生物炭施用對盆栽水稻及菾菜土壤溫室氣體排放之影響

Abstract

生質以熱裂解生產生質能源的固體副產物稱為生物炭 (biochar, BC)。最近許多研究指出，將生物炭施用至土壤中，具有可減少土壤排放溫室氣體、增加土壤碳貯存及增加作物產量等多重效益。除此之外，亦可間接減少能源及生質廢棄物處理的問題。本研究之目的為先建立一 「盆栽試驗土壤溫室氣體排放之測定方法」，再藉由盆栽試驗探究生物炭：(1)對土壤溫室氣體排放之影響、(2)對土壤碳貯存之影響以及 (3)對水稻及菾菜生長與產量之影響。本研究使用人工林疏伐之柳杉廢木屑於290及700 ℃下製成生物炭 (BC290及BC700)，以2%及5%比例施用至酸性的平鎮系 (Pc) 及鹼性的和興系 (Hb) 土壤，於溫室種植水稻及菾菜。試驗共有六種處理：(1) BK1 (對照組I)，不施用生物炭及肥料。(2) BK2 (對照組II)，不施用生物炭但施肥 (每盆水稻施肥量為1 g N - 1 g P - 1 g K，每盆菾菜施肥量為0.5 g N - 0.1 g P- 0.4 g K)。(3) BC290-2%，施用2% BC290生物炭及施肥。 (4) BC290-5%，施用5% BC290生物炭及施肥。 (5) BC700-2%，施用2% BC700生物炭及施肥。(6) BC700-5%，施用5% BC700生物炭及施肥。每處理三重複。盆栽試驗於2011年4月5日開始，定期以前述建立之方法監測土壤排放之溫室氣體 (CO2、CH4及N2O) ，並計算二氧化碳當量，以評估施用生物炭對盆栽土壤溫室氣體排放之影響。以土壤排放二氧化碳累積量配合生物炭之碳添加量估算土壤碳貯存量，以評估施用生物炭對土壤碳貯存之影響。定期採樣及分析土壤性質 (pH、有效性磷及鉀、全氮、CEC及有機質含量)，並定期記錄水稻、菾菜株高及水稻分蘗數，於收穫後測定產量 (穀粒重或乾物重) 以評估施用生物炭對土壤性質、作物生長及產量之影響。結果顯示：本研究建立一「盆栽試驗土壤溫室氣體排放之測定方法」，可供本研究及後續相關研究應用。盆栽試驗結果顯示，施用生物炭對土壤溫室氣體排放之影響，在水稻平鎮系及和興系土壤施用5% BC700可顯著減少土壤排放二氧化碳當量累積量 (p < 0.05)，在菾菜平鎮系土壤施用2% BC700可顯著減少土壤排放二氧化碳當量累積量 (p < 0.05)，但在菾菜和興系土壤施用生物炭則無顯著影響。對土壤碳貯存之影響，無論在水稻平鎮系及和興系土壤或在菾菜平鎮系及和興系土壤，皆以施用5% B700效果最為顯著 (p < 0.05)。對作物生長及產量之影響，在施肥條件下施用生物炭對水稻及菾菜皆無顯著影響。

Biochar (BC) is a byproduct from biomass pyrolysis or gasification which used to produce biofuels. Recent studies have indicated that application of biochar to soils results in reducing greenhouse gas (GHG) emissions from soil, increasing soil carbon sequestration, and improving crop yields. Besides, biochar production could indirectly solve energy and biomass wastes problems. The objectives of this study were first to develop a method to measure greenhouse gas emissions from soil in a pot experiment, and then to examine the effects of biochar application on (1) greenhouse gas emissions from soils, (2) soil carbon sequestration, and (3) crop growth and yield in pot experiments. Biochars were produced at 290 (BC290) and 700℃ (BC700) by slow pyrolysis of Japanese Cedar woodchip thinned from plantation. The acidic Pinchen series (Pc) and alkaline Hoshin series (Hb) soils in Taiwan were selected to be planted with rice and leaf beet, and applied with BC290 or BC700 at a rate of 2% or 5% with or without fertilizers. There were six treatments in this study: (1) BK1 (Control I): applying 0% BC without fertilizer, (2) BK2 (Control II): applying 0% BC with fertilizers (1 g N - 1 g P - 1 g K for rice or 0.5 g N - 0.1 g P- 0.4 g K for leaf beet), (3) BC290-2%: applying 2% BC290 with fertilizers, (4) BC290-5%: applying 5% BC290 with fertilizers, (5) BC700-2%: applying 2% BC700 with fertilizers, and (6) BC700-5%: applying 5% BC700 with fertilizers, and triplicates for each treatment. Pot experiments were started on April 5, 2011. GHG emissions were monitored using closed chamber method during the rice and leaf beet growing periods and further calculated in carbon dioxide equivalent (CO2e). Carbon sequestrations were estimated from the differences between carbon addition (biochar-C) and carbon loss (CO2-C). Soils were sampled periodically and analyzed pH, CEC, available phosphorous, available potassium, total nitrogen, and organic carbon contents. Plant growth (plant height and tiller number) of rice and leaf beet were measured weekly and grain yields or dry matter weights were also measured after harvesting. The method for measuring greenhouse gas emissions from soil in a pot experiment was newly developed and used in this study, and could also be used in other related studies. The results of pot experiments showed that applying 5% BC700 significantly reduced cumulative CO2e emissions from both rice-planted Pc and Hb soils, and applying 2% BC700 significantly reduced cumulative CO2e emission from leaf beet-planted Pc soil compared with control II (p < 0.05). For soil carbon sequestration, the effects of applying 5% BC700 were the most significant in both rice- and leaf beet-planted soils (p < 0.05). As for crop growth and yield, there were no significant effects among all treatments with fertilizers (p > 0.05).