Effectiveness of Ammonium-Nitrogen and Nitrate-Nitrogen in Irrigation Water in Paddy Rice without Topdressed Nitrogen at the Panicle Formation Stage

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  • Ikeda Motoki
    Laboratory of Plant Nutrition Division of Soil Science and Plant Production, Department of Plant Resources, Faculty of Agriculture, Kyushu University
  • Watanabe Takayasu
    Laboratory of Plant Nutrition, Divsion of Soil Science and Plant Production, Department of Plant Resources, Graduate School of Bioresources and Bioenvironmental Sciences, Kyushu University

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Other Title
  • 水稲作における潅漑水に含まれるアンモニウム態窒素及び硝酸態窒素と穂肥窒素の肥効
  • スイトウサク ニ オケル カンガイスイ ニ フクマレル アンモニウムタイ チッソ オヨビ ショウサンタイ チッソ ト ホヒ チッソ ノ ヒコウ

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Abstract

A pot experiment was conducted to evaluate the efficiency of ammonium- and nitrate- nitrogen contained in irrigation water during the reproductive growth period of paddy rice （Oryza sativa L. cv. Hinohikari） that did not receive topdressed nitrogen at the panicle formation stage. lrrigation of water containing a low level of nitrogen （7mgNL^-1） did not increase yields so much compared to topdressed nitrogen. lrrigation of water containing a high level of nitrogen （14mgNL^-1） caused substantial increases in yields with higher concentrations of grain nitrogen. To prevent the accumulation of nitrogen in grains, irrigation of Water containing high levels of nitrogen during the reproductive growth period is not recommended whether topdreSsed nitrogen is applied at the panicle formation stage or not. lrrigation of water containing the high level of nitrogen during the early cultivation period and water containing the low level of nitrogen during the reproductive growth period resulted in the greatest yields of grains with acceptable nitrogen concentrations owing to larger vegetative growth. Because ammonium-nitrogen was recovered effectively both in grains and straws compared to nitrate-nitrogen, ammonium-nitrogen showed greater effects on grain yields and nitrogen content than nitrate-nitrogen.

水稲栽培後半期間の潅漑水に含まれる窒素が潅漑窒素と比べてどの程度の効果をもつかを知るために，灰色低地土を使いポット栽培で穂肥窒素を省略した水稲（品種ヒノヒカリ）にアンモニウム態窒素及び硝酸態窒素を添加した潅漑水を栽培後半期間に潅心した試験を実施した．低濃度窒素（7mgNL^-1）含有水を潅漑したときは，穂肥窒素相当量の窒素が投入されたが収量の増加は小さく穂肥窒素ほどの効果はなかった．高濃度窒素（14mgNL^-1）含有水を潅概したときは，増収効果は穂肥窒素のものより大きかったが籾窒素含有率が顕著に増加した．コメの食味を低下させないためには，穂肥窒素施用の有無にかかわらず栽培後半期間に高濃度窒素含有水を潅概することは避けなければならない．前半期間に高濃度窒素添加水を潅概し穂肥省略で後半期間に低濃度窒素添加水を潅概すると，乱養成長が旺盛なため収量が最大となり籾窒素含有率はそれほど上昇しなかった．いずれの場合も，窒素給源がアンモニウム態窒素のとき潅溜i水由来窒素の利用回が高く増収効果が大きくなった．

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