inputs in the solar greenhouse system. This is in agreement with the results given by StanhillReference Stanhill4 that a large fraction of the total energy inputs were the energy sequestered in the protective structure and fossil fuel for the unheated glasshouse in tomato production.

Table 7. Energy balance indicators for organic pear production in the open field and in the greenhouse.

However, if we only consider field operations excluding the energy sequestered in the protective structure, the solar greenhouse system used slightly less energy per unit of product (3.8 MJ kg−1) than the open-field system (4.6 MJ kg−1). Nevertheless, the total energy inputs were still higher in the solar greenhouse, approximately twice higher than in the open-field system, which was in accordance with the findings reported by Ozkan et al.Reference Ozkan, Fert and Karadeniz26 that conventional grape production in the greenhouse had higher energy inputs but lower energy efficiency than that in the open field, even excluding the energy sequestered in the protective structure.

Comparing economic benefits between the two production systems

Within the range of production systems examined by Fluck and ShawReference Fluck and Shaw3, StanhillReference Stanhill4, Biondi et al.Reference Biondi, Monarca and Panaro5 and El-HelepiReference El-Helepi6 and in the present study, the main driving forces for higher energy inputs associated with protected cultivation were to increase crop yield, to produce out-of-season crops and to obtain more economic benefits, especially in contexts where arable land is limited. In this context, yield, production costs, gross product values, net economic return per land area unit and benefit/cost ratio are crucial factors to be considered. As shown in Table 8, the yield, cost of production, gross product value and net income per land area unit in the greenhouse were doubled in relation to those in the open field. However, the benefit–cost ratio in the open-field system (3.94) was slightly higher than that in the greenhouse system (3.70). A similar result has been found by Ozkan et al.Reference Ozkan, Fert and Karadeniz26—that the benefit/cost ratio was lower in greenhouse grape production compared to the open-field system, while energy efficiency in the greenhouse system was lower than that in the open field.

Table 8. Economic results (per land area unit and per 100 trees) for organic pears produced in the open field and in the greenhouse (excluding the economic expense for the construction of the solar greenhouse).

Note: US $1 equals ¥ 6.85. (December 2008).

However, if the calculation was based on 100 trees, the greenhouse system had lower yield, less net income and much more production cost. The yield and net income per 100 trees in the greenhouse system were 7.3 and 2.21%, respectively, less than in the open field, whereas the gross product values per 100 trees of both organic pear production systems were similar. This was, however, ascribed to 15% higher sale prices of the pears produced in the greenhouse system due to harvesting 2–3 months earlier than those in the open field. It can be concluded that the higher tree density in the greenhouse was some kind of strategy to increase yields and obtain higher net income in places where arable land is limited.

Strategies to reduce energy inputs for organic pear production in the greenhouse

Since the protective structure represents by far the largest energy cost in the solar greenhouse system, any potential reduction in the energy inputs for this component would improve the system. Prolonging the life span of the structure, reducing polyethylene thicknessReference Fluck and Shaw3 or reusing plastic for mulchingReference Baker, Henning, Jenni and Stewart27 would all result in a reduced total energy input and increased energy efficiency in the greenhouse production system. For instance, if the life span of the solar greenhouse could be prolonged from 20 to 30 years, 25% of the energy sequestered in the construction of the solar greenhouse would be saved. In addition, as suggested by Munoz et al.Reference Munoz, Anton, Nunez, Paranjpe, Arino, Castells and Montero28, attention should be given to the use of recycled material in building the protective structures. Also, reusing the black polyethylene mulch to control weeds in the greenhouse system would reduce the energy input by 33 GJ ha−1.

Conclusions

Energy consumption per land area unit and per unit of product are fundamental indicators to assess the environmental impact of crop production. The current findings indicate that due to the high energy cost of protective structures, both energy efficiency in terms of output/input ratio and energy productivity are higher in an open-field pear system than in a solar greenhouse, resulting in more energy intensive production in the greenhouse system. Among the inputs, the protective structure accounts for the main part of the energy demands in the greenhouse production system, while organic fertilizer application uses most energy in the open-field system. Including all components of the system, the open-field system may be more in compliance with the expectations of environmental soundness in organic farming than the solar greenhouse. However, given the higher net income per land area unit in the organic greenhouse production system, the traditional Chinese solar greenhouse may have potential to be developed into a viable organic production system. This will require successful development of less energy costly protective structures through increased use of recycled materials and improved durability.

Acknowledgements

A sponsorship to the first author by the China Scholarship Council, additional support by the Danish Food Industry Agency through the GlobalOrg project and the collaboration with the participating farmers and companies are gratefully acknowledged.

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Figure 0

Figure 1. Structure of the traditional Chinese solar greenhouse: 1, concrete north wall; 2, the back roof; 3, the heat insulation mattress; 4, the frame of the front roof; 5, the ditch for preventing greenhouse heat loss through horizontal soil heat conduction.

Figure 1

Table 1. Field operations in organic pear production systems in the Beijing area.

Figure 2

Table 2. Energy equivalents of inputs of consumables and human labor and outputs.

Figure 3

Table 3. Energy equivalents of machinery and hardware used in the study.

Figure 4

Table 4. Energy equivalents of inputs for the traditional Chinese solar greenhouse. (The construction of the solar greenhouse was sourced from the GB/T 19561–2004. ‘Rules for constructing the energy saving sunlight greenhouse in cold zones’, issued by the General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) and Standardization Administration of the People's Republic of China in 2004.).

Figure 5

Table 5. Energy inputs (GJ ha−1) for field operations in the open field and in the greenhouse systems.

Figure 6

Table 6. Total energy input (GJ ha−1) in the form of fossil and renewable energy in organic pear production in the open field and greenhouse systems.

Figure 7

Table 7. Energy balance indicators for organic pear production in the open field and in the greenhouse.

Figure 8

Table 8. Economic results (per land area unit and per 100 trees) for organic pears produced in the open field and in the greenhouse (excluding the economic expense for the construction of the solar greenhouse).