嘉磷塞為目前台灣登記範圍最廣，且實際使用也最普遍之非選擇性系統型除草劑。本研究以嘉磷塞1.64～16.4 g ai ha-1 之系列低劑量(登記量1.64 kg ai ha-1 之1/100~1/1000)，處理幼穗分化期、孕穗期及抽穗期等不同生育期之稻株，並定期調查株高、葉數、分蘗數等農藝性狀，及藥劑對稻株產量與產量成分之影響，以探討嘉磷塞低劑量處理引起水稻生育抑制之藥害反應。幼穗分化期之稻株對嘉磷塞的反應較孕穗期及抽穗期者敏感，一、二期作之產量抑制率依序分別為41%及25%。孕穗期稻株於一期作之產量抑制率(35%)則較抽穗期(25%)為高。分析嘉磷塞16.4 g ai ha-1 處理劑量對水稻產量成分之影響，百粒重在各處理時期上差異不明顯。幼穗分化期之平均穗數與粒數，亦較孕穗期及抽穗期者顯著減少，不同處理時期間之反應趨勢與產量的表現極為一致。嘉磷塞處理對穀粒不稔率之影響，仍以幼穗分化期的不稔率最高(一、二期作依序分別為12%及23%)，次為孕穗期，抽穗期在一期作之不稔率僅7%與對照株無明顯差異。分析嘉磷塞處理之稻株產量與穗數及粒數之相關性，顯示產量的增減與穗數及粒數的變化均呈顯著線性關係。嘉磷塞處理引起之稻株產量降低，主要為粒數及穗數的減少，其次為不稔率的增加，穀粒重在處理間無明顯差異。不同劑量嘉磷塞處理幼穗分化期稻株，對株高、葉數、分蘗數等農藝性狀之影響，調查結果顯示處理劑量間的差異不明顯。檢測發生藥害的稻株徵狀，主要是稻穗無法正常抽出，及穀粒發生外穎褐化的異常現象，導致穗數的減少及不稔率的增加。本研究中嘉磷塞之非致死劑量，雖然對水稻營養生長無明顯抑制，但對穗數的生成及穀粒之發育有顯著抑制作用，因而造成產量的降低。

Glyphosate is used extensively worldwide for postemergence control of annual andperennial broadleaf, grass and sedge weeds. Field studies were conducted in 2007 toinvestigate response of rice plant to sub-lethal rates of glyphosate (isopropyl amine salt)in terms of agronomic characteristics, yield and yield components when appliedpostemergence at 0, 1.64, 8.20, and 16.4 g ai ha-1 to transplanted rice at panicleinitiation, boot and heading growth stages. Yields in this study were reduced thegreatest when glyphosate was applied at panicle initiation stage. In the first croppingseason, yield was reduced 41% when glyphosate was applied at 16.4 g ai ha-1 at panicleinitiation, 35% when applied at boot stage, and 25% when applied at heading stage.Panicle number and seed number responded to glyphosate applied rates similar to riceyield. Unfilled grain percentage was highest at panicle initiation stage with glyphosatetreatment.Grain yield and yield components of rice plant respond to low rates ofglyphosate had a similar tendency. However, in this study, glyphosate treatment did notcause any inhibition in plant height, leaf number and tiller number.