Adaptability of Dwarf Napiergrass under Cut-and-carry and Grazing Systems for Smallholder Beef Farmers in Southern Kyushu, Japan

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Smallholder beef farmers, particularly in isolated islands, were highly aged, holding limited arable lands with poor machinery equipment. Demand for herbage production increases rapidly due to high cost of imported herbage supply. We investigated the adaptability of dwarf napiergrass (Pennisetum purpureum Schumach) of late-heading type (dwarf-late, DL) to 12 sites including isolated islands in 3 Prefectures of southern Kyushu by determining soil properties, plant growth characters, herbage yield and quality, and overwintering ability in 2007-2009. The dry matter (DM) yield of DL napiergrass ranged in 0.7-13.6 and 0.2-15.8 Mg/ha/yr in 2007 and 2008, respectively. There were significantly positive correlations between N fertilizer supply and DM yield (r = 0.844, P < 0.01 and r = 0.928; P < 0.001 in 2007 and 2008, respectively). However, not only by the rate of fertilizer application, DM yield was also variable depending on soil fertility and weed control across the examined sites. Herbage quality in leaf blade and stem inclusive of leaf sheath, as assessed by in vitro DM digestibility and crude protein (CP) content, ranged in 56-76% and 6-18%, respectively. In some cases, CP content declined below the critical level as a feed for breeding cows, since the herbage quality in leaf blade had significantly negative correlation with cutting interval (P < 0.05). Results revealed that DL napiergrass should adapt to the examined sites including isolated islands in the established and subsequent years. However, it is necessary to maintain the satisfactory level of herbage yield and quality by the minimum fertilizer application at least more than 100 kg N/ha/yr, and the optimum soil condition, cutting interval and weed control after establishment.南九州の，特に離島などにおける小規模肉牛農家では，高齢化，耕地の不足，機械化の遅れなどの問題を抱え，飼料価格の高騰などから，自給粗飼料生産に対する要望が高まっている．そこで本研究は，南九州の宮崎，熊本，鹿児島3県の離島を含む12調査地点における矮性ネピアグラスの適応性を，土壌特性，植物体の成長形質，飼料の収量と品質および越冬性に関して，2007年と2008年に調査したものである．矮性ネピアグラスの乾物収量は，2007年では0.7～13.6トン/ha，2008年では0.2～15.8トン/haの地域間差異が認められた．N肥料供給量と乾物収量との間に両年ともに有意な正の相関関係があったが，乾物収量には，土壌の肥沃度や雑草防除の良否の影響も認められた．飼料品質としてのin vitro乾物消化率（IVDMD）と粗タンパク質（CP）含量は，両年ともにそれぞれ約56～76％，6～18％の範囲であり，CP含量は刈取り間隔との間に負の相関関係があることなどから，繁殖雌牛飼養にとっての限界値を下回る場合が認められ，矮性ネピアグラスのみの給与の場合には，施肥量を年間150 kg N/ha以上に挙げることが必要であった．したがって，矮性ネピアグラスは，適切な土壌条件の土地を選択し，最低年間100 kg N/ha以上の施肥と適切な雑草防除を行えば，離島を含む南九州において造成後2年間は，粗飼料として満足しうる収量と品質を挙げ，適応可能であることが示された．
2011-03-00

Adaptability of Dwarf Napiergrass under Cut-and-carry and Grazing Systems for Smallholder Beef Farmers in Southern Kyushu, Japan

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