不同農耕生態系之雜草相差異─雙期作水田及水旱田輪作之比較

Abstract

農作的耕種制度及管理方式，不僅影響田間作物的生育，亦會改變雜草發生的數量與種類。為期瞭解雙期作水田農耕生態系(paddy-paddy agro-ecosystem; PP)及一期作水稻、二期作落花生水旱田輪作農耕生態系(paddy-upland rotation agro-ecosystem; PU)等的雜草相變化及其差異，本研究於行政院農業委員會農業試驗所溪口農場之長期農業生態系研究(Long-term Agricultural Ecological Research; LTER)試驗場址進行調查。該兩種生態系內分別包括慣行農耕(conventional cropping system; CC) 及低投施農耕(low-input cropping system; LC)兩種處理系統，合計探討及分析四種農耕生態系組合(即PP-CC、PP-LC、PU-CC 及PU-LC)對雜草發生之影響。結果顯示四種農耕生態系中一期作所發生的雜草科別數及種別數，均少於二期作；PP-CC、PP-LC、PU-CC 及PU-LC 四種農耕生態系的田區雜草密度於一期作之平均依序為1.8、4.4、9.9 及3.3 pl m-2，二期作為29.1、24.6、5.9、9.8 pl m-2。雜草生質量大致呈現二期作高於一期作，且PU 農耕生態系大於PP 農耕生態系、CC 處理高於LC 處理之趨勢。PP 生態系在一期作以千屈菜科(Lythraceae) 雜草所占密度最高， 高達85% ， 二期作則以玄參科(Scrophulariaceae) 雜草發生頻率最高，PP-CC 及PP-LC 分別為47%及39%。PU 生態系在一期作水田環境下的PU-CC 系統，以菊科(Compositae)雜草最多(35%)，在二期作的旱作(落花生)環境下， 無論PU-CC 或PU-LC 皆以菊科雜草分佈最多，分別為73%及53%。以個別雜草物種而言，PP-CC 及PP-LC 在一期作皆以水莧菜之密度最高，其次依序為芒稷(Echinochloa colona) 、母草(Lindernia procumbens)、多花水莧(Ammannia multiflora)、滿天星(Alternanthera sessilis)及其他種類，二期作則以母草最多(125.6 pl m-2)。PU-CC 及PU-LC 在一期作以霍香薊(Ageratum conyzoides) 及香附子(Cyperus rothundus)發生較多，二期作主要為旱生型雜草種類，尤以霍香薊及鱧腸(Eclipta prostrata)為優勢雜草，分別為34.9 及36.4 pl m-2。另水莧菜(Ammannia baccifera)、母草、泥花草(Lindernia antipoda)、霍香薊、鱧腸、香附子等雜草可全年分布並散見於水田或水旱田輪作試驗田區中，惟除了香附子為多年生雜草外，其餘雜草群落組成皆為一年生闊葉雜草。 The growing style and field type of a cropping system affect not only performance of a crop but infestation of weed populations, including their emergence, propagation and prevalence. This field experiment was conducted to study differences in weed population and density between paddy-paddy (PP) and paddy-upland rotation (PU) agro-ecosystems set up as Long-term Agricultural Ecological Research (LTER) trial. Each agro-ecosystem was further divided into conventional (CC) and low-input (LC) treatments, making up 4 different agroecosystems for the trial, namely, PP-CC, PP-LC, PU-CC and PU-LC. Results showed that numbers of weed family and weed species were higher in the growing season of first-half year than those in the second-half in all trial fields. The average weed densities of PP-CC, PP-LC, PU-CC and PU-LC were 1.8, 4.4, 9.9 and 3.3 pl m-2 in First Crop, and were 29.1, 24.6, 5.9 and 9.8 pl m-2 in Second Crop, respectively. Likewise, generally weed biomass was higher in the second cropping season than in the first cropping season, in PU agro-system than in PP agro-ecosystem, and in CC treatment than in LC treatment. In the PP agro-ecosystem, weeds of family Lythraceae had the highest density (nearly 85%) in the first crop, but weeds of Scrophulariaceae were the highest in the second crop, 47% in PP-CC and 39% in PP-LC. In the PU agro-ecosystem, weeds of the Compositae reached 35% in PU-CC in the first crop, and about 73% in PU-CC and 53% in PU-LC in the second crop. Plants of Ammannia baccifera was the most predominant weed species found in both PP-CC and PP-LC in the first crop season, followed by Echinochloa colona, Lindernia procumbens, Ammannia multiflora, and Alternanthera sessilis,; whereas, Lindernia procumbens (125.6 plant m-2) was prevalent in the second crop season. Plants of Ageratum conyzoides and Cyperus rotundus were superior weed species in both PU-CC and PU-LC in the first-half, while upland weed species were the majority in the second-half, especially Ageratum conyzoides (34.9 pl m-2) and Eclipta prostrate (36.4 pl m-2). Plants of weed species Ammannia baccifera, Lindernia procumbens, Ageratum conyzoides, Eclipta prostrate, Cyperus rotundus and Lindernia antipoda appeared all year round in the experimental fields. Except Cyperus rotundus is a perennial narrow-leaf weed, others are annual broad-leaf weeds.