| Agriculture becomes one of the main energy consumption industries in China from the last decades. In the context of global energy crisis, how to reduce energy consumption is a focus of sustainable development of agriculture in the future. With the development of agricultural technology, the form of agriculture is changing from traditional agriculture to protected agriculture. Protected agriculture, which is an important part of agriculture, is one of the high energy consumption agro-ecosystems. The improvement of resource utilization and facility construction will change the energy consumption of protected agriculture. The premise of optimizing facility layout and energy consumption is quantitatively analyzing of the status of energy consumption in protected agriculture life cycle and accurately predicting energy-saving potential in the future. The optimization of greenhouse crop production system operation program and the improvement of design progress play important roles in guiding energy saving of protected agriculture. The objective of this study is to quantitatively estimate energy consumption of three types of protected agriculture ecosystems by using life cycle assessment (LCA) and a model-based decision support system for temperature set point optimization for greenhouse heating considering both greenhouse construction and crop production. The key factors that impact the energy consumption were determined. Based on above results, scenario analysis of energy-saving potential under improved resource utilization of crop production and greenhouse materialss were conducted. Assessments of the total production cost and economic feasibility of energy-saving potential were performed by using cost analysis.1. The status of energy consumption in greenhouse production system:energy consumption per unit yield for greenhouse tomato and cucumber production were quantitatively estimated by using LCA based on literature and experimental data. The results show that the range of energy consumption per unit yield of tomato and cucumber grown in solar greenhouses in north of China (32°N-48°N) were 2.80 MJ-kg-1～4.17 MJ-kg-1 and 2.90 MJ-kg-1～4.33 MJ-kg-1, respectively. The regional difference was not obvious. The key factors determined energy consumption were construction (58%-70%), nitrogen fertilizer (6%-17%), irrigation water (5%-9%)and pesticide (2%-14%). The Energy consumption of greenhouse wall accounts for approximately 45% of total energy consumption caused by greenhouse construction. Plastic multi-span greenhouse is the representative type of modern greenhouses and can be found all around China. The range of energy consumption per unit yield of tomato and cucumber grown in plastic greenhouses were 11.0 MJ.kg-1～270.0 MJ-kg-1 and 14.0 MJ-kg-1～280.0 MJ-kg-1, respectively. Energy consumption of temperature control accounts for 80%-99% of total energy consumption, and was increased with the increasing of latitude. Plastic tunnel greenhouse can be used for long-term production in the south of china. The range of energy consumption per unit yield for tomato and cucumber grown in plastic tunnels were 1.24 MJ-kg-1-2.10 MJ-kg-1 and 1.32 MJ-kg-1～2.42 MJ-kg-1, respectively. The key factors determined energy consumption of plastic tunnels were construction (17%～31%), nitrogen fertilizer (7%～33%), pesticide (6%-16%)and human labor (9%～15%). The average value of energy ratio of renewable resource of solar greenhouse ecosystem, plastic tunnel greenhouse ecosystem and plastic multi-span greenhouse ecosystem were about 60%-70%,40%,0%.2. Energy-saving potential of greenhouse ecosystems:setting three scenarios 3ased on the current status of energy consumption and the key factors that impact energy consumption and assessing energy-saving potential of different greenhouse ecosystems through scenario analysis.(1) Scenario 1:Improve resource utilization of crop production and only consider the improvements of nitrogen use efficiency, water use efficiency and pesticide use efficiency. ①Assume that the yield was constant and the mount of nitrogen fertilizer, irrigation and pesticide were reduced, NUE and WUE achieved the advanced countries and pesticide use efficiency increased 10% of domestic level. The results show that energy consumption per unit yield for tomato production in solar greenhouse ecosystem, multi-span greenhouse ecosystem and plastic tunnel greenhouse ecosystem decreased, respectively,5.8%-11.0%,0.2%-3.7% and 12.1%～20.1%, and for cucumber production, energy consumption per unit yield decreased 7.1%～13.0%,0.2%-3.5% and 12.6%-18.3%, respectively. ②Assumed that and the mount of nitrogen fertilizer, irrigation and pesticide were sufficient and the yield was predicted in the future by using the Model-Management of Nitrogen Concentration in the Nutrient Solution For Soilless Cultivated Cucumber Crops in Greenhouse, only consider the plastic multi-span greenhouse ecosystem for cucumber production. The results show that the energy consumption per unit yield for cucumber production in plastic multi-span greenhouse decreased 50%.