The Effect of Weeds on Rice in Paddy Field (I). Weed Species and Population Density

Abstract

The effect of weeds on rice was evaluated on five species of weeds at 3 population densities and two fertility levels in the first and second crops of 1968. Echinochloq crusgalli, Cyperus difformis, Marsilea quadrifolia, Monochoria vaginalis, and Spirodela polyrhiza reduced grain yield of rice by 84.9, 71.7, 62.0, 61.7, and 9.0%, respectively, Population density of 100 and 200 weeds per m2 reduced 51.3 and 64.4% of grain yields, respcctively when compared with weed-free treatment. Echinochloa crusgalli and Cyperus difformis reduced more grain yield of rice at high fertility level while Monochoria vaginalis and Marsilea quadrifolia caused more damage at less fertilized field. Echinochloa crusgalli and Marsilea quadrifolia reduced grain yield of rice more or less similarly in both crops but Monochoria vaginalis and Cyperus difformis caused heavier damage in the second crop. The number of panicles per plant suffered the greatest damage, followed by the number of grains per panicle but the 100-grain weight and the fertility percentage were only slightly affected.

嘉義農業試驗分所曾於民國57年第1、2期作在網室內舉行盆栽試驗，調查不同密度之主要水田雜草在不同肥力下對水稻為害之程度，初步結果顯示稗草、三角草、田字草、鴨舌草及浮萍分別減產84.9、71.7、62.0、61.7與9.0%。雜草密度每平方公尺100支與200支者較無草之對照處理分別減產51.3及64.4%，稗草與三角草在重肥區為害情形勝於輕肥區，惟鴨舌草與田字草則恰恰相反。稗草與田子草之為害情形，第1期作與第2期作相若，但鴨舌草與三角草之為害情形則以第2期作較為嚴重。產量構成因素中以每株穗數為害最重，每穗粒數次之，而百粒重與稔實率則未見其害。