不同溫度製備之生物炭對坡耕地土壤養分滯留能力之影響

坡地農田主要依賴大量化肥及耕犁的慣行農法，除了會造成土壤酸化及嚴重退化外，在熱帶及亞熱帶地區，有機質分解快速而過量，在強降雨下，容易造成過剩的養分流失，進而導致下游地區發生泥砂災害及水質污染等環境威脅。而生物炭(Biochar)逐漸被視為可有效改善土壤性質的土壤改良劑；然而，於坡耕地施用生物炭在降雨發生時，對沖蝕、逕流及淋洗作用的影響及對土壤的養分滯留能力影響仍需研究與討論。本研究利用桃花心木(Swietenia humilis)木屑於高溫厭氧下裂解之300°C與600°C木屑炭及未燒製之木屑，分別施用1%及2% (w/w)至肥力低且需多次施肥的砂土中，並以小白菜的氮肥、磷肥及鉀肥推薦量為基準施用肥料，養治100天後進行養分分析與模擬降雨試驗(50 mm hr-1降雨強度)，以評估木屑炭對砂土之水力特性及養份滯留能力之影響。本研究結果顯示砂土施用木屑炭後，物理性質方面可顯著降低土壤2.9-7.5 %的孔隙率，並能增加土壤1.7-3.8 %的團粒粒徑及58.9-124 %水力傳導度，以增加土壤的滲透能力；而化學性質方面則能提高土壤17-75 %的有機質、27-66 %總氮含量與12-33 %的pH值；但養治100天後，土壤因受到硝化作用影響，使土壤pH值顯著下降，而添加600°C木屑炭的土壤仍呈弱鹼性，因此造成土壤中的氮素約有30%轉為氨氣而流失，使土壤總氮顯著減少。在養治100天結束後，進行連續2小時的模擬降雨，木屑及生物炭可顯著增加土壤的初始含水量及容水量，並可顯著增加入滲及滲漏並減少逕流與土壤流失量；而在降雨30分鐘後，土壤含水量及入滲已逐漸趨於平衡狀態，因此入滲減少及逕流、土壤流失、滲漏及有效雨量增加的趨勢皆亦同趨於平衡態狀。添加木屑可顯著降少土壤流失路徑下的TN、NH4+–N及Bray-1磷之損失量，並可減少地表逕流所產生的養分流失及重力水的TN含量；而添加生物炭則皆能顯著降低土壤流失途徑下的OC、TN、NH4+–N、Bray-1磷及Exc. K，並可顯著減少地表逕流及重力水所產生的養分流失。SOC、TN、NH4+–N、NO3-–N、Bray-1磷及Exc. K之主要流失途徑皆為滲漏過程受到淋洗所損失，其中而對照組之OC及TN之主要途徑則為地表逕流及滲漏兩種途徑引起的。結論是添加木屑炭對砂土的養分滯留能力是有幫助的。

關鍵字

生物炭；模擬降雨；土壤沖蝕；地表逕流；滲漏；淋洗；養分流失

並列摘要

Slopeland farming mainly relies on large amounts of fertilizers and plowing on conventional farming, causing soil acidification and severe degradation. In tropical and subtropical regions, organic matter decomposes rapidly and excessively. Under heavy rainfall, overdose nutrients are easily lost, leading to the occurrence of environmental hazards such as mud and sand disasters and water pollution downstream. Biochar has been considered as a soil properties that can effectively improve soil properties. Thus, the application of biochar on sloping farmland during erosion occurs to erosion, runoff and the effect of leaching and its effect on soil nutrient retention capacity need to be further explored. In this study, woodchip biochar (WB),pyrolized under different temperatures (0°C, 300°C and 600°C), were applied to an infertile sandy cultivated soil at application rates of 1 % and 2 % (w/w). Incubation experiment was conducted for 100 days consecutively. At the end of the incubation, a simulated rainfall (50 mm hr-1) was performed to evaluate the hydrological properties and nutrient retention capacity of biochar-treated soils. The results of this study showed that the application of woodchip biochar could significantly reduce soil porosity by 2.9–7.5 %, and increase soil aggregate size and hydraulic conductivity by 1.7–3.8 % and 58.9-124%. As for chemical properties, the application of biochar increased soil organic matter, total nitrogen and soil pH by 17–75 %, 27–66 % and 12–33 %. Post-incubation, simulated rainfall was conducted for 2 hours. The results from of treatments sawdust (W), lowly temperatures pyrolized woodchip biochar (LWB), and high temperatures pyrolized woodchip biochar (HWB) showed a significant increase in the initial soil moisture content, water holdng content and rainfall infiltration, significantly reduced runoff and soil losses. After 30 minutes of rainfall, the soil moisture content and infiltration have gradually tended to be in equilibrium. Additionally, the addition of sawdust treatment significantly reduces the losses of TN, NH4+–N and Bray–1 P in runoffs. Furthermore, the addition of biochar can significantly reduce the losses of SOC, TN, NH4+–N and Bray-1 P, and Exc. K by erosion, runoff and through infiltration. In conclusion, the addition of biochar could effectively improve the retention capacity of nutrients in tropical sandy soil.