(2) Scenario 2:Improve greenhouse materials and change cob wall-bamboo framework solar greenhouse into cob wall-steel framework or brick wall-steel framework. The results show that energy consumption per unit yield for tomato and cucumber production in cob wall-steel framework solar greenhouse further decreased 6.8%-7.9% and 6.5%-8.0%, respectively, compared with cob wall-bamboo framework solar greenhouse. However, brick wall-steel framework solar greenhouse ecosystem increased energy consumption by 10.9%-12.7% and 10.5%～12.8%, respectively, for tomato and cucumber production.(3) Scenario 3:Improve resource utilization of crop production and greenhouse materials. The results show that energy consumption per unit yield for tomato and cucumber production in cob wall-steel framework solar greenhouse decreased 14.1%-18.1% and 13.8%-18.9%, respectively. Brick wall-steel framework solar greenhouse ecosystem in most regions increased energy consumption by 0%-6.1% and 0%-7.0% for tomato and cucumber production, respectively.3. Economic feasibility of energy-saving potential in different scenarios for greenhouse crop production. Evaluate the cost per unit yield and the change of cost in different scenarios by using cost analysis based on the price data of the production materials. The results show that the ranges of cost per unit yield for tomato and cucumber production in solar greenhouses were 0.68 yuan-kg-1-1.16 yuan-kg-1 and 0.77 yuan-kg-1-1.23 yuan-kg-1, respectively. The ranges of cost per unit yield in plastic multi-span greenhouse were 0.98 yuan-kg-1～5.97 yuan-kg-1 and 0.96 yuan-kg-1-5.72 yuan-kg-1, respectively. The key factors determined the cost were the amount and the price of coal in the local area. The ranges of cost per unit yield for plastic tunnel greenhouse wer 0.99 yuan-kg-1～1.76 yuan·kg-1 and 1.08 yuan·kg-1～2.07 yuan-kg-1, respectively. Improve resource utilization of crop production:If the yield was constant and the mount of nitrogen fertilizer, irrigation and pesticide were reduced not only saved energy but also reduced cost slightly, especially solar greenhouse ecosystem and plastic tunnel greenhouse ecosystem. If the the mount of nitrogen fertilizer, irrigation and pesticide were sufficient and the yield was improved would decreased the cost per uint yield of multi-span greenhouse ecosystem, obviously. Cost per unit yield for tomato and cucumber production in cob wall-steel framework solar greenhouse decreased 8.06%-10.26% and 7.68%～10.46%, respectively, by improving greenhouse materials compared with cob wall-bamboo framework solar greenhouse. However, brick wall-steel framework solar greenhouse ecosystem increased cost by 2.14%-8.06% and 2.22%-8.45%, respectively, for tomato and cucumber production. Considering the improvement of resource utilization of crop production and greenhouse materials, the cost per unit yield for tomato and cucumber production in cob wall-steel framework solar greenhouse decreased 9.34%-11.56% and 9.59%～11.95%, respectively; brick wall-steel framework solar greenhouse ecosystem increased cost by 0.97%-7.02% andO.29%-7.06%, respectively.In summary, in order to reduce energy consumption, greenhouse materials and resource utilization of crop production should be improved for solar greenhouse ecosystem and resource utilization should be improved for plastic tunnel greenhouse. The energy-saving potential of plastic multi-span greenhouse ecosystem is small expect the yield level was improved.This study provided reference to estimate the contribution of energy saving of protected agriculture to the whole agricultural ecosystem. Further studies on the potential and methods of energy saving will provide indispensable data and decision support for developing energy saving programs of agriculture and optimizing facility layout. |
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