以生命週期評估法探討臺灣高山茶生產對環境之影響

Abstract

農業活動所產生的溫室氣體占全球排放量的13.5%，因此，發展環境親和的栽培方式以達到資源永續經營之目標，是目前的重要課題。而生命週期評估技術(Life Cycle Assessment, LCA) 即是在此領域中發展出的主要工具平臺，可用於農產品的環境衝擊評估。本試驗的研究對象是臺灣高山茶，其種植地區位於海拔高度一千公尺以上的茶園，是最具臺灣特色的烏龍茶之一，其高經濟價值更促進了高山茶業的發展。然而，高海拔茶區自1970 年代末期興起至今，國內關於此類農業生產對環境所造成的影響之研究卻相當稀少，且目前國內外的茶葉生產之 LCA 研究報告，皆未探討田間栽培所產生的溫室氣體量。故本試驗採用生命週期評估的技術，針對臺灣慣行高山茶生產過程中所造成的環境衝擊，進行整體調查與熱點分析，以期建立臺灣高山茶生命週期評估系統，並達到環境親和農業之目的。 本試驗選用南投縣仁愛鄉茶區，海拔1,300 公尺的慣行高山茶園為試驗地點，進行成木期高山茶園之生命週期分析。分析的系統邊界包含原物料與田間栽培、加工製造及包裝配送等，最終以單位面積及單位重量茶葉評估各式環境衝擊，如溫室效應潛勢、碳足跡、優養化及酸化等。結果顯示，成木期高山茶園每公斤茶乾的碳足跡為25.03 kg CO2 eq，而茶園每年每公頃的碳足跡為27,839.5 kg CO2 eq。主要的環境衝擊來自於田間溫室氣體氧化亞氮 (N2O) 的釋放，其排放量平均值高達1331.61 μg N/m2hr，占總生產過程之碳排放量比例74.3%，不宜被忽略。而其高排放量之原因，主要來自於高山茶園的高氮肥施用量、茶園土壤表層殘枝落葉的長年堆積與高山氣候類型所致。故為了使整個評估系統更貼近實際排放量，在此試驗中，將茶園田間溫室氣體的量測與分析方式列入討論，以期進一步達成更完善的高山茶葉生命週期評估系統。

There is about 13.5% artificially greenhouse gas emission generating from agriculture production. Hence it is an important issue to develop an eco-friendly cropping system for sustainable agriculture. Life cycle assessment (LCA) is a method that can be applied to evaluate the environmental impacts of a product, process, or activity throughout its life cycle. LCA can also be used on agriculture products. This study is aim to calculate the environmental impacts of Taiwan high-mountain tea which is an aromatic beverage grown at altitudes higher than 1,000 meters above sea level. Because of its high economic value, it has drawn many people to cultivate high-mountain tea since late 1970s. However, few research has been applied on its environmental impacts. Other life cycle assessment researches of tea products seldom paid attention to greenhouse gas emission from tea field. Therefore this study attempts to analyze hot spots of the environmental impacts of the production process of conventional high-mountain tea. The field experiment was conducted in a conventional tea field at Ren’ai Township, Nantou County which altitude is about 1300 meters above sea level. The system boundary of life cycle assessment consisted of three stages: raw material acquisition of farm inputs (such as fertilizers and pesticides), farming management practices (such as irrigation, weeding and pruning, etc.), tea leaves harvesting, tea processing, packaging and distribution. The impact categories included global warming potential, acidification, eutrophication and energy consumption, and the functional unit was per kilogram of tea or per hectare of farming area. According to the results, the GWP was 25.03 kg CO2 eq/ kg and 27,839.5 kg CO2 eq/ha. The main environmental impact came from field greenhouse gas emission of nitrous oxide (N2O) which was 1331.61μg N/m2 hr accounting for 74.3% of GWP. The reason of this high emission derived from heavy doses of N fertilizers application and thick layer of organic materials on the surface of soil by crop residue accumulation. As a result, this study put field emission into consideration to make the LCA system of Taiwan high-mountain tea more complete to fit in the real phenomenon.