本試驗於1997~1998年在國立台灣大學農業試驗場進行，第一期稻作收穫後於其田間撒播覆蓋作物田菁（Sesbania roxburghii Merr.），俟田菁成長後噴施除草劑嘉磷塞（glyphosate）將其殺死，以其枯死植株敷蓋田面，再以不整地方式栽培青割玉米台南19號，並噴施或不噴施萌前除草劑拉草（alachlor）及草脫淨（atrazine），探討田菁覆蓋及敷蓋對不整地栽培之青割玉米（Zea may L.）生育、雜草覆蓋率、青割產量以及飼料（含氮量 ×6.25）品質之影響。青割玉米播種後65天，田中的雜草以長梗滿天星（Alternanthera philoxeroides）較多，其次為昭和草（Erechites valerianaefolia）、龍葵（Solanum nigrum）及刺莧（Amarathus spinosus），都屬於闊葉雜草，僅有少數的禾本科雜草如稗（Echinochloa crusgalli）及牛筋草（Eleusine indica）。不整地的試區田面雜草覆蓋率都比整地的試區低，田菁敷蓋及不整地但未施用萌前除草劑的處理，其雜草覆蓋率亦只有11.7%，顯示田菁敷蓋及採用不整地栽培兩者均可降低雜草的發生。青割玉米的株高、穗位高、穗位葉片葉綠素含量及總可消化養分（total digestible nutrient），不論整地方式、有無田菁敷蓋以及萌前除草劑的施用與否，各處理間皆沒有顯著差異。鮮重產量以田菁敷蓋及不整地但未施用萌前除草劑的處理最高，每公頃達到43.2公噸，其他各處理也在37.9~39.8公噸之間。另外，有田菁敷蓋的處理，青割玉米植株的含氮總量有較高的趨勢。本試驗結果顯示台灣北部一期稻作收穫後之水田，立即種植覆蓋作物田菁並以其枯死植株敷蓋田面，再以不整地方式栽培青割玉米，可以降低雜草的發生及減少除草劑的施用，對青割玉米的產量、飼料營養品質不會造成影響，值得應用推廣。
Effects of Sesbania Mulch and No-Tillage Practices on Weed Management and Yield of Forage Corn
Yi-Chuan Chiu Wen-Fu Tsai
Department of Agronomy,
This experiment was conducted to investigate the effect of sesbania (Sesbania roxburghii Merr.) mulch and no-tillage practices on the agronomic characters, weed coverage, yield and forage quality of forage corn (Zea may L, cv. Tainan 19) at the Agriculture Experimental Farm, National Taiwan University. The cover crop sesbania was seeded immediately after the first crop of rice harvested. After two months of growth, it was killed by the herbicide glyphosate and used for mulch. The forage corn was then planted without tillage. Two preemergence herbicides, alachlor and atrazine, applied as tank-mix, were also included in the experiment.
During the growth period of forage corn, broadleaf weed species were found dominant in the field, such as alligator alternanthera (Alternanthera philoxeroides), nodding burnweed (Erechites valerianaefolia), black nightshade (Solanum nigrum) and thorn amaranth (Amarathus spinosus). The grass weeds such as barnyardgrass (Echinochloa crusgalli), goosegrass (Eleusine indica) were also found but less in number. Weed coverage was lowest (4~5%) in no-tillage treatment in combination with the application of preemergence herbicides. No-tillage and sesbania mulch treatment without the application of preemergence herbicides also obtained a relatively low weed coverage (11.7%). These results indicated that cover crop mulch and no-tillage treatments could reduce weed growth in the corn field.
The plant and ear heights, chlorophyll content, and total digestible nutrient of forage corn were not different significantly among treatments. Sesbania mulch in combination with no-tillage practice obtained the highest fresh yield of 43.2 Mg/ha. It was also found that forage corn plants contained relatively higher nitrogen in all the sesbania mulch treatments.
Key words: Forage corn, mulch, no-tillage, sesbania, weed coverage.