台灣北部現行耕作制度對農田土壤溫室氣體（CO2、CH4、N2O）釋出之影響

Abstract

本研究目的為探討台灣北部現行耕作制度對農田土壤溫室氣體（CO2、CH4、 N2O）釋出之影響，並評估其對農田土壤溫室氣體排放之減量潛力。本研究在台灣北部之苗栗區農業改良場轄區內之四戶農家所有但不同耕作制度之農田土壤，以密閉罩法進行三種溫室氣體（CH4、CO2、N2O）釋出量之田間估測。結果顯示：台灣北部四種耕作制度間之溫室氣體排放總量以二氧化碳當量計算之，其在水田－水田、水田－旱田、旱田－水田與旱田－旱田四種耕作制度中分別為：20,707、8,486、13,324與7,399 kg C ha-1 y-1，以「旱田－旱田」為最低，最高則是「水田－水田」。因此我們若採用適當之耕作制度，其溫室氣體釋出之減量潛力估計平均約為7,460 kg C ha-1 y-1（範圍在1,087至13,308 kg C ha-1 y-1之間）。以逐步迴歸分別統計分析三種溫室氣體與土壤因子間關係之結果，對CO2而言「水田－水田」耕作制度下的顯著貢獻因子依序為：總體密度與土溫（P＜0.05），「水田－旱田」耕作制度下依序為：氣溫、pH、有機質含量與無機態氮含量（P＜0.05），「旱田－水田」耕作制度下依序為：氣溫、總體密度、pH、比導電度與水分充滿孔隙率（WFPS）（P＜0.05），而「旱田－旱田」則是：總體密度、硝酸態氮含量、土溫與比導電度（P＜0.05）。對CH4而言「水田－水田」耕作制度下的顯著貢獻因子依序為：總體密度、土溫、無機態氮含量、水分含量與比導電度（P＜0.05），「水田－旱田」耕作制度下依序為：無機氮態含量、土溫、pH與水分含量（P＜0.05），「旱田－水田」耕作制度下依序為：土溫與總氮含量（P＜0.05），而「旱田－旱田」則是：銨態氮含量、水分含量與無機態氮含量（P＜0.05）。對N2O而言「水田－水田」耕作制度下的顯著貢獻因子依序為：總體密度、硝酸態氮含量與土溫（P＜0.05），「水田－旱田」耕作制度下依序為：氣溫、水分含量、WFPS與無機氮態含量（P＜0.05），「旱田－水田」耕作制度下依序為：氣溫、有機質含量、總體密度、比導電度與WFPS（P＜0.05），而「旱田－旱田」則是：總體密與硝酸態氮含量（P＜0.05）。

Effects of current four cropping systems, including paddy-paddy, paddy-upland, upland-paddy, and upland-upland on emissions of greenhouse gases (CO2, CH4, N2O) from agricultural soils in northern Taiwan were examined by a closed chamber method. The results showed that the total emissions of the three greenhouse gases (expressed as total CO2 equivalent) for the four cropping systems (paddy-paddy, paddy-upland, upland-paddy, upland-upland) were 20,707, 8,486, 13,324, and 7,399 kg C ha-1 y-1, respectively. The mitigation potential of total greenhouse gases emissions could range from 1,087 to 13,308 kg C ha-1 y-1, with a mean value of 7,460 kg C ha-1 y-1. The results of forward stepwise regression analysis showed that the significant contributing factors to CO2 fluxes in the decreasing order were bulk density (BD), and soil temperature (Ts) for paddy-paddy cropping system; were air temperature (Ta), pH, organic mater content (OM), and inorganic nitrogen content (IN) for paddy-upland cropping system; were Ta, BD, electronic conductivity (EC), and water filled pores spaces (WFPS) for upland-paddy system; and were BD, nitrate content (NO3-), Ts, and EC for upland-upland system (P＜0.05). The significant contributing factors to CH4 fluxes in the decreasing order were BD, Ts, IN, water content (WC), and EC for paddy-paddy cropping system; were IN, Ts, pH, and WC for paddy-upland cropping system; were Ts, and total nitrogen content (TN) for upland-paddy system; and were ammonium content (NH4+), WC, and IN for upland-upland system (P＜0.05). The significant contributing factors to N2O fluxes in the decreasing order were BD, NO3-, and Ts for paddy-paddy cropping system; were Ta, WC, WFPS, and IN for paddy-upland cropping system; were Ta, OM, BD, EC, and WFPS for upland-paddy system; and were BD, and NO3- for upland-upland system (P＜0.05).