水稻田農事經營對水生動物多樣性之影響

Abstract

農田生物多樣性隨著綠色革命的發展而廣泛降低，如何進行水稻田生物多樣性保育已成為農田永續利用的重要課題。地景組成與農事經營是農田生物多樣性保育的重要因子，然而如何透過農事操作提高農田生物多樣性，同時兼顧農作產量仍需更多研究探討。本研究在2021年一期稻作期間，於苗栗縣通霄鎮的田鱉米農場設置36個3×3m樣區，設計不同秧距、挲草頻度、及封壟時湛水與否樣區，透過18目方網底拖採集水生動物及直接採樣稻穗，比較不同農事操作在秧苗分蘗最盛之封壟前後期對水生動物多樣性的差異和稻穀產量的影響。結果顯示在大多情況下，水生動物多樣性與插秧後天數、秧距、水深、雜草覆蓋度、及封壟時湛水呈正相關。在農事操作部分，後期秧距較疏、封壟時湛水有較高的水生動物多樣性；前期秧距較密、挲草頻度較低、後期秧距較疏、封壟時湛水有較高的福壽螺族群量；而秧距較疏、挲草頻度較高、封壟時湛水則會有較低的稻穀產量。藉由釐清不同操作對生物多樣性和產量的影響，農人可仔細評估農事操作，以建立合適的農事經營模式。本研究建議於水稻田間保留部分缺秧嚴重的區塊不進行補秧，提供後期秧距較疏的空間；安排封壟前適量的1－2次挲草，以幫助抑制福壽螺族群量；並在水稻田與田埂交界處配置排水溝渠，做為維持低擾動、水深較深且長期湛水空間。此操作有助於提高水生動物多樣性，節省勞力付出，並能兼顧稻穀的生產品質與產量。

While the Green Revolution developing, farmland biodiversity has decreased globally and biodiversity conservation of rice paddies has become an important issue for environmental sustainability of farmland. Landscape composition and farming management have been considered the most dominant factors in farmland biodiversity conservation. However, it is remained understudied on how to implement farming practices that benefit both biodiversity and yield. I conducted a field experiment in the 2021 summer in Tianbei Rice field, Tongsiao, Miaoli County. A total of 36 3×3m plots were established to examine the effects of seedling spacing, frequency of weeding, and watering at rice canopy closure on aquatic animal diversity and rice yield, before and after the highest tillering time. I collected aquatic animals through 18 mesh square net dragging and sampled rice ears to compare the effects of different farming practices. Results show that most aquatic animal diversity indices were positively correlated with days after transplanting, seeding spacing, water depth, weed presence, and watering at rice canopy closure. Larger seedling spacing at later stage and the watering at rice canopy closure had higher diversity of aquatic animals; while smaller seedling spacing at early stage, lower frequency of weeding, larger seedling spacing at later stage, and watering at rice canopy closure had higher density of apple snails; larger seedling spacing, watering at rice canopy closure had lower rice yields. Therefore, farmers could evaluate their farming practice carefully and establish proper farming management. It is suggested to select some spare areas without filing up seedlings to create larger seedling spacing area, arrange an appropriate amount of weeding 1-2 times to control apple snails population, and set up drainage ditches between rice field and ridge to maintain low disturbance, deep water depth and long-time watering place. These practices could help improve the biodiversity of aquatic animals, save labor and meanwhile benefit rice yield and quality.