本文研究旨在探討田間自然發生雜草之除草時期及除草次數對整地栽培玉米臺農一號(Zea mays L. cv. Tainung No.1)產量之影響。田間試驗係於1992年秋作及1993春作在臺灣省農業試驗所農場進行。由所內氣象觀測站收集之資料顯示，此兩生長季節期間氣候條件互異。根據試驗結果，無論秋作或春作在玉米生育期內實施除草兩次均顯著提高產量，其中以播種後第四及第八週各除草一次者分別在秋作及春作增產10及49%者為最高。在一次除草處理當中，則以播後第6週除草者獲得最大產量；秋、春作各增產5及21%。進一步分析產量性狀後發現，秋作二次除草增產主要在於每株穗重與籽粒重及100-粒籽粒重之增加。春作處理中除了播後8週除草一次者外，增產主因則在於穗長、每株穗重與籽粒重、及100-粒籽粒重等性狀之增加，而二次除草之玉米每株籽粒數亦顯著上升。二次除草處理在秋、春作均改進玉米植株之生物產量、收獲指數及籽粒產量，惟一次除草處理中僅播後6週除草者得到類似效果。試驗亦顯示，秋作玉米收獲指數皆高於春作者。本文據此建議，整地玉米栽培期間以除草兩次對增產效果顯著，因故僅能實施一次除草處理時，以玉米播後6週後除草可獲得較佳增產效果。

Field experiments utilizing naturally occurring weed populations wer conducted to study the effects of weeding timing and the numbers of weeding practice on yield of corn (Zea mays L. cv. Tainung No.1)ing the experimental farm of Taiwan Agricultural Research Institute in the fall crop of 1992 and the spring crop of 1993. An adversed distribution of climatic factors during the growing seasons was shown. Corn yield was increased as weeding practices applied two times during the growing seasons of 1992 and 1993. Kernel yields were increased approximately 12 and 49% for Fall 1992 and Spring 1993, respectively. Weeding practice applied at 6 weeds attained the maximal increase of yield in one-weeding practices, an increase of 5% for the fall crop and 25% for the spring crop was recorded. It appeared that weights of ear and kernel per plant and 100-kernel weight were the yield components increased in two-weeding treatments in Fall 1992.In Spring 1993,ear length,welghts of ear and kernel per plant, and 100-kernel weight were increased by weed removals except at one-weeding at 8 weeds after planting. Additionaily kernel number per plant was enhanced in two-weeding practice treatments in 1993.Weed control applie twice during the growing seasons improved the biological yield, harvest index and kernel yield,while only weeding at 6 weeks after planting in one weeding treatments increased these parameters in both seasons. It was also indicated that harvest index obtained from the fall crop was higher than that from the spring crop.The results suggested that weeding practices applied two times during the growing season significantly enhanced biological yield, yield components and harvest index and therefore kernel yield. Weeding at 6 weks after planting is acceptable for both crop seasons on returns of considerable yield when considering the production cost by selecting one-weeding practice.