茶園施肥對北勢溪之影響

Abstract

茶園為北勢溪集水區內主要的農業產業，茶園耕種方式會使部分表土裸露，遇暴雨時易沖刷表土進而進入河川水體，其地表逕流挾帶氮、磷等營養源，進入河川水庫水體，導致水質污染、水庫優養化等問題。本研究主要目的為探討茶園施肥對北勢溪水體的影響。場址選定兩處慣行(conventional)茶園和兩處有機(organic)茶園進行水質監測，探討其地表逕流水質施肥前後差異，另於實驗室內架設一組模場，用以推估慣行茶園全年總磷排放量。 由研究結果得知，不管是慣行茶園還是有機茶園，其施肥後的地表逕流水質濃度都比施肥前的高出許多，尤其以總氮濃度之增加最為明顯，施肥後最高可增加3.5倍之多。在農藥檢測的部分，四座茶園經六次的農藥採樣分析，測得唯有祥順茶園在10月7日的地表逕流中，有檢測出嘉磷賽0.432 ppm，推測原因係該單次除草劑施藥量過多之故，若按照指示以常態噴灑農藥，則應無農藥殘留問題之慮。以尚青茶園的水質監測結果搭配由PNPI指標歸納出的高潛勢污染茶園面積計算地表逕流對北勢溪水體的衝擊，結果顯示在總磷的部分，高污染潛勢茶園會造成北勢溪水體總磷濃度增加23%至207%不等之比例；而在總氮的部分，濃度則會增加0.4%至13.4%。在實驗模場實驗的部分，隨著施肥量的增加地表逕流中總磷濃度也隨之增加，而在不同降雨強度試驗中，相同降雨延時下地表逕流中總磷濃度隨著降雨強度下降而增加。在推估茶園全年磷排放量的部分，尚青和祥順茶園的結果分別為29.1 kg/ha-yr和29.2 kg/ha-yr，佔年度施磷量的11.6%和13.3%。

Tea plantations are main agricultural industry in Peishih river catchment. The farming methods of tea plantations will cause some soil bared. When rain fall down, some soils will be taken into the river by overland flow. Nitrogen, phosphorus and other nutrients which was contained in soils will lead to water pollution and eutrophication. This study explores fertilizing tea plantations impact on Peishih river. The experimental results shows that after the fertilization, the concentration of total nitrogen in surface runoff water will increase 3.5 time than before the fertilization. In six times pesticides detection, only N-(Phosphonomethyl) Glycine was detected once. The reason is using more than usual amount of Glycine usage. According to the results of the impact assessment, high-pollution potential tea plantations will increase 23% to 207% concentration of total phosphorus and increase 0.4% to 13.4% concentration of total nitrogen in Peishih river. This study estimates the annual amount of phosphorus emissions of tea plantation by a laboratory scale experiment. And the results of annual amount of phosphorus emissions are 29.1 kg/ha-yr and 29.2 kg/ha-yr. That account for 1% and 2% of annual amount of phosphorus fertilization.