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本報告は荒廃草地の更新の際，雑草防除対策として生態的防除を行うことを目的とした．完全耕起後の土壌表面の気象環境を利用したエゾノギシギシの枯死や凍死など生態的防除にアプローチするため，冬季における耕起がエゾノギシギシの株と実生に及ぼす影響を試験し，耕起と気象環境との関連の基に雑草防除に対するその有効性を検討した． 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900m）の腐植質火山灰土壌からなる草地造成後20数年経過したエゾノギシギシ繁茂の荒廃牧草地において行った．実験処理区の設定を6つとし，処理1区は10月上旬においてのみ耕起する区，いわば慣行的な方法を用いる区であり，これを対照区とした．処理2区～6区については，順次耕起を増やし，同6区は10月上旬以降，翌年3月上旬まで毎月耕起する区とした．それぞれの処理区を幅180cm，縦500cmとし耕転機を用いて耕起した．耕起における耕転機による走行回数は，10月上旬においてのみ5回とし，11月以降は3回とした．測定値の計測については，1m^2当たりのエゾノギシギシ株の萌芽を含む茎数ならびにその種子の発芽を含む茎数を調査した．測定日は実験期間である2001年10月～2002年3月間，それぞれ実験処理区の耕起直前の10月26日，そして耕起後，越冬前の年内12月3日，越冬後翌年1月9日，2月9日，3月1日および早春4月3日である． エゾノギシギシ株の萌芽後の茎数への影響：対照区の場合，1m^2当たりのエゾノギシギシ株の茎数は10月（25.7本）＜1月（32本）＜4月（68.0本）と，漸次増加が認められた．処理2区の茎数は10月（20.3本）＜1月（4.7本）＜4月（4.3本）と激減した．処理3区～6区においても同様な傾向が認められ，特に5区および6区の翌年4月においては0.3本以下となった．対照区の同茎数に対する処理2区～6区の同茎数の割合は，翌年1月の場合いずれも15％以下（p＜0.01）となり，翌年4月においては，特に処理3区～6区の場合，0.02％以下を示した（P＜0.01）． エゾノギシギシ種子発芽後の茎数への影響：対照区の場合，1m^2当たりのエゾノギシギシ種子発芽後の茎数は10月（7.7本）＜1月（9.4本）＜4月（22.0本）と，冬季においても増加が認められた．しかし，対照区の茎数に対する処理2区～6区の茎数の割合は，12月時点で41％以下（p＜0.01）を示し，翌年1月以後，処理2区～6区それぞれの茎数はすべて0.0本となった． 対照区の場合，冬季におけるエゾノギシギシの直根が萌芽能力を有している地下部の温度は氷点下に至らず，2月の日中は平均最高気温10℃以上を示した結果，同植物の茎数増加に至ったものと考えられる．処理2区～6区の場合については，エゾノギシギシ株の萌芽後および種子発芽後それぞれの茎数が順次減少した要因として，晩秋から冬季にふけて耕耘機により地下約20cm深く何度も撹拌された結果，それらは断根などの物理的損傷を受け枯死したことが考えられる．また，冬季の土壌表面の最低温度は氷点下を示した結果，掘り起こされた同株や実生の乾燥や凍結による枯死，あるいは霜柱形成における根切れによるものなど気象環境に起因したことが考えられる． 本研究の結果，九州中部高原地域における草地更新の際，冬季の多回耕起法はエゾノギシギシの株や実生に対して物理的あるいは気象環境的に大きな影響を及ぼすことが明らかとなり，エゾノギシギシ防除の有効性が示唆された．
This study was designed to examine effects of different methods of cultivating degrading pastures on the stem emergence and seedling of Rumex obtusifolius L. (abbreviated to Ro) in winter. The objective was to examine a mechanism for the growth and germination of Ro for its ecological control as weed in the renovation ofdegrading pastures. The experiment was carried out in degrading pasture sods that were established more than 20 years ago and have been covered with Ro in the field at Kuju Agricultural Research Center of Kyushu University located at an altimde of 900 m in the middle of Kyushu highlands area. The treatment No.1 (control) was the experiment for cultivating only once in the first ten days of October. ln the treatments No.2 to No.6 there were additions of cultivating in the same period of the following months; November (No.2), November and December (No.3),･･, every month until next March (No.6). in each treatment, the sods were cultivated 500 cm in length, 180 cm in width and 20 cm in depth by a rotary machine. The sods were cultivated 5 times at the cultivation in October, and 3 times in each of the following months. in these experiments the number of stems and that of seedlings of Ro per m2 were measured for 6 months (before winter: October 26, 2001; winter: December 3, 2001, January 9 and February 9, 2002; spring: March 1 and April 3, 2002) prior to each cultivation of the sods. The temperature and precipitation in the field were also measured during this experimental period. The number of stems of Ro increased in the order of October (25.7) < January (32.0) < March (62.0) < April (68.0) in the case of control. The treatment No.2 showed a drastic decrease in the order of October (20.3) > January (4.7) > April (4.3). There were also large decreases in the case of No.3～No.6, especially Nos.5 and 6 showed a decrease to O.3 or less in next April. Wnen compared with control, the number of stems in No.2 ～ No.6 in January was less than 15 % (p < O.05) with an extraordinary decrease (less than 0.02 %, p < 0.01) for No.3 in next April. The number of seedlings of Ro increased even in winter in the order of October (7.7) < January (9.4) < April (22.0) in the case of control. In the treatments No.2～No.6 there was a reduction to 41 % or less (p < 0.0l) of control in December, and at last they showed 0.0 after January. In the case of control, the number of stems and that of seedlings of the plant increased in winter. It is conceivable that the tap root of Ro in winter could have the ability of stem emergence because the average of minimum temperature of 5 cm below the soil surface did not show a minus degree and the average of maximum temperature was over 10℃. However, the number of stems and that of seedlings of Ro in the treatments No.2～No.6 gradually decreased in February. It is also conceivable that those plants withered and died of the physical damage such as the root cutting caused by cultivating the soil to the depth of about 20 cm using the rotary machine from late autumn to winter repeatedly. In addition there was an effect of weather conditions such as drying and freezing as a result of minus degrees of the minimum temperature of the soil surface in winter. The results from this study suggested that the method of cultivating degrading pastures in winter controlled stem emergence and seedlings of Ro, especially affected seedlings physically or environmentally. The present method would be extremely effective to improve the renovation technology of grasslands in terms of ecological control of Rumex obtusifolius as weed in the middle of Kyushu highlands area.show more
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