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本報告では，追播における堆肥を含む混合覆土が追播オーチャードグラス（Dactylis glomerata L.）とエゾノギシギシ（Rumex obtusifolis L.）の茎数並びに全牧草の乾物収量に及ぼす影響について検討を行い，併せて荒廃草地の植生回復に対する新追播法の効果をも考察した． 実験は九州中部高原地域に位置する当圃場（九州大学農学部附属農場高原農業実験実習場，久住山中腹標高約950m...）において行った．実験区を3つ設けた．まず，覆土区については，草地用条播機を用いて溝（平均幅3.45cm，平均深さ3.53cm）を切り，その後，手播きにより覆土（平均覆土幅5.45cm，平均覆土厚6.55cm）を行った．その覆土はオールインワンタイプのものとして，堆肥と肥料と培養土（粘土質培養土）に種子を混入したものである．つぎに，無覆土区については，堆肥と培養土を除いたものを施与した．また，対照区には，覆土区に施与するもの相当量を全面散布した． 追播オーチャードグラスのスタンドが確立する追播2年後の春における同茎数は，対照区（0.0本）＜無覆土（7.63本）＜覆土区（9.29本）の順となり，それぞれの処理区間において有意差（p＜1％）が認められた．また，追播前における1m^2当たりのエゾノギシギシの茎数に対する追播2年後の同茎数割合は，覆土区（86.6％）＜無覆土区（88.0％）＜対照区（138.0％）の順となり，追播後，対照区が大きく増加したのに対し覆土区と無覆土区は減少した．特に覆土区は対照区の63％の値を示し，両処理区間には有意差（p＜1％）が認められた．さらに，追播2年後における1m^2当たりの牧草の乾物収量は，対照区（261.5g）＜無覆土（448.9g）＜覆土区（655.3g）の順で，それぞれの処理区間で有意差が認められ，覆土区は対照区の2.5倍（p＜1％）の乾物収量を示した． 本研究の結果，草地用条播機を用いた追播の際有機質である堆肥を含む覆土を行うことは追群オーチャードグラスの茎数増加にきわめて有効であり，また覆土が有する遮光機能により強害雑草であるエゾノギシギシの発芽抑制に対しても効果があることなどから，追播草地の牧草収量増加に大きく寄与することが明らかとなった．
This study was designed to examine stem emergence of Dactylis glomerata L. (abbreviated to Dg) and Rumex obtsifolis L. (abbreviated to Ro) and total yield of grasses as affected by covering the seed-bed with a mixture of composts, fertilizers, seeds and soil in directly drilled pasture sward. The objective was to examine a mechanism for stem emergence of Dg making a contribution to total yield of grasses by the ecological control of growth and germination of Ro in the renovation of degrading pastures. The experiment was carried out in the degrading pasture sods that had been covered with Ro since the establishment twenty and several years ago in the field at Kuju Agricultural Research Center of Kyushu University located at an altitude of 950 m in the middle of Kyushu highland area. Three experimental treatments were set up. The treatment No.1 was drill seeding covering the seed-bed (3.45 cm wide and 3.53 cm deep) with a mixture of composts, fertilizers, seeds of Dg and commercial clay soil (5.45 cm wide and 6.55 cm thick) on October 1, 2001. The treatment No.2 was the drill seeding without covering the seed-bed, where there was a dressing of fertilizers and seeds without composts and commercial clay soil on October 1, 2001. The treatment No.3, which was the control, was broadcasting the mixture of composts, fertilizers, seeds of Dg and commercial clay soil over the pasture sward on October 1, 2001 without drilling. In these experiments, measurements were made on May 2, 2003 for the number of stems of Dg in the area of 5.45 cm × 100 cm and total dry matter yield per m^2 of grasses. The number of stems of Ro per m^2 was measured on September 6, 2001 (about one month before drilling on October 1), and then on May 2, 2003 (about two years and a half after the drilling on October 1, 2001). The temperature and precipitation in the field were also measured during this experimental period. The number of stems of Dg in the area of 5.45 cm × 100 cm on May 2, 2003 increased significantly (p<0.0l) in the order of control (4.1) < non-covering (7.63) < covering (9.29). The percentage of Ro stems in total stems per m^2 showed changes between September 6, 2001 (about one month before drilling) and May 2, 2003 (about two years and a half after the drilling), covering (86.6 %) < non-covering (88.0 %) < control (130.8 %) with 63 % lower (p<0.01) in covering compared with control. The tota1 dry matter yield of grasses per m^2 on May 2, 2003 showed a significant increase (p<0.01) in the order of control (261.5g) < non-covering (448.9g) < covering (655.3g), 250 % difference between covering and control. The results from this study suggested that the method of drill seeding covering the seed-bed with a mixture of composts, fertilizers, Dg seeds and soil increased the number of Dg stems and total dry matter yield of grasses by decreasing the number of Ro stems in the directly drilled pasture sward. The present method would make a contribution to simple methods of grass- land renovation technology in terms of recovering vegetation by the ecological control of Rumex obtsifolis as weed in the middle of Kyushu highlands area.続きを見る
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